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+The Project Gutenberg EBook of American Rural Highways, by T. R. Agg
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: American Rural Highways
+
+Author: T. R. Agg
+
+Release Date: July 16, 2009 [EBook #29420]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK AMERICAN RURAL HIGHWAYS ***
+
+
+
+
+Produced by Tom Roch, Richard J. Shiffer and the Online
+Distributed Proofreading Team at https://www.pgdp.net (This
+file was produced from images produced by Core Historical
+Literature in Agriculture (CHLA), Cornell University)
+
+
+
+
+
+[Transcriber's Note: Every effort has been made to replicate
+this text as faithfully as possible, including obsolete and
+variant spellings and other inconsistencies. Text that has been
+changed to correct an obvious error is noted at the end of this
+ebook.
+
+Also, on pages 47-48, the Greek letter theta is represented by
+THETA. In chemical and mathematical notations, a subscript is
+enclosed in braces and preceded by an underscore (e.g., H_{2}O.)]
+
+
+
+
+  AGRICULTURAL ENGINEERING SERIES
+
+  E. B. MCCORMICK, CONSULTING EDITOR
+
+
+  FORMERLY DEAN OF ENGINEERING DIVISION
+  KANSAS STATE AGRICULTURAL COLLEGE
+
+
+
+
+  AMERICAN
+
+  RURAL HIGHWAYS
+
+
+
+  _McGraw-Hill Book Co. Inc._
+
+  PUBLISHERS OF BOOKS FOR
+
+
+  Coal Age -- Electric Railway Journal
+  Electrical World -- Engineering News-Record
+  American Machinist -- Ingenieria Internacional
+  Engineering & Mining Journal -- Power
+  Chemical & Metallurgical Engineering
+  Electrical Merchandising
+
+
+  [Illustration: _Frontispiece_]
+
+
+
+
+  AMERICAN
+  RURAL HIGHWAYS
+
+
+  BY
+
+  T. R. AGG, C.E.
+
+
+  PROFESSOR OF HIGHWAY ENGINEERING
+  IOWA STATE COLLEGE
+
+
+
+  FIRST EDITION
+
+
+
+  MCGRAW-HILL BOOK COMPANY, INC.
+  NEW YORK: 239 WEST 39TH STREET
+  LONDON: 6 & 8 BOUVERIE ST., E. C. 4
+  1920
+
+
+  COPYRIGHT, 1920, BY THE
+  McGRAW-HILL BOOK COMPANY, INC.
+
+
+
+
+PREFACE
+
+
+AMERICAN RURAL HIGHWAYS was written for use as a text or reference in
+courses dealing with rural highways and intended for agricultural
+engineers, students in agriculture and for short courses and extension
+courses. The reader is assumed to have familiarity with drawing and
+surveying, but the text is adapted primarily for students who do not
+receive training along the lines of the usual course in Highway or
+Civil Engineering.
+
+The text is intended to familiarize the student with the relation of
+highway improvement to national progress, to indicate the various
+problems of highway administration and to set forth the usual methods
+of design and construction for rural highways in sufficient detail to
+establish a clear understanding of the distinguishing characteristics
+and relative serviceability of each of the common types of roadway
+surface.
+
+Experience with classes made up of students in agriculture or
+agricultural engineering and with trade school students in road making
+served as a guide in the selection and arrangement of the material.
+Detailed discussion of tests of materials and of the theory of design
+has to a considerable extent been eliminated as being outside of the
+scope of the course for which the text is intended.
+
+In the preparation of American Rural Highways reference was had to
+many books on highway subjects and to current periodical literature.
+Wherever direct extracts were made from such source, appropriate
+acknowledgment appears in the text.
+
+                                             T. R. AGG
+
+  AMES, IOWA,
+  AUGUST 18, 1920.
+
+
+
+
+CONTENTS
+
+
+PREFACE                                                            vii
+
+
+CHAPTER I
+
+THE PURPOSE AND UTILITY OF HIGHWAYS
+
+Transportation Problem--National in Scope--Development in
+Traffic--Location or Farm to Market Traffic--Farm to Farm
+Traffic--Inter-City Traffic--Inter-County and Inter-State
+Traffic--Rural Education--Rural Social Life--Good Roads and
+Commerce                                                          1-12
+
+
+CHAPTER II
+
+HIGHWAY ADMINISTRATION
+
+Township Administration--County Administration--State
+Administration--Federal Administration--Special Assessments--Zone
+Method of Assessing--General Taxation--Vehicle Taxes--Sinking
+Fund Bonds--Annuity Bonds--Serial Bonds--Comparison of Methods
+of Issuing Bonds--Desirability of Road Bonds                      13-28
+
+
+CHAPTER III
+
+DRAINAGE OF ROADS
+
+The Necessity for Drainage--Importance of Design--Surface
+Drainage--Run-off--Ordinary Design of Ditches--Underground
+Water--Tile Drains--Lying Tile--Culverts--Length of Culvert--
+Farm Entrance Culverts--Metal Pipe--Clay and Cement Concrete
+Pipe--Concrete Pipe--Endwalls for Culverts--Reinforced Concrete
+Box Culverts--Drop Inlet Culverts                                29-41
+
+
+CHAPTER IV
+
+ROAD DESIGN
+
+Necessity for Planning--Road Plans--Problems of Design--
+Preliminary Investigations--Road Surveys--Alignment--
+Intersections--Superelevation--Tractive Resistance--Rolling
+Resistance--Internal Resistance--Air Resistance--Effect of
+Trades--Energy Loss on Account of Grades--Undulating Roads--
+Guard Railing--Width of Roadway--Cross Section--Control of
+Erosion--Private Entrances--Æsthetics                            42-62
+
+
+CHAPTER V
+
+EARTH ROADS
+
+Variations in Soils--Variation in Rainfall--Cross Sections
+Elevating Grader--Maney Grader--Slip Scraper--Fresno
+Scraper--Elevating Grader Work--Use of Blade Grader--
+Costs--Maintenance--Value of Earth Roads                         63-73
+
+
+CHAPTER VI
+
+SAND-CLAY AND GRAVEL ROADS
+
+The Binder--Top-soil or Natural Mixtures--Sand-clay on Sandy
+Roads--Sand-clay on Clay or Loam--Characteristics--Natural
+Gravel--The Ideal Road Gravel--Permissible Size of Pebbles--
+Wearing Properties--Utilizing Natural Gravels--Thickness
+of Layer--Preparation of the Road--Trench Method--Surface
+Method--Maintenance                                              74-88
+
+
+CHAPTER VII
+
+BROKEN STONE ROAD SURFACES
+
+Design--Properties of the Stone--Kinds of Rocks used for
+Macadam--Sizes of Stone--Earth Work--Foundation for the
+Macadam--Telford Foundation--Placing the Broken Stone--
+Rolling--Spreading Screenings--Bituminous Surfaces--Maintenance
+Characteristics                                                  89-97
+
+
+CHAPTER VIII
+
+CEMENT CONCRETE ROADS
+
+Destructive Agencies--Design--Concrete Materials--Fine
+Aggregate--Proportions--Measuring Materials--Preparation of the
+Earth Foundation--Placing Concrete for Two-course Road--Curing
+the Concrete--Expansion Joints--Reinforcing--Bituminous Coatings
+on Concrete Surfaces--Characteristics--Maintenance              98-105
+
+
+CHAPTER IX
+
+VITRIFIED BRICK ROADS
+
+Vitrified Brick--Paving Brick--Repressed Brick--Vitrified Fiber
+Brick--Wire-cut-lug Brick--Tests for Quality--Other Tests--
+Foundation--Sand Bedding Course--Sand Mortar Bedding Course--
+Green Concrete Bedding Course--Bituminous Fillers--Mastic
+Fillers--Marginal Curb                                         106-115
+
+
+CHAPTER X
+
+BITUMINOUS ROAD MATERIALS AND THEIR USE
+
+Classes of Bituminous Materials--Coal Tar--Water Gas Tar--Natural
+Asphalt--Petroleum Asphalt--Mixtures--Classification According to
+Consistency--Road Oils--Liquid Asphalts--Asphalt Cements--
+Fillers--Bitumen--Specifications--Surface Treatments--Applying
+the Bituminous Binder--Finishing the Surface--Patching--
+Penetration Macadam--Foundation--Upper or Wearing Course--
+Patching Characteristics--Hot Mixed Macadam--Foundation--Sizes
+of Stone--Mixing the Wearing Stone--Placing and Wearing
+Surface--Seal Coat--Characteristics--Asphaltic Concrete--
+Bitulithic or Warrenite--Topeka Asphaltic Concrete--Foundation
+--Placing the Surface--Characteristics                         116-129
+
+
+CHAPTER XI
+
+MAINTENANCE OF HIGHWAYS
+
+Petrol Maintenance--Gang Maintenance--Maintenance of Earth,
+Sand-clay, Gravel and Macadam Roads                            130-134
+
+
+Index                                                              135
+
+
+
+
+AMERICAN RURAL HIGHWAYS
+
+
+
+
+CHAPTER I
+
+THE PURPOSE AND UTILITY OF HIGHWAYS
+
+
+THE DEVELOPMENT OF HIGHWAY SYSTEMS
+
+=Transportation Problem.=--Public highways, like many other familiar
+things, are utilized constantly with little thought of how
+indispensable they are to the conduct of the business of a nation or
+of the intimate relation they bear to the everyday life of any
+community. The degree to which a nation or a community perfects its
+transportation facilities is an index of its industrial progress and
+public highways constitute an important element in the national
+transportation system. It is to be expected that the average citizen
+will think of the public highway only when it affects his own
+activities and that he will concern himself but little with the broad
+problem of highway improvement unless it be brought forcibly to his
+attention through taxation or by publicity connected with the
+advancement of specific projects.
+
+=National in Scope.=--The improvement and extension of the highway
+system is of national importance just as is development and extension
+of railways, and concerted action throughout a nation is a
+prerequisite to an adequate policy in regard to either. It is
+inconceivable that any community in a nation can prosper greatly
+without some benefit accruing to many other parts of the country.
+Increased consumption, which always accompanies material prosperity,
+means increased production somewhere, and people purchase from many
+varied sources to supply the things that they want. Good
+transportation facilities contribute greatly to community prosperity
+and indirectly to national prosperity, and the benefits of highly
+improved public highways are therefore national in scope. This fact
+has been recognized in Europe, notably in England, France and Belgium,
+where the public highways are administered largely as national
+utilities.
+
+Until recent years, highway improvement in the United States has been
+subordinated to other more pressing public improvements, but during
+the World War the inadequacy of the transportation system of the
+United States became apparent. While such an unprecedented load upon
+transportation facilities may not recur for many years, it has become
+apparent that more rapid progress in highway improvement is necessary
+and in the United States the subject is now likely to receive
+attention commensurate with its importance.
+
+=Development of Traffic.=--The character and extent of the highway
+improvement needed in any locality is dependent entirely on the
+demands of traffic. In sparsely settled areas, particularly those that
+are semi-arid or arid, the amount of traffic on local roads is likely
+to be small and the unimproved trails or natural roads adequate. But
+as an area develops either on account of agricultural progress or the
+establishment of industrial enterprises, the use of the public
+highways both for business and for pleasure increases and the old
+trails are gradually improved to meet, at least to some degree, the
+new demands of traffic. In sparsely settled areas, it is possible for
+the public to accommodate its use of the highways to the physical
+condition thereof, and business is more or less regulated according to
+the condition of the roads. This is not always pleasant or economical
+but is the only possible arrangement. In populous districts, with
+diversified activities, it becomes imperative to have year-round
+usable roads in order to transact with reasonable dispatch the regular
+business of the industries. Anything less will handicap normal
+community progress.
+
+The advent of the motor driven vehicle in the United States has
+resulted in a greatly increased use of the public highways of
+agricultural areas, even of those that are sparsely populated, because
+of the convenience of the motor vehicle both for passenger and for
+freight service. Probably in excess of 90 per cent of the tonnage
+passing over the rural highways in the United States is carried by
+motor vehicles. This class of traffic has really just developed and no
+one can predict what it will be in ten years, yet it has already
+introduced into the highway problem an element that has revolutionized
+methods of construction and maintenance.
+
+A different set of traffic conditions exists in those parts of the
+United States where large areas are devoted primarily to industrial
+pursuits, the agricultural development being of secondary importance.
+Public highways connecting the industrial centers are indispensable
+adjuncts to the business facilities in such communities and are
+ordinarily subjected to a very large volume and tonnage of traffic
+consisting principally of motor vehicles. The roads first selected for
+improvement will not be those serving the agricultural interests of
+the district, but rather those serving the industrial centers.
+Inter-city roads of great durability and relatively high cost are
+necessary for such traffic conditions.
+
+Not infrequently the transportation needs will require a system of
+both inter-city and rural highways in the same community. There are
+few areas in the United States where there is no agricultural
+development. It is apparent therefore that the nature of the highway
+systems and the administrative organization under which they are built
+and maintained will differ in various states or areas according to
+the nature of development of that area agriculturally and
+industrially. In planning improvements of highway systems, it is
+recognized that one or more of several groups of traffic may be
+encountered and that the extent and nature of the improvement must be
+such as will meet the requirements of all classes of traffic, the most
+important being first provided for, and that of lesser importance as
+rapidly as finances permit.
+
+
+KINDS OF TRAFFIC ON PUBLIC HIGHWAYS
+
+=Local or Farm to Market Traffic.=--In strictly agricultural
+communities the principal use of the highways will pertain to
+agricultural activities and most of it will be between the farm and
+the most convenient market center. In the ordinary state, the number
+of rural families will not average more than six to eight per square
+mile, but in some districts it may reach twenty families per square
+mile. The travel from the district around a market center will
+originate in this rather sparsely populated area and converge onto a
+few main roads leading to market. The outlying or feeder roads will be
+used by only a few families, but the density of traffic will increase
+nearer the market centers and consequently the roads nearer town will
+be much more heavily traveled than the outlying ones. It is apparent
+therefore that considerable difference may exist in the kind of
+construction adequate for the various sections of road where farm
+traffic is the principal consideration. This traffic is made up of
+horse drawn wagons, transporting farm products and of horse drawn and
+motor passenger vehicles, the motor traffic comprising 80 per cent or
+more of the volume of traffic and a greater per cent of the tonnage.
+Motor trucks are now employed to some extent for marketing farm
+products and, where surfaced highways have been provided, this class
+of traffic is superseding horse drawn traffic.
+
+=Farm to Farm Traffic.=--In the ordinary prosecution of farming
+operations, a considerable amount of neighborhood travel is
+inevitable. Farmers help each other with certain kinds of work,
+exchange commodities such as seed, machinery and farm animals and
+visit back and forth both for business and pleasure. To accommodate
+this traffic, it is desirable to provide good neighborhood roads.
+Traffic of this sort follows no particular route and can to some
+extent accommodate itself to the condition of the highways without
+entailing financial loss, although some discomfort and some
+inconvenience may result from inadequate highway facilities. This
+traffic will be partly motor and partly horse drawn, but the
+proportion of motor driven is large.
+
+=Inter-city Traffic.=--In strictly agricultural districts there is a
+large amount of travel between towns, both for business and for
+pleasure. The pleasure travel is mostly in motor vehicles and a
+considerable part of the business traffic is the same, although horse
+drawn vehicles are employed to some extent.
+
+In industrial districts there is a large volume of this class of
+traffic consisting of motor passenger vehicles used for business and
+for pleasure and of motor freight vehicles used for general business
+purposes. In addition, there is certain to be a large amount of motor
+truck freight traffic incident to the particular industrial pursuits
+of the cities. Where adequate public highways connect industrial
+centers, there is invariably a very large amount of inter-city
+traffic, due in part to the needs of industry and in part to
+concentration of population in industrial centers.
+
+=Inter-County and Inter-State Traffic.=--Automobile touring is a
+popular means of relaxation, especially on the part of those who live
+in the cities, although it is by no means confined to them. Traffic of
+this kind follows the routes where roads are best and passes entirely
+across a county, attracted by some public gathering. Often it is
+inter-state in character, made up of tourists who are traveling to
+distant pleasure resorts. Such traffic at present constitutes a
+relatively small part of the travel on public highways, except on
+certain favorable routes, but as the wealth of the country increases
+and good touring roads are numerous, long distance travel will
+increase and will eventually necessitate the construction of a number
+of well maintained national highways, located with reference to the
+convenience of the automobile tourist.
+
+
+PUBLIC HIGHWAYS AND COMMUNITY LIFE
+
+It is well to recognize the intimate relation public highways bear to
+the economic progress of a nation. Normal development of all of the
+diverse activities of a people depends very largely upon the highway
+policy that is adopted and whether the actual construction of
+serviceable roads keeps pace with transportation needs.
+
+=Rural Education.=--It has become increasingly apparent during the
+World War that the demand upon North America for food stuffs is to
+become more and more insistent as the years pass. Already the
+consumption in the United States has approached quite closely to the
+average production and yet the population is constantly increasing.
+The time is not far distant when greater production will be required
+of the agricultural area in North America in order to meet the home
+demand for foodstuffs, and many thousands of tons will be needed for
+export. This need can only be met by agricultural methods that will
+increase greatly the present yield of the soil. The adoption of better
+agricultural methods must of necessity be preceded by the technical
+training of the school children who will be the farmers of the next
+generation, which can best be accomplished in graded schools with well
+equipped laboratories and with suitably trained teachers. The problem
+of providing such schools in rural communities has, in some instances,
+been solved by consolidating a number of rural school districts and
+constructing a well equipped building to accommodate the students from
+an area several miles square. An educational system of this sort can
+reach its highest usefulness only when adequate public highways
+facilitate attendance of pupils. The whole trend of rural educational
+progress is toward a system which is predicated upon a comprehensive
+highway policy in the district.
+
+=Rural Social Life.=--Closely allied to the rural educational problem
+is the rural social problem. Motor cars and good roads do a great deal
+to eliminate the isolation and lack of social opportunity that has
+characterized rural life in the United States. A high order of
+citizenship in rural communities is essential to the solution of many
+problems of rural economics, and such citizens will not live away from
+the social opportunities of modern life. The rural school house and
+the rural church may become social centers and local plays, moving
+picture shows and lectures and entertainments of other kinds made
+available to those who live in the country. Their enjoyment of these
+social opportunities will be much more general if the public highways
+are at all times in a condition to be traveled in comfort. Good homes
+and good schools on good roads are prerequisites to the solution of
+many rural problems.
+
+If there is opportunity for those who live in the cities to get some
+adequate idea of rural life and the conditions under which farming
+operations are carried on it will correct many misunderstandings of
+the broad problems of food production and distribution. Reference has
+frequently been made to the seeming desire on the part of city people
+to get into the country, and, by facilitating the realization of this
+desire, a great social service is rendered.
+
+=Good Roads and Commerce.=--That good highways are almost as necessary
+as are railroads to the commercial development of a nation is
+recognized but, unlike the railroads, the highways are not operated
+for direct profit and the responsibility of securing consideration of
+the demand for improvements is not centralized. Therefore, sentiment
+for road improvement has been of slow growth, and important projects
+are often delayed until long after the need for them was manifest.
+Movements to secure financial support for highway improvement must go
+through the slow process of legislative enactment, encountering all of
+the uncertainties of political action, and the resulting financial
+plan is likely to be inadequate and often inequitable.
+
+The whole commercial structure of a nation rests upon transportation,
+and the highways are a part of the transportation system. The highway
+problem can never receive adequate consideration until public highways
+are recognized as an indispensable element in the business equipment
+of a nation.
+
+During the World War all transportation facilities were taxed to the
+limit, and motor trucks were utilized for long distance freight
+haulage to an extent not previously considered practicable. As a
+result, the interest in the motor truck as an addition to the
+transportation equipment of the nation, has been greatly stimulated.
+Many haulage companies have entered the freight transportation field,
+delivering commodities by truck to distances of a hundred miles or
+more.
+
+The part the motor truck will play in the future can only be
+estimated, but it seems clear that the most promising field is for
+shipments destined to or originating in a city of some size and a
+warehouse or store not on a railroad spur, and especially when the
+shipments are less than car load lots. The delays and expense incident
+to handling small shipments of freight through the terminals of a
+large city and carting from the unloading station to the warehouse or
+other destination constitute a considerable item in the cost of
+transportation.
+
+Mr. Charles Whiting Baker, Consulting Editor of _Engineering
+News-Record_, states:[1]
+
+     [1] Engineering News Record, July 10, 1919.
+
+     "It costs today as much to haul a ton of farm produce ten miles
+     to a railway station as it does to haul it a thousand miles over
+     a heavy-traffic trunk-line railway. It often costs more today to
+     transport a ton of merchandise from its arrival in a long train
+     in the freight yard on the outskirts of a great city to its
+     deposit in the warehouse of a merchant four or five miles away
+     than it has cost to haul it over a thousand miles of railway
+     line."
+
+Nevertheless it seems probable that new methods of operating the motor
+truck transport, and possibly new types of trucks or trucks and
+trailers will be developed so that freight traffic over many roads
+will be of considerable tonnage and an established part of the
+transportation system of the nation. In the article above referred to
+are given the following data relative to the cost of hauling on
+improved roads by motor truck and these cost estimates are based on
+the best information available at this time. They should be considered
+as approximate only, but serve to indicate the limitations of the
+truck as a competitor of the steam railway.
+
+  TABLE 1
+
+  TRUCK OPERATION COSTS, FROM REPORTS BY SIX MOTOR TRUCK
+  OPERATORS, DIRECT CHARGES PER DAY
+
+  +---------+-------+-------+-------+-------+-------+-------+-----------
+            |   A   |   B   |   C   |   D   |   E   |   F   | Average
+            |       |       |       |       |       |       |     Total
+  +---------+-------+-------+-------+-------+-------+-------+-----------
+  Driver    | $5.00 | $5.20 | $5.00 | $5.00 | $5.17 | $5.50 |  $5.13
+  Tires     |  3.00 |  3.75 |  2.00 |  2.00 |  2.00 |  3.00 |   2.68
+  Oil, etc. |   .30 |  ...  |   .30 |   .50 |   .25 |   .25 |    .35
+  Gasoline  |  3.00 |  4.00 |  3.50 |  4.65 |  2.08 |  3.75 |   3.50
+            |       |       |       |       |       |       | ------
+            |       |       |       |       |       |       |     $11.66
+  +---------+-------+-------+-------+-------+-------+-------+-----------
+
+
+  INDIRECT CHARGES PER DAY
+
+  -------------+------+------+------+------+------+------+------------
+               |      |      |      |      |      |      | Average
+               |   A  |   B  |   C  |   D      E  |   F  |      Total
+  -------------+------+------+------+------+------+------+------------
+  Depreciation | $3.50| $4.19| $3.60| $3.40| $3.67| $4.00| $3.77
+  Interest     |  1.20|  1.26|  1.08|  1.22|  1.10|  1.00|  1.15
+  Insurance    |  1.50|  2.54|  1.26|  2.10|   .86|   .50|  1.47
+  Garage       |  1.00|  1.20|  1.00|  1.00|   .89|  1.00|  1.01
+  Maintenance  |   .50|   ...|   .50|   ...|  1.00|   ...|   .75
+  Overhaul     |  1.33|  2.75|  1.80|  1.60|  2.00|  3.00|  2.07
+  License      |   .17|   .27|   .20|   .20|   .20|   .20|   .20
+  Body upkeep  |   .25|   ...|   .30|   .10|   .40|   ...|   .27
+               |      |      |      |      |      |      | ----
+               |      |      |      |      |      |      |      $10.69
+  Supervision  |   .50|  2.93|  2.05|  1.90|  ... |  ... |  1.90  1.90
+  Lost time    |  2.20|  ... |  1.67|  3.40|  2.50|  1.97|  2.57  2.57
+               | -----| -----| -----| -----| -----| -----| -----------
+               | 23.45| 28.09| 24.26| 28.07| 22.12| 24.17|       26.82
+  -------------+------+------+------+------+------+------+------------
+
+  TABLE 2
+
+  OVERHEAD CHARGES PER YEAR FOR A 5-TON CAPACITY GASOLINE
+  MOTOR TRUCK RUNNING AN AVERAGE OF 50 MILES PER DAY
+  FOR 240 DAYS PER YEAR
+
+  Driver's wages[1]                                               $1500
+  Depreciation (20% on $6000 investment)                           1200
+  Interest (6% on $6000 investment)                                 360
+  Insurance                                                         450
+  Garage (rental, upkeep, etc.)                                     300
+  Maintenance, minor repairs and supplies, tire chains, tools,
+  lamps, springs, equipment, etc. (estimated)                       300
+  Complete overhaul once a year                                     600
+  License fee                                                        60
+  Body upkeep, repairs, painting, etc.                               90
+  Supervision                                                       696
+                                                                  -----
+  Total per annum                                                 $5556
+
+  Overhead charges per day for 240 days in the year,
+  actual operation                                            $23.15
+  Overhead charges per mile for 50 miles per day                 .463
+
+    [1] In the above table the driver's wages have been placed under
+    overhead charges because the driver is paid by the month and his
+    wages continue even though the truck is idle because of repairs,
+    bad weather or lack of business, unless, of course, the idleness
+    should be of long duration, when the driver might be laid off.
+
+  DIRECT CHARGES PER DAY AND PER MILE FOR 5-TON TRUCK
+  OPERATED AS ABOVE
+
+  ------------------------------------------------+---------+---------
+                                                  |  Cost   |  Cost
+                                                  | per day | per mile
+  ------------------------------------------------+---------+---------
+  Tires (based on present tire guarantee)         |  $3.00  |  $0.06
+  Lubricants                                      |    .50  |    .01
+  Gasoline (3-1/2 miles per gal., 14 gal. at 25c) |   3.50  |    .07
+                                                  |  -----  |  -----
+                                                  |   7.00  |   0.14
+  ------------------------------------------------+---------+---------
+
+  Total of overhead and direct charges for 240 days per year operation,
+      per day                                                    $30.15
+  Per mile                                                          .603
+  Cost per ton-mile for full loads one way and empty returning      .2412
+  Cost per ton-mile for full loads one way and half load returning  .16
+
+The significance of these figures becomes apparent when they are
+compared with the cost of hauling freight over trunk-line railways
+with heavy traffic where the cost per ton-mile, including terminal
+charges, ranges from 1.7 _mills_ per ton-mile to 4.4 _mills_ per
+ton-mile.
+
+In view of these facts it seems reasonable to suppose that motor
+vehicles for use on the public highways are more likely to be employed
+to supplement the rail transport than to compete with it. To the
+actual cost of operation of motor trucks given in Table 2, there
+should be added the proportionate cost of maintaining the highway for
+the use of the truck, which is partly covered by the item "License
+Fee" in the table. The license fee would necessarily be considerably
+larger if it were to compensate adequately for the wear on the
+highways over which the trucks operate. This will still further
+increase the cost of hauling by motor truck.
+
+Motor trucks are employed for many kinds of hauling where their speed
+and consequently their daily capacity is an advantage over team
+hauling that is decidedly worth while. It probably could be shown
+that for many kinds of hauling, teams are more economical than motor
+trucks, but when promptness and speed and the consequent effect on
+dependent activities are considered, the motor truck often has a
+distinct advantage, and the use of the truck to replace horse drawn
+vans is progressing rapidly. This is true not only in the cities, but
+also in the smaller towns and in the country. Motor trucks have been
+adopted in a great many communities for delivery of farm products to
+market, and this use of the truck is certain to increase rapidly. But
+trucks in this service will use the secondary roads as well as the
+main or primary roads.
+
+These observations emphasize the extent to which the highway policy of
+the nation must be predicated on the use of the highways by motor
+vehicles.
+
+
+
+
+CHAPTER II
+
+HIGHWAY ADMINISTRATION
+
+
+The systems of highway administration extant in the various political
+units in the United States present a patchwork of overlapping
+authority and undetermined responsibility. Highway laws are being
+constantly revised by state legislatures and with each revision there
+is some change in administrative methods and often the changes are
+revolutionary in character. In most states, the trend is away from
+county and township administration and toward state administration,
+with provision for considerable participation by the federal
+government.
+
+It will be pertinent to consider briefly the present functions of each
+of the administrative authorities having duties in connection with
+highway work in the United States, although these duties vary greatly
+in the several states and change periodically with the action of
+legislatures.
+
+=Township Administration.=--Township or "Town" authority is a survival
+of the old New England town government and the town board consists of
+three or more trustees who hold office for fixed terms. The usual term
+is three years, but is less in some states. The incumbent is generally
+a man who has other responsibilities of a public or private nature and
+who gives but little of his time to highway matters. In some states
+the pay is a fixed annual salary and in others a per diem with some
+limitation on the amount that may be drawn in any one year, which
+limitation may be statutory or may be by common consent.
+
+The township highway commissioners or trustees have jurisdiction over
+certain of the roads in the township, usually best described as all
+roads not by law placed under the jurisdiction of some other
+authority. In certain instances, the township authorities have charge
+of all of the roads in the township, which would mean that no "county"
+or "state" roads happened to be laid out in that township. It is a
+matter of general observation that the trend of legislation is toward
+removing from the jurisdiction of the township officials all roads
+except those upon which the traffic is principally local in character.
+The actual mileage of roads in the United States that is at present
+administered by township officials is large, probably constituting not
+less than seventy per cent of the total mileage.
+
+In most states the township officials are responsible for the
+maintenance of the roads under their jurisdiction and also supervise
+such new construction as is undertaken. This includes the construction
+of culverts and bridges as a rule, but in some states the county board
+of supervisors is responsible for all of the bridge and culvert work
+on the township roads. In other states, the township board is
+responsible only for bridges or culverts that cost less than a certain
+amount specified by law (usually about $1000) and the county board
+provides for the construction and upkeep of the more expensive bridges
+and culverts.
+
+Funds for the work carried out by the township road officials are
+obtained by general taxation, the amount that may be levied being
+limited by statute and the actual levy being any amount up to the
+maximum that the township board deems necessary for its purposes. It
+is the general observation that the tax levy is usually the maximum
+permitted by law.
+
+In many states, township officials are permitted to issue bonds for
+road construction, almost invariably, however, with the restriction
+that each issue must be approved by the voters of the township. There
+is always a provision that the total amount of bonds outstanding must
+not exceed the constitutional limit in force in the state. In several
+states, the townships have large amounts of road bonds outstanding.
+
+=County Administration.=--In some states the county is the smallest
+administrative unit in the road system. A county board, called the
+board of county supervisors or board of county commissioners
+consisting of from three to fifteen members, is the administrative
+authority. Its members are elected for fixed terms which vary in
+length from one to five years. The county board usually has many
+public responsibilities other than highway administration, and is
+generally made up of men with considerably more business ability than
+the average township board.
+
+The county board has jurisdiction over all of the highways in the
+county in some states, and in others it has charge of only the more
+important highways. In most states, the laws set forth specifically
+what highways shall be under the jurisdiction of the county
+authorities.
+
+In addition to having direct supervision of the improvement and
+maintenance of the roads assigned to county administration, the county
+boards in some states arrange for the construction of all culverts and
+bridges on the roads that are under township supervision, or at least
+the more expensive bridges and culverts on such roads. Sometimes this
+is accomplished by granting county aid for township bridges, under
+which system the county pays a part of the cost of the construction of
+bridges on the township roads. The amount of aid varies, but is
+generally about one-half of the cost, and the township and county
+officials jointly assume the responsibility of arranging for the
+construction by contract or otherwise.
+
+The county board obtains funds for road work through a direct tax on
+all property in the county, the maximum rate being limited by statute.
+County boards are also authorized to issue bonds for road construction
+under statutory restrictions and limitations similar to those
+effective in the township as to total amount issued, and many
+millions of dollars' worth of highway bonds have been issued by
+county authorities in the United States.
+
+=State Administration.=--In a state, the administrative authority in
+highway matters is vested in a board of commissioners usually
+consisting of three or more members. In a few states, the
+administrative authority is delegated to a single commissioner. Where
+the authority is vested in a board, that board is usually appointed by
+the governor. In several states one or more members of the commission
+hold that position _ex officio_; for example, in several states the
+governor is by law a member of the commission, in others the secretary
+of state or the dean of engineering at the State University or the
+state geologist is a member of the commission. Where the
+administrative authority is a single commissioner he may be elected
+along with other state officers, but this is the case in only a few
+states.
+
+The authority of the state highway department varies in the several
+states, but in general the departments serve in the dual capacity of
+general advisers to the county and township authorities on road
+matters and as the executive authority responsible for the
+construction of those highways that are built entirely or in part from
+state or federal funds.
+
+State highway departments consist of the commission or commissioner,
+and the technical and clerical staff required to perform the duties
+imposed on the state organization. To some extent the state highway
+departments are able to encourage economical and correct construction
+of highways by the township and county authorities by furnishing them
+standard plans and specifications and by formulating regulations to
+govern the character of construction, but such efforts are likely to
+be more or less ineffective unless the state authority has supervision
+of the allotment of state or federal funds to the various counties and
+townships. Nevertheless, most state highway departments do a great
+deal of advisory work in connection with the highway construction
+carried out by county and township authorities.
+
+State highway departments are supported by funds obtained in various
+ways, laws differing greatly in this respect. The necessary support is
+in some states appropriated from funds obtained by general taxation,
+and is in others obtained from automobile license fees. In still
+others, the funds are secured by a combination of the two methods
+mentioned above. In addition to these support funds, a certain part of
+the money obtained as federal aid may be employed for the engineering
+and inspection costs on federal aid roads. The above mentioned funds
+are required to maintain the state highway department. In addition,
+the departments have supervision of the expenditures of construction
+funds which can be used for road construction and maintenance, and may
+not be expended for salaries or other overhead expense.
+
+In a number of states, automobile license fees are set aside for
+financing road construction and maintenance, and the work paid for
+from the fees is carried out under the supervision of the state
+highway department.
+
+In a number of instances, state bonds have been issued for road
+construction, and the expenditure of the proceeds of the sale of road
+bonds has usually been supervised by the state highway department.
+
+All federal aid funds allotted to a state must be expended under the
+direction of the state highway department.
+
+=Federal Administration.=--Federal authority in highway work is vested
+in the Bureau of Public Roads of the United States Department of
+Agriculture. The official head is the Secretary of Agriculture, but
+the administrative head is the Director of the Bureau. In this Bureau
+are the various instrumentalities needed for carrying on
+investigations and furnishing information to the various states on
+highway subjects. The Bureau also supervises the construction of
+federal aid roads in a general way through district engineers, each
+of whom looks after the work in several states.
+
+Funds for the support of the Bureau of Public Roads are obtained from
+congressional appropriations to the Department of Agriculture and from
+a percentage of the funds appropriated for federal aid.
+
+Federal aid is money appropriated by Congress to be distributed to the
+various states to stimulate road construction. It is granted to the
+states on the condition that the states will expend at least an equal
+amount on the projects involved. The states in turn usually give a
+suitable part of the state allotment to each county. There are various
+limitations as to the amount of federal aid per mile of road and the
+type of construction that may be employed, but these are matters of
+regulation that change from time to time.
+
+It will be seen that each of the administrative authorities, except
+the Bureau of Public Roads, is to some extent subservient to a higher
+authority, and the Bureau of Public Roads is supervised by the United
+States Congress. Considerable diplomacy is required on the part of any
+administrative authority if his contact with other officials is to be
+without friction. This is especially true in connection with the
+formulation of a policy regarding the types of construction to be
+adopted for an improvement. The responsibility for the selection is
+variously placed on the township, county or state authority, the laws
+not being uniform in this respect. If state or federal funds are
+allotted to an improvement, the state authority either makes the
+selection of the type of construction or the selection is made by some
+subordinate authority subject to the approval of the state highway
+department. Where the improvement is paid for exclusively with
+township or county funds, the selection is often made by the township
+or county authority without review by higher authority. Many abuses
+have crept into highway administration through the unscrupulous
+methods of promoters of the sale of road materials or road machinery.
+A great deal of the selling activity of the agents for these
+commodities is entirely irreproachable, but it is well known that such
+is not always the case. As a result, the tendency of legislation is to
+require the state highway department to approve contracts for
+materials or construction entered into by the township or county
+authorities. The state highway departments can secure the requisite
+technical experts to determine the merits of materials and equipment
+and, in spite of some glaring examples of inefficiency or worse, have
+made a good record for impartiality and integrity as custodians of the
+funds for which they are responsible.
+
+
+HIGHWAY FINANCE
+
+The paramount problem in highway administration is the development of
+an adequate financial plan for carrying on road improvement. The
+necessary expenditures are enormous, although the money so expended is
+probably much less than the actual benefit resulting from the
+improvements.
+
+=Special Assessments.=--There is presumed to be a direct and
+recognized benefit conferred on farm lands by the construction of
+improved highways adjacent thereto. Therefore, it is equitable to
+charge a part of the cost against the lands so benefited.
+
+The principle of paying for public improvements by a special
+assessment upon private property has been long established and a large
+proportion of the public improvements in the cities and towns have
+been made financially possible through the medium of special
+assessments on abutting and adjacent property. The same principle has
+been applied to the financing of drainage projects for reclaiming farm
+lands. Recently the special assessment method has come into limited
+use in financing rural highway improvements. The policy in such cases
+is to assess the abutting and adjacent property in a zone along the
+improved road for a percentage of the cost of the improvement. The
+amount so assessed does not ordinarily exceed one-fourth of the total
+cost of the improvement and may be considerably less. The assessment
+is spread over an area extending back from one to six miles from the
+improved road. The assessment area is generally divided into about
+four zones parallel to the road. The zone next the road is assessed at
+a rate arbitrarily determined as a fair measure of the benefit, and
+each succeeding zone is assessed at a somewhat lower rate. Generally
+about three-fourths of the total assessment is placed on the half of
+the assessment area lying next to the road.
+
+Many systems of making assessments have been proposed which are
+mechanical in application after the area and rate of distribution of
+benefit have been established, but in practice it is always found
+necessary to make adjustments on individual parcels of land because of
+variation in benefits received and it is impossible to eliminate the
+exercise of human judgment in equalizing the assessments.
+
+=Zone Method of Assessing.=--The area to be assessed on each side of
+the improved road is divided into zones usually four in number, but a
+larger or smaller number of zones may be adopted. The rate for each
+zone is then arbitrarily determined. For a typical case, the first of
+four zones would receive an assessment of 50 per cent of the amount to
+be borne by the area; the second zone 25 per cent, the third 15 per
+cent and the fourth 10 per cent. Other percentages sometimes adopted
+are 45, 25, 20 and 10 and 60, 20, 15 and 5. The set of percentages
+first mentioned seems to insure the most equitable distribution for an
+area all of which is substantially equally productive.
+
+When a road, for the improvement of which an assessment is being made,
+lies on two or more sides of a parcel of land all of which is within
+the assessment area, the rate is arbitrarily reduced to relieve that
+parcel of land somewhat, or the assessment is first spread as above
+outlined and afterward equalized as judgment dictates.
+
+In applying the zone method some difficulty is encountered in
+determining an equitable distribution on those parcels of land lying
+partly in one zone and partly in another, but the rate may be arrived
+at with reasonable accuracy by pro-rating in accordance with the exact
+conditions.
+
+In. Fig. 1, let it be assumed that the assessment area is to be two
+miles wide, one mile on each side of the road and the various
+ownerships to be indicated by the parcels of land numbered 1 to 8, as
+shown. Each zone for the assessment of the 3-1/4 mile section is 1/4
+mile wide and the rates for the several zones are 50, 25, 15 and 10
+per cent respectively. Let it be assumed that the portion of the cost
+of the 3-1/4 miles of road to be assessed on the area shown is
+$20,000. The assessment would then be as follows:
+
+  ------+-------+----------------------+------------+-------------
+        |       |  Rate × frontage on  | Amount of  |
+  Parcel|  Rate |  improved road =     | Assessment |  Assessment
+        |       |  assessment units    | per unit[1]|
+    1   |    2  |         3            |     4      |      5
+  ------+-------+----------------------+------------+-------------
+    1   |  a 50 |  50 × 2640 = 132,000 | $0.016655  |  $1558.46
+        |  b 75 |  75 × 1320 =  99,000 |            |   1153.90
+    2   |    40 |  40 × 2640 = 105,600 |            |   1230.77
+    3   |    10 |  10 × 2640 =  26,400 |            |    307.69
+    4   |    25 |  25 × 1320 =  33,000 |            |    384.66
+    5   | [2]85 |  85 × 5280 = 448,800 |            |   5230.88
+    6   |    15 |  15 × 5280 =  79,200 |            |   923.08
+    7   | [2]65 |  65 × 7920 = 514,800 |            |   6000.00
+    8   |    35 |  35 × 7920 = 277,200 |            |   3230.77
+        |       |  ------------------- |            | -----------
+        |       |            1,716,000 |            | $20000.00
+  ------+-------+----------------------+------------+-------------
+
+    [1] The assessment per unit is obtained by dividing the total
+    assessment by the total of column three.
+
+    [2] On these two parcels, it is decided that more than half of
+    the zone rate should apply to the half of the zone toward the
+    improved road, but some modification of the rates adopted might be
+    justified.
+
+[Illustration: Fig. 1]
+
+The assessment of the cost of the east and west one-mile section of
+road is made up in like manner, and let it be assumed that the portion
+of the cost of this road that is to be assessed on the area shown is
+$5500. The assessment area will be one mile wide and each zone
+one-fourth mile in width and the rates for each zone the same as
+before.
+
+  ------+-------+----------------------+------------+-------------
+        |       |  Rate × frontage on  | Amount of  |
+  Parcel| Rate  |  improved road =     | Assessment | Assessment
+        |       |  assessment units    | per unit   |
+  ------|-------+----------------------+------------+-------------
+  1     | a 75  |  75 x 1320 =  99,000 | $0.010417  |  $1031.25
+        | b 15  |  15 x 2640 =  39,600 |            |    412.49
+  2     |   75  |  75 x 2640 = 198,000 |            |   2062.53
+  3     |   50  |  50 x 1320 =  66,000 |            |    687.51
+  4     | a 25  |  25 x 1320 =  33,000 |            |    756.25
+        | b 15  |  15 x 2640 =  39,600 |            |
+  5     |   10  |  10 x 3300 =  33,000 |            |    343.73
+  6     |   10  |  10 x 1980 =  19,800 |            |    206.24
+  ------|-------|                      |            |-------------
+        |       |              528,000 |            |   5500.00
+  ------+-------+----------------------+------------+-------------
+
+It will be noted that the combined assessment for the two sections of
+road is especially heavy on parcels 1, 2 and 3. In order to prevent
+unjust charges against such properties, laws usually limit the total
+assessment against any parcel of land to a fixed percentage of a fair
+market value or of the assessed value. The assessment on these parcels
+would be reduced as seemed expedient and the deficit would be
+distributed over the remainder of the area in the same manner as the
+original assessment was spread. In practice such re-distribution is
+ordinarily made by the arbitrary adjustment in accordance with what
+the authorized officials consider to be fair and equitable. The method
+outlined is merely a mechanical means of securing distribution and
+must not be considered as an infallible method of making the
+assessment. It is always necessary to review the results in the light
+of the actual benefits to be presumed for each parcel of land.
+Nevertheless, the method outlined will prove equitable in a majority
+of cases.
+
+=General Taxation.=--There is a general community benefit derived from
+the construction of good roads in that the actual cost of marketing
+farm products is lessened with a resulting lowering of the price to
+the consumer. The benefit also accrues from the greater facility with
+which all community business may be conducted. The introduction of
+better opportunities for social, religious and educational activities
+in the rural districts which results from improved highways is also a
+community benefit of no mean importance. A part of the cost of road
+improvement may therefore be equitably paid from funds obtained by
+general taxation.
+
+A considerable portion of the current expense of maintaining the
+township and county highway work and at least a part of the cost of
+maintaining state highway activities is met from funds obtained by
+general taxation. Likewise, the funds required for the amortization of
+bond issues are often obtained from general taxation although vehicle
+license fees are sometimes used for that purpose.
+
+General taxes are levied on all taxable property in a political unit
+under statutory provisions regulating the amount of the levy and the
+purpose for which the revenue is to be used. In the aggregate, the
+road taxes are large but in the township or county the rate is
+generally small compared to some other taxes, such as the school tax.
+
+=Vehicle Taxes.=--The great direct benefit derived by those who
+actually operate vehicles over the roads justifies the policy of
+requiring a vehicle to pay a license fee in lieu of other taxes, the
+funds so obtained to be used for the construction and maintenance of
+public highways. In practice, this method has already been applied to
+motor vehicles in most states and has proven to be an important source
+of revenue. Its application to horse-drawn vehicles has not been
+attempted, due probably to the fact that such horse-drawn vehicles as
+use the public highways are also employed about the farm or in the
+towns and the determination of an equitable basis for taxation
+involves many difficulties.
+
+The rate of the fee for motor vehicles should be based on their
+destructive effect on the road so far as that is possible. The scale
+of fees should therefore take account of weight and speed of vehicle
+and if the license is in lieu of all other taxes, it should also be
+graduated with the cost of the vehicle.
+
+When funds are thus derived, every precaution should be taken to
+insure that the money is used judiciously for construction and
+especially for maintenance on those roads most useful to motor
+traffic.
+
+=Highway Bonds.=--Bond issues for road improvement afford a means of
+constructing roads and paying for them while they are being used. A
+very large volume of such bonds are outstanding in the United States.
+Road bonds should be issued only for durable types of improvement and
+the life of the bond should be well within the probable useful life of
+the road surface. It is customary and highly desirable that the
+general nature and extent of the improvement be established before the
+bonds are issued. It is desirable that bond issues be subject to
+approval by referendum before issue and that is provided in every
+instance.
+
+Highway bonds are of three classes known as Sinking Fund, Annuity and
+Serial Bonds, respectively. The earlier bonds issued were almost all
+of the sinking fund class, but in recent years the serial bond has
+been widely employed and is probably the most satisfactory to
+administer.
+
+=Sinking Fund Bonds.=[1]--When this type of bond is employed, the
+amount of the expenditure for road improvement is determined upon and
+the length of the period during which tax payments shall be made is
+settled. To employ a concrete example, it may be assumed that $100,000
+is to be expended for road work and is to be paid at the end of ten
+years. The interest rate on the bonds will vary with the condition of
+the bond market and the stability of the political unit issuing the
+bonds, but is usually about 5 per cent. Knowing these factors, the
+amount to be added to the sinking fund each year is computed. In order
+to pay the interest on the bonds, a tax of suitable rate is levied,
+and in order to retire the bonds at the end of the period, a sum is
+set aside each year which is supposed to be invested and draw interest
+which will be added to the principle, and the principle and interest
+comprise the sinking fund. The principle of the sinking fund is
+obtained by tax levies, a sum being added to the principle of the
+sinking fund each year.
+
+    [1] For a more detailed discussion of highway bonds see Bulletin
+    136, U. S. Dept. of Agriculture, which is the basis of this
+    discussion.
+
+The success of this method of financing depends upon the proper
+administration of the sinking fund. It must be invested with fidelity
+and the fund be kept intact. Usually the sinking fund cannot be
+invested at as high a rate of interest as the bonds bear and there is
+some loss as a result. Road bonds bearing 5 per cent interest can
+usually be sold at par while the sinking fund will usually net about 3
+or 3-1/2 per cent interest. The total cost of a bond issue will be
+greater by the sinking fund method than by either of the other methods
+described.
+
+=Annuity Bonds.=--Annuity bonds are drawn in such a manner that the
+amount of the payment for principle and interest is the same each year
+during the life of the bond. When the amount of the issue and the rate
+of interest has been determined and the amount of the desired annual
+payment has been determined, the number of years the bonds must run is
+computed.
+
+This method is convenient in that the amount of the tax to be levied
+each year remains constant.
+
+=Serial Bonds.=--Serial bonds are drawn so that a uniform amount of
+the principle is retired each year after retirement starts and the
+total interest payments decrease each year after the first bonds are
+retired. The first bond may not be retired for a number of years after
+the issue of the bonds, but when it once starts retirement proceeds at
+a constant rate annually.
+
+=Comparison of Methods of Issuing Bonds.=--The relative costs of
+financing by either of the three methods depends upon the rate of
+interest in each case and the net rate secured on the sinking fund
+provided for retiring sinking fund bonds.
+
+For comparative purposes, some typical examples are given in Table 3.
+These illustrate the differences in total cost of securing $100,000 by
+each of the three methods at various interest rates.
+
+  TABLE 3
+
+  TOTAL COST OF A LOAN OF $100,000 FOR 20 YEARS, INTEREST
+  COMPOUNDED ANNUALLY
+
+  ---------+---------------------------------------+---------+---------
+  Annual   |        Sinking Fund Compounded        |         |
+  Interest |              Annually at              |         |
+  on Bonds +----------+----------------+-----------+ Annuity |  Serial
+           |3 per cent| 3-1/2 per cent | 4 per cent|         |
+  ---------+----------+----------------+-----------+---------+---------
+  4        | $154,431 | $150,722       | $147,163  |$147,163 | $142,000
+  4-1/2    |  164,431 |  160,722       |  157,163  | 153,752 |  147,250
+  5        |  174,431 |  170,722       |  167,163  | 160,485 |  152,500
+  5-1/2    |  184,431 |  180,722       |  177,163  | 167,359 |  157,750
+  6        |  194,431 |  190,722       |  187,163  | 174,369 |  163,000
+  ---------+----------+----------------+-----------+---------+---------
+
+=Desirability of Road Bonds.=--In theory the bond method of financing
+enables the highway authorities to construct a large mileage of roads
+in a few years and spreads the cost over the period during which the
+public is being benefited. Better prices are obtained on contracts for
+a large mileage than for smaller jobs, and the community can receive
+the benefit more quickly than where construction proceeds piecemeal
+with current funds. The vital consideration is to insure that the term
+of the bonds is well within the useful life of the road, and that
+ample provision is made to maintain the roads during that period.
+Under proper restrictions the bond method of financing is to be
+commended. The bonds are an attractive investment and readily
+marketable on satisfactory terms.
+
+
+
+
+CHAPTER III
+
+DRAINAGE OF ROADS
+
+
+=The Necessity for Drainage.=--The importance of drainage for all
+roads subject to the effects of storm or underground water has always
+been recognized by road builders, but during recent years constantly
+increasing attention has been given to this phase of road
+construction. It is unfortunate that there has in the past been some
+tendency to consider elaborate drainage provisions less necessary
+where rigid types of surfaces were employed. It has become apparent,
+from the nature of the defects observed in all sorts of road surfaces,
+that to neglect or minimize the importance of drainage in connection
+with either earth roads or any class of surfaced roads is to invite
+rapid deterioration of some sections of the roadway surface and to add
+to maintenance costs.
+
+The degree to which lack of drainage provisions affect the
+serviceability of the road surface varies with the amount of
+precipitation in the locality and the manner in which it is
+distributed throughout the year. In the humid areas of the United
+States, which are, roughly, those portions east of a north and south
+line passing through Omaha and Kansas City, together with the northern
+part of the Pacific slope, precipitation is generally in excess of 30
+inches per year and fairly well distributed throughout the year, but
+with seasonal variations in rate. In these areas, the effect of the
+precipitation, both as regards its tendency to lower the stability of
+soils and as an eroding agent, must be carefully provided against in
+highway design.
+
+Outside of the areas mentioned above, the precipitation is much less
+than 30 inches per year and its effect as an agent of erosion is of
+greatest significance, although in restricted areas there may be short
+periods when the soil is made unstable by ground water.
+
+=Importance of Design.=--The drainage system for a proposed road
+improvement ought to be designed with as much care as any other
+element, and, to do so, a study must be made of all factors that have
+any bearing on the drainage requirements and the probable
+effectiveness of the proposed drainage system. The well established
+principles of land drainage should be followed so far as applicable.
+
+The basic principle of road drainage is to minimize the effect of
+water to such an extent that there will always be a layer of
+comparatively dry soil of appreciable thickness under the traveled
+part of the road. This layer should probably never be less than two
+feet thick and for soils of a structure favorable to capillary action
+it should be at least three feet thick. The means employed to
+accomplish the requisite drainage will be as various as the conditions
+encountered.
+
+=Surface Drainage.=--The drainage method which is by far the most
+nearly general in application is that which utilizes open ditches, and
+the system which employs these ditches is usually referred to as
+surface drainage. The full possibilities of this method of minimizing
+the effects of storm water are rarely fully utilized in road
+construction. Very frequently, deterioration of a road surface is
+directly attributable to failure to provide adequately for the removal
+of the storm water or water from the melting of snow that has fallen
+on the road, or water that flows to the road from land adjacent
+thereto. Surface water can usually most cheaply and expeditiously be
+carried away in open ditches, although special conditions are
+occasionally encountered which require supplementary tile drains. The
+cross section commonly adopted for roads lends itself naturally to the
+construction of drainage ditches at the sides of the traveled way, and
+these are usually the principal dependence for the disposal of storm
+water.
+
+=Run-off.=--The capacity required of side ditches to insure
+satisfactory surface drainage will be affected by the amount and
+nature of the precipitation in the region where the road is built. The
+annual rainfall in a region may amount to several feet, but may be
+well distributed throughout the year with an absence of excessive
+rainfall for short periods, that is, flood conditions may rarely
+occur. In other areas, the annual rainfall may be comparatively small
+but the precipitation occurs at a very high rate, that is, flood
+conditions may be common, or it may be at a low rate extending over a
+considerable period. These peculiarities must be known before an
+adequate drainage system can be planned.
+
+It is almost universally true in the United States that precipitation
+at a very high rate will be for a relatively short duration, and
+during these short periods, which usually do not exceed thirty
+minutes, a portion of the water that falls on the areas adjacent to
+the road and that drains to the road ditches will soak into the soil
+and therefore not reach the ditches along the road. The extent to
+which the water is taken up by the soil will vary with the porosity
+and slope of the land and the character of the growth thereon.
+Cultivated land will absorb nearly all of the water from showers up to
+fifteen or twenty minutes duration; grass land a somewhat smaller
+percentage; and hard baked or other impervious soil will absorb a
+comparatively small amount. Rocky ground and steep slopes will absorb
+very little storm water.
+
+The surface of the road is designed to turn water rapidly to the
+ditches, but when the material is the natural soil, there is always
+considerable absorption of storm water. Surfaces such as sandclay,
+gravel and macadam do not absorb to exceed 10 per cent of the
+precipitation during short showers. Bituminous surfaces, brick and
+concrete pavements, do not absorb an appreciable amount of storm
+water.
+
+Generally it is best to assume that if a rain lasts for forty-five
+minutes or more, all of the water will run off, as the soil will reach
+a state of saturation in that time. This is not true of deep sand, but
+is for nearly all other soils.
+
+The ditch capacity needed will therefore depend upon the area drained,
+the character of the soil, the slopes and the rainfall characteristics
+of the region, and upon the nature of the road surface.
+
+For a required capacity, the cross section area of the ditch will vary
+inversely as the grade, because the velocity of flow increases with an
+increase in the grade of the ditch. If the surface water must be
+carried along the road for distances exceeding five or six hundred
+feet, the ditch must be constructed of increasing capacity toward the
+outlet in order to accommodate the accumulated volume of water.
+
+The velocity of flow varies not only with the grade, but with the
+shape of the cross section, cleanness of the channel, the depth of the
+water in the channel, alignment of the channel and the kind of
+material in which the channel is formed. It is not necessary to go to
+great refinement in the design of the side ditches for the ordinary
+case where the water is carried along the road for only a few hundred
+feet. The ditches are made of ample capacity by using the commonly
+accepted cross section for a road, which will be discussed in a later
+paragraph. But where large areas must be drained by the road ditches,
+it is desirable carefully to design the side ditches. The basis for
+that design is too lengthy to be included herein, and reference should
+be made to a standard treatise on the subject.
+
+=Ordinary Design of Ditches.=--For grades of one per cent or less on
+roads in the humid area, the bottom of the ditch should be at least
+three and one-half feet lower than the traveled surface of the road,
+except for very sandy soil. For grades greater than one per cent, this
+depth may be decreased one foot, and for grades of four per cent and
+upward, the depth may be still less. These general rules for depth are
+susceptible of variation but are believed to be the minimum except in
+arid or semi-arid climates. It is far better to be too liberal in
+ditch allowance than to be too conservative. In arid or semi-arid
+regions, the ditch design will be based on the necessity of providing
+for flood flow and preventing damage through erosion. Ordinary
+drainage requirements will be satisfactory with the ditch about one
+foot deep.
+
+If the topography is such that it is evident considerable storm water
+will flow from the adjacent land to the road ditches, the design must
+be modified to take this into account. Sometimes such water can be
+diverted by ditches well back from the road, and thus prevented from
+flowing into the side ditches along the roadway. It is especially
+desirable to divert water, which would otherwise flow down the slope
+of a cut, by means of a ditch on the hill-side above the upper edge of
+the slope of the cut.
+
+Ditches are not effective unless they afford a free flow throughout
+their length and have an outlet to a drainage channel of ample
+capacity. Therefore, ditch grades should be established by survey,
+especially if the gradient is less than one per cent, and the
+construction work should be checked to insure that the ditch is
+actually constructed as planned. A few high places in the ditch will
+greatly reduce the effectiveness, although these may appear at the
+time of construction to be slight. Constricted places, such as might
+be due to a small amount of loose earth left in the ditch, are always
+to be avoided.
+
+Where the side ditch passes from a cut to the berm alongside a fill,
+the ditch should be excavated throughout in the undisturbed natural
+soil, five feet or more from the toe of the slope of the fill, and
+along the filled portion of the road there should be a berm of three
+or four feet between the toe of the slope of the fill and the near
+edge of the ditch.
+
+=Underground Water.=--In a preceding paragraph, mention was made of
+the fact that only a part of the storm water runs off over the surface
+of the ground, the larger part being absorbed by the soil. The water
+thus absorbed flows downward through the pores in the soil until it is
+deflected laterally by some physical characteristic of the soil
+structure. The movement of underground water is affected by many
+circumstances, but only two conditions need be discussed herein.
+
+Underground water, like surface water, tends to attain a level
+surface, but in so doing it may need to flow long distances through
+the pores of the soil, and to overcome the resistance incident to so
+doing some head will be required. That is to say, the water will be
+higher at some places than at others. If a cut is made in grading the
+road, the road surface may actually be lower than the ground water
+level in the land adjoining the road. As a result, the water will seep
+out of the side slopes in the cut and keep the ditches wet, or even
+furnish enough water to occasion a flow in the ditch. Similarly, the
+higher head of the underground water near the top of a hill may result
+in ground water coming quite close to the surface some distance down
+the hill. The remedy in both cases is tile underdrains alongside the
+road to lower the ground water level so that it cannot affect the road
+surface.
+
+Sometimes the ground water encounters an impervious stratum as it
+flows downward through the soil, or one that is less pervious than the
+surface soil. When such is the case, the water will follow along this
+stratum, and should there be an outcrop of the dense stratum, a spring
+will be found at that place. This may be on a highway. The impervious
+stratum may not actually outcrop but may lie only a few feet under the
+surface of the road, in which case, the road surface will be so water
+soaked as to be unstable. The so-called "seepy places" so often noted
+along a road are generally the result of this condition. This
+condition can be corrected by tile laid so as to intercept the flow at
+a depth that precludes damage to the road. Commonly, the tile will be
+laid diagonally across the road some distance above the section where
+the effect of the water is noted, and will be turned parallel to the
+road at the ditch line and carried under one of the side ditches to an
+outlet.
+
+=Tile Drains.=--Where the soil and climatic conditions are such that
+the roadway at times becomes unstable because of underground water
+rising to a level not far below the road surface, the ground water
+level is lowered by means of tile underdrains. The function of the
+tile drains in such cases is precisely the same as when employed in
+land drainage; to lower the ground water level.
+
+=Laying Tile.=--The tile lines are usually laid in trenches parallel
+to the center line of the road near the ditch line and at least 4 feet
+deep so as to keep the ground water level well down. They must be
+carefully laid to line and grade. A good outlet must be provided and
+the last few joints of pipe should be bell-and-spigot sewer pipe with
+the joints filled with cement mortar. The opening of the tile should
+be covered with a coarse screen to prevent animals from nesting in the
+tile.
+
+It is frequently necessary to lay a line of tile at the toe of the
+slope in cuts to intercept water that will percolate under the road
+from the banks at the sides. In some cases, it is desirable to
+back-fill the tile trench with gravel or broken stone to insure rapid
+penetration of surface water to the tile. In other instances, it is
+advantageous to place catch basins about every three or four hundred
+feet. These may be of concrete or of tile placed on end or may be
+blind catch basins formed by filling a section of the trench with
+broken stone. When a blind catch basin is used, the top should be
+built up into a mound, and for a tile or concrete catch basin, a
+grating of the beehive type should be used, so that flow to the tile
+will not be obstructed by weeds and other trash that is carried to the
+catch basin.
+
+=Culverts.=--Culverts and bridges are a part of the drainage system
+and the distinction between the two is merely a matter of size.
+Generally, structures of spans less than about eight feet are classed
+as culverts, but the practice is not uniform. In this discussion
+culverts will be defined as of spans of 8 feet or less.
+
+Numerous culverts are required to afford passage for storm water and
+small streams crosswise of the road, and their aggregate cost is a
+large item in the cost of road improvement. The size of the waterway
+of a culvert required in any location will be estimated by an
+inspection of the stream and existing structure, and by determining
+the extent and physical characteristics of the drainage area.
+Sometimes there is sufficient evidence at the site to indicate quite
+closely the size required, but this should always be checked by
+run-off computations. The drainage area contributing water to the
+stream passing through the culvert under consideration is computed
+from contour maps or from a survey of the ground, and the size of
+culvert determined by one of the empirical formulas applicable to that
+purpose. In these formulas, the solution depends upon the proper
+selection of a factor "C" which varies in accordance with the nature
+of the drainage area. Two of these that are quite widely used are as
+follows:
+
+  _Myers' Formula: a = CA_
+
+Where _a_ = area of cross section of culvert in square feet. _A_ =
+area in acres of the drainage area above culvert. _C_ a factor varying
+from 1 for flat country to 4 for mountainous country or rocky soil,
+the exact value to be selected after an inspection of the drainage
+area.
+
+_Talbot's Formula_: Area of waterway in square feet =
+
+  _C_ [Square root of] ((Drainage area in acres)^3)
+
+     Transcriber's Note: The above formula used the mathematical
+     square root symbol in the original. One should read it as "C
+     times the square root of the Drainage area in acres cubed."
+
+_C_ being variable according to circumstances thus:
+
+"For steep and rocky ground _C_ varies from 2/3 to 1. For rolling
+agricultural country, subject to floods at times of melting snow, and
+with length of valley three or four times its width, _C_ is about 1/3,
+and if stream is longer in proportion to the area, decrease _C_. In
+districts not affected by accumulated snow, and where the length of
+valley is several times its width, 1/5 or 1/6 or even less may be
+used. _C_ should be increased for steep side slopes, especially if the
+upper part of the valley has a much greater fall than the channel at
+the culvert. The value of _C_ to be used in any case is determined
+after an inspection of the drainage area."
+
+[Illustration: Fig. 2. Design of Pipe Culvert and Bulkhead]
+
+=Length of Culvert.=--The clear length between end walls on a culvert
+should be at least equal to the width of the roadway between ditches.
+This is a minimum of 20 feet for secondary roads and ranges from 24 to
+30 feet for main roads. The headwall to the culvert should not be a
+monument, but should be no higher than needed to prevent vehicles from
+leaving the roadway at the culvert.
+
+=Farm Entrance Culverts.=--At farm entrances, culverts are required to
+carry the farm driveway across the side ditch of the road. These
+culverts are usually about 16 feet along, and should be of a size
+adequate to take the flow of the side ditch. The farm entrance culvert
+should be of such design that it can be easily removed to permit
+cleaning out the ditches with a road grader.
+
+
+TYPES OF CULVERTS
+
+Culverts constructed of concrete and poured in place are called box
+culverts because of the rectangular form of the cross section.
+Culverts of pre-cast pipe are known as pipe culverts. Several forms of
+pipe culvert are in general use.
+
+[Illustration: Fig. 3.--Typical Concrete Box Culvert]
+
+=Metal Pipe.=--These may be of cast iron, steel or wrought iron. The
+cast iron pipe is very durable but expensive and heavy to handle and
+is not widely used in highway construction. Steel pipe has been
+employed to a limited extent but its durability is questioned. At
+least it is known that the pipe made from uncoated, light sheet steel
+is not very durable. Sheet iron and sheets made from alloy iron
+coated with spelter have been extensively used and seem to be durable,
+especially when laid deep enough to eliminate possibility of damage
+from heavy loads. To insure reasonable resistance to corrosion, the
+metal sheets should be coated with at least one and one-half ounces of
+spelter per square foot of sheet and the sheets should not be lighter
+than 16 gauge for small sizes and should be heavier for the larger
+sizes.
+
+=Clay and Cement Concrete Pipe.=--The ordinary burned clay bell and
+spigot pipe that is employed for sewer construction is sometimes used
+for culverts. It must be very carefully bedded, preferably on a
+concrete cradle and the joints filled with cement mortar. Culverts of
+this type have a tendency to break under unusual loads, such as
+traction engines or trucks. They may be damaged by the pressure from
+freezing water, particularly when successive freezing and thawing
+results in the culvert filling with mushy snow, which subsequently
+freezes.
+
+=Concrete Pipe.=--Reinforced concrete pipe is a satisfactory material
+for culverts, if the pipe is properly designed. The pipe should be
+carefully laid on a firm earth bed with earth carefully back-filled
+and tamped around the pipe. The joints in the pipe should be filled
+with cement mortar, or should be of a design that will be tight.
+
+=Endwalls for Culverts.=--A substantial retaining wall is placed at
+each end of the culvert barrel, whatever the type. This is to prevent
+the end of the culvert from becoming choked with earth and to retain
+the roadway at the culvert. It also indicates to the drivers the
+location of the end of the culvert. The endwall extends a foot or more
+below the floor of the culvert to prevent water from cutting under the
+barrel. Plain concrete or stone masonry are most commonly used for
+culvert endwalls.
+
+[Illustration: Fig. 4.--Two Types of Drop Inlet Culvert]
+
+=Reinforced Concrete Box Culverts.=--The pipe culvert is limited in
+application to the smaller waterways. Reinforced concrete is
+extensively used for culverts of all sizes, but especially for the
+larger ones. These are usually constructed with endwalls integral with
+the barrel of the culvert. Culverts of this type must be designed for
+the loads anticipated to insure suitable strength and stability, and
+must be constructed of a good quality of concrete. Figs. 2 and 3 show
+designs for pipe and box culverts.
+
+[Illustration: Fig. 5.--Drop Inlet Culvert]
+
+=Drop Inlet Culverts.=--In some locations erosion has begun in the
+fields adjacent to a culvert and it will probably continue until the
+stream above the culvert has eroded to about the level of the floor of
+the culvert. This is a reason for placing the culvert as high as the
+roadway will permit, so long as the area above the culvert will be
+properly drained. Considerable reclamation of land is possible if the
+culvert is constructed with a box at the inlet and as shown in Fig. 4.
+The area up-stream from the culvert will not erode below the level of
+the top of the box at the inlet end.
+
+Where the stream crossing the road has eroded to considerable depth or
+has considerable fall, as would sometimes be the case on side hill
+roads, the culvert barrel would follow the general slope of the ditch
+but should have a drop inlet. This type of culvert is shown in Fig.
+5.
+
+
+
+
+CHAPTER IV
+
+ROAD DESIGN
+
+
+=Necessity for Planning.=--Sometimes highway improvement is the result
+of spasmodic and carelessly directed work carried out at odd times on
+various sections of a road, finally resulting in the worst places
+being at least temporarily bettered. The grade on the steepest hills
+is probably reduced somewhat and some of the worst of the low lying
+sections are filled in and thereby raised. Short sections of surfacing
+such as gravel or broken stone may be placed here and there. From the
+standpoint of the responsible official, the road has been "improved,"
+but too often such work does not produce an improvement that lasts,
+and sometimes it is not even of any great immediate benefit to those
+who use the roads. In nearly every instance such work costs more in
+money and labor that it is worth.
+
+Lasting improvement of public highways can be brought about only
+through systematic and correlated construction carried on for a series
+of years. In other words, there must be a road improvement policy
+which will be made effective through some agency that is so organized
+that its policies will be perpetuated and is clothed with enough
+authority to be capable of enforcing the essential features of good
+design and of securing the proper construction of improvements.
+
+Details of highway construction and design must vary with many local
+conditions and types of surface. The limits of grades and the many
+other details of design may properly be adopted for a specific piece
+of work only after an adequate investigation of the local requirements
+and in the light of wide experience in supervising road improvement.
+
+New ideas are constantly being injected into the art of road building,
+but these are disseminated somewhat slowly, so that valuable devices
+and improvements in methods remain long unknown except to the
+comparatively few who have the means for informing themselves of all
+such developments.
+
+It follows then that the logical system of conducting road improvement
+is through an agency of continuing personnel which will supervise the
+preparation of suitable plans and direct the construction in
+accordance with the most recent experience.
+
+=Road Plans.=--The information shown on the plans prepared for road
+improvement varies somewhat with the design and with the ideas of the
+engineer as to what constitutes necessary information, but in general
+the plans show the existing road and the new construction contemplated
+in an amount of detail depending principally upon the character of the
+construction. Simple plans suffice for grade reduction or reshaping an
+earth road surface, while for the construction of paved roads, the
+plans must be worked out in considerable detail. The essential
+requirement is that there be given on the plans all information
+necessary to enable the construction to be carried out according to
+the intentions of the engineer, that all parts of the work fit
+together, that the culverts are of the proper size and located at the
+proper places, ditches drain properly, grades are reduced to the
+predetermined rate, that excavated material is utilized and that an
+exact record of the work done is retained. Plans are indispensable to
+economical road construction and the preparation of the plans is the
+work of the expert in road design, that is, the highway engineer.
+
+=Problem of Design.=--The problem of road design is to prepare plans
+for a road improvement with the various details so correlated as to
+insure in the road constructed in accordance therewith the maximum of
+safety, convenience and economy to the users thereof. The degree to
+which the design will be effective will depend to a considerable
+extent upon the financial limitations imposed upon the engineer, but
+skill and effort on the plans will do a great deal to offset financial
+handicap and no pains should be spared in the preparation of the
+plans. Moreover, the plans must afford all of the information needed
+by the contractor in preparing a bid for the work.
+
+=Preliminary Investigation.=--The first step in road improvement is to
+secure an adequate idea of the existing conditions on the road or
+roads involved. The detail to which this information need go will
+depend entirely upon the purpose of the preliminary investigation, for
+before a definite plan is prepared, it may be necessary to choose the
+best from among several available routes. For this purpose, it is not
+always necessary to make an actual instrument survey of the several
+routes. A hasty reconnaissance will usually be sufficient. This is
+made by walking or riding over the road and noting, in a suitable book
+or upon prepared blanks, the information needed. The items of
+information recorded will usually be as follows: distances, grades,
+type of soil on the road and nature of existing surface, character of
+drainage, location of bridges and culverts and the type of each with
+notes as to its condition, location of railway crossings and notes as
+to type, location of intersecting roads, farm entrances, and all
+similar features that have a bearing on the choice of routes. These
+data can be obtained in a comparatively short time by a skilled
+observer who may drive over the road in a motor car. Sometimes it may
+be desirable to make a more careful study of some certain sections of
+road and this may be done by waking over the section in question in
+order to make a more deliberate survey of the features to be
+considered than is possible when riding in a motor car.
+
+Factors other than relative lengths of routes will obviously determine
+the cost of improvement and the comparative merits of the improved
+roads. Some special characteristic of a road, such as bad railroad
+crossings or a few bad hills, may eliminate a route, or availability
+of materials along a route may offset disadvantages of alignment or
+grade.
+
+In special cases, complete surveys of routes may be required finally
+to select the best route, but these instances are few in number.
+
+=Road Surveys.=--When a road has been definitely selected for
+improvement, a careful survey is made to furnish information for the
+preparation of the plans. This will consist of a transit survey and a
+level survey.
+
+The transit survey is made by running a line between established
+corners following the recorded route of the road, or if no records are
+available or the road is irregular in alignment, by establishing
+arbitrary reference points and running a line along the center line of
+the existing road or parallel thereto. The topography is referenced to
+this line in such completeness that it can be reproduced on the plans.
+The level survey consists in taking levels on cross sections of the
+road at one hundred foot intervals, and oftener if there are abrupt
+changes in grade. Special level determinations are made at streams,
+railroad crossings, intersecting roads or lanes and wherever it
+appears some special features of the terrain should be recorded.
+
+From the surveys and such other information as has been assembled
+relative to the project, a plan is prepared which embodies a design
+presumed to provide for an improvement in accordance with the best
+highway practice.
+
+
+THE PROBLEM OF DESIGN
+
+It will be convenient to consider separately the components of a road
+design, although in the actual design the consideration of these
+cannot be separated because all parts of the plan must fit together.
+
+=Alignment.=--The alignment of the road is determined to a
+considerable extent by the existing right-of-way, which may follow
+section lines, regardless of topography, as is the case with many
+roads in the prairie states, or it may follow the valleys, ridges, or
+other favorable location in hilly country. In many places the roads of
+necessity wind around among the hills in order to avoid excessive
+grades. In designing an improvement, it is generally desirable to
+follow the existing right-of-way so far as possible. But the element
+of safety must not be lost sight of, and curves should not preclude a
+view ahead for sufficient distance to insure safety to vehicles. The
+necessary length of clear view ahead is usually assumed to be 250
+feet, but probably 200 feet is a satisfactory compromise distance when
+a greater distance cannot be obtained at reasonable cost. To secure
+suitable sight distance, the curves must be of long radii, and where
+possible the right-of-way on the inside of the curve should be cleared
+of trees or brush that will obstruct the view. Where the topography
+will not permit a long radius curve and the view is obstructed by an
+embankment or by growing crops or other growth, it is desirable to
+separate the tracks around the curve to eliminate the possibility of
+accidents on the curve. This is readily accomplished if the road is
+surfaced, but if it is not surfaced, the same end is accomplished by
+making the earth road of ample width at the curve.
+
+Relocations should be resorted to whenever they shorten distances or
+reduce grades sufficiently to compensate for the cost.
+
+=Intersections.=--At road intersections, it is always difficult to
+design a curve that entirely meets the requirements of safety because
+there is not enough room in the right-of-way, and enough additional
+right-of-way must be secured to permit the proper design. It is not
+necessary to provide an intersection that is adapted to high speed
+traffic, where main roads cross, but, on the contrary, a design that
+automatically causes traffic to slow up has distinct advantages.
+
+Where a main route, improved with a hard surface, crosses secondary
+roads, it is satisfactory to continue the paved surface across the
+intersecting road at normal width and make no provision for the
+intersecting road traffic other than a properly graded approach at the
+intersection.
+
+=Superelevation.=--On all curved sections of road, other than
+intersections, account is taken of the tendency of motor cars to skid
+toward the outside of the curve. This tendency is counteracted by
+designing the cross section with superelevation.
+
+[Illustration: Fig. 6]
+
+In Fig. 6, _F_ represents the tangential force that tends to cause
+skidding. _W_ represents the weight of the vehicle in pounds, THETA
+= the angle of superelevated surface _c-d_, with the horizontal _c-a_.
+_R_ represents the radius of the curve upon which the vehicle is
+moving. _w_ is the component of the weight parallel to the surface
+_c-d_, _v_ = velocity of the vehicle in feet per second. _m_ = mass
+of vehicle = _W/g  THETA_
+
+
+                  _w_ = _W_ tan _THETA_
+
+
+               _mv^2_     _wv^2_
+       _F_ =  -------  =  ------
+                _R_        _gR_
+
+If _F_ = _w_ there will be no tendency to skid; hence the rate of
+superelevation necessary in any case is as follows:
+
+
+                         _Wv^2_
+      _W_ tan _THETA_ = -------
+                          _gR_
+
+
+                          _v^2_
+          tan _THETA_ = -------
+                          _gR_
+
+
+The amount of superelevation required, therefore, varies as the square
+of the velocity and inversely as the radius of the curve.
+
+Theoretically, the amount of the superelevation should increase with a
+decrease in the radius of the curve and should also increase as the
+square of the speed of the vehicle. On account of the variation in
+speeds of the vehicles, the superelevation for curves on a highway can
+only be designed to suit the average speed. At turns approaching
+ninety degrees, the curve is likely to be of such short radius that it
+is impossible to maintain the ordinary road speed around the curve,
+even with the maximum superelevation permissible. It is good practice
+to provide the theoretical superelevation on all curves having radii
+greater than 300 feet for vehicle speeds of the maximum allowed by
+law, which is generally about 25 miles per hour. Where the radii are
+less than 300 feet, the theoretical superelevation for the maximum
+vehicle speeds gives a superelevation too great for motor trucks and
+horse drawn vehicles and generally no charge is made in superelevation
+for radii less than 300 feet, but all such curves are constructed with
+the same superelevation as the curve with 300 foot radius.
+
+The diagram in Fig. 7 shows the theoretical superelevation for various
+curve radii.
+
+[Illustration: Fig. 7. Curves showing Theoretical Superelevation for
+Various Degrees of Curve for Various Speeds of Vehicle]
+
+At the intersection of important highways, the problem is complicated
+by the necessity for providing for through traffic in both directions
+and for traffic which may turn in either direction and the engineer
+must provide safe roadways for each class of traffic.
+
+=Tractive Resistance.=--The adoption of a policy regarding the grades
+on a road involves an understanding of the effect of variation in the
+character of the surface and in rate of grade upon the energy required
+to transport a load over the highway. The forces that oppose the
+movement of a horse drawn vehicle are fairly well understood and their
+magnitude has been measured by several observers, but comparatively
+little is known about the forces opposing translation of rubber tired
+self-propelled vehicles.
+
+The resistance to translation of a vehicle is made up of three
+elements: resistance of the road surface to the rolling wheel,
+resistance of the air to the movement of the vehicle and internal
+friction in the vehicle itself.
+
+=Rolling Resistance.=--When the wheel of a vehicle rolls over a road
+surface, both the wheel and the surface are distorted. If the wheel
+has steel tires and the road surface is plastic, there will be
+considerable distortion of the road surface and very little of the
+wheel. A soft rubber tire will be distorted considerably by a brick
+road surface. Between these extremes there are innumerable
+combinations of tire and road surface encountered, but there is always
+a certain amount of distortion of either road surface or wheel, or of
+both, which has the same effect upon the force necessary for
+translation as a slight upward grade. When both the tire and the road
+surface strongly resist distortion (as steel tires on vitrified brick
+paving), the resistance to translation is low but the factor of impact
+is likely to be introduced. Where impact is present, energy is used up
+in the pounding and grinding of the wheels on the surface, and this
+factor increases as the speed of translation, and may be a
+considerable item. Impact is especially significant on rough roads
+with motor vehicles, particularly trucks, traveling at high speed.
+These two factors (impact and rolling resistance) combined constitute
+the major part of the resistance to translation for horse drawn
+vehicles.
+
+=Internal Resistance.=--For horse drawn vehicles, the internal
+resistance consists of axle friction, which is small in amount. For
+self-propelled vehicles, the internal resistance consists of axle
+friction and friction in the driving mechanism, of which gear
+friction and the churning of oil in the gear boxes is a large item.
+Internal friction is of significance in all self-propelled vehicles
+and especially so at high speeds.
+
+=Air Resistance.=--At slow speeds, the resistance of still air to
+translation is small, but as the speed increases, the air resistance
+increases rapidly and at the usual speed of the passenger automobile
+on the road becomes a very considerable part of the total resistance
+to translation. This factor has no significance in connection with
+horse drawn vehicles, but is to be taken into account when dealing
+with self-propelled vehicles at speeds in excess of five miles per
+hour.
+
+Many determinations of tractive resistance with horse drawn vehicles
+have been made from time to time and these show values that are fairly
+consistent when the inevitable variations in surfaces of the same type
+are taken into account. Table 4 is a composite made up of values
+selected from various reliable sources and Table 5 is from experiments
+by Professor J. B. Davidson on California highways.
+
+  TABLE 4
+
+  AVERAGE TRACTIVE RESISTANCE OF ROAD SURFACES TO STEEL TIRED
+  VEHICLES
+
+  Surface               Tractive force per ton
+
+  Earth packed and dry           100
+  Earth dusty                    106
+  Earth muddy                    190
+  Sand loose                     320
+  Gravel good                     51
+  Gravel loose                   147
+  Cinders well-packed             92
+  Oiled road--dry                 61
+  Oiled road--wet                108
+  Macadam--very good              38
+  Macadam--average                46
+  Sheet asphalt                   38
+  Asphaltic concrete              40
+  Vitrified brick--new            56
+  Wood block--good                33
+  Wood block--poor                42
+  Cobblestone                     54
+  Granite tramway                 27
+  Asphalt block                   52
+  Granite block                   47
+
+  TABLE 5
+
+  TRACTIVE RESISTANCES TO STEEL TIRED VEHICLES[1]
+
+  ----------+-----------------+-----------------+-----------+-----------
+            |                 |    Condition    | Tractive  | Resistance
+   Test No. |  Kind of Road   |     of Road     | Total lb. | per ton lb.
+  ----------+-----------------+-----------------+-----------+-----------
+   29-30-31 | Concrete        |Good, excellent  |    83.0   |   27.6
+            |   (unsurfaced)  |                 |           |
+   [2]11-12 | Concrete        |Good, excellent  |    90.0   |   30.0
+            |    (unsurfaced) |                 |           |
+   26-27-28 | Concrete 3/8-in.|Good, excellent  |   147.6   |   49.2
+            |   surface       |                 |           |
+            |   asphaltic oil |                 |           |
+            |   and screenings|                 |           |
+      13-14 | Concrete 3/8-in.|Good, excellent  |   155.0   |   51.6
+            |   surface       |                 |           |
+            |   asphaltic oil |                 |           |
+            |   and screenings|                 |           |
+       9-10 | Macadam,        |Good, excellent  |   193.0   |   64.3
+            |   water-bound   |                 |           |
+      22-23 | Topeka on       |Good, excellent  |   205.5   |   68.5
+            |   concrete      |                 |           |
+          8 | Gravel          |Compact, good    |   225.0   |   75.0
+            |                 |  condition      |           |
+   [3]45-48 | Oil macadam     |Good, new        |   234.5   |   78.2
+   [4]46-47 | Oil macadam     |Good, new        |   244.0   |   81.3
+         38 | Gravel          |Packed, in       |   247.0   |   82.3
+            |                 |  good condition |           |
+   18-19-20 | Topeka on plank |Good condition,  |   265.0   |   88.3
+            |                 |  soft, wagon    |           |
+            |                 |  left marks     |           |
+         34 | Earth road      |Firm, 1-1/2-in.  |   276.0   |   92.0
+            |                 |  fine loose dust|           |
+      24-25 | Topeka on plank |Good condition,  |   278.0   |   92.6
+            |                 |  but soft       |           |
+      1-2-5 | Earth road      |Dust 3/4 to 2 in.|   298.0   |   99.3
+        3-3 | Earth           |Mud, stiff, firm |   654.0   |  218.0
+            |                 |  underneath     |           |
+        6-7 | Gravel          |Loose, not packed|   789.0   |  263.0
+  ----------+-----------------+-----------------+-----------+-----------
+
+    [1] Prof. J. B. Davidson in _Engineering News-Record_, August 17,
+    1918.
+
+    [2] Graphic record indicates that the load was being accelerated
+    when test was started.
+
+    [3] Drawn with motor truck at 2-1/2 miles per hour.
+
+    [4] Drawn with motor truck at 5 miles per hour.
+
+Comparatively few data are available showing the tractive resistance
+of motor vehicles, but the following tables are based on sufficient
+data to serve to illustrate the general trend.
+
+These data on the tractive resistances of an electric truck with solid
+rubber tires on asphalt and bitulithic, wood, brick and granite block,
+water-bonded and tar macadam, cinder and gravel road surfaces were
+obtained by A. E. Kennelly and O. R. Schurig in the research division
+of the electrical engineering department of the Massachusetts
+Institute of Technology, and are published in Bulletin No. 10 of the
+division.
+
+An electric truck was run over measured sections, ranging from 400 to
+2600 feet in length, surfaced with these various materials, at certain
+speeds per hour, ranging from about 8 to about 15.5 miles per hour.
+The result of the observations of speeds, tractive resistances,
+conditions of surfaces, etc., were collected and studied in various
+combinations.
+
+  TABLE 6
+
+  ----------------------+-----------------------+-----------+----------
+                        |                       | Tractive  | Tractive
+                        |                       |Resistance |Resistance
+    Type of Surface     | Condition of Surface  |  in lbs.  |  in lbs.
+                        |                       |  per ton  |  per ton
+                        |                       | 10 miles  |12.4 miles
+                        |                       |  per hr.  |  per hr.
+  ----------------------+-----------------------+-----------+----------
+  Asphalt               | Good                  |   20.4    |
+  Asphalt               | Poor                  |   22.6    |   25.5
+  Wood block            | Good                  |   24.2    |   25.3
+  Brick block           | Good                  |   24.6    |   26.6
+  Granite block         | Good                  |   40.3    |   45.75
+  Brick block           | Slightly worn         |   25.1    |   28.0
+  Granite block with    |                       |           |
+    cement joints       | Good                  |   25.5    |   30.2
+  Macadam, water bonded | Dry and hard          |   23.3    |   25.8
+  Macadam, water bonded | Fair, heavily oiled   |   35.9    |   38.7
+  Macadam, water bonded | Poor, damp, some holes|   36.3    |   41.6
+  Tar macadam           | Good                  |   25.7    |   28.0
+  Tar macadam           | Very soft             |   36.8    |   38.7
+  Tar macadam           | Many holes, soft,     |           |
+                        |  extremely poor       |   52.4    |   60.6
+  Cinder                | Fair, hard            |   27.5    |   30.6
+  Gravel                | Fair, dusty           |   30.4    |   33.0
+  ----------------------+-----------------------+-----------+----------
+
+[Illustration: Fig. 8]
+
+=Effect of Grades.=--Grades increase or decrease the resistance to
+translation due to the fact that there is a component of the weight of
+the vehicles parallel to the road surface and opposite in direction to
+the motion when the load is ascending the hill and in the same
+direction when the vehicle is descending. In Fig. 8 _W_ represents the
+weight of the vehicle, acting vertically downward, _w_ is the
+component of the weight perpendicular to the road surface and _W_{2}_
+is the component parallel to the road surface.
+
+    _W_{2}_     = _W_ tan _THETA_.
+
+    tan _THETA_ = 0.01 × per cent of grade.
+
+    _W_{2}_     = 0.01 _W_ × per cent grade.
+
+    _W_{2}_     = 0.01 × 2000 × per cent of grade, for each ton
+                      of weight of vehicle.
+
+  Hence _W_{2}_ = 20 lbs. per ton of load for each one per cent of
+                      grade.
+
+The gravity force acting upon a vehicle parallel to the surface on a
+grade is therefore 20 lbs. per ton for each one per cent of grade and
+this force tends either to retard or to accelerate the movement of the
+vehicle.
+
+Let _F_ = the sum of all forces opposing the translation of a vehicle.
+
+  _F = f_{r} + f_{i} + f_{p} + f_{a} + f_{g}_     (1)
+
+where
+
+  _f_{r}_ = rolling resistance of road surface.
+  _f_{i}_ = resistance due to internal friction in the vehicle.
+  _f_{p}_ = resistance due to impact of the road surface.
+  _f_{a}_ = resistance due to air.
+  _f_{g}_ = resistance due to grade, which is positive when
+      ascending and negative when descending.
+
+All of the above in pounds per ton of 2000 lbs.
+
+Let _T_ = the tractive effort applied to the vehicle by any means.
+
+_T_ >= must be greater than _F_ in order to move the vehicle.
+
+By an inspection of (1), it will be seen that for a given vehicle and
+any type of road surface, all terms are constant except _f_{a}_ and
+_f_{g}_. _f_{a}_ varies as the speed of the vehicle and the driver can
+materially decrease _f_{a}_ by reducing speed. _f_{g}_ varies with the
+rate of grade. For any vehicle loaded for satisfactory operation on a
+level road with the power available, the limiting condition is the
+factor _f_{g}_. If the load is such as barely to permit motion on a
+level road, any hill will stall the vehicle. Therefore, in practice
+the load is always so adjusted that there is an excess of power on a
+level road. If draft animals are employed the load is usually about
+one fourth of that which the animals could actually move by their
+maximum effort for a short period. With motor vehicles, the excess
+power is provided for by gearing.
+
+If it be assured a load of convenient size is being moved on a level
+road by draft animals, there is a limit to the rate of grade up which
+the load can be drawn by the maximum effort of the animals.
+
+Tests indicate that the horse can pull at a speed of 2-1/2 miles per
+hour, an amount equal to 1/8 to 1/10 of its weight, and for short
+intervals can pull 3/4 of its weight. The maximum effort possible is
+therefore six times the average pull, but this is possible for only
+short intervals. A very short steep hill would afford a condition
+where such effort would be utilized. But for hills of any length, that
+is, one hundred feet or more but not to exceed five hundred feet, it
+is safe to count on the draft animal pulling three times his normal
+pulling power for sustained effort.
+
+The limiting grade for the horse drawn vehicle is therefore one
+requiring, to overcome the effect of grade, or _f_{g}_, a pull in
+excess of three times that exerted on the level.
+
+A team of draft animals weighing 1800 lbs. each could exert a
+continuous pull of about 1/10 of their weight or 360 lbs. If it be
+assumed that the character of the vehicle and the road surface is such
+that _f_{r}_ + _f_{i}_ + _f_{p}_ + _f_{a}_ = 100 lbs. per gross ton on
+a level section of road, then the gross load for the team would be 3.6
+tons. The same team could for a short time exert an additional pull of
+three times 360 lbs. or 1080 lbs. For each 1 per cent of grade a pull
+of 20 lbs. per ton would be required or _f_{g}_ for the 3.6 tons load
+would be 72 lbs. for each per cent of grade. At that rate, the
+limiting grade for the team would be fifteen per cent.
+
+If, however, the character of the vehicle and the road surface were
+such that _f_{r}_ + _f_{i}_ + _f_{p}_ + _f_{a}_ = 60 lbs. per gross
+ton on a level section of road, the gross load for the team on the
+level would be 6 tons, and the limiting grade 9 per cent.
+
+The above discussion serves to illustrate the desirability of adopting
+a low ruling or limiting grade for roads to be surfaced with a
+material having low tractive resistance and the poor economy of
+adopting a low ruling grade for earth roads or roads to be surfaced
+with material of high tractive resistance.
+
+It may be questioned whether horse drawn traffic should be the
+limiting consideration for main trunk line highways, but it is
+certain that for a number of years horse drawn traffic will be a
+factor on secondary roads.
+
+In the case of motor vehicles, excess power is provided by means of
+gears and no difficulty is encountered in moving vehicles over grades
+up to 12 or 15 per cent, so that any grade that would ordinarily be
+tolerated on a main highway will present no obstacle to motor
+vehicles, but the economy of such design is yet to be investigated.
+
+=Energy Loss on Account of Grades.=--Whether a vehicle is horse drawn
+or motor driven, energy has been expended in moving it up a hill. A
+part of this energy has been required to overcome the various
+resistances other than grade, and that has been dissipated, but the
+energy required to translate the vehicle against the resistance due to
+grade has been transformed into potential energy and can be partially
+or wholly recovered when the vehicle descends a grade, provided the
+physical conditions permit its utilization. If the grade is so steep
+as to cause the vehicle to accelerate rapidly, the brakes must be
+applied and loss of energy results. The coasting grade is dependent
+upon the character of the surface and the nature of the vehicle. In
+the cases discussed in the preceding paragraph, the coasting grades
+would be five per cent and three per cent respectively. For horse
+drawn vehicles then the economical grades would be three and five per
+cent, which again emphasizes the necessity of lower grades on roads
+that are surfaced than on roads with no wearing surface other than the
+natural soil.
+
+The theory of grades is somewhat different when motor vehicles are
+considered, since it is allowable to permit considerably higher speed
+than with horse drawn vehicles before applying the brakes and the
+effect of grade can be utilized not only in translating the vehicle
+down the grade, but also in overcoming resistances due to mechanical
+friction and the air. On long grades, a speed might be attained that
+would require the use of the brake or the same condition might apply
+on very steep short grades. There is at present insufficient data on
+the tractive resistance and air resistance with motor vehicles to
+permit the establishing of rules relative to grade, but experience
+indicates a few general principles that may be accepted.
+
+If a hill is of such rate of grade and of such length that it is not
+necessary to use the brake it may be assumed that no energy loss
+results so far as motor vehicles are concerned. Where there is no turn
+at the bottom of the hill and the physical condition of the road
+permits speeds up to thirty-five or forty miles per hour grades of
+five per cent are permissible if the length does not exceed five
+hundred feet and grades of three per cent one thousand feet long are
+allowable. It is a rather settled conviction among highway engineers
+that on trunk line highways the maximum grade should be six per cent,
+unless a very large amount of grading is necessary to reach that
+grade.
+
+=Undulating Roads.=--Many hills exist upon highways, the grade of
+which is much below the maximum permissible. If there are grades
+ranging from 0 to 4 per cent, with a few hills upon which it is
+impracticable to reach a grade of less than six per cent, it is
+questionable economy to reduce the grades that are already lower than
+the allowable maximum. It is especially unjustifiable to incur expense
+in reducing a grade from two per cent to one and one-half per cent on
+a road upon which there are also grades in excess of that amount. The
+undulating road is not uneconomical unless the grades are above the
+allowable maximum or are exceptionally long or the alignment follows
+short radius curves.
+
+=Safety Considerations.=--On hills it is especially desirable to
+provide for safety and curves on hills are always more dangerous than
+on level sections of road. Therefore, it is desirable to provide as
+flat grades as possible at the curves and to cut away the berm at the
+side of the road so as to give a view ahead for about three hundred
+feet. Whether a road be level or on a hill, safety should always be
+considered and the most important safety precaution is to provide a
+clear view ahead for a sufficient distance to enable motor vehicle
+drivers to avoid accidents.
+
+[Illustration: Fig. 9.--Types of Guard Rails]
+
+=Guard Railing.=--When a section of road is on an embankment, guard
+rails are provided at the top of the side slope to serve as warnings
+of danger, and to prevent vehicles from actually going over the
+embankment in case of skidding, or if for any reason the driver loses
+control. These are usually strongly built, but would hardly restrain a
+vehicle which struck at high speed. But they are adequate for the
+protection of a driver who uses reasonable care. A typical guard rail
+is shown in Fig. 9, but many other designs of similar nature are
+employed. At very dangerous turns a solid plank wall six or eight feet
+high is sometimes built of such substantial construction as to
+withstand the severest shock without being displaced.
+
+Trees, shrubs and the berms at the side of the road in cuts are
+particularly likely to obstruct the view and should be cleared or cut
+back so far as is necessary to provide the proper sight distance.
+
+=Width of Roadway.=--For roads carrying mixed traffic, 9 feet of width
+is needed for a single line of vehicles and 18 feet for 2 lines of
+vehicles. In accordance with the above, secondary roads, carrying
+perhaps 25 to 50 vehicles per day, may have an available traveled way
+18 feet wide. Those more heavily traveled may require room for three
+vehicles to pass at any place and therefore have an available traveled
+way 30 feet wide. Greater width is seldom required on rural highways,
+and 20 feet is the prevailing width for main highways.
+
+=Cross Section.=--The cross section of the road is designed to give
+the required width of traveled way, and, in addition, provide the
+drainage channels that may be needed. In regions of small rainfall the
+side ditches will be of small capacity or may be entirely omitted, but
+usually some ditch is provided. The transition from the traveled way
+to ditch should be a gradual slope so as to avoid the danger incident
+to abrupt change in the shape of the cross section. The depth of ditch
+may be varied without changing to width or slope of the traveled part
+of the road as shown in Fig. 10.
+
+[Illustration: Fig. 10]
+
+=Control of Erosion.=--The construction of a highway may be utilized
+to control general erosion to some extent, particularly when public
+highways exist every mile or two and are laid out on a gridiron
+system, as is the case in many of the prairie states. The streams
+cross the highways at frequent intervals and the culverts can be
+placed so as effectually to prevent an increase in depth of the
+stream. This will to some extent limit the erosion above the culvert
+and if such culverts are built every mile or two along the stream,
+considerable effect is produced.
+
+Where small streams have their origin a short distance from a culvert
+under which they pass, it is sometimes advisable to provide tile for
+carrying the water under the road, instead of the culvert, and, by
+continuing the tile into the drainage area of the culvert, eliminate
+the flow of surface water and reclaim considerable areas of land.
+
+Erosion in the ditches along a highway can be prevented by
+constructing weirs across the ditch at frequent intervals, thus
+effectually preventing an increase in the depth of the ditch.
+
+Wherever water flows at a velocity sufficient to produce erosion or
+where the drainage channel changes abruptly from a higher to a lower
+level, paved gutters, tile or pipe channels should be employed to
+prevent erosion.
+
+=Private Entrances.=--Entrance to private property along the highway
+is by means of driveways leading off the main road. These should
+always be provided for in the design so as to insure easy and
+convenient access to the property. The driveways will usually cross
+the side ditch along the road and culverts will be required to carry
+the water under the driveway. Driveways that cross a gutter by means
+of a pavement in the gutter are usually unsatisfactory, and to cross
+the gutter without providing a pavement is to insure stoppage of the
+flow at the crossing. The culvert at a driveway entrance must be large
+enough to take the ditch water readily or it will divert the water to
+the roadway itself. Generally end walls on such culverts are not
+required as in the case of culverts across a highway.
+
+=Aesthetics.=--Much of the traffic on the public highways is for
+pleasure and relaxation and anything that tends to increase the
+attractiveness of the highways is to be encouraged. Usually the
+roadside is a mass of bloom in the fall, goldenrod, asters and other
+hardy annuals being especially beautiful. In some states wild roses
+and other low bushes are planted to serve the two-fold purpose of
+assisting to prevent erosion and to beautify the roadside. In humid
+areas trees of any considerable size shade the road surface and are a
+distinct disadvantage to roads surfaced with the less durable
+materials such as sand-clay or gravel. It is doubtful if the same is
+true of paved surfaces, but the trees should be far enough back from
+the traveled way to afford a clear view ahead. Shrubs are not
+objectionable from any view-point and are to be encouraged for their
+beauty, so long as they do not obstruct the view at turns.
+
+
+
+
+CHAPTER V
+
+EARTH ROADS
+
+
+Highways constructed without the addition of surfacing material to the
+natural soil of the right-of-way are usually called earth roads. But
+if the natural soil exhibits peculiar characteristics or is of a
+distinct type, the road may be referred to by some distinctive name
+indicating that fact. Hence, roads are referred to as clay, gumbo,
+sandy or caliche roads as local custom may elect. In each case,
+however, the wearing surface consists of the natural soil, which may
+have been shaped and smoothed for traffic or may be in its natural
+state except for a trackway formed by the vehicles that have used it.
+
+=Variations in Soils.=--The nature of the existing soil will obviously
+determine the serviceability and physical characteristics of the road
+surface it affords. That is to say that even under the most favorable
+conditions some earth roads will be much more serviceable than others,
+due to the better stability of the natural soil. Some soils are dense
+and somewhat tough when dry and therefore resist to a degree the
+tendency of vehicles to grind away the particles and dissipate them in
+the form of dust. Such soils retain a reasonably smooth trackway in
+dry weather even when subjected to considerable traffic. Other soils
+do not possess the inherent tenacity and stability to enable them to
+resist the action of wheels and consequently grind away rapidly. Roads
+on such soils become very dusty. These are the extremes and between
+them are many types of soils or mixtures of soils possessing varying
+degrees of stability, and, in consequence, differing rates of wear.
+Similarly the various soils exhibit different degrees of stability
+when wet.
+
+It is to be expected that soils will differ with the geographical
+location, for it is well known that there is a great variation in
+soils in the various parts of the world. But wide differences are also
+encountered in the soil on roads very near each other and even on
+successive stretches of the same road. It is for this reason that
+earth roads often exhibit great differences in serviceability even in
+a restricted area.
+
+=Variation in Rainfall.=--The stability of a soil and its ability to
+support the weight of vehicles varies greatly with the amount of water
+in the soil. A certain small amount of moisture in the soil is
+beneficial in that practically every soil compacts more readily when
+moist than when dry because the moisture aids in binding together the
+particles. But most soils also become unstable when the amount of
+water present is in excess of that small amount referred to above and
+the stability decreases very rapidly as the amount of water in the
+soil increases.
+
+The serviceability of an earth road will change continually as the
+moisture content of the soil changes and consequently the general
+utility of the earth road system in any locality is dependent to a
+considerable extent upon the amount and seasonal distribution of
+precipitation. The methods of maintaining earth roads appropriate to
+any locality must of necessity be adapted to the climatic conditions,
+and the amount of work required to give the highest possible degree of
+serviceability will be exceedingly variable from season to season and
+from place to place. In regions of great humidity, earth roads may be
+expected to have a low average of serviceability, while in arid
+regions they may possess sufficient durability for a considerable
+volume of traffic. The design adopted for earth roads and the methods
+of maintenance followed should therefore be carefully evolved to meet
+the soil and climate conditions where the roads are located. These
+will differ greatly throughout a state or even a county.
+
+=Cross Sections.=--The general principles of road design were set
+forth in Chapter IV. In Fig. 11 are shown typical cross sections for
+earth roads adapted to various conditions as indicated. It is not
+apparent that one form of ditch is particularly preferable to the
+other and since some engineers prefer the V section and others the
+trapezoidal section both are shown. It would appear that the V shaped
+ditch is somewhat the easier to construct with the blade grader while
+the trapezoidal is readily excavated with the slip or fresno scraper.
+The ditch capacity required and consequently the dimensions will
+depend upon the drainage requirements, as was pointed out in Chapter
+III.
+
+[Illustration: Fig. 11. Cross Section for Earth Roads]
+
+
+EARTH ROADS IN REGIONS OF CONSIDERABLE RAINFALL
+
+In the zones where the annual precipitation exceeds 30 inches
+distributed over several months, earth roads will be unserviceable for
+a considerable period each year unless they are constructed so as to
+minimize the effect of water. This is done by providing for the best
+possible drainage and by adopting a method of maintenance that will
+restore the surface to a smooth condition as quickly as possible after
+a period of rainy weather or after the "frost comes out" in the
+spring.
+
+Before the construction of the desired cross section is undertaken,
+all of the grade reduction should be completed, except for minor cuts
+which can be handled with the elevating grader in the manner that will
+be described presently.
+
+Where any considerable change in grade is to be effected, the earth
+can be moved in several ways and of these the most economical cannot
+be readily determined. Ordinarily a contractor or a county will use
+the equipment that happens to be at hand even though some other might
+be more advantageous.
+
+=Elevating Grader.=--Where the topography is such as to permit its
+use, the elevating grader is employed in grade reduction to load the
+earth into dump wagons in which it is hauled to the fill or waste
+bank. The elevating grader consists essentially of a heavy shear plow
+or disc plow which loosens the earth and deposits it on a moving
+canvas apron. The apron carries the material up an incline and
+deposits it into a wagon which is driven along under the end of the
+apron. When the wagon is loaded, the grader is stopped while the
+loaded wagon is hauled out and an empty one drawn into position. The
+motive power for the elevating grader is either a tractor or five or
+six teams of mules. For many kinds of work, particularly where
+frequent turning is necessary or where the ground is yielding, mules
+are preferable to a tractor. The apron is operated by gearing from the
+rear wheels of the grader. Generally four mules are hitched to a
+pusher in the rear of the grader and six or eight in the lead. This
+method of grade reduction is particularly advantageous when the
+material must be hauled a distance of 500 yards or more, because wagon
+hauling in such cases is the most economical method to employ. A
+tractor may be used to draw the elevating grader and one having a
+commercial rating of 30 to 45 horsepower is required.
+
+=Maney Grader.=--If the haul is long and the nature of the cut will
+not permit the use of the elevating grader because of excessive grades
+or lack of room for turning, a grader of the Maney type may be used.
+This consists of a scoop of about one cubic yard capacity, suspended
+from a four-wheel wagon gear. When loading, the scoop is let down and
+filled in the same manner as a two-wheeled scraper or "wheeler." The
+pull required to fill a Maney grader is so great that a tractor is
+ordinarily employed in place of a "snap" team. The tractor is hitched
+at the end of the tongue, without interfering with the team drawing
+the grader. One team readily handles the grader after it is loaded.
+For this service a tractor having a commercial rationing of 25 to 30
+horsepower is required.
+
+=Wheel Scraper.=--For moving earth for distances between 150 and 500
+yards, the wheel scraper of a capacity of about 1-1/2 yards is quite
+generally employed. The soil must be loosened with a plow before it
+can conveniently be loaded into the wheeler and a heavy plow is
+ordinarily employed for that purpose. Two furrows with the plow will
+loosen a strip of earth about as wide as the scoop of the scraper and
+if more is loosened it will be packed down by the scrapers wheeling in
+place to load. A helper or "snap" team is employed to assist in
+loading, after which the wheel scraper is handled by one team.
+
+=Slip Scraper.=--The slip scraper differs from the wheel scraper in
+that the scoop is not suspended from wheels but is dragged along the
+ground. It is drawn by one team and the capacity is two to five cubic
+feet, but the material spills out to some extent as the scraper is
+dragged along and the method is not suitable for long hauls, 100 feet
+being about the economical limit.
+
+=Fresno Scraper.=--The Fresno scraper is one form of slip scraper
+requiring four horses or mules for efficient work. It differs
+somewhat from the ordinary slip scraper in shape and is of larger
+capacity, but is a drag type of scraper much favored in the western
+states.
+
+
+SHAPING TO PROPER CROSS SECTION
+
+If a road has been graded so that the profile is satisfactory or if
+the existing profile of the location is satisfactory, and the surface
+is to be shaped to a prescribed cross section, either the elevating
+grader or the blade grader may be employed.
+
+=Elevating Grader Work.=--If the elevating grader is used in shaping
+the earth road, the apron will be lowered and the material will be
+excavated at the sides of the road and deposited on the middle
+portion. If slight changes in grade are desired, wagons will accompany
+the grader and catch under the apron at the high places and haul the
+material to the low places. After the earth has been deposited it must
+be worked over to secure the correct cross section and be made
+passable for vehicles. This requires that clods be broken, weeds and
+grass that are mixed with the earth be removed by harrowing and
+forking and that the surface be carefully smoothed with a blade
+grader. This latter operation will have to be repeated several times
+before a satisfactory surface is secured. But this miscellaneous work
+is highly important and under no circumstances ought to be neglected.
+Nothing so detracts from an otherwise creditable piece of work as
+failure to provide a smooth surface for the use of vehicles. It is
+especially uncomfortable for the users of a highway if sods and weeds
+in quantity are left in the road after it has been graded. The humus
+that will be left in the soil as the vegetable matter decays increases
+the porosity of the road surface making it more absorbent than soil
+without humus. This increases the susceptibility to softening from
+storm water or ground water.
+
+The tractor can advantageously be used to draw the elevating grader on
+this class of work, but will be greatly handicapped if there are wet
+sections along the road, through which the tractor must be driven. In
+many cases its use is prohibited by such conditions and for all-round
+service of this character, mules are preferred for motive power.
+
+[Illustration: Fig. 12.--Tractor-grader Outfit]
+
+=Use of Blade Grader.=--Heavy blade graders designed to be drawn by a
+tractor are suitable for shaping the earth road. Some of these have
+blades 12 feet long and excellent control for regulating the depth of
+cutting. Often two such graders are operated tandem. These machines
+have a device which permits the operator to steer the grader
+independently of the tractor. Thus the grader can be steered off to
+the side to cut out the ditches, while the tractor continues to travel
+on the firm part of the road. Earth moved with the blade grader is
+usually fairly free from large lumps and can readily be smoothed to a
+satisfactory surface for the use of traffic. The sods and weeds will
+be drawn into the road along with the earth just as they are when the
+elevating grader is employed. Precaution must therefore be taken to
+eliminate them before the vegetable matter decays, and to smooth the
+surface for the use of traffic.
+
+=Costs.=--The cost of shaping an earth road in the manner described
+above will vary through rather wide limits because the nature and
+amount of work to be done varies so greatly. Some roads can be graded
+satisfactorily for $300.00 per mile, while others will cost $700.00.
+But $425.00 per mile may be taken as an average for blade or elevating
+grader work plus a moderate amount of grade reduction in the way of
+removing slight knolls. For the amount of grade reduction necessary in
+rolling country, followed by grader shaping, $1000.00 to $1800.00 per
+mile will be required. The method is not adapted to rolling country
+where the roads are undulating and require some grade reduction on
+every hill. For hilly roads one of the methods described for grade
+reduction will be required and the cost will obviously depend upon the
+amount of earth moved. Averages of cost figures mean nothing in such
+cases as the cost may reach $10,000.00 per mile, or may be as low as
+$2000.00 per mile.
+
+=Maintenance.=--Regardless of the care with which an earth road has
+been graded, it will be yielding and will readily absorb water for a
+long time after the completion of the work. The condition of the
+surface will naturally deteriorate rapidly during the first season it
+is used unless the road receives the constant maintenance that is a
+prerequisite to satisfactory serviceability. The road drag is
+generally recommended for this purpose, and if a drag is properly used
+it will serve to restore the shape of the surface as fast as it is
+destroyed by traffic.
+
+Good results with the drag depend upon choosing the proper time to
+drag and upon doing the work in the right way when using the drag. The
+best time to drag is as soon after a rain as the road has dried out
+enough to pack under traffic. If the work is done while the road is
+too wet, the first vehicles traveling the road after it has been
+dragged will make ruts and to a considerable extent offset the good
+done by the drag. If the road is too dry, the drag will not smooth the
+irregularities. A little observation will be required to determine the
+proper time for dragging on any particular soil, but usually after a
+rain or thaw there is a period lasting a day or two when conditions
+are about right.
+
+[Illustration: Fig. 13.--Road Drag]
+
+The drag is used merely to restore the shape of the surface and to do
+so a small amount of material is drawn toward the middle of the road.
+But there must not be a ridge of loose material left in the middle
+after the work is completed. Some patrolmen start at one side of the
+road and gradually work across the road on successive trips, finally
+finishing up at the side opposite that at which the start was made.
+The next dragging should start on the opposite side from the first if
+that method is followed.
+
+By shifting his weight on the drag, the operator can adjust the
+cutting edge so that very little loose material is moved crosswise of
+the road and that is the proper method to pursue. In that case no
+ridge will remain at the middle of the road. If a slight one is left
+it should be removed by a final trip with the drag.
+
+In addition to the dragging, weeds must be cut along the road about
+twice a year, the ditches must be kept cleaned out and culverts open.
+
+All of the maintenance for 10 miles of earth road can be accomplished
+by one man giving his entire time to the work, and that is the only
+method that has proven adequate to the problem.
+
+
+EARTH ROADS IN ARID REGIONS
+
+In areas where the rainfall is less than 18 inches per year, and
+especially where it is 10 inches or less, an entirely different road
+problem exists. The effect of precipitation is of significance
+primarily from the standpoint of erosion, and the design of cross
+section and ditches and the culvert provisions are entirely different
+from those necessary in humid regions.
+
+Frequently the rainfall in semi-arid regions will be seasonal and
+provision must be made to care for a large volume of water during the
+rainy season, but, in general, road design is adapted to prevention of
+erosion rather than to elimination of ground water effects, or the
+softening effects of surface water. Generally the rainy period does
+not last long enough to warrant expensive construction to eliminate
+its general effects. In fact, the saturation of the soil is more
+likely to be a benefit than otherwise.
+
+Earth roads are likely to be satisfactory except where the traffic is
+sufficient to grind the surface into dust to such an extent that an
+excessive dust layer is produced. In such locations the problem is one
+of providing a durable surface unaffected by long continued dry
+weather.
+
+Grade reduction will have the same importance as in humid areas and
+will be carried out in the same way.
+
+Maintenance will consist in repairing the damage from occasional
+floods and in removing or preventing accumulations of drifting sand
+or dust. Crude petroleum oils have been satisfactory for maintenance
+in such locations when used on stable soils.
+
+=Value of Earth Roads.=--The serviceability of the earth road depends
+to a large extent upon the care exercised in its maintenance. The only
+part of earth road construction that is permanent is the grade
+reduction. The cross section that is so carefully shaped at
+considerable cost may flatten out in one or two years, especially if
+the road goes through unusually wet periods. Traffic will continually
+seek a new track during the period when the road is muddy and is as
+likely to cross the ditch to the sod near the fence as to use any
+other part of the road. Continual and persistent maintenance is
+therefore essential to even reasonable serviceability. At best the
+earth road will be a poor facility for a considerable period each year
+in the regions of year-around rainfall. In most localities, roads of
+distinctly minor importance are of necessity only earth roads and for
+the comparatively small territory they serve and the small amount of
+traffic, they probably serve the purpose. For roads of any importance
+in the humid areas of the United States, the earth road cannot carry
+satisfactorily the traffic of a prosperous and busy community.
+
+
+
+
+CHAPTER VI
+
+SAND-CLAY AND GRAVEL ROADS
+
+
+In Chapter IV, mention was made of the variation in serviceability of
+road surfaces composed of the natural soil existing on the
+right-of-way of the road. It has been found that soils of a clayey
+nature in which there is a considerable percentage of sand usually
+afford a serviceable road surface for light or moderate traffic,
+especially in areas where climatic conditions are favorable. A study
+of these soils, together with the construction of experimental roads
+of various mixtures of sand and clay, has led to a fairly
+comprehensive understanding of the principles of construction and
+range of capacity of this type of road surface, which is known as the
+sand-clay road.
+
+The sand-clay road surface consists of a natural or artificial mixture
+of sand and clay, in which the amount of clay is somewhat greater than
+sufficient to fill the voids in the dry sand. It may be assumed that
+the sand contains 40 per cent of voids and that at least 45 per cent
+of clay is required to fill the voids and bind the sand grains
+together, because the clay spreads the sand grains apart during the
+mixing, thus having the effect of increasing the voids. As a matter of
+experiment, it is found to be impractical to secure by available
+construction methods mixtures of sufficient uniformity to render it
+necessary to exercise great exactness in proportioning the components,
+but reasonable care in proportioning the materials is desirable.
+
+Successful utilization of this type of surface requires considerable
+study of available materials and investigations of their behavior when
+combined. Extensive and exhaustive experiments have been conducted
+with sand-clay mixtures in various places where they are widely used
+for road surfaces and the following general principles have been
+deduced.
+
+=The Binder.=--In the sand-clay road, stability is obtained by
+utilizing the bonding properties possessed to some degree by all
+soils. Naturally this characteristic may be expected to vary widely
+with the several types of soil. It is generally considered to be a
+common property of clay, but the term clay is a general one that is
+often applied to soils differing greatly in physical characteristics
+and the term therefore loses its significance in this connection.
+Those soils that are properly and technically called clay are
+decidedly sticky when wet and are the best materials for sand-clay
+construction. Of the clays, those that produce a tough sticky mud are
+best. This can be tested by mixing a small quantity into a stiff mud
+and molding it into a ball and immersing in water. If the ball retains
+its shape for some little time, it is likely to prove a very
+satisfactory binder, but, if it becomes plastic and loses its shape,
+it will be an inferior binder, as a general rule. The ball clay, as
+the former is called, may be of any color common to soils, not
+necessarily yellow or reddish as is sometimes supposed. Likewise,
+balls of mixtures containing varying percentages of sand and the
+binder to be used may be made up and immersed in water. The mixture
+that holds its shape longest is of course the best combination of the
+materials and indicates the mixture to use in the construction.
+
+An ideal, or even a fairly satisfactory soil for a binder may not
+exist in the vicinity of a proposed improvement, and consequently an
+inferior binder is frequently the only material available.
+
+Sometimes deposits of clay or gravel contain a considerable percentage
+of gypsum which serves as a binder and is particularly effective when
+used in combination with clay and sand or gravel.
+
+In many places a soil of the type used for adobe and called "caliche"
+may be found and this is an excellent binder for sand or gravel.
+
+=Top-Soil or Natural Mixtures.=--Deposits consisting of a natural
+mixture of sand and clay in which the ingredients happen to exist in
+about the correct relative proportions for sand-clay road surfaces are
+found in many localities. These mixtures are commonly referred to as
+top-soil. If the deposits are somewhat deficient either in sand or
+clay, they can be utilized if the proper corrections in the
+proportions are made during construction. Very satisfactory road
+surfaces are sometimes constructed with mixtures that appear to be far
+from ideal in composition, but experience and frequent trials are
+needed to determine the best way in which to handle these mixtures.
+
+=Sand-Clay Surfaces on Sandy Roads.=--Sand-clay surfaces may be
+constructed on naturally sandy roads either by adding clay and mixing
+it with the sand to secure the desired composition, or a layer of a
+natural sand-clay mixture, caliche or sand-clay-gypsum may be placed
+on top of the sand.
+
+The most widely used method is to mix clay or other binder with the
+sand. Since there is no need to provide for ditches to carry storm
+water on a deep sand soil, the sand is graded off nearly flat across
+the road and no ditches are provided. The clay is dumped on the road
+in a layer about 8 inches thick and is then mixed into the sand. It is
+desired to mix enough sand with the clay to produce a mixture composed
+of approximately 1/3 clay and 2/3 sand. The mixing is accomplished in
+various ways, the most common being to use a heavy plow at first and
+to follow this with a heavy disc harrow. The mixing is a tedious and
+disagreeable process, but its thorough accomplishment is
+indispensable. The mixing is most readily done when the materials are
+saturated with water and in practice it is customary to depend upon
+rain for the water, although in the final stages water may be hauled
+and sprinkled on the road to facilitate final completion of the
+mixing. After the mixing has been completed, the surface is smoothed
+with the blade grader and is kept smooth until it dries out. Repeated
+dragging will be required, during the first year especially, and to
+some extent each year in order to keep the surface smooth, but the
+dragging can be successfully accomplished only when the road is wet.
+
+[Illustration: Fig. 14.--Cross Sections for Sand-Clay Roads]
+
+In regions where several months of continued hot, dry weather is to be
+expected each year, the sand-clay mixture is likely to break through
+unless it is of considerable thickness and generally the surface layer
+is made much thicker than for regions where the annual rainfall is
+fairly well distributed. This is especially necessary when the binder
+is of inferior quality. It is not uncommon in such cases to make the
+sand-clay surface as much as two feet thick.
+
+As the mixing progresses it may appear that patches here and there are
+deficient in either clay or sand and the mixture in these places is
+corrected by the addition of a little sand or clay as may be
+required.
+
+If the top-soil is used it is deposited on the sand in the required
+quantity and is remixed in place to insure uniformity. If either sand
+or clay is needed to give a satisfactory mixture, the proper material
+is added and mixed in as the work progresses. The surface is finally
+smoothed by means of the grader and drag.
+
+=Sand-Clay on Clay or Loam.=--If the existing road is of clay or loam,
+ample drainage will be required as discussed in Chapter IV. The
+surface may be constructed of a natural sand-clay mixture or of a sand
+mixed with the natural soil. If the former, the surface of the
+existing road is prepared by grading so as to insure good drainage and
+the natural mixture is then deposited and the surface completed as
+described in the preceding section.
+
+If the surface is formed by mixing sand with the existing soil, the
+sands may be deposited in a layer about six inches thick which will
+gradually mix with the soil as the road is used. A second application
+of sand may follow in a year or two if it is needed. Such a road
+surface will lack uniformity of composition and it seems preferable to
+mix the sand with the soil by plowing and discing as previously
+described.
+
+=Characteristics.=--Sand-clay road surfaces do not have sufficient
+durability for heavily traveled highways, but will be satisfactory for
+a moderate amount of traffic. These surfaces have maximum
+serviceability when moist, not wet, and consequently are not as
+durable in dry climates as in humid areas. They are likely to become
+sticky and unstable in continued wet weather and to become friable and
+wear into chuck holes in long continued dry weather. At their best,
+they are dustless, somewhat resilient and of low tractive resistance.
+
+GRAVEL ROAD SURFACES
+
+[Illustration: Fig. 15.--Cross Sections for Gravel Highways]
+
+=Natural Gravel.=--Gravel is the name given to a material consisting
+of a mixture of more or less rounded stones, sand and earthy material,
+which is found in natural deposits. These deposits exist in almost
+every part of North America, being especially numerous in the
+glaciated areas, but by no means confined to them. Gravel deposits
+consist of pieces of rock varying in size from those of a cubic yard
+or more in volume to the finest stone dust, but with pieces ranging in
+size from that which will pass a 3-inch ring down to fine sand
+predominating. The larger pieces are usually more or less rounded and
+the finer particles may be rounded or may be angular. Many varieties
+of rocks are to be found among the gravel pebbles, but the rocks of
+igneous origin and possessing a considerable degree of hardness
+generally predominate. Intermixed with the pieces of rock there is
+likely to be clay or other soil, the quantity varying greatly in
+different deposits and even in various places in the same deposits.
+
+Often there are found deposits of material which are by the layman
+termed gravel, which are really clayey sand or sand containing a few
+pebbles, but which are of value to the road builder for the sand clay
+type of surfacing. The term gravel is exceedingly general and unless
+specifically defined, gives little indication of the exact nature of
+to which it is applied.
+
+  TABLE 7
+
+  SHOWING CEMENTING PROPERTIES OF SEVERAL SAMPLES OF
+  GRAVEL
+
+  -----------------+----------------------------
+                   |       Cementing Value
+  Per Cent Clay by +---------------+------------
+      Weight       | As Received   |  Washed
+  -----------------+---------------+------------
+        4.4        |      276      |      43
+        6.4        |      105      |     285
+        5.1        |      241      |      70
+       14.5        |      500      |     279
+        8.5        |      500      |     112
+       10.1        |      300      |     267
+       14.8        |      500      |     107
+        7.5        |      184      |     198
+       16.5        |      500      |     428
+        2.0        |      185      |     239
+        1.5        |      500      |     500
+        4.5        |      212      |     204
+        2.5        |      116      |     363
+  -----------------+---------------+------------
+
+The value of any gravel for road surfacing depends upon the degree to
+which it possesses the properties of an ideal gravel for road
+surfacing. Ideal gravel is seldom encountered, but a consideration of
+its characteristics serves to establish a measure by which to estimate
+the probable value of any deposit.
+
+=The Ideal Road Gravel.=--The ideal road gravel is a mixture of
+pebbles, sand and earthy material, the pieces varying from coarse to
+fine in such a manner that when the gravel is compacted into a road
+surface the spaces between the larger pebbles are filled with the
+finer material. The pebbles are of a variety of rock that is highly
+resistant to wear so that the road surface made from the gravel will
+have the quality of durability. The gravel possesses good cementing
+properties, insuring that the pieces will hold together in the road
+surface. The cementing property may be due to the rock powder in the
+deposit or to earthy material mixed with the rock particles, or to
+both. Table 7 shows the results of a number of tests made upon gravels
+and indicates that the cementing property of the gravel does not
+always depend upon the clay content.
+
+=Permissible Size of Pebbles.=--The larger pebbles in the gravel are
+less likely to crush under loads than smaller pebbles of the same sort
+of rock, but if the rock is of some of the tougher varieties such as
+trap, there is very little likelihood of even the smaller pebbles
+crushing. If the pebbles are of rock of medium toughness, the smaller
+pebbles might be crushed under the heavier loads. It is the usual
+practice to permit gravel to be used for the foundation course in
+which the pebbles are as large as will pass a 3-1/2-inch circular
+screen opening, and for the wearing course, as large as will pass a
+2-1/2-inch circular screen opening. If larger pebbles are allowed in
+the wearing course, the surface is certain to become rough after a
+time. If the gravel is to be placed in a single course as is a very
+common practice, then the maximum size should not exceed that which
+will pass a 2-1/2-inch circular screen opening.
+
+The Wisconsin Highway Commission has constructed a very large mileage
+of excellent gravel roads and the sizes specified for their roads are
+as follows:
+
+     "_Bottom Course Gravel_.--Bottom course shall consist of a
+     mixture of gravel, sand and clay with the proportions and various
+     sizes as follows:
+
+     "All to pass a two-inch screen and to have at least sixty and not
+     more than seventy-five per cent retained on a quarter-inch
+     screen; at least twenty-five and not more than seventy-five per
+     cent of the total coarse aggregate to be retained on a one-inch
+     screen; at least sixty-five and not more than eighty-five per
+     cent of the total fine aggregate to be retained on a two
+     hundred-mesh sieve."
+
+     "_Top Course Gravel_.--Top course shall consist of a mixture of
+     gravel, sand and clay with the proportions of the various sizes
+     as follows:
+
+     "All to pass a one-inch screen and to have at least fifty and not
+     more than seventy-five per cent retained on a quarter-inch
+     screen; at least twenty-five and not more than seventy-five per
+     cent of the total coarse aggregate (material over one-fourth inch
+     in size) to be retained on a one-half-inch screen; at least
+     sixty-five and not more than eighty-five per cent of the total
+     fine aggregate (material under one-fourth inch in size) to be
+     retained on a two hundred-mesh sieve."
+
+     "_Screened Gravel and Sand Mixtures_.--Where it is impossible to
+     obtain run of bank gravel containing the necessary binder in its
+     natural state, screened gravel shall be used and the necessary
+     sand and clay binder added as directed by the engineer. Gravel
+     and sand shall be delivered on the work separately. Clay binder
+     shall be obtained from approved pits and added as directed by the
+     engineer."
+
+     "_Run of Bank Gravel_.--When run of bank gravel is permitted
+     either for one course or two course work, the size shall not
+     exceed that specified for bottom or top course. If necessary, the
+     contractor shall pass all the material through a two-inch screen
+     for the bottom course, and through a one-inch screen for the top
+     course. When the work consists of only one course, the material
+     shall be of the sizes as specified for the top course. The
+     necessary binder shall be contained in the material in its
+     natural state, excepting that a small percentage of clay binder
+     may be added as directed by the Engineer."
+
+=Wearing Properties.=--A certain amount of grinding action takes place
+on the road surface under the direct action of wheels, especially
+those with steel tires. Where rubber tired traffic predominates, this
+action is much less severe than where steel tired vehicles
+predominate, but the tendency exists on all roads. In addition, there
+is distortion of the layer of gravel under heavy loads which causes
+the pieces of stone in the surface to rub against each other and to
+wear away slowly.
+
+The gravel road in the very best condition is slightly uneven but
+there is comparatively little jar imparted to vehicles, and,
+consequently, little impact on the surface. When somewhat worn, the
+impact becomes a factor of some importance and the pounding of
+vehicles has a very destructive action on the surface. Soft pebbles
+will be reduced to dust in a comparatively short time.
+
+The degree to which any gravel resists the destructive action of
+traffic depends upon the varieties of rock represented by the pebbles
+in the gravel. If the pebbles are mostly from rocks of good wearing
+properties, that quality will be imparted to the road surface. If
+mostly from rocks of little durability, the same characteristic will
+be imparted to the road surface. A very good general notion of the
+probable durability of gravel can therefore be obtained by a careful
+visual examination of the material and classification of the rock
+varieties represented by the pebbles.
+
+=Utilizing Natural Gravels.=--Gravel road construction is advantageous
+only when it can be accomplished at low first cost. This usually
+presupposes a local supply of gravel that can be utilized, or at any
+rate a supply that need not be shipped a long distance. In the nature
+of things, such deposits are likely to be deficient in some of the
+desirable characteristics, and may be deficient in most of them. By
+various means, the defects in the materials can be partially corrected
+while constructing the road.
+
+If the gravel deposit consists of layers of varying composition as
+regards size and clay content, the material may be loosened from the
+exposed face and allowed to fall to the bottom of the pit thereby
+becoming mixed to a sufficient extent to produce a reasonably uniform
+product. If deficient in clay, it often proves feasible to add a small
+part of the clay over-burden, thereby insuring enough binder.
+Sometimes adjoining deposits will consist one of relatively fine
+material, the other of relatively coarse. These may be mixed on the
+work by first placing the coarse material in a layer about 5 inches
+thick and adding the finer material in a similar layer. The two will
+mix very rapidly during the operations of spreading and shaping.
+
+When deposits contain pebbles larger than will pass a 3-1/2-inch ring,
+these larger stones will prove to be undesirable if placed on the
+road, as they are almost sure to work to the surface of the gravel
+layer and become a source of annoyance to the users of the road.
+Oversize stone can be removed while loading the gravel or while
+spreading it, if care is exercised and not too large a proportion is
+oversize. It is preferable however to remove the oversize by means of
+screens at the pit. Usually on large jobs the oversize is crushed and
+mixed with the supply so as to utilize what is really the best part of
+the material.
+
+Gravels deficient in bonding material are often encountered in
+deposits where there is insufficient overburden to give enough
+additional binder or where the overburden is of a material unsuitable
+for binder. Such materials may be utilized by adding binder in the
+form of clay after the gravel has been placed on the road.
+
+Almost any gravel deposit can be utilized in some way if the material
+is of a durable nature, regardless of other characteristics. The
+serviceability of a gravel road will depend largely on how nearly the
+gravel approaches the ideal, but variations in the manipulations will
+do much to overcome deficiencies in materials.
+
+=Thickness of Layer.=--The thickness of the layer of gravel required
+depends both upon the type of soil upon which it is placed and the
+nature of the traffic to which the road will be subjected. Gravel
+surfaces should not ordinarily be constructed on highways carrying
+heavy truck traffic, but if gross loads of three or four tons are the
+heaviest anticipated, the gravel will be reasonably stable. On such
+roads, a layer of well compacted gravel ten inches thick will support
+the loads if a well drained earth foundation is provided. If but
+little truck traffic is anticipated and loads up to three tons on
+steel tires are the average, a layer 8 inches thick will be
+sufficient. In dry climates, a layer six inches thick will be
+adequate if it can be kept from raveling.
+
+On secondary roads, carrying principally farm-to-market traffic, and
+not a great volume of that, the above thicknesses may be reduced about
+one-fourth.
+
+The exact thickness needed for any particular road is a matter for
+special study on account of the variations in the gravels and in the
+supporting power of the soil upon which they are placed.
+
+
+PLACING GRAVEL
+
+=Preparation of the Road.=--The roadway that is to be surfaced with
+gravel is first brought to the desired grade and cross section. It
+would be advantageous if this could be done a year before the gravel
+is placed so that no settlement of the earth foundation would occur
+after the gravel surface is completed. But if that is impractical, the
+grading may be done just prior to placing the gravel, providing
+appropriate methods are adopted for securing compacted fills.
+
+=Trench Method.=--Two distinct methods of placing the gravel are in
+general use, known as the trench method and the surface or feather
+edge method respectively. The method to adopt for any particular road
+will depend largely on certain conditions that will be explained
+later.
+
+In the trench method, a trench of the proper width and depth for
+receiving the gravel is excavated in the earth road surface and the
+gravel is placed therein.
+
+The trench is formed by plowing a few furrows and scraping out the
+loosened earth with a blade grader. The loose material is generally
+moved out laterally to build up earth berms or "shoulders" alongside
+the gravel. Into this trench the gravel is dumped in the proper
+quantity to give the required thickness after being compacted.
+
+The greatest care must be exercised in spreading the gravel to
+eliminate unevenness where the loads were deposited. An ordinary blade
+grader is one of the best and most economical implements to use for
+spreading the gravel. When the gravel has been deposited in the trench
+for a distance of a thousand feet or more, the spreading is
+accomplished by dragging the surface repeatedly with the blade grader,
+the work being continued until all waviness disappears. The gravel is
+then thoroughly and repeatedly harrowed with a heavy stiff tooth
+harrow to mix thoroughly the fine and coarse gravel so as to produce
+as nearly a uniform mixture as may be. The gravel is then finally
+smoothed with the blade grader.
+
+The gravel may be compacted by rolling or may be allowed to pack from
+the action of traffic. The former is greatly to be preferred where
+practicable. The rolling is performed with a three-wheeled
+self-propelled roller weighing about 8 tons and must be done while the
+gravel is wet. Generally a sprinkling wagon is used to wet down the
+gravel, but advantage is always taken of rains to facilitate the work.
+The gravel must be spread in layers not over 5 or 6 inches thick to
+get the desired results, which means that for an ordinary gravel road
+about 10 inches thick, the gravel will be placed in two layers of
+about equal thickness, each of which will be rolled.
+
+The gravel will compact slowly even if it is not rolled, but generally
+does not become stable until the material is thoroughly soaked by
+rains. Then it will begin to pack, but will become badly rutted and
+uneven during the process. During this period the surface must be kept
+smooth by means of the blade grader. The drag does not suffice for
+this purpose, tending to accentuate the unevenness rather than to
+correct it.
+
+If gravel is placed in a trench in dense soil and rainy weather
+ensues, sufficient water will be held in the trench to cause
+unevenness from foundation settlement and the gravel will become mixed
+with the soil to some extent and be thereby wasted. Trenches cut from
+the road bed upon which the gravel is placed, to the side ditches,
+will relieve this condition by affording an outlet for the surplus
+water. Nevertheless some difficulty may be expected if the trench
+method is used and wet weather prevails. If it is possible to close
+the road against traffic until the road is dry the method is
+applicable. Moreover, in long-continued dry weather, the dispersion
+and loss of considerable gravel from the action of automobile traffic
+is avoided because the gravel is held between substantial earth berms
+and the gravel will pack better and hold its shape longer when
+constructed by the trench method than otherwise.
+
+=Surface Method.=--The surface method is one in which the gravel is
+placed on the graded earth road surface without earth shoulders to
+hold the gravel in place. It is also sometimes called the feather-edge
+method. Except for the manner of placing as just mentioned, the
+several operations are conducted in the same general manner as for the
+trench method. The gravel does not compact as quickly as in the trench
+method and a considerable loss of material is likely to result from
+the effect of automobile traffic while the gravel is loose. But it has
+the advantage of being free from difficulties in wet weather and in
+some locations is therefore preferable to the trench method. It is
+particularly applicable to those projects on which the placing of
+gravel continues throughout the winter, the gravel being dumped and
+spread, to be finally smoothed and finished in the early summer.
+
+=Bonding.=--Where gravels deficient in binder are utilized, clay for
+binder is sometimes added as the gravel is placed on the road. This
+may be done by spreading the clay on top of the lower course of
+gravel, placing the upper layer and sprinkling and rolling until the
+clay squeezes up through the surface layer. It may also be
+accomplished by spreading dry clay on the upper course before it is
+harrowed and then harrowing to mix it with the gravel. Both methods
+are practiced, but the former is believed to be preferable. A third
+method is to separate the sand and pebbles and to mix the clay binder
+with the sand and then spread the sand on top of the pebbles and mix
+by harrowing.
+
+=Maintenance.=--Gravel surfaces require careful maintenance,
+especially during the first season the road is used. The gravel will
+compact slowly and during the process will be rutted and otherwise
+disturbed by traffic. It is important during this period to restore
+the shape once a week or at least twice a month. The light blade
+grader is usually employed for the purpose so long as the gravel is
+somewhat loose. Later a drag of the type known as the planer will
+prove to be the most effective. Figure 16 shows a type of drag that is
+very satisfactory for use on gravel roads.
+
+[Illustration: Fig. 16.--Road Planer]
+
+
+
+
+CHAPTER VII
+
+BROKEN STONE ROAD SURFACES
+
+
+The broken stone road surface, or macadam road as it is usually
+termed, consists of a layer of broken stone, bonded or cemented
+together by means of stone dust and water. The surface may or may not
+be coated with some bituminous material.
+
+=Design.=--It has been an accepted assumption that the macadam road
+surface is somewhat more stable than the gravel road surface of equal
+thickness, and since this is probably the consensus of opinion of
+engineers familiar with both types, it may be accepted until
+experimental data are available on the subject.
+
+The thickness of the layer of macadam required for a road will depend
+upon the same factors that were considered in connection with the
+thickness of the gravel surface, i.e., kind of stone used, character
+of earth foundation and nature of the traffic.
+
+The standard macadam surface where good earth foundation is to be had
+and where the loads do not exceed about four tons has for years been
+eight inches thick. For heavier loads or inferior foundation, a
+somewhat greater thickness would be employed, but the best practice
+would probably provide a foundation course of the Telford type for
+doubtful foundation conditions, especially for the extremely uncertain
+cases. For soils of very good supporting strength such as very sandy
+loam or deep sand or for arid regions where stable foundation is
+always assured the thickness of the macadam might be reduced to six
+inches. It should be borne in mind that the broken stone road is not
+adapted to the traffic carried by trunk line highways in populous
+districts, but is rather a type permissible on secondary roads and
+usually adequate for local roads. It should never be employed for
+roads carrying any considerable volume of passenger automobile traffic
+or motor truck traffic. If surfaced with a bituminous material it will
+carry up to 1200 passenger automobiles per day, but not to exceed
+fifty trucks.
+
+=Properties of the Stone.=--The stone employed for the broken stone
+road should possess the qualities of hardness and toughness and should
+be capable of resisting abrasion sufficiently well to have reasonable
+life under the traffic to which it is subjected. Since the traffic may
+vary from very light on some roads to far beyond the limit of the
+economical capacity of this type of pavement on others, it follows
+that any particular deposit of stone might be durable enough for some
+roads, while for others it might be entirely inadequate. As a general
+rule it has been found that stone that wears away at a moderate rate
+will, when used for water-bound macadam surface, result in a smoother
+trackway than one that will wear very slowly. It is not therefore
+altogether certain that the most durable stone to be had should be
+selected for a particular road. This is especially true now that the
+water-bound macadam surface has been largely superseded for trunk line
+highways and other heavily traveled roads, and is employed in
+locations where service conditions are not severe.
+
+The stone employed for the water-bound macadam surface must possess
+good cementing properties, because the surface depends for stability
+primarily upon the bonding action of the dust from the broken stone.
+This is in contrast to the gravel road, where little dependence is
+placed upon the bonding effect of the rock dust. In preparing the
+stone for macadam surfaces, the ledge rock is crushed and screened,
+and in that way a supply of the finer particles, which are a part of
+the output of the crusher, is obtained for use in bonding the
+surface. This finely broken material, usually called screenings, is
+essential to the construction of the water-bound type of surface.
+Rocks vary considerably in the cementing properties of the dust, but
+usually the rocks classed as "trap," such as andesite, gabbro and
+rhyolite, and schist and basalt possess good cementing properties.
+Limestones usually possess good cementing properties, but some of the
+dolomitic limestones are of low cementing value. Quartz, sandstone and
+the granites are of low cementing value.
+
+=Kinds of Rocks Used for Macadam.=--Limestone and chert are the two
+sedimentary rocks, employed most extensively for broken stone roads.
+These rocks are found in widely distributed areas and vary in physical
+characteristics from very soft material of no use to the road builder
+to materials possessing considerable durability. It is desirable to
+carefully test out the deposits of these materials before using to
+ascertain the probable value of the rock, for the construction of the
+road surface.
+
+Of the igneous rocks, those classed as trap are best known to the road
+builder and many of the deposits of trap rock afford an excellent
+material for broken stone roads where the severest conditions of
+traffic are encountered. The trap rocks are tough and durable and
+generally possess excellent cementing properties.
+
+Granite and sandstone are seldom used for water-bound macadam as they
+possess poor cementing properties and a binder of some kind must be
+added to cement the pieces together. For this purpose clay or the
+screenings from some other variety of stone may be utilized.
+
+Some other materials are occasionally employed for the construction of
+macadam surfaces. Of these, oyster or marine shells, burnt shale, and
+slag are most common.
+
+Shells and slag are of rather low durability but possess good
+cementing properties. Shale is a makeshift suitable only for very
+light traffic roads.
+
+=Sizes of Stone.=--The stone for the wearing course of a macadam road
+should be as large as practicable, because the larger the pieces the
+more durable the surface. If the individual stones are too large it is
+difficult to secure a smooth surface, and large stones will be readily
+loosened by tipping as the wheels roll over them. These considerations
+limit the size to a maximum of that which will pass a 2-1/2-inch
+screen. Stone of excellent wearing qualities may be somewhat smaller,
+but never less than that which will just pass a 1-1/2-inch screen.
+
+For the lower course, the size is not particularly important except
+where the earth foundation is such as to require special construction.
+It is not uncommon to use the same size of stone for both upper and
+lower course and yet in many instances stone up to that which will
+just pass a 3-1/2-inch screen is used for the lower course. Stone much
+smaller in size may also be used successfully, but if the stone is
+broken to a smaller size than is required, unnecessary expense is
+incurred.
+
+The bonding material is the finer portion of the product of the
+crusher, which is called screenings. This material may be so finely
+crushed as to pass a one-fourth inch screen, or may be so coarse as to
+just pass a one-half inch screen, but in any case must contain all of
+the dust and fine material produced by the crusher.
+
+Where the soil and drainage conditions demand an especially stable
+foundation course, the Telford type is used. The Telford foundation
+consists of a layer of stones of various dimensions that can be laid
+so as to give a thickness of 8 inches. These large stones are placed
+by hand and therefore the size requirements are not rigid. Stones
+having one dimension about 8 inches and the others not over 10 or 12
+inches are satisfactory.
+
+=Earth Work.=--A thoroughly drained and stable earth foundation is
+essential to success with the macadam type of surface. Before placing
+the stone, the road must be shaped to the proper cross section and
+all grade reduction work completed. Preferably heavy fills should have
+a year to settle before the macadam surface is placed. Side ditches,
+necessary culverts and tile drains should be constructed as required
+for drainage. The earth work is often carried out in connection with
+the construction of the macadam surface, being completed just ahead of
+the surfacing. In that case, the fills must be carefully rolled as
+they are placed. The road bed may be shaped in connection with the
+other earthwork. If the road has been brought to a satisfactory grade
+some time prior to placing the macadam, the road bed for the broken
+stone will be prepared as needed for placing the stone.
+
+=Foundation for the Macadam.=--Macadam surfaces are quite generally
+placed in a trench as described in the trench method for placing
+gravel. It is an almost universal practice to compact the layer of
+stone by rolling with an 8- or 10-ton power roller, and if the stone
+is not held between substantial earth berms or shoulders, the rolling
+merely serves to spread the stone out over the road bed instead of
+compacting it. If an attempt is made to roll broken stone which has
+been placed on a yielding foundation, no benefit results, but on the
+contrary the stone is likely to be forced down into the soil. To
+insure that the layer of broken stone can be compacted by rolling, it
+is first necessary to roll the earth foundation until it becomes hard
+and unyielding. If soft or yielding places appear during the rolling
+these should be corrected by tile drains or by removing the earth from
+the spongy place and back-filling with material that will compact when
+rolled.
+
+It is not always easy to determine why these soft places exist in what
+appears to be a well drained roadway, especially since they are as
+likely to be found on fills as anywhere else. Apparently they are due
+to local pockets of porous soil held by denser soil so that the water
+does not readily drain away. It is usually true that such places are
+observed during the season of frequent precipitation more often than
+during other seasons of the year.
+
+In dry climates, the difficulties of securing suitable foundations for
+the broken stone road are largely eliminated, but it may be observed
+that this type of surface is not suitable for such climates unless
+some sort of bituminous binder is employed to hold the stones in
+place. The cementing power of the stone dust is inadequate when the
+surface is continually dry.
+
+[Illustration: Fig. 17.--Cross Section for Macadam]
+
+=Telford Foundation.=--When the Telford type of foundation is
+employed, the earth subgrade is prepared and then the Telford stone
+placed carefully by hand. The spaces between the large stones are
+filled with the spalls broken from the larger stones in fitting them
+in place. When completed the base is rolled with a heavy roller to
+secure a firm unyielding layer. The thickness is generally about eight
+inches. Any fairly sound stone may be used for the Telford base.
+
+=Placing the Broken Stone.=--It has been found impracticable properly
+to roll a greater thickness than about 5 or 6 inches of loose stone,
+therefore, the stone for the macadam surface is usually placed in two
+layers, the first or lower layer being rolled before the next layer is
+placed. The stone is hauled in dump wagons, trucks or dump cars,
+dumped on the road bed and spread by hand rakes or by means of a blade
+grader and is then rolled. To insure the proper thickness the loads
+are accurately spaced to spread to the proper thickness.
+
+=Rolling.=--A three-wheeled or "macadam" type of roller, of the
+self-propelled type, is best for compacting the broken stone road. The
+weight varies from eight to fifteen tons, but for most conditions the
+ten or twelve ton size seems to be preferable. On Telford base
+construction, a heavier machine is desirable and for very hard stone
+it may be successfully employed.
+
+The first trip with the roller is made along the edge of the stone and
+each successive trip is made a little nearer the middle until finally
+one half of the strip of stone has been rolled. The roller is then
+taken to the opposite side of the roadway and the operation repeated
+on the other half. The rolling is continued until the stone is
+thoroughly compacted, which is evidenced by the fact that the roller
+makes but a slight track in the surface.
+
+The second layer of stone is then placed and rolled in the same manner
+as the first.
+
+=Spreading Screenings.=--After the upper course has been rolled, the
+screenings are spread on it from piles alongside the road, enough
+being used to fill the voids in the layer of stone and furnish a
+slight excess. As the screenings are spread they are rolled to work
+them into the voids. When these are filled, the surface is sprinkled
+thoroughly by means of an ordinary street sprinkling cart and again
+rolled. In this way the dust and water are mixed into a mortar which
+fills the crevices between the stones. This mortar hardens in a few
+days, giving a bond that is weak, but sufficient for the purpose if
+the traffic is not too heavy. A broken stone road finished in this way
+is called a water-bound macadam, and is ready for traffic in three or
+four days after completion.
+
+=Bituminous Surfaces.=--On account of the inadequacy of the
+water-bound macadam when subjected to motor traffic and to obviate the
+tendency of broken stone surfaces to loosen in dry weather, there has
+been developed a method of covering the surface with a bituminous
+material such as tar or asphalt. This will be described in detail in a
+later chapter.
+
+=Maintenance.=--Even under favorable conditions as regards kind and
+amount of traffic the macadam road requires constant maintenance. The
+first effect of traffic will be to brush away the fine materials used
+for bonding the surface, thus exposing the larger stones in such a way
+that they are rather easily loosened and removed from the surface by
+wheels and the hoofs of animals. This finer material must be replaced
+as fast as it is removed so as to protect the surface. Either stone
+dust or clayey sand may be used, but clay if used alone is likely to
+be sticky when wet and prove to be worse than the condition it was
+expected to correct. In time, ruts and depressions will appear, either
+as the gradual effect of wear, which will inevitably effect some
+portions of the surface more than others, or on account of subsidence
+of the foundation. Uneven places are repaired by first loosening the
+stone, then restoring the cross section by adding new material and
+tamping or rolling it in place.
+
+If a bituminous coating has been applied, it will eventually peel off
+in places and these places must be recoated as soon as practicable.
+
+Eventually the surface will be worn to such an extent that an entirely
+new wearing surface must be added. This is done by loosening the
+entire surface to a depth of 3 or 4 inches and then adding a new layer
+of broken stone. The loosening is sometimes accomplished by means of
+heavy spikes inserted in the roller wheels, and at others by means of
+a special tool known as a scarifier.
+
+The new surface is placed and rolled in precisely the same manner as
+the wearing surface of the original construction, but the layer may
+not be as thick as the original wearing course. A new course will not
+bond to the old surface unless the old macadam has been thoroughly
+broken up first.
+
+=Characteristics.=--The water-bound macadam is a dusty, somewhat rough
+surface of low durability for rubber tired vehicles. It has long been
+the standard rural highway for steel tired vehicles, but cannot carry
+any considerable amount of motor traffic. It is easily repaired. When
+finished with a bituminous surface its durability is greatly increased
+and the dust is eliminated. It does not seem to be sufficiently rigid
+for truck traffic, unless placed on exceptionally good foundation.
+
+
+
+
+CHAPTER VIII
+
+CEMENT CONCRETE ROADS
+
+
+The cement concrete road is one of the later developments in highway
+construction, but the type has had sufficient use to show that it is
+one of the satisfactory types for heavy mixed traffic, and, where the
+proper materials are available, it is one of the economical types of
+construction.
+
+=Destructive Agencies.=--It is well to have clearly in mind at the
+outset that the concrete in a road surface is subjected to certain
+destructive agencies not usually significant in connection with the
+use of concrete, and these are so often disregarded that the average
+serviceability of the concrete road surface is sometimes much lower
+than it would be if built with due regard for the effect of traffic on
+concrete surfaces. In most structural uses of concrete, its strength
+in compression only is utilized, and the factor of safety is such as
+to eliminate to some extent failures due to inferior materials or
+workmanship.
+
+The concrete road surface is subjected to compression under wheel
+loads, to bending, causing tension in the concrete, to abrasion from
+wheels, and to tension and compression due to effect of temperature.
+The weight of the wheel loads may cause sufficient distortion of the
+road slab to produce rupture. The aggregates may be crushed under
+wheel loads if the material is too soft. Abrasion from steel tired
+vehicles wears away the concrete unless it is hard and durable.
+Changes in dimension due to the effect of change in temperature
+introduce tension or compression into the road slab and may result in
+cracks. Freezing and thawing in the subgrade subjects the slab to
+vertical movement and discontinuous support with the result that
+longitudinal and transverse cracks occur.
+
+The foregoing indicates the importance of securing good concrete for
+road surfacing, and that is accomplished by using suitable aggregates,
+by proper design of the road surface and by following established
+construction methods.
+
+=Design.=--The widths usually adopted for concrete roads are: for
+single track roads, 9 or 10 feet, and for double track roads, 18 or 20
+feet. The thickness is 6 to 8 inches at the middle, varying with
+climatic conditions and with the kind of soil upon which the concrete
+is laid. The thickness at the edge is 1 inch less than at the middle
+except that 6-inch surfaces are usually of uniform thickness, the
+total crown being 2 inches. The thickness of the two course pavement
+is the same as would be used for a single course pavement in the same
+location. The surface of either width has a total crown of one or two
+inches to insure water running off the surface. The earth foundation
+is often flat, the crown being obtained by making the slab thicker at
+the middle than at the edge. Fig. 18 shows cross section for concrete
+roads.
+
+[Illustration: Fig. 18.--Cross Section for Concrete Highway]
+
+In the state of California, concrete roads four or five inches thick
+and surfaced with a bituminous carpet mat have been successfully
+constructed. Similar designs have been used in a few other places, but
+for general practice it is unsafe to depend upon such a thin slab.
+Climatic and soil conditions probably account for the success of the
+thin roads in California.
+
+=Concrete Materials.=--The coarse aggregate for the concrete may be
+broken stone or pebbles screened from natural gravel. Durability is
+necessary, but it is also important to have uniformity in the concrete
+so that the road surface will wear uniformly and consequently keep
+smooth. Supplies of broken stone are likely to contain a small
+percentage of soft pieces and such of these as are at the surface when
+the concrete is finished will crush under traffic, leaving a pit in
+the surface. Pebbles screened from gravel are also likely to be
+variable in durability and should be carefully inspected if they are
+to be used as aggregate for concrete roads. The harder limestones,
+some sandstones, pebbles from many of the gravel deposits and
+practically all of the igneous rocks make satisfactory aggregates for
+the concrete road.
+
+Sometimes none of the coarse aggregates readily available are
+sufficiently durable or uniform for the wearing surface of the
+concrete road, but a suitable aggregate may be obtained at relatively
+high price by shipping considerable distances. In such cases what is
+known as the two course type of concrete road is employed. The wearing
+course usually is about 2 inches thick and is constructed with
+selected aggregates of good quality shipped in for the purpose. The
+lower course is constructed of aggregates which do not possess the
+desired qualities for a wearing course, but which are satisfactory for
+concrete not subjected to abrasion. The aggregates for the wearing
+course will be selected with the same regard for uniformity and
+durability that would be the case if they were for the one course
+pavement.
+
+Bank run gravel, or run of the crusher stone, is generally not
+sufficiently uniform as regards proportion of fine and coarse material
+to produce uniformity in the concrete, and the use of aggregates of
+that character is not permissible for the wearing course, but under
+proper inspection they may be used for the lower course of two course
+pavements.
+
+=Fine Aggregate.=--The fine aggregate is generally natural sand, but a
+mixture of natural sand and stone screenings is sometimes employed.
+The fine aggregate of whatever character must be clean, free from
+organic matter and sand, must contain no appreciable amount of mica,
+feldspar, alkali, shale or similar deleterious substances and not
+exceed two and one-half per cent of clay and silt. The sand is of such
+a range of sizes that all will pass the one-fourth-inch sieve and that
+not exceeding about five per cent will pass the 100-mesh sieve.
+
+=Proportions.=--Various mixtures for the concrete are employed because
+these may properly vary to some extent with the exact character and
+grading of the aggregates. Experience seems to have shown that the
+concrete used for the wearing surface should have a crushing strength
+of at least 2500 pounds per square inch, and the mixture adopted is
+based on the requirements that will give the desired crushing
+strength. The common mixture for the one course pavement is one part
+cement, two parts sand and three and one-half parts coarse aggregate.
+For the wearing course of the two-course type of pavement, a mixture
+of the same kind is very often specified.
+
+While these are perhaps the most widely adopted proportions, many
+others have been used, especially where the aggregates exhibit
+peculiarities or the traffic conditions are unusual. It is desired to
+emphasize that the purpose is to obtain concrete of the desired
+strength and there can be no such thing as "standard" proportions.
+
+=Measuring Materials.=--In considering the methods employed for
+measuring aggregates, emphasis should be placed on the futility of
+rigid requirements for the aggregates, both as regards quality and
+range of sizes, if the materials are carelessly proportioned at the
+mixer. If even reasonably near uniform wearing qualities are to be
+secured throughout the entire area of the concrete road surface,
+successive batches of concrete must be alike, and to insure that, the
+aggregates including the water in each batch of concrete must be mixed
+in exactly the same proportions. The aggregates are measured in
+various ways, all essentially alike in that the intent is to insure
+exactly the same amount of each ingredient for each batch of concrete.
+
+One method is to place bottomless boxes in wheelbarrows, fill the
+boxes level full and then lift off the box. Another is to use a
+wheelbarrow with a bed of such shape that the contents will be a
+multiple of 1 cubic foot when level full. For the larger jobs, the
+aggregates are hauled in industrial cars, each having sufficient
+capacity for a batch of concrete. The car body is provided with a
+partition so as to separate the fine and coarse material.
+
+The water is measured in a tank which automatically refills to the
+same level each time it is emptied and when adjusted for a mixture
+will introduce the proper amount of water for each batch. It is highly
+important to use the least amount of water that will produce workable
+concrete.
+
+=Preparation of the Earth Foundation.=--The concrete road is generally
+placed directly on the natural soil which has been brought to the
+proper cross section. Some engineers advocate that in preparing the
+subgrade, the earth be thoroughly rolled; others prefer not to roll
+the subgrade. If fills of considerable depth are constructed, they
+should either be rolled as built or else should be allowed to settle
+for some months before the concrete road is placed, preferably the
+latter.
+
+=Placing the Concrete.=--The concrete is placed between substantial
+side forms of a height equal to the thickness of the concrete road
+slab at the edge, and is shaped roughly by means of shovels.
+
+Various methods have been developed for striking the surface to the
+exact shape desired and smoothing it. If hand finishing methods are
+employed, a plank template is cut to the prescribed cross section and
+the concrete is shaped by drawing the template along the side forms.
+Sometimes the template is used as a tamper, being moved along very
+slowly accompanied by an up and down motion that tends to tamp the
+concrete. The template is then drawn along a second time to smooth the
+surface finally.
+
+After the surface has been struck off by hand, it is finally smoothed,
+first by rolling crosswise with a slight hand roller about 8 inches in
+diameter and 30 inches long. The final finish is effected by dragging
+a piece of web belting back and forth across the surface.
+
+Machines designed to tamp the concrete and strike it off to the
+required cross section are also employed for finishing. The machine is
+power operated and is carried on wheels that run on the side forms,
+and the machine moves slowly along as the tamping progresses. The
+concrete is tamped, struck off to shape and smoothed with the belt at
+one operation. This method of finishing produces denser and stronger
+concrete than can be produced by hand finishing methods.
+
+=Placing Concrete for Two-course Road.=--The methods employed for the
+two-course concrete road are much the same as for the one-course road.
+The concrete for the lower course is placed and struck off by means of
+hand tools, and after that course has progressed a few feet, the upper
+course is placed and finished as has been described for the one-course
+road.
+
+=Curing the Concrete.=--The setting action of cement is a chemical
+process, not merely a drying out of the water introduced in mixing the
+concrete. The chemical action is progressive for a long time, but is
+more rapid during the first few hours than during the later periods,
+and the concrete reaches about three-fourths of its maximum strength
+at the end of seven days. During the setting period and particularly
+during the first few days, plenty of water must be available to the
+cement.
+
+To prevent too rapid loss of water from the concrete during the
+setting period, the surface must be protected from the wind and sun.
+This is accomplished by first covering with canvas as soon as the
+concrete has hardened sufficiently and by later covering with earth,
+to a depth of two inches. The earth covering is kept wet for about ten
+days and is left in place for about one month.
+
+In some places the ponding method of curing is adopted. The surface is
+divided into sections by earthen dikes and the space inside the dikes
+filled with water to a depth of two or three inches. The water
+covering is maintained for two weeks or longer.
+
+No traffic is permitted on the surface for one month, and in cold
+weather traffic may be kept off the surface for a longer period.
+
+=Expansion Joints.=--To permit the concrete slab to accommodate itself
+to changes in dimension due to temperature changes, expansion joints
+1/2 inch wide are placed about every thirty feet. These consist of a
+sheet of some prepared bituminous material placed in position as the
+concrete is poured.
+
+Experience seems to indicate that in spite of the expansion joints,
+the concrete will crack more or less and many engineers think it
+advisable to omit expansion joints in constructing the pavement and
+when cracks develop to pour bituminous material into them, thus
+forming expansion joints.
+
+The prevailing practice in rural highway construction is to omit the
+expansion joints, but they are commonly adopted in city pavements.
+
+=Reinforcing.=--To minimize the cracking, either bar or wire mesh
+reinforcing is used in the concrete. If bars are used they are placed
+in the concrete as it is poured so as to form a belt around each
+section about 15 feet square. If the mesh type is employed, a part of
+the layer of concrete is placed and smoothed off and a strip of the
+mesh laid in place. Additional concrete is then poured on top of the
+mesh to bring the slab to the required thickness.
+
+=Bituminous Coatings on Concrete Surfaces.=--The concrete road surface
+is sometimes coated with a layer of bituminous material and stone
+chips or gravel pebbles. This is particularly advisable where no
+really satisfactory aggregates are available and the concrete surface
+would not possess sufficient durability. The bituminous material is
+applied hot to the surface and is then covered with stone chips or
+gravel pebbles, ranging in size from 3/4 inch down to 1/4 inch, the
+resulting coating being about 3/4 inch thick. Many failures of this
+type of surface have been recorded due to the difficulty of securing
+adhesion to the concrete. This seems to be due in part to inability to
+get the proper bituminous materials and in part to climatic effects.
+Considerable progress has been made in developing this type of surface
+and it may eventually become a satisfactory maintenance method.
+
+=Characteristics.=--The concrete road is of a granular texture and is
+not slippery. It is of course rigid and noisy for steel tired
+vehicles. It is an excellent automobile road and its low tractive
+resistance makes it a desirable surface for horse drawn vehicles. It
+possesses a high degree of durability if properly constructed. It is
+likely to crack indiscriminately but as a general rule the cracks are
+not a serious defect.
+
+=Maintenance.=--The cracks that appear in the concrete surface are
+filled once or twice a year, tar or asphalt being employed. The dust
+and detritus is cleaned out of the cracks and the hot filler poured
+in, with enough excess overflowing to protect the edges.
+
+
+
+
+CHAPTER IX
+
+VITRIFIED BRICK ROADS
+
+
+Vitrified brick roads consist of a foundation course of Portland
+cement concrete, broken stone or slag macadam, or of brick laid flat,
+the first named being by far the most generally used, and a wearing
+course of vitrified brick.
+
+=Vitrified Brick.=--Vitrified brick are made from clay of such a
+character that when heated to the required temperature they will fuse
+into a glassy texture. Brick roads are constructed on roads carrying
+the severest of traffic and the brick must therefore be tough and of
+high resistance to wear.
+
+Not all of the clays from which brick may be manufactured will produce
+a product suitable for road construction, and paving brick, even
+though truly vitrified, are of different degrees of durability,
+depending upon the nature of the clay and the care exercised in the
+manufacture.
+
+Paving brick are manufactured by the stiff mud process, which means
+that the clay is molded into form in a relatively dry condition. To
+accomplish this, considerable pressure is exerted in forcing the
+column of clay through the dies, which form the prism from which the
+brick are cut. If the clay is unsuitable in character or is not
+properly ground and mixed, the brick will possess planes of weakness
+between the various layers of clay which have been pressed together,
+and these planes, called laminations, are a source of weakness if too
+marked. It is usual to specify that the brick used for road surfaces
+shall be free from marked laminations.
+
+If the brick is not properly burned it will be only partly vitrified
+and therefore not of maximum durability. It is customary to specify
+that the brick shall show a glassy fracture indicating complete
+vitrification.
+
+Various defects of a minor nature occasionally develop in the brick
+during the successive steps in the manufacturing process. Check cracks
+resulting from the burning or from too rapid cooling are often
+encountered, but unless these are deep, that is 3/16 inch or more,
+they do not impair the wearing quality of the brick, nor indicate
+structural weakness. Kiln marks are formed on some of the brick due to
+the weight of the brick above in the kiln. These depressions are not
+objectionable unless the brick are so distorted that they will not lie
+evenly in the pavement.
+
+Spacing lugs or raised letters are formed on one face of the brick to
+insure sufficient space between the brick for the filler. These lugs
+or letters are not less than 1/8 inch nor more than 1/4 inch high and
+of such design that they will not obstruct the free flow of filler
+into the joints between the brick.
+
+Several varieties of paving brick are to be had, the difference being
+principally in the design or size.
+
+=Repressed Brick.=--In this type of brick the spacing lugs are formed
+by pressing the green brick, after it has been cut to size, into a
+mold on one face of which are recessed letters or other devices into
+which the clay is pressed, thus forming the spacing lugs.
+
+=Vertical Fiber Brick.=--These brick are designed to be laid with one
+wire-cut face up and spacing is provided by two or more beads on the
+side of the brick. Sometimes the vertical fiber brick has no spacing
+lug, it being contended that the irregularities of the brick are such
+as to provide all of the space required. In practice this does not
+always work out, as the brick are so regular in shape that when laid
+there is too little space between the brick to permit the introduction
+of a suitable filler. The use of brick without spacing lugs is just
+beginning and is not yet a generally accepted practice.
+
+=Wire-cut-lug Brick.=--This is a type of non-repressed brick which has
+spacing lugs provided by cutting one face in a special manner which
+provided lugs for spacing. In this type the wire cut face is the one
+between the brick as they are laid in the pavement.
+
+=Tests for Quality.=--The standard test for quality of paving brick is
+the rattler test. The brick rattler consists of a barrel of 14 sides
+24 inches long, mounted so as to rotate at a speed between 29.5 and
+30.5 revolutions per minute. The duration of a test is 1800
+revolutions. Ten brick constitute a charge and these are placed in the
+rattler along with 300 lbs. of cast iron spheres. The spheres are of
+two sizes, the smaller being 1-7/8 inch in diameter when new, and the
+larger 3-3/4 inches in diameter when new. Ten of the larger spheres
+are used and the balance of the charge is made up of the small size.
+
+When tested in the standard manner the loss allowable for the several
+classes of service are as follows:
+
+  ------------+---------------+----------------
+              |               |   Maximum Loss
+    Traffic   |  Average Loss |   for any Brick
+  ------------+---------------+----------------
+    Heavy     |   20 per cent |    24 per cent
+    Medium    |   22 per cent |    26 per cent
+    Light     |   25 per cent |    28 per cent
+  ------------+---------------+----------------
+
+=Other Tests.=--Sometimes the absorption test is specified for paving
+brick, but it is rarely a vitrified brick that will pass the rattler
+tests which fails to pass a reasonable absorption test. Absorption of
+water in an amount exceeding 4 per cent indicates incomplete
+vitrification and failure of such brick is almost certain during the
+rattler tests.
+
+The cross breaking test is also sometimes employed, but generally
+only to check the general quality of the brick. Failure in service
+more frequently occurs from excessive wear than from any other cause
+and the cross breaking test has little significance, except for brick
+less than 3 inches thick, which are to be laid on a sand bedding
+course.
+
+=Foundation.=--The foundation for brick roads is usually of Portland
+cement concrete, the thickness varying with the nature of the traffic
+and the kind of soil upon which the pavement is built. For well
+drained soils and normal highway traffic, 5 inches is the ordinary
+thickness of foundation. Under favorable conditions such as locations
+with sandy soils or in semi-arid or arid regions where the soil is
+always stable, the foundation may be four inches thick, and a
+considerable mileage of brick road has been built with concrete
+foundations less than four inches thick.
+
+In other locations the soil and traffic conditions require a base six
+inches or more in thickness, and the proper thickness can be
+determined only after all of the factors involved are known and have
+been analyzed. It is impractical to adopt a standard thickness of
+foundation that will be equally economical for all locations and all
+kinds of traffic. As the brick pavement is essentially a heavy traffic
+type of surface, the design cannot be varied greatly with similar
+foundation conditions because the weight of individual loads is the
+significant factor and this does not vary so much as the volume of
+traffic. A variation in volume of traffic may be compensated for by a
+variation in the quality of the brick as already set forth.
+
+The mixtures for the concrete foundation vary widely because of the
+variation in the aggregates employed. If the fine and coarse aggregate
+for the concrete are of good quality a mixture of one part cement, two
+and one-half parts sand and five parts of coarse aggregate would
+insure concrete of adequate strength. A somewhat leaner mixture is
+sometimes employed and would be satisfactory if the aggregates were of
+exceptional concrete making quality. Mixtures of sand and pebbles
+(unscreened gravel) may also be used if care is exercised to secure a
+mixture of adequate strength. The proportion will of necessity vary
+with each particular material and the discussion of the various
+considerations involved may be obtained from various standard works on
+concrete and concrete materials.
+
+Broken stone macadam is sometimes utilized for the foundation course
+of the brick pavement and such foundations are constructed as
+water-bound, which is described in a previous chapter. The thickness,
+like that of the concrete foundation, varies with the soil conditions
+and the weight of the loads that are expected to use the road. The
+macadam is placed in a single layer and is rolled and bonded with
+screenings as described in the chapter dealing with water-bound
+macadam. Six inches is a common thickness for the macadam base. This
+type of foundation should be employed only where the soil is quite
+stable and where material costs are such as to insure that the macadam
+base is materially cheaper than one of concrete. This would usually be
+in locations where the cost of cement is high because of long hauls
+and where suitable macadam materials may be obtained close at hand.
+
+Old macadam roads are sometimes utilized for the foundation for the
+brick surface, but the instances where this is permissible are
+comparatively few in number. When an old macadam is to be used it is
+reshaped to the proper cross section and re-rolled and bonded so as to
+afford a stable foundation of the proper cross slope.
+
+
+BEDDING COURSE FOR BRICK SURFACES
+
+In order to equalize the variations in size and shape of the brick,
+they are laid on a bedding course composed of material into which the
+brick may be forced by rolling. In this way the upper surfaces of all
+brick can be brought to the proper elevation to insure smoothness and
+easy riding qualities. Several kinds of bedding course are now
+employed.
+
+=Sand Bedding Course.=--The sand bedding course has been referred to
+as a sand cushion, but as a matter of experience the cushion effect is
+slight, although sometimes pavements have become uneven because the
+brick have pushed down into the sand after the pavement was used for a
+time. The sand for the bedding course should preferably be fine
+grained, all particles passing the eight mesh sieve, but ordinary
+concrete sand is satisfactory. The sand need not be clean, as a
+comparatively large percentage of silt or clay does not impair the
+usefulness of the material.
+
+[Illustration: Fig. 19.--Cross Sections for Brick Highways]
+
+=Sand Mortar Bedding Course.=--In order to eliminate the tendency for
+the straight sand bedding course to shift because of the impact of
+traffic on the brick, a lean cement mortar is sometimes employed
+rather than the straight sand. Sand and cement in the ratio of one
+part cement to four or five parts of sand are mixed dry, and after the
+brick have been rolled, is moistened to furnish water to hydrate the
+cement. The sand employed is ordinary clean concrete sand.
+
+=Green Concrete Bedding Course.=--In the monolithic type of brick
+road construction, the brick are laid directly on the green concrete
+base before the concrete has taken a set and the irregularities of the
+brick are taken up by rolling them until bedded in concrete.
+
+
+FILLERS FOR BRICK SURFACES
+
+The spaces between the brick are filled with some material that will
+prevent the brick from being displaced and prevent water getting to
+the bedding course. A suitable filler must adhere to the brick and
+fill completely the spaces between them. It must withstand traffic so
+as to remain intact in the joints and when in place it must be rigid
+enough to prevent displacement of the brick.
+
+=Cement Grout Filler.=--One of the most commonly used fillers for
+brick pavements consists of a grout composed of Portland cement and
+fine sand. When properly mixed and applied the grout filler meets all
+requirements for a filler except that it is non-elastic and some means
+must be adopted for caring for pavement expansion.
+
+=Bituminous Fillers.=--Asphaltic materials and tars are widely used as
+fillers for brick pavements. Such fillers are of high melting point
+and consequently solid at ordinary temperature. They are poured into
+the joints hot and when they cool are firm enough to comply with the
+requirements for a filler. In addition, they have enough ductility to
+accommodate the expansion of the pavement due to temperature changes.
+
+=Mastic Fillers.=--Mastic consists of a mixture of about equal volumes
+of fine sand and a solid bituminous material. The mixture is prepared
+at high temperature and is worked into the joints between the brick
+while hot. When cool it resembles the straight bituminous filler
+except that the mastic is somewhat more resistant to wear than the
+straight bituminous filler.
+
+EXPANSION JOINTS
+
+It is recognized that brick will expand and contract with changes in
+temperature. When a bituminous or mastic filler is employed there is
+sufficient yield to the filler to accommodate the change in dimension
+in the brick, but when the grout filler is used either the expansion
+joint must be provided or the pavement must be designed to withstand
+the compression due to expansion of the brick. Expansion joints may
+consist of a sheet of bituminous mastic prepared for the purpose and
+set in place in the pavement. The sheet of joint material is simply
+inserted between courses of brick at the proper place.
+
+Another method of forming an expansion joint consists in placing a
+strip of wood between courses of brick at the place where a joint is
+required. After the pavement has been grouted, the wooden strip is
+pulled out and the joint is filled with a suitable bituminous filler.
+
+=Marginal Curb.=--If the sand bedding course is employed, it is
+necessary to provide curbing along the sides of the brick to hold the
+bedding course in place. The curb is usually constructed integral with
+the base and of concrete of the same mixture as the base. The width of
+the curb is usually six inches and the top of the curb is at the same
+elevation as the edge of brick surface.
+
+
+CONSTRUCTION OF THE SURFACE
+
+Before the construction of a brick surface should be undertaken on a
+road, the drainage should be provided for even more completely than
+for a less costly type of surface since it does not pay to jeopardize
+the stability of the pavement by failure to provide adequately for the
+stability of the supporting soil. Grades should also be reduced to the
+economical limit.
+
+The earth subgrade is brought to the proper elevation and cross
+section and is thoroughly rolled. If there are places where the soil
+will not compact properly under rolling, these places are corrected by
+taking out the material and back filling with new material that will
+properly compact under the roller.
+
+The aggregates for the concrete may be distributed along on the
+prepared subgrade or may be stored in stock piles or bins at
+convenient points. If stored on the subgrade, a traction mixer is
+employed which is drawn along the road as the work progresses, the
+materials being placed directly in the mixer. If stored at a central
+point, they may be transported to the mixer on the road and dumped
+directly into the mixer, or the mixer may be set up at the storage
+piles and the concrete hauled in trucks to the road where it is
+deposited and shaped.
+
+The concrete is spread to the proper thickness and tamped either by
+hand or by machinery. If the marginal curb is to be employed, it is
+constructed immediately after the concrete for the base has been
+finished but before the cement begins to set.
+
+After the foundation concrete has set, the bedding course is spread
+and struck off to the proper thickness. When the bedding course
+consists of sand-cement mortar, the sand and cement are mixed dry and
+spread to prescribed thickness. It is considered to be desirable to
+roll the sand bedding course with a light hand roller before the brick
+are placed, but the sand-cement bedding course is not rolled. The
+bedding course must be carefully shaped by means of a templet or
+strike board before the brick are placed.
+
+The brick are laid in straight courses across the pavement, with the
+spacing lugs all in the same direction if brick with spacing lugs are
+employed, and with the lugs in contact with the brick of adjoining
+courses. If brick without spacing lugs are used they are laid loosely
+so that there will be room for the filler between the brick of
+adjoining courses.
+
+After the brick have been laid they are rolled to bed them in the sand
+or sand-mortar bedding course and thus secure a smooth surface. For
+this purpose a light, power driven, tandem roller is used and the
+rolling is continued until the brick are thoroughly bedded. Any
+defective brick that are noted are removed and replaced with good
+brick and after this culling has been completed the surface is once
+more thoroughly rolled. If a cement-sand bedding course is employed,
+the surface is sprinkled just after the final rolling so that water
+will flow down between the brick and moisten the bedding course
+sufficiently to cause the cement to set. In some cases, the
+sand-cement bedding course is sprinkled just before the brick are laid
+but in warm weather the setting would take place before the brick
+could be rolled if that were done. In cool weather the setting is
+sufficiently slow to permit rolling before the bedding course hardens.
+
+The filler is applied to the surface after the rolling. If the
+bituminous type of filler is employed, the hot filler is poured onto
+the surface and worked into the joints by means of squeegees, with
+comparatively little material left on the surface. In some instances
+cone-shaped pouring pots are employed and the material is poured
+directly into the joints.
+
+The cement grout filler is applied in the same general manner as the
+bituminous filler. The grout, consisting of equal parts of sand and
+cement, is mixed to a thin consistency and poured onto the surface and
+is then worked into the joints with squeegees. Two or more
+applications are usually required to effect a complete filling of the
+joints. The surface should be covered with sand and be kept moist
+until the cement grout has set.
+
+
+
+
+CHAPTER X
+
+BITUMINOUS ROAD MATERIALS AND THEIR USE
+
+
+Tars and asphaltic materials of various kinds are widely used for road
+construction and maintenance, especially for road surfaces subjected
+to motor traffic. Materials of this character that are employed in
+highway work possess varying degrees of adhesiveness, and while they
+may be semi-solid or viscous liquids at air temperature, they melt on
+the application of heat and can be made sufficiently fluid to mix with
+the mineral aggregates that may be used in the road surface. Upon
+cooling, the bituminous materials return to the previous state and
+impart a certain amount of plasticity to the mixture, at the same time
+serving as a binding or cementing agent, which is sufficiently stable
+for many classes of road construction.
+
+=Classes of Bituminous Materials.=--Bituminous materials may be
+classified, according to the source from which they are obtained, as
+coal tars, water gas tars, native or natural asphalts and oil or
+petroleum asphalts.
+
+=Coal Tar.=--Coal tar is obtained as a by-product in the manufacture
+of illuminating gas from coal. It is also obtained in the manufacture
+of coke from coal. The tar thus obtained is manufactured into products
+that are used for dust layers on gravel or macadam roads, binders for
+macadam and gravel surfaces, fillers for brick, wood block and stone
+block pavements and for expansion joints. These various materials
+differ mainly in their consistency at air temperature. (They may
+differ widely in chemical composition, but that need not be considered
+herein.)
+
+=Water Gas Tar.=--Water gas tar is obtained as a by-product in the
+manufacture of illuminating gas from crude petroleum. It is used for
+the same kinds of construction as coal tar, and the products utilized
+for the several purposes, like the coal tars, differ mainly in
+consistency.
+
+=Natural Asphalt.=--Natural asphalt is found in deposits at many
+places in the world, existing in beds or pools where it has exuded
+from the earth or as veins in cavities in the rocks. It is of varying
+composition and consistency, but those kinds in most general use are
+solid or very viscous liquids at air temperature. Of the deposits that
+have been developed on a commercial scale, the Trinidad lake in the
+British West Indies and Bermudez deposit in Venezuela are best known.
+Both of these materials are too hard in the natural state to be used
+for road construction, and are softened, or fluxed as it is called,
+with fluid petroleum oil before being used.
+
+=Petroleum Asphalt.=--Petroleum asphalt is a residue remaining after
+the fluid products have been distilled from petroleum. Residues of
+this sort are not always suitable for road construction, but a number
+of brands of road material are obtained from this source. Oil asphalts
+are used for dust layers, for binders for macadam roads, for asphalt
+cements for sheet pavement surfaces, and for fillers for block
+pavements and expansion joints.
+
+=Mixtures.=--Water gas tars and asphalts are sometimes mixed to
+produce road materials, and likewise native asphalts and residues
+obtained from petroleum are sometimes mixed to produce asphalt cements
+for paving mixtures.
+
+=Classification according to Consistency.=--The various bituminous
+materials may be classified according to consistency in discussing the
+various uses to which they may be put.
+
+=Road Oils.=--Road oils are fluid petroleum oils of such consistency
+that they may be applied cold or by heating slightly. They are used
+as dust layers on earth, gravel and macadam surfaces. Their efficacy
+depends upon the binding properties of the small amount of asphaltic
+material that is contained in the oil.
+
+=Liquid Asphalts.=--These are somewhat less fluid than the road oils,
+and must always be heated before application, but are viscous liquids
+at ordinary temperature. These materials are obtained from crude
+petroleum or semi-solid native bitumens, in which case they are
+usually called malthas. Both coal tars and water gas tars of
+semi-solid consistency are also employed for the same class of
+construction as the liquid asphalts.
+
+These materials are used for carpeting mediums on macadam roads and as
+cementing agents in the construction of hot-mixed macadam.
+
+=Asphalt Cements.=--The solid asphaltic materials used for hot-mixed
+types of construction are called asphalt cements. They may be
+petroleum residues or native asphalts fluxed with petroleum oils. They
+are solids at ordinary temperature and must be heated to a temperature
+in excess of two hundred and fifty degrees before they are
+sufficiently fluid to use. Asphalt cements are used for sheet asphalt
+and asphaltic concrete construction and for hot-mixed bituminous
+macadam.
+
+=Fillers.=--Fillers are solid asphalts or tars that are used for
+filling expansion joints in rigid pavements and for filling the spaces
+between the blocks in brick, wood block and stone block pavements.
+
+=Bitumen.=--Bituminous materials are all soluble to a greater or
+lesser extent in carbon disulphide and the soluble portion is called
+bitumen. It is the bitumen that gives to the materials the cementing
+properties utilized in road construction. Mixtures of mineral
+aggregates and bituminous materials for various purposes are
+proportioned with bitumen as a basis. Therefore, less of an asphalt
+containing one hundred per cent bitumen will be used than of one
+containing less than one hundred per cent of bitumen.
+
+  TABLE 8
+
+  PROPERTIES OF ASPHALTIC ROAD MATERIALS
+
+  (A) Material
+  (B) Specific Gravity
+  (C) Consistency
+  (D) Solubility in CS_2, Per Cent
+  (E) Solubility of Bitumen in CCl_4, Per Cent
+  (F) Solubility of Bitumen in 86° Naphtha, Per Cent
+  (G) Fixed Carbon, Per Cent
+  (H) Flash Point
+  (I) Ductility
+  -------------------------+---------+----------+----------+------------
+           (A)             |   (B)   |    (C)   |   (D)    |    (E)
+  -------------------------+---------+----------+----------+------------
+  Mexican oil asphalts     |1.03-1.05|As desired| 99.5-99.9|99.5-99.9
+  California oil asphalts  |1.02-1.04|As desired|   99.9   |    99.9
+  Texas oil asphalts       |1.01-1.03|As desired|   99.9   |    99.9
+  Bermudez  natural asphalt|1.07     |    25    |    95    |     99+
+  Trinidad natural asphalt |1.40     |     7    |  56-57   |     100
+  Bermudez asphalt cement  |1.04-1.06|Up to 135 |  95-97   |99.5 or more
+  -------------------------+---------+----------+----------+------------
+
+  -------------------------+---------+----------+----------+------------
+           (A)             |   (F)   |   (G)    |   (H)    |     (I)
+  -------------------------+---------+----------+----------+------------
+  Mexican oil asphalts     |  70-80  |   13-16  | 200°C. up|   60-100
+  California oil asphalts  |  75-80  |   10-12  | 200°C. up|   100+
+  Texas oil asphalts       |  75-80  |   12-14  | 200°C. up|   50-100
+  Bermudez  natural asphalt|  68-70  |   13-14  |    ...   |    ...
+  Trinidad natural asphalt |  64-65  |   10-11  |    ...   |    ...
+  Bermudez asphalt cement  |  77-80  |   11-12  |  175-200 |   25-50
+  -------------------------+---------+----------+----------+------------
+
+=Specifications.=--Some properties of bituminous materials can be
+varied in the process of manufacture, while others are inherent in the
+material and cannot be changed in the process of manufacture.
+Specifications must therefore be drawn with care to insure that the
+requirements can be met by satisfactory materials. But certain
+properties, such as specific gravity, may vary greatly among materials
+equally satisfactory for construction purposes. One should not be
+misled by apparent differences in the characteristics of materials,
+because these may simply be natural peculiarities which have no
+bearing on the usefulness of the material. There are given in Table 8
+the properties of some of the commonly used bituminous materials and
+the properties that can be varied in the process of manufacture are
+indicated with an asterisk. A variation in these properties will
+usually result in some change of other properties, but generally not a
+great change.
+
+
+SURFACES IN WHICH BITUMINOUS MATERIALS ARE UTILIZED
+
+I. Surface Treatments
+
+Attention has been directed to the rapid deterioration of water-bound
+macadam when subjected to passenger automobile traffic.
+
+In water-bound macadam the stones are held in place by a weak cement
+composed of stone dust and water, and this cement is not sufficiently
+strong to hold the stones in place when they are subjected to the
+shear of automobile tires. In finishing the water-bound macadam
+surface, the spaces between the stones are filled with screening and
+in addition a layer about one-fourth inch thick is left on the
+surface.
+
+The automobile traffic first brushes aside all of the screenings and
+smaller particles of rock, exposing the larger stones. These gradually
+loosen as the road is used and are brushed aside. When this effect
+begins, the road is said to be raveling. Various lengths of time may
+elapse from the time the road is first finished until raveling begins,
+depending upon the character of the stone, the weather and the amount
+of motor traffic. During the period before raveling starts, it is
+comparatively easy to restore the road surface at any time by the
+addition of screenings or clay and sand. Usually there will be a few
+small areas of the surface that, on account of faulty construction,
+will ravel or become rutted much earlier than the remainder of the
+surface. These can be repaired by the methods described in the chapter
+on "Water-bound Macadam Construction." When the surface begins to
+ravel seriously, maintenance becomes much more difficult and in order
+to prevent raveling and the difficulties of maintenance thereafter,
+the macadam surface is often coated with a bituminous material.
+
+[Illustration: Fig. 20.--Oiling a Gravel Road]
+
+If there is any dust or screenings on the road surface, the bituminous
+material will not adhere to the stones and will soon flake off under
+traffic. The surface of the macadam must therefore be thoroughly
+cleaned before the bituminous material is applied. The usual practice
+is to finish the road as water-bound macadam, and permit traffic on it
+for a sufficient length of time to show any weak places in the surface
+and at the same time thoroughly to season the surface. If any
+defective places appear, they are repaired and when the surface
+exhibits satisfactory stability, but before it begins to ravel, the
+bituminous surface is applied. There will ordinarily be some stone
+dust and some screenings remaining on the surface at the time
+bituminous treatment is undertaken, and there may also be some caked
+mud or other foreign material. All of this must be removed so as to
+expose the stones throughout.
+
+=Applying the Bituminous Binder.=--The bituminous binder may be
+delivered in tank cars, which is desirable if the work is near a
+railroad siding, or ample tank wagon service is available for long
+hauls so that the tank will not be held up too long. Often it is
+desirable to purchase the binder in barrels and haul these to the site
+of the work in advance of beginning the construction of the surface.
+
+The bituminous material may be applied by means of hand spreading cans
+not unlike an ordinary garden watering pot, except that a slotted
+nozzle is substituted for the ordinary perforated one. If hand methods
+are employed for spreading, the bituminous material is heated in open
+kettles and then spread on the surface, the quantity required usually
+being about one-half gallon per square yard of surface. The
+temperature of the binder should be great enough to insure fluidity
+and the road should be dry at the time of the application. As soon as
+the material has been spread, the surface is finished with a dressing
+of chips.
+
+=Finishing the Surface.=--For surface dressing the best material is
+stone chips ranging in size from about 1 inch down to one-fourth inch.
+But the chips must be of durable material, or they will quickly grind
+into dust. They must be free from dust when applied, as the presence
+of any considerable amount of dust interferes with the proper
+finishing of the surface. The stone chips are rolled into the surface,
+a sufficient quantity being used to just cover the surface.
+
+=Patching.=--It almost always happens that some small areas will not
+be properly cleaned or that for some unknown reason the coating peels
+off the surface. Such places must be promptly patched to prevent them
+enlarging under the action of traffic. This work is usually done by
+patrolmen, who inspect the road at frequent intervals and make the
+necessary repairs. The patrolman is equipped with a small heating
+kettle, a spreading can and the necessary brushes, tampers and
+miscellaneous tools needed for the repair work. The place to be
+patched is carefully cleaned, coated with bituminous binder and stone
+chips and tamped until dense and solid. Repairs made in this way are
+exceedingly important in that they arrest deterioration in its early
+stages and maintain a high degree of serviceability.
+
+
+II. Penetration Macadam
+
+A considerable mileage of macadam has been constructed in which an
+attempt was made to eliminate the difficulties of maintenance by a
+method of construction that involves applying a bituminous binder in
+such a manner as to permit it to penetrate two inches or more into the
+surface. It is expected that the binder will coat the stones to such
+an extent as to increase materially the stability of the bituminous
+macadam over the surface treated one. It is also expected that less
+difficulty will be encountered in maintaining a surface of bituminous
+material and stone chips on this type of road than on the water-bound
+macadam. The extent to which these expectations have been realized has
+varied to a marked degree and although some excellent surfaces have
+been constructed by this method, the results have as a rule been
+neither uniform nor entirely satisfactory. It seems to be apparent
+that good results cannot be obtained unless the materials are entirely
+suitable and the construction is carried out with unusual skill.
+
+=Foundation.=--The foundation or lower course consists of a layer of
+broken stone six inches thick placed on a well drained and thoroughly
+rolled earth subgrade. In exceptional cases, the Telford type of
+foundation might be employed.
+
+The lower course of broken stone is finished in the same manner as
+water-bound macadam, being bonded with stone screenings or with fine
+gravel of high clay content.
+
+Since this course is in reality the foundation of the surface, it is
+necessary to secure stability by appropriate construction methods,
+exactly as in constructing water-bound macadam.
+
+[Illustration: Fig. 21.--Type of Roller used on Gravel and Macadam
+Roads]
+
+=Upper or Wearing Course.=--The wearing course consists of a layer of
+stone about two and one-half inches thick. The stone is placed and
+rolled and the spaces between the stones partially filled with some
+suitable bituminous material. The bituminous material is usually
+applied by means of a mechanical spreading device connected to a tank
+wagon. The bituminous materials employed for this class of
+construction are semi-solid in character and must be heated to give
+them sufficient fluidity for application. They may be heated in the
+tank wagon which is used for the application or they may be heated in
+separate tanks and transferred to the distributing wagon for
+spreading. Some kind of a nozzle or group of nozzles is employed for
+spreading the material so that it can be delivered in the form of a
+spray or at least in a thin fan-shaped stream and can be distributed
+in a fairly uniform layer over the stone. The binder will cool rather
+rapidly after it is applied, but meanwhile will flow into the openings
+between the stones and will form over the surface stones a coating of
+slight thickness.
+
+The surface of the macadam is next covered with a layer of chips of
+tough rock, similar to the material used for the final dressing in
+surface treatments. These are carefully brushed into the openings
+between the larger stones by means of heavy brush brooms. This is an
+exceedingly important part of the work and often a much neglected part
+of the construction.
+
+The surface is then covered with a second application of bituminous
+material, somewhat less in quantity than required for the first
+treatment and the surface again covered with stone chips and brushed.
+
+The surface is then thoroughly rolled and is ready for traffic.
+
+=Patching.=--As in the case of surface treatments, there are likely to
+be places that, on account of defects in the construction, will fail
+soon after the road is placed under traffic. These will quickly
+enlarge unless they are repaired promptly. The repairs are made by
+loosening the stone in the area affected and adding new stone as
+needed and then pouring on the necessary amount of bituminous material
+to coat the stones. Allowance must be made for the compression of the
+material by tamping so that a depression does not result. The stones
+are carefully tamped to place and covered with chips which are also
+tamped.
+
+=Characteristics.=--The penetration macadam is a surface well adapted
+to motor traffic if the individual vehicles are not too heavy. It is
+likely to squeeze out of shape under motor truck traffic, becoming
+seriously uneven and uncomfortable for traffic. Its durability is
+materially affected by the construction methods followed.
+
+
+III. Hot Mixed Macadam
+
+The wearing course of the mixed macadam is composed of graded broken
+stone or gravel and a bituminous binder. Usually the bituminous
+material only is heated prior to the mixing, but sometimes the stone
+is also heated.
+
+=Foundation.=--The lower course, which serves as the foundation, is
+either broken stone macadam, gravel or concrete.
+
+Where a foundation of broken stone is used, it is constructed of the
+materials and in the manner described for the foundation of the
+penetration macadam. Quite often a badly worn macadam or gravel road
+is used for the foundation and a new wearing course provided by adding
+a mixed macadam surface. If such is the case, the old surface is
+worked over so as to restore the shape sufficiently and to insure that
+it is everywhere of sufficient thickness.
+
+Portland cement concrete is sometimes used as a foundation for the
+mixed macadam, but not often. Usually if the traffic is of a character
+requiring a concrete foundation, it is desirable to use a better
+wearing course than the mixed macadam, and the asphaltic concrete or
+sheet asphalt type of surface is employed. It is necessary to finish
+the surface of the concrete base with some device that will leave the
+surface rough to prevent the macadam from creeping. A knobbed tamper
+which leaves numerous irregular depressions about 2 inches in diameter
+and three-fourths inch deep is often employed.
+
+=Sizes of Stone.=--For the wearing surface, stone ranging in size from
+2 inches down to one-fourth inch is usually employed. If the stone is
+of good quality the maximum size may be but 1-1/2 inches, but soft or
+even medium stone of that size are likely to crush under traffic. The
+stone for the base course should preferably be from 3 inches down, but
+any available size will be satisfactory if the layer is well rolled
+and bonded. The base course is constructed in the same manner as
+water-bound macadam and any material satisfactory for the base course
+of macadam will serve for the base course of mixed macadam. Screenings
+having good bonding properties will also be required for the base
+course.
+
+=Mixing and Wearing Surface.=--Several methods are employed in mixing
+the wearing surface. The simplest is to mix by hand with shovels. The
+aggregates are heated in improvised heaters which may consist of
+nothing more than a metal pipe two or three feet in diameter, around
+which the stone is piled. The mixing platform is usually a metal plate
+sometimes arranged so that it can be heated by means of a fire
+underneath. The bituminous material is heated in kettles. For some
+mixtures, the stone is not heated, but the bituminous material is
+always heated. The batch of stone is placed on the mixing platform,
+the bituminous material added and the materials mixed by hand.
+
+Machine mixing is practiced much more extensively than hand mixing,
+being both more rapid and cheaper. The mixer is similar to a concrete
+mixer except that the drum is arranged so that it can be heated. The
+hot stone and the bituminous binder are put into the drum and mixed
+for the requisite length of time. Sometimes the stone is mixed cold,
+the bituminous material only being heated.
+
+=Placing the Wearing Surface.=--The hot mixture is carted to the road
+and spread to such thickness that after rolling the wearing surface
+will be not less than two inches thick. The hot mixture is dumped and
+then spread by means of shovels to the approximate thickness and the
+spreading completed by means of rakes. The surface is then rolled
+either with a tandem or a three-wheeled roller until thoroughly
+compressed.
+
+=Seal Coat.=--After the rolling has been completed, the surface is
+covered with hot bituminous cement and dressed with pea gravel or
+stone chips and again rolled. Traffic may be permitted in twenty-four
+hours.
+
+=Characteristics.=--The mixed macadam is a somewhat resilient surface
+of excellent riding qualities and considerable durability for medium
+traffic. It is likely to creep and become uneven when subjected to
+heavy loads. The seal coat will wear off in two or three years and
+will require replacing.
+
+
+IV. Asphaltic Concrete
+
+Asphaltic concrete is a name given to a road surface mixture which is
+composed of graded stone, graded sand and asphalt cement. This type is
+designated as asphaltic concrete because of the analogy of the mixture
+to Portland cement concrete.
+
+Asphaltic concrete is of two general types known as bitulithic, or
+Warrenite, and Topeka asphaltic concrete, respectively, the
+differences being in the nature of the mixture.
+
+=Bitulithic or Warrenite.=--The stone employed for these types is
+graded down from a size about equal to one-half of the thickness of
+the wearing course, and stone passing a 1-1/4 or 1-1/2-inch screen is
+usually specified. From the maximum size the stone is graded down to
+the finest particles produced by the crusher. The range of sizes of
+stone will vary with the source of the supply, and in order to secure
+the desired density in the mixture, varying amounts of graded sand and
+mineral dust, such as ground limestone or Portland cement, are added
+to the broken stone. Usually the resulting mixture contains less than
+fifteen per cent of voids, and to this carefully graded mineral
+aggregate there is added enough asphalt cement to bind together the
+particles.
+
+=Topeka Asphaltic Concrete.=--In this type of asphaltic concrete, the
+mineral aggregate consists of a mixture of carefully graded sand and
+of broken stone of such size that all will pass a one-half-inch screen
+and graded down to the fine dust produced by the crusher. To this
+mixture is added about nine per cent of Portland cement or limestone
+dust. The voids in the mixture are usually about twenty-five per
+cent.
+
+It will be seen that the essential differences between the Bitulithic
+and Topeka types are these: the Topeka type contains a larger
+percentage of voids and stone of a smaller maximum size than the
+Bitulithic. Both types have been extensively employed for city paving,
+but the Bitulithic and Warrenite types have also been used to some
+extent for rural highways. The Topeka type has been used but little
+for rural highways.
+
+=Foundation.=--The foundation for the asphaltic concrete may be an old
+macadam road, a base course constructed of broken stone or Portland
+cement concrete, the latter being used much more extensively than
+either of the other types.
+
+Sometimes asphaltic concrete is used for resurfacing water-bound
+macadam or gravel roads when the traffic has increased to the point
+where the cost of maintenance of the water-bound macadam has become
+excessive. The existing surface is repaired and the cross section is
+restored, or possibly flattened somewhat.
+
+=Placing the Surface.=--The stone, sand and asphalt cement are heated
+to the required temperature and combined in the proper proportions and
+are then thoroughly mixed by a mechanical mixer. The mixture is hauled
+directly to the road and is dumped and spread by means of rakes. It is
+then rolled thoroughly while still hot, a three-wheeled roller being
+most satisfactory. After rolling, a seal coat of hot asphalt cement is
+spread over the surface and covered with hot stone chips about 1/4
+inch in size. The surface can be opened to traffic immediately after
+the surface has been completed.
+
+=Characteristics.=--The asphaltic concrete surface is of excellent
+riding properties, is easily repaired and of moderate durability. It
+is a particularly desirable surface for pleasure automobile riding and
+for horse drawn traffic.
+
+
+
+
+CHAPTER XI
+
+MAINTENANCE OF HIGHWAYS
+
+
+Proper maintenance of highways is equally important with proper
+construction. With nearly all types of road construction, the need for
+maintenance arises soon after the surface is placed under traffic and
+is continuous thereafter. The nature and amount of maintenance work
+varies greatly among the several types of surface and the organization
+suitable for a system of highways will depend to a considerable extent
+upon the kinds of surfaces that are to be maintained.
+
+The upkeep of a road may be conveniently considered as of two kinds,
+viz., (1) that which has to do with the wearing surface and earth
+shoulders or berms upon which there is some traffic and (2) that which
+has to do with the side ditches and drainage structures and keeping
+the roadside in presentable condition. Both kinds of work are usually
+carried out by the same organization, but whereas the nature of the
+work indicated under (1) will vary with the type of wearing surface
+and with all variations in traffic, that which is indicated under (2)
+will be nearly constant in any locality.
+
+
+ORGANIZATION FOR MAINTENANCE
+
+Maintenance of highways is preferably under the administration of the
+same authority as construction and when an improvement is undertaken
+under the jurisdiction of a State Highway Department, the completed
+improvement is ordinarily maintained under the state authority. If
+the improvement is made by county authorities, the maintenance is also
+carried out under county authority.
+
+The nature of the organization of maintenance forces is dependent upon
+the kind of roads to be cared for and must of necessity be varied in
+any instance as conditions demand. In general, either maintenance
+gangs or patrolmen are employed and often both are used on the same
+road system.
+
+=Patrol Maintenance.=--Where this system is in operation, the highway
+system is divided into patrol districts of from six to eighteen miles
+of highway and a single patrolman is placed in charge of each
+district. He is provided with all of the necessary tools and materials
+required in his district and performs all of the work required in the
+ordinary upkeep of the highway. He should work under the direction of
+the county engineer or the district engineer for the state highway
+department, because his work involves the use of materials and
+processes requiring technical supervision.
+
+=Gang Maintenance.=--The maintenance gang may be employed for some
+types of road surface in lieu of the patrolman or with other types of
+surface may be employed to supplement the work of the patrolman. The
+maintenance gang consists of three to ten men and is furnished all of
+the tools and materials required for the particular kind of work they
+do. Ordinarily the gang goes over the roads assigned to it once each
+season and performs those repair operations requiring more work than
+the patrolman can find time for. The work of the maintenance gang like
+that of the patrolman should be under engineering supervision.
+
+=Maintenance of Earth, Sand-clay, Gravel and Macadam Roads.=--The
+ordinary upkeep of earth, sand-clay, gravel and macadam surfaces is
+most readily accomplished by the patrol method, since constant care is
+required to keep the roads in a condition of maximum service ability.
+
+The tools required for each patrolman may include the following:
+
+  1 shovel              1 spade
+  1 stone rake          1 pick
+  1 scythe              1 tamper
+  1 or more road drags  1 mowing machine for cutting weeds
+  1 wheelbarrow           (sometimes)
+  1 light truck         1 small kit carpenter's tools
+
+The work of the patrolman consists in keeping the surface of the road
+smooth by dragging, repairing chuck holes by tamping in fresh material
+of the appropriate kind, keeping the ditches and culverts free from
+obstruction, cutting weeds and repairing bridge floors if they are of
+plank construction. Removal of snow drifts is sometimes a part of the
+patrolman's duty, but more often that is done by special gangs.
+Usually the patrolman is authorized to hire teams for dragging and
+cutting weeds.
+
+When an earth road requires to be re-graded so as to restore the
+cross-section and deepen the ditches, a gang is sent in to perform
+that work, as it is obviously impossible for the patrolman to perform
+work, of that kind.
+
+If the gravel road is being maintained with a bituminous carpet coat,
+the patrolman will be furnished the necessary tools to enable him to
+patch the surface with bituminous material as necessity requires.
+
+When the surface deteriorates to such an extent that a new carpet coat
+is required, the gang system is employed for all work connected with
+resurfacing, instead of attempting to have the work done by patrolmen.
+
+The maintenance of the macadam road is carried out in much the same
+manner as that of the gravel road. The binder of stone dust or clayey
+sand is renewed as often as it is swept off by traffic. Depressions or
+ruts are repaired by first loosening the surface with a pick and then
+adding broken stone and screenings to restore the surface.
+
+When the macadam reaches the stage where entire resurfacing is
+needed, the work is performed by gangs organized and equipped for the
+purpose; and likewise when the surface is being maintained with a
+bituminous carpet, the renewal of the carpet coat is performed by
+special gangs, but the ordinary upkeep of the surface by patching is
+handled by a patrolman.
+
+
+MAINTENANCE OF MIXED BITUMINOUS SURFACES
+
+[Illustration: Fig. 22.--Scarafier used in Gravel Road Maintenance]
+
+These types of surface can be kept in satisfactory condition if they
+are carefully repaired once or twice each season. This work requires
+considerable experience and some special equipment, not ordinarily
+supplied to patrolmen. A gang is organized for the work and supplied
+with the proper equipment. They go over the roads and patch all worn
+places, generally first removing the wearing surface entirely in the
+area affected.
+
+The wearing surface mixture is then prepared and tamped or rolled into
+place. If the area affected is small, tamping is satisfactory, and
+when the area is considerable, rolling is employed. The upkeep of the
+side roads may be accomplished by the same gang but is preferably
+taken care of by patrolmen, who do not attempt any but minor repairs
+to the wearing surface.
+
+
+MAINTENANCE OF BRICK AND CONCRETE ROADS
+
+On brick and concrete roads, the principal work on the wearing surface
+consists in filling the cracks with a suitable bituminous material.
+This work is done by patrolmen or by special gangs and generally will
+be done once each year. The upkeep of the side roads is cared for by
+patrolmen who drag the side roads and cut the weeds as occasion
+requires.
+
+
+
+
+INDEX
+
+
+  Administration county; 15
+    federal; 17
+    highway; 13
+    state; 16
+    township; 13
+
+  Aesthetics; 62
+
+  Aggregate, fine; 101
+
+  Aggregate, coarse; 100
+
+  Air resistance; 51
+
+  Alignment; 46
+
+  Applying bituminous binder; 122
+
+  Asphaltic concrete; 128
+
+  Asphalt, natural; 117
+    liquid; 118
+    petroleum; 117
+
+  Assessments, special; 19
+    zone method; 20
+
+
+  Bedding course, green mortar; 111
+    sand mortar; 111
+    sand bedding mortar; 111
+
+  Binder for gravel; 75
+
+  Bitulithic or warrenite; 128
+
+  Bitumen; 118
+
+  Bituminous coatings on concrete; 105
+
+  Bituminous fillers; 112
+
+  Bituminous road materials and their use; 116
+
+  Bituminous surfaces; 96, 120
+
+  Blade grader; 69
+
+  Bonding; 87
+
+  Bonds, annuity; 26
+    serial; 27
+    sinking fund; 25
+
+  Box culverts; 39
+
+  Brick roads; 113
+
+  Brick, repressed; 107
+    tests of 108;
+    vertical fiber; 107
+    vitrified; 106
+    wire-cut-lug; 108
+
+  Broken stone road surfaces; 89
+
+
+  Cement, asphaltic; 118
+
+  Cement concrete roads; 98
+
+  Cement grout filler; 112
+
+  Characteristics, asphaltic concrete; 129
+    bituminous macadam; 125
+    broken stone; 97
+    concrete; 105
+    mixed macadam; 128
+    sand clay; 78
+
+  Classes of bituminous materials; 116
+
+  Classification according to consistency; 117
+
+  Clay and cement concrete pipe; 39
+
+  Coal tar; 116
+
+  Concrete, asphaltic; 128
+
+  Concrete materials; 100
+
+  Concrete pipe; 39
+
+  Control of erosion; 61
+
+  Costs; 70
+
+  County administration; 15
+
+  Cross sections; 60, 65
+
+  Culverts; 56
+
+  Curing concrete; 103
+
+
+  Design, broken stone roads; 89
+    concrete roads; 99
+    earth roads; 42
+
+  Desirability of road bonds; 27
+
+  Development of traffic; 2
+
+  Drainage, necessity of; 29
+
+  Drainage of roads; 29
+
+
+  Earth roads, in arid regions; 72
+    humid regions; 65
+    value of; 73
+
+  Earth works; 92
+
+  Education, rural; 6
+
+  Effect of grades; 54
+
+  Elevating grader; 66
+
+  Elevating grader work; 68
+
+  End walls for culverts; 39
+
+  Energy loss on account of grades; 57
+
+  Entrances, farm; 37, 61
+
+  Expansion joints; 104
+
+
+  Farm entrance culverts; 37
+
+  Federal administration; 17
+
+  Fillers; 118
+
+  Finance, highway; 19
+
+  Fine aggregate; 101
+
+  Finishing surface of concrete; 122
+
+  Foundation, asphaltic concrete; 129
+    brick; 109
+    macadam; 93
+    mixed macadam; 126
+    penetration macadam; 123
+    Telford; 94
+
+
+  Gang maintenance; 131
+
+  Grader, Maney; 67
+    use of; 69
+
+  Gravel, ideal; 81
+    natural; 83
+    roads; 74
+
+  General taxation; 24
+
+  Good roads and commerce; 7
+
+  Green concrete bedding course; 111
+
+
+  Highway administration; 13
+
+  Highway finance; 19
+    maintenance; 130
+
+
+  Importance of design; 30
+
+  Ideal road gravel; 81
+
+  Inter-city traffic; 5
+
+  Inter-county and inter-state traffic; 5
+
+  Internal resistance; 50
+
+  Intersections; 46
+
+
+  Laying tile; 35
+
+  Length of culvert; 37
+
+  Liquid asphalt; 118
+
+  Local farm to market traffic; 4
+
+
+  Macadam; 89
+
+  Maintenance, concrete; 105
+    earth roads; 70
+    general; 131
+    gravel roads; 88
+    macadam; 96
+    of highways; 130
+    patrol; 131
+
+  Maney grader; 67
+
+  Marginal curb; 113
+
+  Measuring materials; 101
+
+  Metal pipe; 38
+
+  Mixing wearing surface; 127
+
+  Mixtures; 117
+
+
+  Natural asphalt; 117
+    gravel; 79
+
+  Necessity for planning; 42
+    drainage; 29
+
+
+  Patching; 122, 125
+
+  Patrol maintenance; 131
+
+  Pebbles, size of; 80
+
+  Petroleum asphalt; 117
+
+  Placing asphaltic concrete; 129
+
+  Placing broken stone; 94
+
+  Placing concrete; 102, 103
+    mixed macadam; 127
+
+  Plans for roads; 43
+
+  Preliminary investigation; 44
+
+  Preparation of earth foundation; 102
+    of road; 85
+
+  Private entrances; 61
+
+  Properties of stone; 90
+
+  Proportions for concrete roads; 101
+
+  Purpose of highways; 1
+
+
+  Reinforced concrete box culverts; 39
+
+  Reinforcing; 104
+
+  Repressed brick; 107
+
+  Road oils; 117
+
+  Road plans; 43
+
+  Rocks, kind of, for macadam; 91
+
+  Rolling, macadam; 95
+
+  Rolling resistance; 50
+
+  Run-off; 31
+
+  Rural education; 6
+
+  Rural social life; 7
+
+
+  Safety consideration; 58
+
+  Sand bedding course; 111
+
+  Sand clay and gravel road; 74
+
+  Sand mortar bedding course; 111
+
+  Seal coat; 127
+
+  Serial bonds; 27
+
+  Sinking fund bond; 25
+
+  Slip scraper; 67
+
+  Special assessments; 19
+
+  Specifications; 119
+
+  Spreading screenings; 95
+
+  State administration; 16
+
+  Stone, use of; 92
+
+  Surface drainage; 30
+
+  Surfaces, bituminous; 120
+
+  Surface method; 87
+
+  Superelevation; 47
+
+
+  Tests, brick; 108
+
+  Tile drains; 35
+
+  Topeka asphaltic concrete; 128
+
+  Tractive resistance; 52
+
+  Trench method; 85
+
+  Truck operation costs; 9
+
+  Types of culverts; 38
+
+
+  Underground water; 34
+
+  Undulating roads; 58
+
+  Use of blade grader; 69
+
+  Utilizing natural gravels; 83
+
+
+  Value of earth roads; 73
+
+  Variation in rainfall; 64
+
+  Variation in soils; 63
+
+  Vehicle taxes; 24
+
+  Vertical fiber brick; 107
+
+  Vitrified brick roads; 106
+
+  Vitrified brick; 106
+
+
+  Water gas tar; 117
+
+  Width of roadway; 59
+
+  Wire-cut-lug brick; 108
+
+
+  Zone method of assessing; 20
+
+       *       *       *       *       *
+
+[Transcriber's Notes:
+
+The transcriber made these changes to the text to correct obvious
+errors:
+
+   1. p.   5, accomodate --> accommodate
+   2. p.  39, guage --> gauge
+   3. p.  46, enbankment --> embankment
+   4. p.  63, tought --> tough
+   5. p.  68, absorbant --> absorbent
+   6. p.  73, persistant --> persistent
+   7. p.  77, indispensible --> indispensable
+   8. p. 119, aspealt --> asphalt
+   9. p. 127, repaid --> rapid
+  10. p. 130, Vetrified brick; 105 --> Vitrified brick; 106
+  11. p. 130, Virtical --> Vertical
+
+End of Transcriber's Notes]
+
+
+
+
+
+End of the Project Gutenberg EBook of American Rural Highways, by T. R. Agg
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+
+
+<pre>
+
+The Project Gutenberg EBook of American Rural Highways, by T. R. Agg
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: American Rural Highways
+
+Author: T. R. Agg
+
+Release Date: July 16, 2009 [EBook #29420]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK AMERICAN RURAL HIGHWAYS ***
+
+
+
+
+Produced by Tom Roch, Richard J. Shiffer and the Online
+Distributed Proofreading Team at https://www.pgdp.net (This
+file was produced from images produced by Core Historical
+Literature in Agriculture (CHLA), Cornell University)
+
+
+
+
+
+
+</pre>
+
+
+<div class="trans-note">
+<p class="heading">Transcriber's Note</p>
+<p>Every effort has been made to replicate this text as
+faithfully as possible, including obsolete and variant spellings and other
+inconsistencies.  Text that has been changed to correct an obvious error
+is noted at the <a href="#END">end</a> of this ebook.</p>
+</div>
+
+
+<h3 class="spacious">AGRICULTURAL ENGINEERING SERIES</h3>
+
+<h4 class="sc close">E. B. McCORMICK, Consulting Editor</h4>
+
+<h6 class="close">
+FORMERLY DEAN OF ENGINEERING DIVISION<br />
+KANSAS STATE AGRICULTURAL COLLEGE</h6>
+
+<p><br /></p>
+
+<h1>AMERICAN<br />
+
+RURAL HIGHWAYS</h1>
+
+<p><br /></p>
+<p><br /></p>
+
+<h3><i>McGraw-Hill Book Co. Inc.</i></h3>
+
+<h5 class="font-normal">PUBLISHERS OF BOOKS FOR</h5>
+
+<h4>
+Coal Age &mdash; Electric Railway Journal<br />
+Electrical World &mdash; Engineering News-Record<br />
+American Machinist &mdash; Ingenieria Internacional<br />
+Engineering &amp; Mining Journal &mdash; Power<br />
+Chemical &amp; Metallurgical Engineering<br />
+Electrical Merchandising
+</h4>
+
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/i0004.png" width="500" height="270" alt="Frontispiece" title="" />
+<span class="caption">Frontispiece</span>
+</div>
+
+<hr />
+
+<h1>
+AMERICAN<br />
+RURAL HIGHWAYS</h1>
+
+<p><br /></p>
+
+<h4>BY</h4>
+
+
+<h3 class="close">T. R. AGG, C.E.</h3>
+
+<h5 class="close font-normal">PROFESSOR OF HIGHWAY ENGINEERING<br />
+IOWA STATE COLLEGE</h5>
+
+<p><br /></p>
+
+<h4 class="sc">First Edition</h4>
+
+<p><br /></p>
+
+<h3 class="close sc">McGRAW-HILL BOOK COMPANY, Inc.</h3>
+<h4 class="close">NEW YORK: 239 WEST 39TH STREET</h4>
+<h5 class="close font-normal">LONDON: 6 &amp; 8 BOUVERIE ST., E. C. 4</h5>
+<h4 class="close">1920</h4>
+
+<p><br /></p>
+
+<h5 class="font-normal">COPYRIGHT, 1920, BY THE<br />
+McGRAW-HILL BOOK COMPANY, INC.</h5>
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_vii" id="Page_vii">[Pg vii]</a></span></p>
+<h2><a name="PREFACE" id="PREFACE"></a>PREFACE</h2>
+
+
+<p><span class="smcap">American Rural Highways</span> was written for use as a text or reference in
+courses dealing with rural highways and intended for agricultural
+engineers, students in agriculture and for short courses and extension
+courses. The reader is assumed to have familiarity with drawing and
+surveying, but the text is adapted primarily for students who do not
+receive training along the lines of the usual course in Highway or
+Civil Engineering.</p>
+
+<p>The text is intended to familiarize the student with the relation of
+highway improvement to national progress, to indicate the various
+problems of highway administration and to set forth the usual methods
+of design and construction for rural highways in sufficient detail to
+establish a clear understanding of the distinguishing characteristics
+and relative serviceability of each of the common types of roadway
+surface.</p>
+
+<p>Experience with classes made up of students in agriculture or
+agricultural engineering and with trade school students in road making
+served as a guide in the selection and arrangement of the material.
+Detailed discussion of tests of materials and of the theory of design
+has to a considerable extent been eliminated as being outside of the
+scope of the course for which the text is intended.</p>
+
+<p>In the preparation of American Rural Highways reference was had to
+many books on highway subjects and to current periodical literature.
+Wherever direct extracts were made from such source, appropriate
+acknowledgment appears in the text.</p>
+
+<p class="author">T. R. Agg</p>
+<p class="indent sc"><small>
+Ames, Iowa<br />
+August 18, 1920.</small></p>
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_ix" id="Page_ix">[Pg ix]</a></span></p>
+<a name="CONTENTS" id="CONTENTS"></a>
+<h2>CONTENTS</h2>
+
+<div class="toc">
+
+<p class="sc"><a href="#PREFACE">Preface</a></p>
+<p class="tocpage2">vii</p>
+
+<p class="sc center"><a href="#Chapter_I">Chapter I</a></p>
+
+<p class="center">THE PURPOSE AND UTILITY OF HIGHWAYS</p>
+
+<p class="toc">Transportation Problem&mdash;National in Scope&mdash;Development in
+Traffic&mdash;Location or Farm to Market Traffic&mdash;Farm to Farm
+Traffic&mdash;Inter-City Traffic&mdash;Inter-County and Inter-State
+Traffic&mdash;Rural Education&mdash;Rural Social Life&mdash;Good Roads and Commerce</p>
+<p class="tocpage">1-12</p>
+
+
+<p class="sc center"><a href="#Chapter_II">Chapter II</a></p>
+
+<p class="center">HIGHWAY ADMINISTRATION</p>
+
+<p class="toc">Township Administration&mdash;County Administration&mdash;State
+Administration&mdash;Federal Administration&mdash;Special Assessments&mdash;Zone
+Method of Assessing&mdash;General Taxation&mdash;Vehicle Taxes&mdash;Sinking Fund
+Bonds&mdash;Annuity Bonds&mdash;Serial Bonds&mdash;Comparison of Methods of Issuing
+Bonds&mdash;Desirability of Road Bonds</p>
+<p class="tocpage">13-28</p>
+
+
+<p class="sc center"><a href="#Chapter_III">Chapter III</a></p>
+
+<p class="center">DRAINAGE OF ROADS</p>
+
+<p class="toc">The Necessity for Drainage&mdash;Importance of Design&mdash;Surface
+Drainage&mdash;Run-off&mdash;Ordinary Design of Ditches&mdash;Underground Water&mdash;Tile
+Drains&mdash;Lying Tile&mdash;Culverts&mdash;Length of Culvert&mdash;Farm Entrance
+Culverts&mdash;Metal Pipe&mdash;Clay and Cement Concrete Pipe&mdash;Concrete
+Pipe&mdash;Endwalls for Culverts&mdash;Reinforced Concrete Box Culverts&mdash;Drop
+Inlet Culverts</p>
+<p class="tocpage">29-41</p>
+
+
+<p class="sc center"><a href="#Chapter_IV">Chapter IV</a></p>
+
+<p class="center">ROAD DESIGN</p>
+
+<p class="toc">Necessity for Planning&mdash;Road Plans&mdash;Problems of Design&mdash;Preliminary
+Investigations&mdash;Road
+Surveys&mdash;Alignment&mdash;Intersections&mdash;Superelevation&mdash;Tractive
+Resistance&mdash;Rolling Resistance&mdash;Internal Resistance&mdash;Air
+Resistance&mdash;Effect of Trades&mdash;Energy Loss on Account of
+Grades&mdash;Undulating Roads&mdash;Guard Railing&mdash;Width of Roadway&mdash;Cross
+Section&mdash;Control of Erosion&mdash;Private Entrances&mdash;Æsthetics</p>
+<p class="tocpage">42-62</p>
+
+
+<p class="sc center"><a href="#Chapter_V">Chapter V</a><span class="pagenum"><a name="Page_x" id="Page_x">[Pg x]</a></span></p>
+
+<p class="center">EARTH ROADS</p>
+
+<p class="toc">Variations in Soils&mdash;Variation in Rainfall&mdash;Cross Sections Elevating
+Grader&mdash;Maney Grader&mdash;Slip Scraper&mdash;Fresno Scraper&mdash;Elevating Grader
+Work&mdash;Use of Blade Grader&mdash;Costs&mdash;Maintenance&mdash;Value of Earth Roads</p>
+<p class="tocpage">63-73</p>
+
+
+<p class="sc center"><a href="#Chapter_VI">Chapter VI</a></p>
+
+<p class="center">SAND-CLAY AND GRAVEL ROADS</p>
+
+<p class="toc">The Binder&mdash;Top-soil or Natural Mixtures&mdash;Sand-clay on Sandy
+Roads&mdash;Sand-clay on Clay or Loam&mdash;Characteristics&mdash;Natural Gravel&mdash;The
+Ideal Road Gravel&mdash;Permissible Size of Pebbles&mdash;Wearing
+Properties&mdash;Utilizing Natural Gravels&mdash;Thickness of Layer&mdash;Preparation
+of the Road&mdash;Trench Method&mdash;Surface Method&mdash;Maintenance</p>
+<p class="tocpage">74-88</p>
+
+
+<p class="sc center"><a href="#Chapter_VII">Chapter VII</a></p>
+
+<p class="center">BROKEN STONE ROAD SURFACES</p>
+
+<p class="toc">Design&mdash;Properties of the Stone&mdash;Kinds of Rocks used for
+Macadam&mdash;Sizes of Stone&mdash;Earth Work&mdash;Foundation for the
+Macadam&mdash;Telford Foundation&mdash;Placing the Broken
+Stone&mdash;Rolling&mdash;Spreading Screenings&mdash;Bituminous Surfaces&mdash;Maintenance
+Characteristics</p>
+<p class="tocpage">89-97</p>
+
+
+<p class="sc center"><a href="#Chapter_VIII">Chapter VIII</a></p>
+
+<p class="center">CEMENT CONCRETE ROADS</p>
+
+<p class="toc">Destructive Agencies&mdash;Design&mdash;Concrete Materials&mdash;Fine
+Aggregate&mdash;Proportions&mdash;Measuring Materials&mdash;Preparation of the Earth
+Foundation&mdash;Placing Concrete for Two-course Road&mdash;Curing the
+Concrete&mdash;Expansion Joints&mdash;Reinforcing&mdash;Bituminous Coatings on
+Concrete Surfaces&mdash;Characteristics&mdash;Maintenance</p>
+<p class="tocpage">98-105</p>
+
+
+<p class="sc center"><a href="#Chapter_IX">Chapter IX</a></p>
+
+<p class="center">VITRIFIED BRICK ROADS</p>
+
+<p class="toc">Vitrified Brick&mdash;Paving Brick&mdash;Repressed Brick&mdash;Vitrified Fiber
+Brick&mdash;Wire-cut-lug Brick&mdash;Tests for Quality&mdash;Other
+Tests&mdash;Foundation&mdash;Sand Bedding Course&mdash;Sand Mortar Bedding
+Course&mdash;Green Concrete Bedding Course&mdash;Bituminous Fillers&mdash;Mastic
+Fillers&mdash;Marginal Curb</p>
+<p class="tocpage">106-115</p>
+
+
+<p class="sc center"><a href="#Chapter_X">Chapter X</a><span class="pagenum"><a name="Page_xi" id="Page_xi">[Pg xi]</a></span></p>
+
+<p class="center">BITUMINOUS ROAD MATERIALS AND THEIR USE</p>
+
+<p class="toc">Classes of Bituminous Materials&mdash;Coal Tar&mdash;Water Gas Tar&mdash;Natural
+Asphalt&mdash;Petroleum Asphalt&mdash;Mixtures&mdash;Classification According to
+Consistency&mdash;Road Oils&mdash;Liquid Asphalts&mdash;Asphalt
+Cements&mdash;Fillers&mdash;Bitumen&mdash;Specifications&mdash;Surface
+Treatments&mdash;Applying the Bituminous Binder&mdash;Finishing the
+Surface&mdash;Patching&mdash;Penetration Macadam&mdash;Foundation&mdash;Upper or Wearing
+Course&mdash;Patching Characteristics&mdash;Hot Mixed Macadam&mdash;Foundation&mdash;Sizes
+of Stone&mdash;Mixing the Wearing Stone&mdash;Placing and Wearing Surface&mdash;Seal
+Coat&mdash;Characteristics&mdash;Asphaltic Concrete&mdash;Bitulithic or
+Warrenite&mdash;Topeka Asphaltic Concrete&mdash;Foundation&mdash;Placing the
+Surface&mdash;Characteristics</p>
+<p class="tocpage">116-129</p>
+
+
+<p class="sc center"><a href="#Chapter_XI">Chapter XI</a></p>
+
+<p class="center">MAINTENANCE OF HIGHWAYS</p>
+
+<p class="toc">Petrol Maintenance&mdash;Gang Maintenance&mdash;Maintenance of Earth, Sand-clay,
+Gravel and Macadam Roads</p>
+<p class="tocpage">130-134</p>
+
+<p class="sc"><a href="#INDEX">Index</a></p>
+<p class="tocpage2">135</p>
+</div>
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p>
+<h2><a name="AMERICAN_RURAL_HIGHWAYS" id="AMERICAN_RURAL_HIGHWAYS"></a>AMERICAN RURAL HIGHWAYS</h2>
+
+
+<hr />
+<h2><a name="Chapter_I" id="Chapter_I"></a><span class="smcap">Chapter I</span></h2>
+
+<h3>THE PURPOSE AND UTILITY OF HIGHWAYS</h3>
+
+
+<h4 class="sc">The Development of Highway Systems</h4>
+
+<p><b>Transportation Problem.</b>&mdash;Public highways, like many other familiar
+things, are utilized constantly with little thought of how
+indispensable they are to the conduct of the business of a nation or
+of the intimate relation they bear to the everyday life of any
+community. The degree to which a nation or a community perfects its
+transportation facilities is an index of its industrial progress and
+public highways constitute an important element in the national
+transportation system. It is to be expected that the average citizen
+will think of the public highway only when it affects his own
+activities and that he will concern himself but little with the broad
+problem of highway improvement unless it be brought forcibly to his
+attention through taxation or by publicity connected with the
+advancement of specific projects.</p>
+
+<p><b>National in Scope.</b>&mdash;The improvement and extension of the highway
+system is of national importance just as is development and extension
+of railways, and concerted action throughout a nation is a
+prerequisite to an adequate policy in regard to either. It is
+inconceivable that any community in a nation can prosper greatly
+without some benefit accruing to many other parts of the country.
+Increased consumption, which always accompanies material<span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span> prosperity,
+means increased production somewhere, and people purchase from many
+varied sources to supply the things that they want. Good
+transportation facilities contribute greatly to community prosperity
+and indirectly to national prosperity, and the benefits of highly
+improved public highways are therefore national in scope. This fact
+has been recognized in Europe, notably in England, France and Belgium,
+where the public highways are administered largely as national
+utilities.</p>
+
+<p>Until recent years, highway improvement in the United States has been
+subordinated to other more pressing public improvements, but during
+the World War the inadequacy of the transportation system of the
+United States became apparent. While such an unprecedented load upon
+transportation facilities may not recur for many years, it has become
+apparent that more rapid progress in highway improvement is necessary
+and in the United States the subject is now likely to receive
+attention commensurate with its importance.</p>
+
+<p><b>Development of Traffic.</b>&mdash;The character and extent of the highway
+improvement needed in any locality is dependent entirely on the
+demands of traffic. In sparsely settled areas, particularly those that
+are semi-arid or arid, the amount of traffic on local roads is likely
+to be small and the unimproved trails or natural roads adequate. But
+as an area develops either on account of agricultural progress or the
+establishment of industrial enterprises, the use of the public
+highways both for business and for pleasure increases and the old
+trails are gradually improved to meet, at least to some degree, the
+new demands of traffic. In sparsely settled areas, it is possible for
+the public to accommodate its use of the highways to the physical
+condition thereof, and business is more or less regulated according to
+the condition of the roads. This is not always pleasant or economical
+but is the only possible arrangement. In populous districts, with
+diversified activities, it becomes<span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span> imperative to have year-round
+usable roads in order to transact with reasonable dispatch the regular
+business of the industries. Anything less will handicap normal
+community progress.</p>
+
+<p>The advent of the motor driven vehicle in the United States has
+resulted in a greatly increased use of the public highways of
+agricultural areas, even of those that are sparsely populated, because
+of the convenience of the motor vehicle both for passenger and for
+freight service. Probably in excess of 90 per cent of the tonnage
+passing over the rural highways in the United States is carried by
+motor vehicles. This class of traffic has really just developed and no
+one can predict what it will be in ten years, yet it has already
+introduced into the highway problem an element that has revolutionized
+methods of construction and maintenance.</p>
+
+<p>A different set of traffic conditions exists in those parts of the
+United States where large areas are devoted primarily to industrial
+pursuits, the agricultural development being of secondary importance.
+Public highways connecting the industrial centers are indispensable
+adjuncts to the business facilities in such communities and are
+ordinarily subjected to a very large volume and tonnage of traffic
+consisting principally of motor vehicles. The roads first selected for
+improvement will not be those serving the agricultural interests of
+the district, but rather those serving the industrial centers.
+Inter-city roads of great durability and relatively high cost are
+necessary for such traffic conditions.</p>
+
+<p>Not infrequently the transportation needs will require a system of
+both inter-city and rural highways in the same community. There are
+few areas in the United States where there is no agricultural
+development. It is apparent therefore that the nature of the highway
+systems and the administrative organization under which they are built
+and maintained will differ in various states or areas according<span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span> to
+the nature of development of that area agriculturally and
+industrially. In planning improvements of highway systems, it is
+recognized that one or more of several groups of traffic may be
+encountered and that the extent and nature of the improvement must be
+such as will meet the requirements of all classes of traffic, the most
+important being first provided for, and that of lesser importance as
+rapidly as finances permit.</p>
+
+
+<h4 class="sc">Kinds of Traffic on Public Highways</h4>
+
+<p><b>Local or Farm to Market Traffic.</b>&mdash;In strictly agricultural communities
+the principal use of the highways will pertain to agricultural
+activities and most of it will be between the farm and the most
+convenient market center. In the ordinary state, the number of rural
+families will not average more than six to eight per square mile, but
+in some districts it may reach twenty families per square mile. The
+travel from the district around a market center will originate in this
+rather sparsely populated area and converge onto a few main roads
+leading to market. The outlying or feeder roads will be used by only a
+few families, but the density of traffic will increase nearer the
+market centers and consequently the roads nearer town will be much
+more heavily traveled than the outlying ones. It is apparent therefore
+that considerable difference may exist in the kind of construction
+adequate for the various sections of road where farm traffic is the
+principal consideration. This traffic is made up of horse drawn
+wagons, transporting farm products and of horse drawn and motor
+passenger vehicles, the motor traffic comprising 80 per cent or more
+of the volume of traffic and a greater per cent of the tonnage. Motor
+trucks are now employed to some extent for marketing farm products
+and, where surfaced highways have been provided, this class of traffic
+is superseding horse drawn traffic.<span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span></p>
+
+<p><b>Farm to Farm Traffic.</b>&mdash;In the ordinary prosecution of farming
+operations, a considerable amount of neighborhood travel is
+inevitable. Farmers help each other with certain kinds of work,
+exchange commodities such as seed, machinery and farm animals and
+visit back and forth both for business and pleasure. To accommodate
+this traffic, it is desirable to provide good neighborhood roads.
+Traffic of this sort follows no particular route and can to some
+extent accommodate itself to the condition of the highways without
+entailing financial loss, although some discomfort and some
+inconvenience may result from inadequate highway facilities. This
+traffic will be partly motor and partly horse drawn, but the
+proportion of motor driven is large.</p>
+
+<p><b>Inter-city Traffic.</b>&mdash;In strictly agricultural districts there is a
+large amount of travel between towns, both for business and for
+pleasure. The pleasure travel is mostly in motor vehicles and a
+considerable part of the business traffic is the same, although horse
+drawn vehicles are employed to some extent.</p>
+
+<p>In industrial districts there is a large volume of this class of
+traffic consisting of motor passenger vehicles used for business and
+for pleasure and of motor freight vehicles used for general business
+purposes. In addition, there is certain to be a large amount of motor
+truck freight traffic incident to the particular industrial pursuits
+of the cities. Where adequate public highways connect industrial
+centers, there is invariably a very large amount of inter-city
+traffic, due in part to the needs of industry and in part to
+concentration of population in industrial centers.</p>
+
+<p><b>Inter-County and Inter-State Traffic.</b>&mdash;Automobile touring is a popular
+means of relaxation, especially on the part of those who live in the
+cities, although it is by no means confined to them. Traffic of this
+kind follows the routes where roads are best and passes entirely
+across a county, attracted by some public gathering. Often it is
+inter-state in character, made up of tourists who are traveling<span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span> to
+distant pleasure resorts. Such traffic at present constitutes a
+relatively small part of the travel on public highways, except on
+certain favorable routes, but as the wealth of the country increases
+and good touring roads are numerous, long distance travel will
+increase and will eventually necessitate the construction of a number
+of well maintained national highways, located with reference to the
+convenience of the automobile tourist.</p>
+
+
+<h4 class="sc">Public Highways and Community Life</h4>
+
+<p>It is well to recognize the intimate relation public highways bear to
+the economic progress of a nation. Normal development of all of the
+diverse activities of a people depends very largely upon the highway
+policy that is adopted and whether the actual construction of
+serviceable roads keeps pace with transportation needs.</p>
+
+<p><b>Rural Education.</b>&mdash;It has become increasingly apparent during the World
+War that the demand upon North America for food stuffs is to become
+more and more insistent as the years pass. Already the consumption in
+the United States has approached quite closely to the average
+production and yet the population is constantly increasing. The time
+is not far distant when greater production will be required of the
+agricultural area in North America in order to meet the home demand
+for foodstuffs, and many thousands of tons will be needed for export.
+This need can only be met by agricultural methods that will increase
+greatly the present yield of the soil. The adoption of better
+agricultural methods must of necessity be preceded by the technical
+training of the school children who will be the farmers of the next
+generation, which can best be accomplished in graded schools with well
+equipped laboratories and with suitably trained teachers. The problem
+of providing such schools in rural communities has, in some instances,
+been solved by consolidating a number of rural<span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span> school districts and
+constructing a well equipped building to accommodate the students from
+an area several miles square. An educational system of this sort can
+reach its highest usefulness only when adequate public highways
+facilitate attendance of pupils. The whole trend of rural educational
+progress is toward a system which is predicated upon a comprehensive
+highway policy in the district.</p>
+
+<p><b>Rural Social Life.</b>&mdash;Closely allied to the rural educational problem is
+the rural social problem. Motor cars and good roads do a great deal to
+eliminate the isolation and lack of social opportunity that has
+characterized rural life in the United States. A high order of
+citizenship in rural communities is essential to the solution of many
+problems of rural economics, and such citizens will not live away from
+the social opportunities of modern life. The rural school house and
+the rural church may become social centers and local plays, moving
+picture shows and lectures and entertainments of other kinds made
+available to those who live in the country. Their enjoyment of these
+social opportunities will be much more general if the public highways
+are at all times in a condition to be traveled in comfort. Good homes
+and good schools on good roads are prerequisites to the solution of
+many rural problems.</p>
+
+<p>If there is opportunity for those who live in the cities to get some
+adequate idea of rural life and the conditions under which farming
+operations are carried on it will correct many misunderstandings of
+the broad problems of food production and distribution. Reference has
+frequently been made to the seeming desire on the part of city people
+to get into the country, and, by facilitating the realization of this
+desire, a great social service is rendered.</p>
+
+<p><b>Good Roads and Commerce.</b>&mdash;That good highways are almost as necessary
+as are railroads to the commercial development of a nation is
+recognized but, unlike the railroads,<span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span> the highways are not operated
+for direct profit and the responsibility of securing consideration of
+the demand for improvements is not centralized. Therefore, sentiment
+for road improvement has been of slow growth, and important projects
+are often delayed until long after the need for them was manifest.
+Movements to secure financial support for highway improvement must go
+through the slow process of legislative enactment, encountering all of
+the uncertainties of political action, and the resulting financial
+plan is likely to be inadequate and often inequitable.</p>
+
+<p>The whole commercial structure of a nation rests upon transportation,
+and the highways are a part of the transportation system. The highway
+problem can never receive adequate consideration until public highways
+are recognized as an indispensable element in the business equipment
+of a nation.</p>
+
+<p>During the World War all transportation facilities were taxed to the
+limit, and motor trucks were utilized for long distance freight
+haulage to an extent not previously considered practicable. As a
+result, the interest in the motor truck as an addition to the
+transportation equipment of the nation, has been greatly stimulated.
+Many haulage companies have entered the freight transportation field,
+delivering commodities by truck to distances of a hundred miles or
+more.</p>
+
+<p>The part the motor truck will play in the future can only be
+estimated, but it seems clear that the most promising field is for
+shipments destined to or originating in a city of some size and a
+warehouse or store not on a railroad spur, and especially when the
+shipments are less than car load lots. The delays and expense incident
+to handling small shipments of freight through the terminals of a
+large city and carting from the unloading station to the warehouse or
+other destination constitute a considerable item in the cost of
+transportation.<span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span></p>
+
+<p>Mr. Charles Whiting Baker, Consulting Editor of <i>Engineering
+News-Record</i>, states:<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></p>
+
+<blockquote><p>"It costs today as much to haul a ton of farm produce ten miles
+to a railway station as it does to haul it a thousand miles over
+a heavy-traffic trunk-line railway. It often costs more today to
+transport a ton of merchandise from its arrival in a long train
+in the freight yard on the outskirts of a great city to its
+deposit in the warehouse of a merchant four or five miles away
+than it has cost to haul it over a thousand miles of railway
+line."</p></blockquote>
+
+<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1">
+<span class="label">[1]</span></a> Engineering News Record, July 10, 1919.</p>
+</div>
+
+<p>Nevertheless it seems probable that new methods of operating the motor
+truck transport, and possibly new types of trucks or trucks and
+trailers will be developed so that freight traffic over many roads
+will be of considerable tonnage and an established part of the
+transportation system of the nation. In the article above referred to
+are given the following data relative to the cost of hauling on
+improved roads by motor truck and these cost estimates are based on
+the best information available at this time. They should be considered
+as approximate only, but serve to indicate the limitations of the
+truck as a competitor of the steam railway.</p>
+
+
+<h4 class="sc">Table 1</h4>
+
+<h4 class="sc">Truck Operation Costs, from Reports by Six Motor Truck
+Operators, Direct Charges per Day</h4>
+
+
+
+<div class="center">
+<table summary="Truck Operation Costs - Direct Charges">
+<tr><td class="bt bb left">&nbsp;</td><td class="bt bb bl center">A</td><td class="bt bb bl center">B</td><td class="bt bb bl center">C</td><td class="bt bb bl center">D</td><td class="bt bb bl center">E</td><td class="bt bb bl center">F</td><td class="bt bb bl center">Average Total</td><td class="bt bb center">&nbsp;</td></tr>
+<tr><td class="left">Driver</td><td class="bl right">$5.00</td><td class="bl right">$5.20</td><td class="bl right">$5.00</td><td class="bl right">$5.00</td><td class="bl right">$5.17</td><td class="bl right">$5.50</td><td class="bl right">$5.13</td></tr>
+<tr><td class="left">Tires</td><td class="bl right">3.00</td><td class="bl right">3.75</td><td class="bl right">2.00</td><td class="bl right">2.00</td><td class="bl right">2.00</td><td class="bl right">3.00</td><td class="bl right">2.68</td></tr>
+<tr><td class="left">Oil, etc.</td><td class="bl right">.30</td><td class="bl right">...</td><td class="bl right">.30</td><td class="bl right">.50</td><td class="bl right">.25</td><td class="bl right">.25</td><td class="bl right">.35</td></tr>
+<tr><td class="left">Gasoline</td><td class="bl right">3.00</td><td class="bl right">4.00</td><td class="bl right">3.50</td><td class="bl right">4.65</td><td class="bl right">2.08</td><td class="bl right">3.75</td><td class="bl bb right">3.50</td></tr>
+<tr><td class="bb">&nbsp;</td><td class="bb bl">&nbsp;</td><td class="bb bl">&nbsp;</td><td class="bb bl">&nbsp;</td><td class="bb bl">&nbsp;</td><td class="bb bl">&nbsp;</td><td class="bb bl">&nbsp;</td><td class="bb bl">&nbsp;</td><td class="bb">$11.66</td></tr>
+</table></div>
+
+<p><span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span></p>
+
+<h4 class="sc">Indirect Charges per Day</h4>
+
+
+
+
+<div class="center">
+<table summary="Truck Operation Costs - Indirect Charges">
+<tr><td class="bt bb left">&nbsp;</td><td class="bt bb bl center">A</td><td class="bt bb bl center">B</td><td class="bt bb bl center">C</td><td class="bt bb bl center">D</td><td class="bt bb bl center">E</td><td class="bt bb bl center">F</td><td class="bt bb bl center">Average Total</td><td class="bt bb">&nbsp;</td></tr>
+<tr><td align="left">Depreciation</td><td class="bl right">$3.50</td><td class="bl right">$4.19</td><td class="bl right">$3.60</td><td class="bl right">$3.40</td><td class="bl right">$3.67</td><td class="bl right">$4.00</td><td class="bl right">$3.77</td></tr>
+<tr><td align="left">Interest</td><td class="bl right">1.20</td><td class="bl right">1.26</td><td class="bl right">1.08</td><td class="bl right">1.22</td><td class="bl right">1.10</td><td class="bl right">1.00</td><td class="bl right">1.15</td></tr>
+<tr><td align="left">Insurance</td><td class="bl right">1.50</td><td class="bl right">2.54</td><td class="bl right">1.26</td><td class="bl right">2.10</td><td class="bl right">.86</td><td class="bl right">.50</td><td class="bl right">1.47</td></tr>
+<tr><td align="left">Garage</td><td class="bl right">1.00</td><td class="bl right">1.20</td><td class="bl right">1.00</td><td class="bl right">1.00</td><td class="bl right">.89</td><td class="bl right">1.00</td><td class="bl right">1.01</td></tr>
+<tr><td align="left">Maintenance</td><td class="bl right">.50</td><td class="bl right">...</td><td class="bl right">.50</td><td class="bl right">...</td><td class="bl right">1.00</td><td class="bl right">...</td><td class="bl right">.75</td></tr>
+<tr><td align="left">Overhaul</td><td class="bl right">1.33</td><td class="bl right">2.75</td><td class="bl right">1.80</td><td class="bl right">1.60</td><td class="bl right">2.00</td><td class="bl right">3.00</td><td class="bl right">2.07</td></tr>
+<tr><td align="left">License</td><td class="bl right">.17</td><td class="bl right">.27</td><td class="bl right">.20</td><td class="bl right">.20</td><td class="bl right">.20</td><td class="bl right">.20</td><td class="bl right">.20</td></tr>
+<tr><td align="left">Body upkeep</td><td class="bl right">.25</td><td class="bl right">...</td><td class="bl right">.30</td><td class="bl right">.10</td><td class="bl right">.40</td><td class="bl right">...</td><td class="bl bb right">.27</td></tr>
+<tr><td>&nbsp;</td><td class="bl right">&nbsp;</td><td class="bl right">&nbsp;</td><td class="bl right">&nbsp;</td><td class="bl right">&nbsp;</td><td class="bl right">&nbsp;</td><td class="bl right">&nbsp;</td><td class="bl right">&nbsp;</td><td class="right">$10.69</td></tr>
+<tr><td align="left">Supervision</td><td class="bl right">.50</td><td class="bl right">2.93</td><td class="bl right">2.05</td><td class="bl right">1.90</td><td class="bl right">...</td><td class="bl right">...</td><td class="bl right">1.90</td><td class="right">1.90</td></tr>
+<tr><td align="left">Lost time</td><td class="bl right">2.20</td><td class="bl right">...</td><td class="bl right">1.67</td><td class="bl right">3.40</td><td class="bl right">2.50</td><td class="bl right">1.97</td><td class="bl right">2.57</td><td class="right">2.57</td></tr>
+<tr><td class="bb"></td><td class="bt bb bl right">23.45</td><td class="bt bb bl right">28.09</td><td class="bt bb bl right">24.26</td><td class="bt bb bl right">28.07</td><td class="bt bb bl right">22.12</td><td class="bt bb bl right">24.17</td><td class="bt bb bl right">&nbsp;</td><td class="bt bb right">26.82</td></tr>
+</table></div>
+
+<h4 class="sc">Table 2</h4>
+<h4 class="sc">Overhead Charges per Year for a 5-ton Capacity Gasoline
+Motor Truck Running an Average of 50 Miles per Day
+for 240 Days per Year</h4>
+
+
+<div class="center">
+<table summary="Overhead Charges">
+<tr><td align="left">Driver's wages<a name="FNanchor_1_2" id="FNanchor_1_2"></a><a href="#Footnote_1_2" class="fnanchor">[1]</a></td><td align="right">$1500</td></tr>
+<tr><td align="left">Depreciation (20% on $6000 investment)</td><td align="right">1200</td></tr>
+<tr><td align="left">Interest (6% on $6000 investment)</td><td align="right">360</td></tr>
+<tr><td align="left">Insurance</td><td align="right">450</td></tr>
+<tr><td align="left">Garage (rental, upkeep, etc.)</td><td align="right">300</td></tr>
+<tr><td align="left">Maintenance, minor repairs and supplies, tire chains,<br />tools, lamps, springs, equipment, etc. (estimated</td><td align="right">300</td></tr>
+<tr><td align="left">Complete overhaul once a year</td><td align="right">600</td></tr>
+<tr><td align="left">License fee</td><td align="right">60</td></tr>
+<tr><td align="left">Body upkeep, repairs, painting, etc.</td><td align="right">90</td></tr>
+<tr><td align="left">Supervision</td><td class="bb right">696</td></tr>
+<tr><td class="left indent">Total per annum</td><td align="right">$5556</td></tr>
+</table></div>
+
+<div class="center">
+<table summary="Overhead Charges">
+<tr><td align="left">Overhead charges per day for 240 days in the year, actual operation</td><td align="right">$23.15&nbsp;&nbsp;</td></tr>
+<tr><td align="left">Overhead charges per mile for 50 miles per day</td><td align="right">.463</td></tr>
+</table></div>
+
+<div class="footnote"><p><a name="Footnote_1_2" id="Footnote_1_2"></a><a href="#FNanchor_1_2"><span class="label">[1]</span></a> In the above table the driver's wages have been placed
+under overhead charges because the driver is paid by the month and his
+wages continue even though the truck is idle because of repairs, bad
+weather or lack of business, unless, of course, the idleness should be
+of long duration, when the driver might be laid off.<span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span></p></div>
+
+
+<h4 class="sc">Direct Charges per Day and per Mile for 5-ton Truck
+Operated as Above</h4>
+
+<div class="center">
+<table summary="Direct Charges">
+<tr><td class="bt bb">&nbsp;</td><td class="bt bb bl center">Cost per day</td><td class="bt bb bl center">Cost per mile</td></tr>
+<tr><td class="left">Tires (based on present tire guarantee)</td><td class="bl right">$3.00</td><td class="bl right">$0.06</td></tr>
+<tr><td class="left">Lubricants</td><td class="bl right">.50</td><td class="bl right">.01</td></tr>
+<tr><td class="left">Gasoline (3&frac12; miles per gal., 14 gal. at 25c)</td><td class="bl bb right">3.50</td><td class="bl bb right">.07</td></tr>
+<tr><td class="bb">&nbsp;</td><td class="bb bl right">7.00</td><td class="bb bl right">0.14</td></tr>
+</table></div>
+
+
+<div class="center">
+<table summary="Total Charges">
+<tr><td align="left">Total of overhead and direct charges for 240 days per year operation, per day</td><td align="right">$30.15&nbsp;&nbsp;&nbsp;</td></tr>
+<tr><td align="left">Per mile</td><td align="right">.603&nbsp;&nbsp;</td></tr>
+<tr><td align="left">Cost per ton-mile for full loads one way and empty returning</td><td align="right">.2412</td></tr>
+<tr><td align="left">Cost per ton-mile for full loads one way and half load returning</td><td align="right">.16&nbsp;&nbsp;&nbsp;</td></tr>
+</table></div>
+
+<p>The significance of these figures becomes apparent when they are
+compared with the cost of hauling freight over trunk-line railways
+with heavy traffic where the cost per ton-mile, including terminal
+charges, ranges from 1.7 <i>mills</i> per ton-mile to 4.4 <i>mills</i> per
+ton-mile.</p>
+
+<p>In view of these facts it seems reasonable to suppose that motor
+vehicles for use on the public highways are more likely to be employed
+to supplement the rail transport than to compete with it. To the
+actual cost of operation of motor trucks given in Table 2, there
+should be added the proportionate cost of maintaining the highway for
+the use of the truck, which is partly covered by the item "License
+Fee" in the table. The license fee would necessarily be considerably
+larger if it were to compensate adequately for the wear on the
+highways over which the trucks operate. This will still further
+increase the cost of hauling by motor truck.</p>
+
+<p>Motor trucks are employed for many kinds of hauling where their speed
+and consequently their daily capacity is an advantage over team
+hauling that is decidedly worth<span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span> while. It probably could be shown
+that for many kinds of hauling, teams are more economical than motor
+trucks, but when promptness and speed and the consequent effect on
+dependent activities are considered, the motor truck often has a
+distinct advantage, and the use of the truck to replace horse drawn
+vans is progressing rapidly. This is true not only in the cities, but
+also in the smaller towns and in the country. Motor trucks have been
+adopted in a great many communities for delivery of farm products to
+market, and this use of the truck is certain to increase rapidly. But
+trucks in this service will use the secondary roads as well as the
+main or primary roads.</p>
+
+<p>These observations emphasize the extent to which the highway policy of
+the nation must be predicated on the use of the highways by motor
+vehicles.</p>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span></p>
+<h2><a name="Chapter_II" id="Chapter_II"></a><span class="smcap">Chapter II</span></h2>
+
+<h3>HIGHWAY ADMINISTRATION</h3>
+
+
+<p>The systems of highway administration extant in the various political
+units in the United States present a patchwork of overlapping
+authority and undetermined responsibility. Highway laws are being
+constantly revised by state legislatures and with each revision there
+is some change in administrative methods and often the changes are
+revolutionary in character. In most states, the trend is away from
+county and township administration and toward state administration,
+with provision for considerable participation by the federal
+government.</p>
+
+<p>It will be pertinent to consider briefly the present functions of each
+of the administrative authorities having duties in connection with
+highway work in the United States, although these duties vary greatly
+in the several states and change periodically with the action of
+legislatures.</p>
+
+<p><b>Township Administration.</b>&mdash;Township or "Town" authority is a survival
+of the old New England town government and the town board consists of
+three or more trustees who hold office for fixed terms. The usual term
+is three years, but is less in some states. The incumbent is generally
+a man who has other responsibilities of a public or private nature and
+who gives but little of his time to highway matters. In some states
+the pay is a fixed annual salary and in others a per diem with some
+limitation on the amount that may be drawn in any one year, which
+limitation may be statutory or may be by common consent.</p>
+
+<p>The township highway commissioners or trustees have jurisdiction over
+certain of the roads in the township,<span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span> usually best described as all
+roads not by law placed under the jurisdiction of some other
+authority. In certain instances, the township authorities have charge
+of all of the roads in the township, which would mean that no "county"
+or "state" roads happened to be laid out in that township. It is a
+matter of general observation that the trend of legislation is toward
+removing from the jurisdiction of the township officials all roads
+except those upon which the traffic is principally local in character.
+The actual mileage of roads in the United States that is at present
+administered by township officials is large, probably constituting not
+less than seventy per cent of the total mileage.</p>
+
+<p>In most states the township officials are responsible for the
+maintenance of the roads under their jurisdiction and also supervise
+such new construction as is undertaken. This includes the construction
+of culverts and bridges as a rule, but in some states the county board
+of supervisors is responsible for all of the bridge and culvert work
+on the township roads. In other states, the township board is
+responsible only for bridges or culverts that cost less than a certain
+amount specified by law (usually about $1000) and the county board
+provides for the construction and upkeep of the more expensive bridges
+and culverts.</p>
+
+<p>Funds for the work carried out by the township road officials are
+obtained by general taxation, the amount that may be levied being
+limited by statute and the actual levy being any amount up to the
+maximum that the township board deems necessary for its purposes. It
+is the general observation that the tax levy is usually the maximum
+permitted by law.</p>
+
+<p>In many states, township officials are permitted to issue bonds for
+road construction, almost invariably, however, with the restriction
+that each issue must be approved by the voters of the township. There
+is always a provision that the total amount of bonds outstanding must
+not exceed the constitutional limit in force in the state. In<span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span> several
+states, the townships have large amounts of road bonds outstanding.</p>
+
+<p><b>County Administration.</b>&mdash;In some states the county is the smallest
+administrative unit in the road system. A county board, called the
+board of county supervisors or board of county commissioners
+consisting of from three to fifteen members, is the administrative
+authority. Its members are elected for fixed terms which vary in
+length from one to five years. The county board usually has many
+public responsibilities other than highway administration, and is
+generally made up of men with considerably more business ability than
+the average township board.</p>
+
+<p>The county board has jurisdiction over all of the highways in the
+county in some states, and in others it has charge of only the more
+important highways. In most states, the laws set forth specifically
+what highways shall be under the jurisdiction of the county
+authorities.</p>
+
+<p>In addition to having direct supervision of the improvement and
+maintenance of the roads assigned to county administration, the county
+boards in some states arrange for the construction of all culverts and
+bridges on the roads that are under township supervision, or at least
+the more expensive bridges and culverts on such roads. Sometimes this
+is accomplished by granting county aid for township bridges, under
+which system the county pays a part of the cost of the construction of
+bridges on the township roads. The amount of aid varies, but is
+generally about one-half of the cost, and the township and county
+officials jointly assume the responsibility of arranging for the
+construction by contract or otherwise.</p>
+
+<p>The county board obtains funds for road work through a direct tax on
+all property in the county, the maximum rate being limited by statute.
+County boards are also authorized to issue bonds for road construction
+under statutory restrictions and limitations similar to those
+effective in the township as to total amount issued, and many
+millions<span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span> of dollars' worth of highway bonds have been issued by
+county authorities in the United States.</p>
+
+<p><b>State Administration.</b>&mdash;In a state, the administrative authority in
+highway matters is vested in a board of commissioners usually
+consisting of three or more members. In a few states, the
+administrative authority is delegated to a single commissioner. Where
+the authority is vested in a board, that board is usually appointed by
+the governor. In several states one or more members of the commission
+hold that position <i>ex officio</i>; for example, in several states the
+governor is by law a member of the commission, in others the secretary
+of state or the dean of engineering at the State University or the
+state geologist is a member of the commission. Where the
+administrative authority is a single commissioner he may be elected
+along with other state officers, but this is the case in only a few
+states.</p>
+
+<p>The authority of the state highway department varies in the several
+states, but in general the departments serve in the dual capacity of
+general advisers to the county and township authorities on road
+matters and as the executive authority responsible for the
+construction of those highways that are built entirely or in part from
+state or federal funds.</p>
+
+<p>State highway departments consist of the commission or commissioner,
+and the technical and clerical staff required to perform the duties
+imposed on the state organization. To some extent the state highway
+departments are able to encourage economical and correct construction
+of highways by the township and county authorities by furnishing them
+standard plans and specifications and by formulating regulations to
+govern the character of construction, but such efforts are likely to
+be more or less ineffective unless the state authority has supervision
+of the allotment of state or federal funds to the various counties and
+townships. Nevertheless, most state highway departments do a great
+deal of advisory work in connection<span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span> with the highway construction
+carried out by county and township authorities.</p>
+
+<p>State highway departments are supported by funds obtained in various
+ways, laws differing greatly in this respect. The necessary support is
+in some states appropriated from funds obtained by general taxation,
+and is in others obtained from automobile license fees. In still
+others, the funds are secured by a combination of the two methods
+mentioned above. In addition to these support funds, a certain part of
+the money obtained as federal aid may be employed for the engineering
+and inspection costs on federal aid roads. The above mentioned funds
+are required to maintain the state highway department. In addition,
+the departments have supervision of the expenditures of construction
+funds which can be used for road construction and maintenance, and may
+not be expended for salaries or other overhead expense.</p>
+
+<p>In a number of states, automobile license fees are set aside for
+financing road construction and maintenance, and the work paid for
+from the fees is carried out under the supervision of the state
+highway department.</p>
+
+<p>In a number of instances, state bonds have been issued for road
+construction, and the expenditure of the proceeds of the sale of road
+bonds has usually been supervised by the state highway department.</p>
+
+<p>All federal aid funds allotted to a state must be expended under the
+direction of the state highway department.</p>
+
+<p><b>Federal Administration.</b>&mdash;Federal authority in highway work is vested
+in the Bureau of Public Roads of the United States Department of
+Agriculture. The official head is the Secretary of Agriculture, but
+the administrative head is the Director of the Bureau. In this Bureau
+are the various instrumentalities needed for carrying on
+investigations and furnishing information to the various states on
+highway subjects. The Bureau also supervises the construction of
+federal aid roads in a general way through<span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span> district engineers, each
+of whom looks after the work in several states.</p>
+
+<p>Funds for the support of the Bureau of Public Roads are obtained from
+congressional appropriations to the Department of Agriculture and from
+a percentage of the funds appropriated for federal aid.</p>
+
+<p>Federal aid is money appropriated by Congress to be distributed to the
+various states to stimulate road construction. It is granted to the
+states on the condition that the states will expend at least an equal
+amount on the projects involved. The states in turn usually give a
+suitable part of the state allotment to each county. There are various
+limitations as to the amount of federal aid per mile of road and the
+type of construction that may be employed, but these are matters of
+regulation that change from time to time.</p>
+
+<p>It will be seen that each of the administrative authorities, except
+the Bureau of Public Roads, is to some extent subservient to a higher
+authority, and the Bureau of Public Roads is supervised by the United
+States Congress. Considerable diplomacy is required on the part of any
+administrative authority if his contact with other officials is to be
+without friction. This is especially true in connection with the
+formulation of a policy regarding the types of construction to be
+adopted for an improvement. The responsibility for the selection is
+variously placed on the township, county or state authority, the laws
+not being uniform in this respect. If state or federal funds are
+allotted to an improvement, the state authority either makes the
+selection of the type of construction or the selection is made by some
+subordinate authority subject to the approval of the state highway
+department. Where the improvement is paid for exclusively with
+township or county funds, the selection is often made by the township
+or county authority without review by higher authority. Many abuses
+have crept into highway administration through<span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span> the unscrupulous
+methods of promoters of the sale of road materials or road machinery.
+A great deal of the selling activity of the agents for these
+commodities is entirely irreproachable, but it is well known that such
+is not always the case. As a result, the tendency of legislation is to
+require the state highway department to approve contracts for
+materials or construction entered into by the township or county
+authorities. The state highway departments can secure the requisite
+technical experts to determine the merits of materials and equipment
+and, in spite of some glaring examples of inefficiency or worse, have
+made a good record for impartiality and integrity as custodians of the
+funds for which they are responsible.</p>
+
+
+<h4 class="sc">Highway Finance</h4>
+
+<p>The paramount problem in highway administration is the development of
+an adequate financial plan for carrying on road improvement. The
+necessary expenditures are enormous, although the money so expended is
+probably much less than the actual benefit resulting from the
+improvements.</p>
+
+<p><b>Special Assessments.</b>&mdash;There is presumed to be a direct and recognized
+benefit conferred on farm lands by the construction of improved
+highways adjacent thereto. Therefore, it is equitable to charge a part
+of the cost against the lands so benefited.</p>
+
+<p>The principle of paying for public improvements by a special
+assessment upon private property has been long established and a large
+proportion of the public improvements in the cities and towns have
+been made financially possible through the medium of special
+assessments on abutting and adjacent property. The same principle has
+been applied to the financing of drainage projects for reclaiming farm
+lands. Recently the special assessment method has come into limited
+use in financing rural highway<span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span> improvements. The policy in such cases
+is to assess the abutting and adjacent property in a zone along the
+improved road for a percentage of the cost of the improvement. The
+amount so assessed does not ordinarily exceed one-fourth of the total
+cost of the improvement and may be considerably less. The assessment
+is spread over an area extending back from one to six miles from the
+improved road. The assessment area is generally divided into about
+four zones parallel to the road. The zone next the road is assessed at
+a rate arbitrarily determined as a fair measure of the benefit, and
+each succeeding zone is assessed at a somewhat lower rate. Generally
+about three-fourths of the total assessment is placed on the half of
+the assessment area lying next to the road.</p>
+
+<p>Many systems of making assessments have been proposed which are
+mechanical in application after the area and rate of distribution of
+benefit have been established, but in practice it is always found
+necessary to make adjustments on individual parcels of land because of
+variation in benefits received and it is impossible to eliminate the
+exercise of human judgment in equalizing the assessments.</p>
+
+<p><b>Zone Method of Assessing.</b>&mdash;The area to be assessed on each side of the
+improved road is divided into zones usually four in number, but a
+larger or smaller number of zones may be adopted. The rate for each
+zone is then arbitrarily determined. For a typical case, the first of
+four zones would receive an assessment of 50 per cent of the amount to
+be borne by the area; the second zone 25 per cent, the third 15 per
+cent and the fourth 10 per cent. Other percentages sometimes adopted
+are 45, 25, 20 and 10 and 60, 20, 15 and 5. The set of percentages
+first mentioned seems to insure the most equitable distribution for an
+area all of which is substantially equally productive.</p>
+
+<p>When a road, for the improvement of which an assessment is being made,
+lies on two or more sides of a parcel of land all of which is within
+the assessment area, the rate<span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span> is arbitrarily reduced to relieve that
+parcel of land somewhat, or the assessment is first spread as above
+outlined and afterward equalized as judgment dictates.</p>
+
+<p>In applying the zone method some difficulty is encountered in
+determining an equitable distribution on those parcels of land lying
+partly in one zone and partly in another, but the rate may be arrived
+at with reasonable accuracy by pro-rating in accordance with the exact
+conditions.</p>
+
+<p>In. Fig. 1, let it be assumed that the assessment area is to be two
+miles wide, one mile on each side of the road and the various
+ownerships to be indicated by the parcels of land numbered 1 to 8, as
+shown. Each zone for the assessment of the 3&frac14; mile section is &frac14;
+mile wide and the rates for the several zones are 50, 25, 15 and 10
+per cent respectively. Let it be assumed that the portion of the cost
+of the 3&frac14; miles of road to be assessed on the area shown is
+$20,000. The assessment would then be as follows:</p>
+
+
+
+<div class="center">
+<table summary="Assessment">
+<tr><td class="bt center">Parcel</td><td class="bt bl center">Rate</td><td  colspan="3" class="bt bl center">Rate × frontage on<br />improved road =<br />assessment units</td><td class="bt bl center">Amount of<br />Assessment<br />per unit<a name="FNanchor_1_3" id="FNanchor_1_3"></a><a href="#Footnote_1_3" class="fnanchor">[1]</a></td><td class="bt bl center">Assessment</td></tr>
+<tr><td class="bb center">1</td><td class="bb bl center">2</td><td  colspan="3" class="bb bl center">3</td><td class="bb bl center">4</td><td class="bb bl center">5</td></tr>
+<tr><td class="center">1</td><td class="bl right">a 50</td><td class="bl indent right">50 × 2640</td><td class="center">=</td><td class="left">132,000</td><td class="bl right">$0.016655</td><td class="bl right">$1558.46</td></tr>
+<tr><td class="center"></td><td class="bl right">b 75</td><td class="bl indent right">75 × 1320</td><td class="center">=</td><td class="left">99,000</td><td class="bl right">&nbsp;</td><td class="bl right">1153.90</td></tr>
+<tr><td class="center">2</td><td class="bl right">40</td><td class="bl indent right">40 × 2640</td><td class="center">=</td><td class="left">105,600</td><td class="bl right">&nbsp;</td><td class="bl right">1230.77</td></tr>
+<tr><td class="center">3</td><td class="bl right">10</td><td class="bl indent right">10 × 2640</td><td class="center">=</td><td class="left">26,400</td><td class="bl right">&nbsp;</td><td class="bl right">307.69</td></tr>
+<tr><td class="center">4</td><td class="bl right">25</td><td class="bl indent right">25 × 1320</td><td class="center">=</td><td class="left">33,000</td><td class="bl right">&nbsp;</td><td class="bl right">384.66</td></tr>
+<tr><td class="center">5</td><td class="bl right"><a name="FNanchor_2_4" id="FNanchor_2_4"></a><a href="#Footnote_2_4" class="fnanchor">[2]</a>85</td><td class="bl indent right">85 × 5280</td><td class="center">=</td><td class="left">448,800</td><td class="bl right">&nbsp;</td><td class="bl right">5230.88</td></tr>
+<tr><td class="center">6</td><td class="bl right">15</td><td class="bl indent right">15 × 5280</td><td class="center">=</td><td class="left">79,200</td><td class="bl right">&nbsp;</td><td class="bl right">923.08</td></tr>
+<tr><td class="center">7</td><td class="bl right"><a href="#Footnote_2_4" class="fnanchor">[2]</a>65</td><td class="bl indent right">65 × 7920</td><td class="center">=</td><td class="left">514,800</td><td class="bl right">&nbsp;</td><td class="bl right">6000.00</td></tr>
+<tr><td class="center">8</td><td class="bl right">35</td><td class="bl bb indent right">35 × 7920</td><td class="bb center">=</td><td class="bb left">277,200</td><td class="bl right">&nbsp;</td><td class="bl bb right">3230.77</td></tr>
+<tr><td class="bb center">&nbsp;</td><td class="bb bl right">&nbsp;</td><td class="bb bl">&nbsp;</td><td class="bb">&nbsp;</td><td class="bb right">1,716,000</td><td class="bb bl right">&nbsp;</td><td class="bb bl right">$20000.00</td></tr>
+</table></div>
+
+
+<div class="footnote"><p><a name="Footnote_1_3" id="Footnote_1_3"></a><a href="#FNanchor_1_3"><span class="label">[1]</span></a> The assessment per unit is obtained by dividing the total
+assessment by the total of column three.</p></div>
+
+<div class="footnote"><p><a name="Footnote_2_4" id="Footnote_2_4"></a><a href="#FNanchor_2_4"><span class="label">[2]</span></a> On these two parcels, it is decided that more than half
+of the zone rate should apply to the half of the zone toward the
+improved road, but some modification of the rates adopted might be
+justified.<span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span></p></div>
+
+<div class="figcenter" style="width: 288px;">
+<img src="images/i0033.png" width="282" height="773" alt="Fig. 1" title="" />
+<span class="caption">Fig. 1</span>
+</div>
+
+<p><span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span></p>
+
+<p>The assessment of the cost of the east and west one-mile section of
+road is made up in like manner, and let it be assumed that the portion
+of the cost of this road that is to be assessed on the area shown is
+$5500. The assessment area will be one mile wide and each zone
+one-fourth mile in width and the rates for each zone the same as
+before.</p>
+
+
+<div class="center">
+<table summary="Assessment">
+<tr><td class="bt bb center">Parcel</td><td class="bt bb bl center">Rate</td><td  colspan="3" class="bt bb bl center">Rate × frontage on<br />improved road =<br />assessment units</td><td class="bt bb bl center">Amount of<br />Assessment<br />per unit</td><td class="bt bb bl center">Assessment</td></tr>
+<tr><td class="right">1</td><td class="bl right">a 75</td><td class="bl indent right">75 x 1320</td><td class="center">=</td><td class="left">99,000</td><td class="bl right">$0.010417</td><td class="bl right">$1031.25</td></tr>
+<tr><td class="right">&nbsp;</td><td class="bl right">b 15</td><td class="bl right">15 x 2640</td><td class="center">=</td><td align="left">39,600</td><td class="bl right">&nbsp;</td><td class="bl right">412.49</td></tr>
+<tr><td class="right">2</td><td class="bl right">75</td><td class="bl right">75 x 2640</td><td class="center">=</td><td align="left">198,000</td><td class="bl right">&nbsp;</td><td class="bl right">2062.53</td></tr>
+<tr><td class="right">3</td><td class="bl right">50</td><td class="bl right">50 x 1320</td><td class="center">=</td><td align="left">66,000</td><td class="bl right">&nbsp;</td><td class="bl right">687.51</td></tr>
+<tr><td class="right">4</td><td class="bl right">a 25</td><td class="bl right">25 x 1320</td><td class="center">=</td><td align="left">33,000</td><td class="bl right">&nbsp;</td><td class="bl right">756.25</td></tr>
+<tr><td class="right">&nbsp;</td><td class="bl right">b 15</td><td class="bl right">15 x 2640</td><td class="center">=</td><td align="left">39,600</td><td class="bl right">&nbsp;</td></tr>
+<tr><td class="right">5</td><td class="bl right">10</td><td class="bl right">10 x 3300</td><td class="center">=</td><td align="left">33,000</td><td class="bl right">&nbsp;</td><td class="bl right">343.73</td></tr>
+<tr><td class="bb right">6</td><td class="bb bl right">10</td><td class="bl right">10 x 1980</td><td class="center">=</td><td align="left">19,800</td><td class="bl right">&nbsp;</td><td class="bb bl right">206.24</td></tr>
+<tr><td class="bb right">&nbsp;</td><td class="bb bl right">&nbsp;</td><td class="bb bl right">&nbsp;</td><td class="bb right">&nbsp;</td><td class="bb left">528,000</td><td class="bb bl right">&nbsp;</td><td class="bb bl right">5500.00</td></tr>
+</table></div>
+
+<p>It will be noted that the combined assessment for the two sections of
+road is especially heavy on parcels 1, 2 and 3. In order to prevent
+unjust charges against such properties, laws usually limit the total
+assessment against any parcel of land to a fixed percentage of a fair
+market value or of the assessed value. The assessment on these parcels
+would be reduced as seemed expedient and the deficit would be
+distributed over the remainder of the area in the same manner as the
+original assessment was spread. In practice such re-distribution is
+ordinarily made by the arbitrary adjustment in accordance with what
+the authorized officials consider to be fair and equitable. The method
+outlined is merely a mechanical means of securing distribution and
+must not be considered as an infallible method of making the
+assessment. It is always necessary to review the results in the light
+of the actual benefits to be presumed for<span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span> each parcel of land.
+Nevertheless, the method outlined will prove equitable in a majority
+of cases.</p>
+
+<p><b>General Taxation.</b>&mdash;There is a general community benefit derived from
+the construction of good roads in that the actual cost of marketing
+farm products is lessened with a resulting lowering of the price to
+the consumer. The benefit also accrues from the greater facility with
+which all community business may be conducted. The introduction of
+better opportunities for social, religious and educational activities
+in the rural districts which results from improved highways is also a
+community benefit of no mean importance. A part of the cost of road
+improvement may therefore be equitably paid from funds obtained by
+general taxation.</p>
+
+<p>A considerable portion of the current expense of maintaining the
+township and county highway work and at least a part of the cost of
+maintaining state highway activities is met from funds obtained by
+general taxation. Likewise, the funds required for the amortization of
+bond issues are often obtained from general taxation although vehicle
+license fees are sometimes used for that purpose.</p>
+
+<p>General taxes are levied on all taxable property in a political unit
+under statutory provisions regulating the amount of the levy and the
+purpose for which the revenue is to be used. In the aggregate, the
+road taxes are large but in the township or county the rate is
+generally small compared to some other taxes, such as the school tax.</p>
+
+<p><b>Vehicle Taxes.</b>&mdash;The great direct benefit derived by those who actually
+operate vehicles over the roads justifies the policy of requiring a
+vehicle to pay a license fee in lieu of other taxes, the funds so
+obtained to be used for the construction and maintenance of public
+highways. In practice, this method has already been applied to motor
+vehicles in most states and has proven to be an important source of
+revenue. Its application to horse-drawn vehicles has not been
+attempted, due probably to the fact that such<span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span> horse-drawn vehicles as
+use the public highways are also employed about the farm or in the
+towns and the determination of an equitable basis for taxation
+involves many difficulties.</p>
+
+<p>The rate of the fee for motor vehicles should be based on their
+destructive effect on the road so far as that is possible. The scale
+of fees should therefore take account of weight and speed of vehicle
+and if the license is in lieu of all other taxes, it should also be
+graduated with the cost of the vehicle.</p>
+
+<p>When funds are thus derived, every precaution should be taken to
+insure that the money is used judiciously for construction and
+especially for maintenance on those roads most useful to motor
+traffic.</p>
+
+<p><b>Highway Bonds.</b>&mdash;Bond issues for road improvement afford a means of
+constructing roads and paying for them while they are being used. A
+very large volume of such bonds are outstanding in the United States.
+Road bonds should be issued only for durable types of improvement and
+the life of the bond should be well within the probable useful life of
+the road surface. It is customary and highly desirable that the
+general nature and extent of the improvement be established before the
+bonds are issued. It is desirable that bond issues be subject to
+approval by referendum before issue and that is provided in every
+instance.</p>
+
+<p>Highway bonds are of three classes known as Sinking Fund, Annuity and
+Serial Bonds, respectively. The earlier bonds issued were almost all
+of the sinking fund class, but in recent years the serial bond has
+been widely employed and is probably the most satisfactory to
+administer.</p>
+
+<p><b>Sinking Fund Bonds.</b><a name="FNanchor_1_5" id="FNanchor_1_5"></a><a href="#Footnote_1_5" class="fnanchor">[1]</a>&mdash;When this type of bond is employed, the amount
+of the expenditure for road improvement<span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span> is determined upon and the
+length of the period during which tax payments shall be made is
+settled. To employ a concrete example, it may be assumed that $100,000
+is to be expended for road work and is to be paid at the end of ten
+years. The interest rate on the bonds will vary with the condition of
+the bond market and the stability of the political unit issuing the
+bonds, but is usually about 5 per cent. Knowing these factors, the
+amount to be added to the sinking fund each year is computed. In order
+to pay the interest on the bonds, a tax of suitable rate is levied,
+and in order to retire the bonds at the end of the period, a sum is
+set aside each year which is supposed to be invested and draw interest
+which will be added to the principle, and the principle and interest
+comprise the sinking fund. The principle of the sinking fund is
+obtained by tax levies, a sum being added to the principle of the
+sinking fund each year.</p>
+
+<div class="footnote"><p><a name="Footnote_1_5" id="Footnote_1_5"></a><a href="#FNanchor_1_5"><span class="label">[1]</span></a> For a more detailed discussion of highway bonds see
+Bulletin 136, U. S. Dept. of Agriculture, which is the basis of this
+discussion.</p></div>
+
+<p>The success of this method of financing depends upon the proper
+administration of the sinking fund. It must be invested with fidelity
+and the fund be kept intact. Usually the sinking fund cannot be
+invested at as high a rate of interest as the bonds bear and there is
+some loss as a result. Road bonds bearing 5 per cent interest can
+usually be sold at par while the sinking fund will usually net about 3
+or 3&frac12; per cent interest. The total cost of a bond issue will be
+greater by the sinking fund method than by either of the other methods
+described.</p>
+
+<p><b>Annuity Bonds.</b>&mdash;Annuity bonds are drawn in such a manner that the
+amount of the payment for principle and interest is the same each year
+during the life of the bond. When the amount of the issue and the rate
+of interest has been determined and the amount of the desired annual
+payment has been determined, the number of years the bonds must run is
+computed.</p>
+
+<p>This method is convenient in that the amount of the tax to be levied
+each year remains constant.<span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span></p>
+
+<p><b>Serial Bonds.</b>&mdash;Serial bonds are drawn so that a uniform amount of the
+principle is retired each year after retirement starts and the total
+interest payments decrease each year after the first bonds are
+retired. The first bond may not be retired for a number of years after
+the issue of the bonds, but when it once starts retirement proceeds at
+a constant rate annually.</p>
+
+<p><b>Comparison of Methods of Issuing Bonds.</b>&mdash;The relative costs of
+financing by either of the three methods depends upon the rate of
+interest in each case and the net rate secured on the sinking fund
+provided for retiring sinking fund bonds.</p>
+
+<p>For comparative purposes, some typical examples are given in Table 3.
+These illustrate the differences in total cost of securing $100,000 by
+each of the three methods at various interest rates.</p>
+
+<h4 class="sc">Table 3</h4>
+<h4 class="sc">Total Cost of a Loan of $100,000 for 20 Years, Interest
+Compounded Annually</h4>
+
+
+
+
+<div class="center">
+<table summary="Loan Costs">
+<tr><td rowspan="2" class="bt bb center">Annual<br />Interest<br />on Bonds</td><td colspan="3" class="bt bb bl center">Sinking Fund Compounded<br />Annually at</td><td rowspan="2" class="bt bb bl center">Annuity</td><td rowspan="2" class="bt bb bl center">Serial</td></tr>
+<tr><td class="bb bl indent left">3 per cent</td><td class="bb bl right">3&frac12; per cent</td><td class="bb bl right">4 per cent</td></tr>
+<tr><td class="indent left">4</td><td class="bl right">$154,431</td><td class="bl right">$150,722</td><td class="bl right">$147,163</td><td class="bl right">$147,163</td><td class="bl right">$142,000</td></tr>
+<tr><td class="indent left">4&frac12;</td><td class="bl right">164,431</td><td class="bl right">160,722</td><td class="bl right">157,163</td><td class="bl right">153,752</td><td class="bl right">147,250</td></tr>
+<tr><td class="indent left">5</td><td class="bl right">174,431</td><td class="bl right">170,722</td><td class="bl right">167,163</td><td class="bl right">160,485</td><td class="bl right">152,500</td></tr>
+<tr><td class="indent left">5&frac12;</td><td class="bl right">184,431</td><td class="bl right">180,722</td><td class="bl right">177,163</td><td class="bl right">167,359</td><td class="bl right">157,750</td></tr>
+<tr><td class="bb indent left">6</td><td class="bb bl right">194,431</td><td class="bb bl right">190,722</td><td class="bb bl right">187,163</td><td class="bb bl right">174,369</td><td class="bb bl right">163,000</td></tr>
+</table></div>
+
+<p><b>Desirability of Road Bonds.</b>&mdash;In theory the bond method of financing
+enables the highway authorities to construct a large mileage of roads
+in a few years and spreads the cost over the period during which the
+public is being benefited. Better prices are obtained on contracts for
+a<span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span> large mileage than for smaller jobs, and the community can receive
+the benefit more quickly than where construction proceeds piecemeal
+with current funds. The vital consideration is to insure that the term
+of the bonds is well within the useful life of the road, and that
+ample provision is made to maintain the roads during that period.
+Under proper restrictions the bond method of financing is to be
+commended. The bonds are an attractive investment and readily
+marketable on satisfactory terms.</p>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span></p>
+<h2><a name="Chapter_III" id="Chapter_III"></a><span class="smcap">Chapter III</span></h2>
+
+<h3>DRAINAGE OF ROADS</h3>
+
+
+<p><b>The Necessity for Drainage.</b>&mdash;The importance of drainage for all roads
+subject to the effects of storm or underground water has always been
+recognized by road builders, but during recent years constantly
+increasing attention has been given to this phase of road
+construction. It is unfortunate that there has in the past been some
+tendency to consider elaborate drainage provisions less necessary
+where rigid types of surfaces were employed. It has become apparent,
+from the nature of the defects observed in all sorts of road surfaces,
+that to neglect or minimize the importance of drainage in connection
+with either earth roads or any class of surfaced roads is to invite
+rapid deterioration of some sections of the roadway surface and to add
+to maintenance costs.</p>
+
+<p>The degree to which lack of drainage provisions affect the
+serviceability of the road surface varies with the amount of
+precipitation in the locality and the manner in which it is
+distributed throughout the year. In the humid areas of the United
+States, which are, roughly, those portions east of a north and south
+line passing through Omaha and Kansas City, together with the northern
+part of the Pacific slope, precipitation is generally in excess of 30
+inches per year and fairly well distributed throughout the year, but
+with seasonal variations in rate. In these areas, the effect of the
+precipitation, both as regards its tendency to lower the stability of
+soils and as an eroding agent, must be carefully provided against in
+highway design.<span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span></p>
+
+<p>Outside of the areas mentioned above, the precipitation is much less
+than 30 inches per year and its effect as an agent of erosion is of
+greatest significance, although in restricted areas there may be short
+periods when the soil is made unstable by ground water.</p>
+
+<p><b>Importance of Design.</b>&mdash;The drainage system for a proposed road
+improvement ought to be designed with as much care as any other
+element, and, to do so, a study must be made of all factors that have
+any bearing on the drainage requirements and the probable
+effectiveness of the proposed drainage system. The well established
+principles of land drainage should be followed so far as applicable.</p>
+
+<p>The basic principle of road drainage is to minimize the effect of
+water to such an extent that there will always be a layer of
+comparatively dry soil of appreciable thickness under the traveled
+part of the road. This layer should probably never be less than two
+feet thick and for soils of a structure favorable to capillary action
+it should be at least three feet thick. The means employed to
+accomplish the requisite drainage will be as various as the conditions
+encountered.</p>
+
+<p><b>Surface Drainage.</b>&mdash;The drainage method which is by far the most nearly
+general in application is that which utilizes open ditches, and the
+system which employs these ditches is usually referred to as surface
+drainage. The full possibilities of this method of minimizing the
+effects of storm water are rarely fully utilized in road construction.
+Very frequently, deterioration of a road surface is directly
+attributable to failure to provide adequately for the removal of the
+storm water or water from the melting of snow that has fallen on the
+road, or water that flows to the road from land adjacent thereto.
+Surface water can usually most cheaply and expeditiously be carried
+away in open ditches, although special conditions are occasionally
+encountered which require supplementary tile drains.<span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span> The cross
+section commonly adopted for roads lends itself naturally to the
+construction of drainage ditches at the sides of the traveled way, and
+these are usually the principal dependence for the disposal of storm
+water.</p>
+
+<p><b>Run-off.</b>&mdash;The capacity required of side ditches to insure satisfactory
+surface drainage will be affected by the amount and nature of the
+precipitation in the region where the road is built. The annual
+rainfall in a region may amount to several feet, but may be well
+distributed throughout the year with an absence of excessive rainfall
+for short periods, that is, flood conditions may rarely occur. In
+other areas, the annual rainfall may be comparatively small but the
+precipitation occurs at a very high rate, that is, flood conditions
+may be common, or it may be at a low rate extending over a
+considerable period. These peculiarities must be known before an
+adequate drainage system can be planned.</p>
+
+<p>It is almost universally true in the United States that precipitation
+at a very high rate will be for a relatively short duration, and
+during these short periods, which usually do not exceed thirty
+minutes, a portion of the water that falls on the areas adjacent to
+the road and that drains to the road ditches will soak into the soil
+and therefore not reach the ditches along the road. The extent to
+which the water is taken up by the soil will vary with the porosity
+and slope of the land and the character of the growth thereon.
+Cultivated land will absorb nearly all of the water from showers up to
+fifteen or twenty minutes duration; grass land a somewhat smaller
+percentage; and hard baked or other impervious soil will absorb a
+comparatively small amount. Rocky ground and steep slopes will absorb
+very little storm water.</p>
+
+<p>The surface of the road is designed to turn water rapidly to the
+ditches, but when the material is the natural soil, there is always
+considerable absorption of storm water. Surfaces such as sandclay,
+gravel and macadam do not<span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span> absorb to exceed 10 per cent of the
+precipitation during short showers. Bituminous surfaces, brick and
+concrete pavements, do not absorb an appreciable amount of storm
+water.</p>
+
+<p>Generally it is best to assume that if a rain lasts for forty-five
+minutes or more, all of the water will run off, as the soil will reach
+a state of saturation in that time. This is not true of deep sand, but
+is for nearly all other soils.</p>
+
+<p>The ditch capacity needed will therefore depend upon the area drained,
+the character of the soil, the slopes and the rainfall characteristics
+of the region, and upon the nature of the road surface.</p>
+
+<p>For a required capacity, the cross section area of the ditch will vary
+inversely as the grade, because the velocity of flow increases with an
+increase in the grade of the ditch. If the surface water must be
+carried along the road for distances exceeding five or six hundred
+feet, the ditch must be constructed of increasing capacity toward the
+outlet in order to accommodate the accumulated volume of water.</p>
+
+<p>The velocity of flow varies not only with the grade, but with the
+shape of the cross section, cleanness of the channel, the depth of the
+water in the channel, alignment of the channel and the kind of
+material in which the channel is formed. It is not necessary to go to
+great refinement in the design of the side ditches for the ordinary
+case where the water is carried along the road for only a few hundred
+feet. The ditches are made of ample capacity by using the commonly
+accepted cross section for a road, which will be discussed in a later
+paragraph. But where large areas must be drained by the road ditches,
+it is desirable carefully to design the side ditches. The basis for
+that design is too lengthy to be included herein, and reference should
+be made to a standard treatise on the subject.</p>
+
+<p><b>Ordinary Design of Ditches.</b>&mdash;For grades of one per cent or less on
+roads in the humid area, the bottom of the ditch should be at least
+three and one-half feet lower than<span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span> the traveled surface of the road,
+except for very sandy soil. For grades greater than one per cent, this
+depth may be decreased one foot, and for grades of four per cent and
+upward, the depth may be still less. These general rules for depth are
+susceptible of variation but are believed to be the minimum except in
+arid or semi-arid climates. It is far better to be too liberal in
+ditch allowance than to be too conservative. In arid or semi-arid
+regions, the ditch design will be based on the necessity of providing
+for flood flow and preventing damage through erosion. Ordinary
+drainage requirements will be satisfactory with the ditch about one
+foot deep.</p>
+
+<p>If the topography is such that it is evident considerable storm water
+will flow from the adjacent land to the road ditches, the design must
+be modified to take this into account. Sometimes such water can be
+diverted by ditches well back from the road, and thus prevented from
+flowing into the side ditches along the roadway. It is especially
+desirable to divert water, which would otherwise flow down the slope
+of a cut, by means of a ditch on the hill-side above the upper edge of
+the slope of the cut.</p>
+
+<p>Ditches are not effective unless they afford a free flow throughout
+their length and have an outlet to a drainage channel of ample
+capacity. Therefore, ditch grades should be established by survey,
+especially if the gradient is less than one per cent, and the
+construction work should be checked to insure that the ditch is
+actually constructed as planned. A few high places in the ditch will
+greatly reduce the effectiveness, although these may appear at the
+time of construction to be slight. Constricted places, such as might
+be due to a small amount of loose earth left in the ditch, are always
+to be avoided.</p>
+
+<p>Where the side ditch passes from a cut to the berm alongside a fill,
+the ditch should be excavated throughout in the undisturbed natural
+soil, five feet or more from the toe of the slope of the fill, and
+along the filled portion of the<span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span> road there should be a berm of three
+or four feet between the toe of the slope of the fill and the near
+edge of the ditch.</p>
+
+<p><b>Underground Water.</b>&mdash;In a preceding paragraph, mention was made of the
+fact that only a part of the storm water runs off over the surface of
+the ground, the larger part being absorbed by the soil. The water thus
+absorbed flows downward through the pores in the soil until it is
+deflected laterally by some physical characteristic of the soil
+structure. The movement of underground water is affected by many
+circumstances, but only two conditions need be discussed herein.</p>
+
+<p>Underground water, like surface water, tends to attain a level
+surface, but in so doing it may need to flow long distances through
+the pores of the soil, and to overcome the resistance incident to so
+doing some head will be required. That is to say, the water will be
+higher at some places than at others. If a cut is made in grading the
+road, the road surface may actually be lower than the ground water
+level in the land adjoining the road. As a result, the water will seep
+out of the side slopes in the cut and keep the ditches wet, or even
+furnish enough water to occasion a flow in the ditch. Similarly, the
+higher head of the underground water near the top of a hill may result
+in ground water coming quite close to the surface some distance down
+the hill. The remedy in both cases is tile underdrains alongside the
+road to lower the ground water level so that it cannot affect the road
+surface.</p>
+
+<p>Sometimes the ground water encounters an impervious stratum as it
+flows downward through the soil, or one that is less pervious than the
+surface soil. When such is the case, the water will follow along this
+stratum, and should there be an outcrop of the dense stratum, a spring
+will be found at that place. This may be on a highway. The impervious
+stratum may not actually outcrop but may lie only a few feet under the
+surface of the road, in which<span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span> case, the road surface will be so water
+soaked as to be unstable. The so-called "seepy places" so often noted
+along a road are generally the result of this condition. This
+condition can be corrected by tile laid so as to intercept the flow at
+a depth that precludes damage to the road. Commonly, the tile will be
+laid diagonally across the road some distance above the section where
+the effect of the water is noted, and will be turned parallel to the
+road at the ditch line and carried under one of the side ditches to an
+outlet.</p>
+
+<p><b>Tile Drains.</b>&mdash;Where the soil and climatic conditions are such that the
+roadway at times becomes unstable because of underground water rising
+to a level not far below the road surface, the ground water level is
+lowered by means of tile underdrains. The function of the tile drains
+in such cases is precisely the same as when employed in land drainage;
+to lower the ground water level.</p>
+
+<p><b>Laying Tile.</b>&mdash;The tile lines are usually laid in trenches parallel to
+the center line of the road near the ditch line and at least 4 feet
+deep so as to keep the ground water level well down. They must be
+carefully laid to line and grade. A good outlet must be provided and
+the last few joints of pipe should be bell-and-spigot sewer pipe with
+the joints filled with cement mortar. The opening of the tile should
+be covered with a coarse screen to prevent animals from nesting in the
+tile.</p>
+
+<p>It is frequently necessary to lay a line of tile at the toe of the
+slope in cuts to intercept water that will percolate under the road
+from the banks at the sides. In some cases, it is desirable to
+back-fill the tile trench with gravel or broken stone to insure rapid
+penetration of surface water to the tile. In other instances, it is
+advantageous to place catch basins about every three or four hundred
+feet. These may be of concrete or of tile placed on end or may be
+blind catch basins formed by filling a section of the trench with
+broken stone. When a blind catch basin is used, the top<span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span> should be
+built up into a mound, and for a tile or concrete catch basin, a
+grating of the beehive type should be used, so that flow to the tile
+will not be obstructed by weeds and other trash that is carried to the
+catch basin.</p>
+
+<p><b>Culverts.</b>&mdash;Culverts and bridges are a part of the drainage system and
+the distinction between the two is merely a matter of size. Generally,
+structures of spans less than about eight feet are classed as
+culverts, but the practice is not uniform. In this discussion culverts
+will be defined as of spans of 8 feet or less.</p>
+
+<p>Numerous culverts are required to afford passage for storm water and
+small streams crosswise of the road, and their aggregate cost is a
+large item in the cost of road improvement. The size of the waterway
+of a culvert required in any location will be estimated by an
+inspection of the stream and existing structure, and by determining
+the extent and physical characteristics of the drainage area.
+Sometimes there is sufficient evidence at the site to indicate quite
+closely the size required, but this should always be checked by
+run-off computations. The drainage area contributing water to the
+stream passing through the culvert under consideration is computed
+from contour maps or from a survey of the ground, and the size of
+culvert determined by one of the empirical formulas applicable to that
+purpose. In these formulas, the solution depends upon the proper
+selection of a factor "C" which varies in accordance with the nature
+of the drainage area. Two of these that are quite widely used are as
+follows:</p>
+
+<p class="center">
+<i>Myers' Formula: a = CA</i>
+</p>
+
+<p>Where <i>a</i> = area of cross section of culvert in square feet. <i>A</i> =
+area in acres of the drainage area above culvert. <i>C</i> a factor varying
+from 1 for flat country to 4 for mountainous country or rocky soil,
+the exact value to be selected after an inspection of the drainage
+area.<span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span></p>
+
+<p><i>Talbot's Formula</i>: Area of waterway in square feet =</p>
+
+<div class="center">
+<table style="margin-top:0.5em; margin-bottom:0.5em; text-align: center;"
+    cellpadding="0" cellspacing="0" summary="Talbot's Formula" >
+    <tr>
+        <td class="math" align="right">
+            <i>C</i> = <span style="font-size: 150%;">&radic;</span></td>
+        <td class="math upper_line">
+            &nbsp;(Drainage area in acres)<sup>3</sup></td>
+    </tr>
+</table>
+</div>
+
+<p><i>C</i> being variable according to circumstances thus:</p>
+
+<p>"For steep and rocky ground <i>C</i> varies from 2/3 to 1. For rolling
+agricultural country, subject to floods at times of melting snow, and
+with length of valley three or four times its width, <i>C</i> is about 1/3,
+and if stream is longer in proportion to the area, decrease <i>C</i>. In
+districts not affected by accumulated snow, and where the length of
+valley is several times its width, 1/5 or 1/6 or even less may be
+used. <i>C</i> should be increased for steep side slopes, especially if the
+upper part of the valley has a much greater fall than the channel at
+the culvert. The value of <i>C</i> to be used in any case is determined
+after an inspection of the drainage area."</p>
+
+<div class="figcenter" style="width: 449px;">
+<img src="images/i0048.png" width="449" height="211" alt="Fig. 2. Design of Pipe Culvert and Bulkhead" title="" />
+<span class="caption">Fig. 2. Design of Pipe Culvert and Bulkhead</span>
+</div>
+
+<p><b>Length of Culvert.</b>&mdash;The clear length between end walls on a culvert
+should be at least equal to the width of the roadway between ditches.
+This is a minimum of 20 feet for secondary roads and ranges from 24 to
+30 feet for main roads. The headwall to the culvert should not be a
+monument, but should be no higher than needed to prevent vehicles from
+leaving the roadway at the culvert.</p>
+
+<p><b>Farm Entrance Culverts.</b>&mdash;At farm entrances, culverts are required to
+carry the farm driveway across the side<span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span> ditch of the road. These
+culverts are usually about 16 feet along, and should be of a size
+adequate to take the flow of the side ditch. The farm entrance culvert
+should be of such design that it can be easily removed to permit
+cleaning out the ditches with a road grader.</p>
+
+
+<h4 class="sc">Types of Culverts</h4>
+
+<p>Culverts constructed of concrete and poured in place are called box
+culverts because of the rectangular form of the cross section.
+Culverts of pre-cast pipe are known as pipe culverts. Several forms of
+pipe culvert are in general use.</p>
+
+<div class="figcenter" style="width: 355px;">
+<img src="images/i0049.png" width="355" height="259" alt="Fig. 3.&mdash;Typical Concrete Box Culvert" title="" />
+<span class="caption">Fig. 3.&mdash;Typical Concrete Box Culvert</span>
+</div>
+
+<p><b>Metal Pipe.</b>&mdash;These may be of cast iron, steel or wrought iron. The
+cast iron pipe is very durable but expensive and heavy to handle and
+is not widely used in highway construction. Steel pipe has been
+employed to a limited extent but its durability is questioned. At
+least it is known that the pipe made from uncoated, light sheet steel
+is not very durable. Sheet iron and sheets made<span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span> from alloy iron
+coated with spelter have been extensively used and seem to be durable,
+especially when laid deep enough to eliminate possibility of damage
+from heavy loads. To insure reasonable resistance to corrosion, the
+metal sheets should be coated with at least one and one-half ounces of
+spelter per square foot of sheet and the sheets should not be lighter
+than 16 gauge for small sizes and should be heavier for the larger
+sizes.</p>
+
+<p><b>Clay and Cement Concrete Pipe.</b>&mdash;The ordinary burned clay bell and
+spigot pipe that is employed for sewer construction is sometimes used
+for culverts. It must be very carefully bedded, preferably on a
+concrete cradle and the joints filled with cement mortar. Culverts of
+this type have a tendency to break under unusual loads, such as
+traction engines or trucks. They may be damaged by the pressure from
+freezing water, particularly when successive freezing and thawing
+results in the culvert filling with mushy snow, which subsequently
+freezes.</p>
+
+<p><b>Concrete Pipe.</b>&mdash;Reinforced concrete pipe is a satisfactory material
+for culverts, if the pipe is properly designed. The pipe should be
+carefully laid on a firm earth bed with earth carefully back-filled
+and tamped around the pipe. The joints in the pipe should be filled
+with cement mortar, or should be of a design that will be tight.</p>
+
+<p><b>Endwalls for Culverts.</b>&mdash;A substantial retaining wall is placed at each
+end of the culvert barrel, whatever the type. This is to prevent the
+end of the culvert from becoming choked with earth and to retain the
+roadway at the culvert. It also indicates to the drivers the location
+of the end of the culvert. The endwall extends a foot or more below
+the floor of the culvert to prevent water from cutting under the
+barrel. Plain concrete or stone masonry are most commonly used for
+culvert endwalls.</p>
+
+<p><span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span></p>
+
+<div class="figcenter" style="width: 730px;">
+<img src="images/i0051.png" width="730" height="491" alt="Fig. 4.&mdash;Two Types of Drop Inlet Culvert" title="" />
+<span class="caption">Fig. 4.&mdash;Two Types of Drop Inlet Culvert</span>
+</div>
+
+<p><b>Reinforced Concrete Box Culverts.</b>&mdash;The pipe culvert is limited in
+application to the smaller waterways. Reinforced concrete is
+extensively used for culverts of all sizes,<span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span> but especially for the
+larger ones. These are usually constructed with endwalls integral with
+the barrel of the culvert. Culverts of this type must be designed for
+the loads anticipated to insure suitable strength and stability, and
+must be constructed of a good quality of concrete. Figs. 2 and 3 show
+designs for pipe and box culverts.</p>
+
+<div class="figcenter" style="width: 478px;">
+<img src="images/i0052.png" width="478" height="246" alt="Fig. 5.&mdash;Drop Inlet Culvert" title="" />
+<span class="caption">Fig. 5.&mdash;Drop Inlet Culvert</span>
+</div>
+
+<p><b>Drop Inlet Culverts.</b>&mdash;In some locations erosion has begun in the
+fields adjacent to a culvert and it will probably continue until the
+stream above the culvert has eroded to about the level of the floor of
+the culvert. This is a reason for placing the culvert as high as the
+roadway will permit, so long as the area above the culvert will be
+properly drained. Considerable reclamation of land is possible if the
+culvert is constructed with a box at the inlet and as shown in Fig. 4.
+The area up-stream from the culvert will not erode below the level of
+the top of the box at the inlet end.</p>
+
+<p>Where the stream crossing the road has eroded to considerable depth or
+has considerable fall, as would sometimes be the case on side hill
+roads, the culvert barrel would follow the general slope of the ditch
+but should have a drop inlet. This type of culvert is shown in Fig.
+5.</p>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span></p>
+<h2><a name="Chapter_IV" id="Chapter_IV"></a><span class="smcap">Chapter IV</span></h2>
+
+<h3>ROAD DESIGN</h3>
+
+
+<p><b>Necessity for Planning.</b>&mdash;Sometimes highway improvement is the result
+of spasmodic and carelessly directed work carried out at odd times on
+various sections of a road, finally resulting in the worst places
+being at least temporarily bettered. The grade on the steepest hills
+is probably reduced somewhat and some of the worst of the low lying
+sections are filled in and thereby raised. Short sections of surfacing
+such as gravel or broken stone may be placed here and there. From the
+standpoint of the responsible official, the road has been "improved,"
+but too often such work does not produce an improvement that lasts,
+and sometimes it is not even of any great immediate benefit to those
+who use the roads. In nearly every instance such work costs more in
+money and labor that it is worth.</p>
+
+<p>Lasting improvement of public highways can be brought about only
+through systematic and correlated construction carried on for a series
+of years. In other words, there must be a road improvement policy
+which will be made effective through some agency that is so organized
+that its policies will be perpetuated and is clothed with enough
+authority to be capable of enforcing the essential features of good
+design and of securing the proper construction of improvements.</p>
+
+<p>Details of highway construction and design must vary with many local
+conditions and types of surface. The limits of grades and the many
+other details of design may properly be adopted for a specific piece
+of work only after an adequate investigation of the local requirements
+and<span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span> in the light of wide experience in supervising road improvement.</p>
+
+<p>New ideas are constantly being injected into the art of road building,
+but these are disseminated somewhat slowly, so that valuable devices
+and improvements in methods remain long unknown except to the
+comparatively few who have the means for informing themselves of all
+such developments.</p>
+
+<p>It follows then that the logical system of conducting road improvement
+is through an agency of continuing personnel which will supervise the
+preparation of suitable plans and direct the construction in
+accordance with the most recent experience.</p>
+
+<p><b>Road Plans.</b>&mdash;The information shown on the plans prepared for road
+improvement varies somewhat with the design and with the ideas of the
+engineer as to what constitutes necessary information, but in general
+the plans show the existing road and the new construction contemplated
+in an amount of detail depending principally upon the character of the
+construction. Simple plans suffice for grade reduction or reshaping an
+earth road surface, while for the construction of paved roads, the
+plans must be worked out in considerable detail. The essential
+requirement is that there be given on the plans all information
+necessary to enable the construction to be carried out according to
+the intentions of the engineer, that all parts of the work fit
+together, that the culverts are of the proper size and located at the
+proper places, ditches drain properly, grades are reduced to the
+predetermined rate, that excavated material is utilized and that an
+exact record of the work done is retained. Plans are indispensable to
+economical road construction and the preparation of the plans is the
+work of the expert in road design, that is, the highway engineer.</p>
+
+<p><b>Problem of Design.</b>&mdash;The problem of road design is to prepare plans for
+a road improvement with the various<span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span> details so correlated as to
+insure in the road constructed in accordance therewith the maximum of
+safety, convenience and economy to the users thereof. The degree to
+which the design will be effective will depend to a considerable
+extent upon the financial limitations imposed upon the engineer, but
+skill and effort on the plans will do a great deal to offset financial
+handicap and no pains should be spared in the preparation of the
+plans. Moreover, the plans must afford all of the information needed
+by the contractor in preparing a bid for the work.</p>
+
+<p><b>Preliminary Investigation.</b>&mdash;The first step in road improvement is to
+secure an adequate idea of the existing conditions on the road or
+roads involved. The detail to which this information need go will
+depend entirely upon the purpose of the preliminary investigation, for
+before a definite plan is prepared, it may be necessary to choose the
+best from among several available routes. For this purpose, it is not
+always necessary to make an actual instrument survey of the several
+routes. A hasty reconnaissance will usually be sufficient. This is
+made by walking or riding over the road and noting, in a suitable book
+or upon prepared blanks, the information needed. The items of
+information recorded will usually be as follows: distances, grades,
+type of soil on the road and nature of existing surface, character of
+drainage, location of bridges and culverts and the type of each with
+notes as to its condition, location of railway crossings and notes as
+to type, location of intersecting roads, farm entrances, and all
+similar features that have a bearing on the choice of routes. These
+data can be obtained in a comparatively short time by a skilled
+observer who may drive over the road in a motor car. Sometimes it may
+be desirable to make a more careful study of some certain sections of
+road and this may be done by waking over the section in question in
+order to make a more deliberate survey of the features to be
+considered than is possible when riding in a motor car.<span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span></p>
+
+<p>Factors other than relative lengths of routes will obviously determine
+the cost of improvement and the comparative merits of the improved
+roads. Some special characteristic of a road, such as bad railroad
+crossings or a few bad hills, may eliminate a route, or availability
+of materials along a route may offset disadvantages of alignment or
+grade.</p>
+
+<p>In special cases, complete surveys of routes may be required finally
+to select the best route, but these instances are few in number.</p>
+
+<p><b>Road Surveys.</b>&mdash;When a road has been definitely selected for
+improvement, a careful survey is made to furnish information for the
+preparation of the plans. This will consist of a transit survey and a
+level survey.</p>
+
+<p>The transit survey is made by running a line between established
+corners following the recorded route of the road, or if no records are
+available or the road is irregular in alignment, by establishing
+arbitrary reference points and running a line along the center line of
+the existing road or parallel thereto. The topography is referenced to
+this line in such completeness that it can be reproduced on the plans.
+The level survey consists in taking levels on cross sections of the
+road at one hundred foot intervals, and oftener if there are abrupt
+changes in grade. Special level determinations are made at streams,
+railroad crossings, intersecting roads or lanes and wherever it
+appears some special features of the terrain should be recorded.</p>
+
+<p>From the surveys and such other information as has been assembled
+relative to the project, a plan is prepared which embodies a design
+presumed to provide for an improvement in accordance with the best
+highway practice.</p>
+
+
+<h4 class="sc">The Problem of Design</h4>
+
+<p>It will be convenient to consider separately the components of a road
+design, although in the actual design the<span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span> consideration of these
+cannot be separated because all parts of the plan must fit together.</p>
+
+<p><b>Alignment.</b>&mdash;The alignment of the road is determined to a considerable
+extent by the existing right-of-way, which may follow section lines,
+regardless of topography, as is the case with many roads in the
+prairie states, or it may follow the valleys, ridges, or other
+favorable location in hilly country. In many places the roads of
+necessity wind around among the hills in order to avoid excessive
+grades. In designing an improvement, it is generally desirable to
+follow the existing right-of-way so far as possible. But the element
+of safety must not be lost sight of, and curves should not preclude a
+view ahead for sufficient distance to insure safety to vehicles. The
+necessary length of clear view ahead is usually assumed to be 250
+feet, but probably 200 feet is a satisfactory compromise distance when
+a greater distance cannot be obtained at reasonable cost. To secure
+suitable sight distance, the curves must be of long radii, and where
+possible the right-of-way on the inside of the curve should be cleared
+of trees or brush that will obstruct the view. Where the topography
+will not permit a long radius curve and the view is obstructed by an
+embankment or by growing crops or other growth, it is desirable to
+separate the tracks around the curve to eliminate the possibility of
+accidents on the curve. This is readily accomplished if the road is
+surfaced, but if it is not surfaced, the same end is accomplished by
+making the earth road of ample width at the curve.</p>
+
+<p>Relocations should be resorted to whenever they shorten distances or
+reduce grades sufficiently to compensate for the cost.</p>
+
+<p><b>Intersections.</b>&mdash;At road intersections, it is always difficult to
+design a curve that entirely meets the requirements of safety because
+there is not enough room in the right-of-way, and enough additional
+right-of-way must be secured<span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span> to permit the proper design. It is not
+necessary to provide an intersection that is adapted to high speed
+traffic, where main roads cross, but, on the contrary, a design that
+automatically causes traffic to slow up has distinct advantages.</p>
+
+<p>Where a main route, improved with a hard surface, crosses secondary
+roads, it is satisfactory to continue the paved surface across the
+intersecting road at normal width and make no provision for the
+intersecting road traffic other than a properly graded approach at the
+intersection.</p>
+
+<p><b>Superelevation.</b>&mdash;On all curved sections of road, other than
+intersections, account is taken of the tendency of motor cars to skid
+toward the outside of the curve. This tendency is counteracted by
+designing the cross section with superelevation.</p>
+
+<div class="figcenter" style="width: 381px;">
+<img src="images/i0058.png" width="381" height="244" alt="Fig. 6" title="" />
+<span class="caption">Fig. 6</span>
+</div>
+
+<p>In Fig. 6, <i>F</i> represents the tangential force that tends to cause
+skidding. <i>W</i> represents the weight of the vehicle in pounds, <i>&theta;</i>
+= the angle of superelevated surface <i>c-d</i>, with the horizontal <i>c-a</i>.
+<i>R</i> represents the radius of the curve upon which the vehicle is
+moving. <i>w</i> is the component of the weight parallel to the surface
+<i>c-d</i>, <i>v</i> = velocity<span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span> of the vehicle in feet per second. <i>m</i> = mass
+of vehicle = <sup><i>W</i></sup>&frasl;<sub><i>g</i></sub><i>&nbsp;&nbsp;&theta;</i></p>
+
+<p class="center">
+<i>w = W</i> tan <i>&theta;</i></p>
+
+<div class="center">
+<table class="fraction math" cellpadding="0" cellspacing="0" summary="Formula">
+    <tr>
+        <td rowspan="2"><i>F</i> =</td>
+        <td><i>mv</i><sup>2</sup></td>
+        <td rowspan="2"> = </td>
+        <td><i>wv</i><sup>2</sup></td>
+    </tr>
+    <tr>
+        <td class="upper_line"><i>R</i></td>
+        <td class="upper_line"><i>gR</i></td>
+    </tr>
+</table>
+</div>
+
+<p>If <i>F = w</i> there will be no tendency to skid; hence the rate of
+superelevation necessary in any case is as follows:</p>
+
+<div class="center">
+<table class="fraction math" cellpadding="0" cellspacing="0" summary="Formula">
+    <tr>
+        <td rowspan="2"><i>W</i> tan <i>&theta;</i> =</td>
+        <td><i>Wv</i><sup>2</sup></td>
+    </tr>
+    <tr>
+        <td class="upper_line"><i>gR</i></td>
+    </tr>
+</table>
+
+<table class="fraction math" cellpadding="0" cellspacing="0" summary="Formula">
+    <tr>
+        <td rowspan="2">tan <i>&theta;</i> =</td>
+        <td><i>v</i><sup>2</sup></td>
+    </tr>
+    <tr>
+        <td class="upper_line"><i>gR</i></td>
+    </tr>
+</table>
+</div>
+
+<p>The amount of superelevation required, therefore, varies as the square
+of the velocity and inversely as the radius of the curve.</p>
+
+<p>Theoretically, the amount of the superelevation should increase with a
+decrease in the radius of the curve and should also increase as the
+square of the speed of the vehicle. On account of the variation in
+speeds of the vehicles, the superelevation for curves on a highway can
+only be designed to suit the average speed. At turns approaching
+ninety degrees, the curve is likely to be of such short radius that it
+is impossible to maintain the ordinary road speed around the curve,
+even with the maximum superelevation permissible. It is good practice
+to provide the theoretical superelevation on all curves having radii
+greater than 300 feet for vehicle speeds of the maximum allowed by
+law, which is generally about 25 miles per hour. Where the radii are
+less than 300 feet, the theoretical superelevation for the maximum
+vehicle speeds gives a superelevation too great for motor trucks and
+horse drawn vehicles and generally no charge is made in superelevation
+for radii less than 300 feet, but all such curves are constructed with
+the same superelevation as the curve with 300 foot radius.<span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span></p>
+
+<p>The diagram in Fig. 7 shows the theoretical superelevation for various
+curve radii.</p>
+
+<div class="figcenter" style="width: 436px;">
+<img src="images/i0060.png" width="436" height="473" alt="Fig. 7. Curves showing Theoretical Superelevation for
+Various Degrees of Curve for Various Speeds of Vehicle" title="" />
+<span class="caption">Fig. 7. Curves showing Theoretical Superelevation for
+Various Degrees of Curve for Various Speeds of Vehicle</span>
+</div>
+
+<p>At the intersection of important highways, the problem is complicated
+by the necessity for providing for through traffic in both directions
+and for traffic which may turn in either direction and the engineer
+must provide safe roadways for each class of traffic.</p>
+
+<p><b>Tractive Resistance.</b>&mdash;The adoption of a policy regarding the grades on
+a road involves an understanding of the effect of variation in the
+character of the surface and in rate of grade upon the energy required
+to transport a load<span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span> over the highway. The forces that oppose the
+movement of a horse drawn vehicle are fairly well understood and their
+magnitude has been measured by several observers, but comparatively
+little is known about the forces opposing translation of rubber tired
+self-propelled vehicles.</p>
+
+<p>The resistance to translation of a vehicle is made up of three
+elements: resistance of the road surface to the rolling wheel,
+resistance of the air to the movement of the vehicle and internal
+friction in the vehicle itself.</p>
+
+<p><b>Rolling Resistance.</b>&mdash;When the wheel of a vehicle rolls over a road
+surface, both the wheel and the surface are distorted. If the wheel
+has steel tires and the road surface is plastic, there will be
+considerable distortion of the road surface and very little of the
+wheel. A soft rubber tire will be distorted considerably by a brick
+road surface. Between these extremes there are innumerable
+combinations of tire and road surface encountered, but there is always
+a certain amount of distortion of either road surface or wheel, or of
+both, which has the same effect upon the force necessary for
+translation as a slight upward grade. When both the tire and the road
+surface strongly resist distortion (as steel tires on vitrified brick
+paving), the resistance to translation is low but the factor of impact
+is likely to be introduced. Where impact is present, energy is used up
+in the pounding and grinding of the wheels on the surface, and this
+factor increases as the speed of translation, and may be a
+considerable item. Impact is especially significant on rough roads
+with motor vehicles, particularly trucks, traveling at high speed.
+These two factors (impact and rolling resistance) combined constitute
+the major part of the resistance to translation for horse drawn
+vehicles.</p>
+
+<p><b>Internal Resistance.</b>&mdash;For horse drawn vehicles, the internal
+resistance consists of axle friction, which is small in amount. For
+self-propelled vehicles, the internal resistance consists of axle
+friction and friction in the driving<span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span> mechanism, of which gear
+friction and the churning of oil in the gear boxes is a large item.
+Internal friction is of significance in all self-propelled vehicles
+and especially so at high speeds.</p>
+
+<p><b>Air Resistance.</b>&mdash;At slow speeds, the resistance of still air to
+translation is small, but as the speed increases, the air resistance
+increases rapidly and at the usual speed of the passenger automobile
+on the road becomes a very considerable part of the total resistance
+to translation. This factor has no significance in connection with
+horse drawn vehicles, but is to be taken into account when dealing
+with self-propelled vehicles at speeds in excess of five miles per
+hour.</p>
+
+<p>Many determinations of tractive resistance with horse drawn vehicles
+have been made from time to time and these show values that are fairly
+consistent when the inevitable variations in surfaces of the same type
+are taken into account. Table 4 is a composite made up of values
+selected from various reliable sources and Table 5 is from experiments
+by Professor J. B. Davidson on California highways.</p>
+
+<h4 class="sc">Table 4</h4>
+<h4 class="sc">Average Tractive Resistance of Road Surfaces to Steel Tired
+Vehicles</h4>
+
+
+<div class="center">
+<table summary="Tractive Resistances">
+<tr><td class="center">Surface</td><td class="center">Tractive force per ton</td></tr>
+<tr><td class="left">Earth packed and dry</td><td class="right">100</td></tr>
+<tr><td class="left">Earth dusty</td><td class="right">106</td></tr>
+<tr><td class="left">Earth muddy</td><td class="right">190</td></tr>
+<tr><td class="left">Sand loose</td><td class="right">320</td></tr>
+<tr><td class="left">Gravel good</td><td class="right">51</td></tr>
+<tr><td class="left">Gravel loose</td><td class="right">147</td></tr>
+<tr><td class="left">Cinders well-packed</td><td class="right">92</td></tr>
+<tr><td class="left">Oiled road&mdash;dry</td><td class="right">61</td></tr>
+<tr><td class="left">Oiled road&mdash;wet</td><td class="right">108</td></tr>
+<tr><td class="left">Macadam&mdash;very good</td><td class="right">38</td></tr>
+<tr><td class="left">Macadam&mdash;average</td><td class="right">46</td></tr>
+<tr><td class="left">Sheet asphalt</td><td class="right">38</td></tr>
+<tr><td class="left">Asphaltic concrete</td><td class="right">40</td></tr>
+<tr><td class="left">Vitrified brick&mdash;new</td><td class="right">56</td></tr>
+<tr><td class="left">Wood block&mdash;good</td><td class="right">33</td></tr>
+<tr><td class="left">Wood block&mdash;poor</td><td class="right">42<span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span></td></tr>
+<tr><td class="left">Cobblestone</td><td class="right">54</td></tr>
+<tr><td class="left">Granite tramway</td><td class="right">27</td></tr>
+<tr><td class="left">Asphalt block</td><td class="right">52</td></tr>
+<tr><td class="left">Granite block</td><td class="right">47</td></tr>
+</table></div>
+
+
+<h4 class="sc">Table 5</h4>
+<h4 class="sc">Tractive Resistances to Steel Tired Vehicles<a name="FNanchor_1_6" id="FNanchor_1_6"></a><a href="#Footnote_1_6" class="fnanchor">[1]</a></h4>
+
+
+
+<div class="center">
+<table class="dense" summary="Tractive Resistance to Steel Tired Vehicles">
+<tr><td class="bt bb center">Test No.</td><td class="bt bb center">Kind of Road</td><td class="bt bb center">Condition of Road</td><td class="bt bb center">Tractive<br />Total lb.</td><td class="bt bb center">Resistance<br />per ton lb.</td></tr>
+<tr><td class="right">29-30-31</td><td class="left">Concrete (unsurfaced)</td><td class="left">Good, excellent</td><td class="right">83.0</td><td class="right">27.6</td></tr>
+<tr><td class="right"><a name="FNanchor_2_7" id="FNanchor_2_7"></a><a href="#Footnote_2_7" class="fnanchor">[2]</a>11-12</td><td class="left">Concrete (unsurfaced)</td><td class="left">Good, excellent</td><td class="right">90.0</td><td class="right">30.0</td></tr>
+<tr><td class="right">26-27-28</td><td class="left">Concrete 3/8-in. surface asphaltic oil and screenings</td><td class="left">Good, excellent</td><td class="right">147.6</td><td class="right">49.2</td></tr>
+<tr><td class="right">13-14</td><td class="left">Concrete 3/8-in. surface asphaltic oil and screenings</td><td class="left">Good, excellent</td><td class="right">155.0</td><td class="right">51.6</td></tr>
+<tr><td class="right">9-10</td><td class="left">Macadam, water-bound</td><td class="left">Good, excellent</td><td class="right">193.0</td><td class="right">64.3</td></tr>
+<tr><td class="right">22-23</td><td class="left">Topeka on concrete</td><td class="left">Good, excellent</td><td class="right">205.5</td><td class="right">68.5</td></tr>
+<tr><td class="right">8</td><td class="left">Gravel</td><td class="left">Compact, good condition</td><td class="right">225.0</td><td class="right">75.0</td></tr>
+<tr><td class="right"><a name="FNanchor_3_8" id="FNanchor_3_8"></a><a href="#Footnote_3_8" class="fnanchor">[3]</a>45-48</td><td class="left">Oil macadam</td><td class="left">Good, new</td><td class="right">234.5</td><td class="right">78.2</td></tr>
+<tr><td class="right"><a name="FNanchor_4_9" id="FNanchor_4_9"></a><a href="#Footnote_4_9" class="fnanchor">[4]</a>46-47</td><td class="left">Oil macadam</td><td class="left">Good, new</td><td class="right">244.0</td><td class="right">81.3</td></tr>
+<tr><td class="right">38</td><td class="left">Gravel</td><td class="left">Packed, in good condition</td><td class="right">247.0</td><td class="right">82.3</td></tr>
+<tr><td class="right">18-19-20</td><td class="left">Topeka on plank</td><td class="left">Good condition, soft, wagon left marks</td><td class="right">265.0</td><td class="right">88.3</td></tr>
+<tr><td class="right">34</td><td class="left">Earth road</td><td class="left">Firm, 1&frac12;-in. fine loose dust</td><td class="right">276.0</td><td class="right">92.0</td></tr>
+<tr><td class="right">24-25</td><td class="left">Topeka on plank</td><td class="left">Good condition, but soft</td><td class="right">278.0</td><td class="right">92.6</td></tr>
+<tr><td class="right">1-2-5</td><td class="left">Earth road</td><td class="left">Dust &frac34; to 2 in.</td><td class="right">298.0</td><td class="right">99.3</td></tr>
+<tr><td class="right">3-3</td><td class="left">Earth</td><td class="left">Mud, stiff, firm underneath</td><td class="right">654.0</td><td class="right">218.0</td></tr>
+<tr><td class="bb right">6-7</td><td class="bb left">Gravel</td><td class="bb left">Loose, not packed</td><td class="bb right">789.0</td><td class="bb right">263.0</td></tr>
+</table></div>
+
+
+<div class="footnote"><p><a name="Footnote_1_6" id="Footnote_1_6"></a><a href="#FNanchor_1_6"><span class="label">[1]</span></a> Prof. J. B. Davidson in <i>Engineering News-Record</i>, August
+17, 1918.</p></div>
+
+<div class="footnote"><p><a name="Footnote_2_7" id="Footnote_2_7"></a><a href="#FNanchor_2_7"><span class="label">[2]</span></a> Graphic record indicates that the load was being
+accelerated when test was started.</p></div>
+
+<div class="footnote"><p><a name="Footnote_3_8" id="Footnote_3_8"></a><a href="#FNanchor_3_8"><span class="label">[3]</span></a> Drawn with motor truck at 2&frac12; miles per hour.</p></div>
+
+<div class="footnote"><p><a name="Footnote_4_9" id="Footnote_4_9"></a><a href="#FNanchor_4_9"><span class="label">[4]</span></a> Drawn with motor truck at 5 miles per hour.<span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span></p></div>
+
+<p>Comparatively few data are available showing the tractive resistance
+of motor vehicles, but the following tables are based on sufficient
+data to serve to illustrate the general trend.</p>
+
+<p>These data on the tractive resistances of an electric truck with solid
+rubber tires on asphalt and bitulithic, wood, brick and granite block,
+water-bonded and tar macadam, cinder and gravel road surfaces were
+obtained by A. E. Kennelly and O. R. Schurig in the research division
+of the electrical engineering department of the Massachusetts
+Institute of Technology, and are published in Bulletin No. 10 of the
+division.</p>
+
+<p>An electric truck was run over measured sections, ranging from 400 to
+2600 feet in length, surfaced with these various materials, at certain
+speeds per hour, ranging from about 8 to about 15.5 miles per hour.
+The result of the observations of speeds, tractive resistances,
+conditions of surfaces, etc., were collected and studied in various
+combinations.</p>
+
+<h4 class="sc">Table 6</h4>
+
+
+<div class="center">
+<table summary="Tractive Resistance Studies">
+<tr><td class="bt bb center">Type of Surface</td><td class="bt bb bl center">Condition of Surface</td><td class="bt bb bl center">Tractive<br />Resistance<br />in lbs.<br />per ton<br />10 miles<br />per hr.</td><td class="bt bb bl center">Tractive<br />Resistance<br />in lbs.<br />per ton<br />12.4 miles<br />per hr.</td></tr>
+<tr><td class="left">Asphalt</td><td class="bl left">Good</td><td class="bl right">20.4</td><td class="bl">&nbsp;</td></tr>
+<tr><td class="left">Asphalt</td><td class="bl left">Poor</td><td class="bl right">22.6</td><td class="bl right">25.5</td></tr>
+<tr><td class="left">Wood block</td><td class="bl left">Good</td><td class="bl right">24.2</td><td class="bl right">25.3</td></tr>
+<tr><td class="left">Brick block</td><td class="bl left">Good</td><td class="bl right">24.6</td><td class="bl right">26.6</td></tr>
+<tr><td class="left">Granite block</td><td class="bl left">Good</td><td class="bl right">40.3</td><td class="bl right">45.75</td></tr>
+<tr><td class="left">Brick block</td><td class="bl left">Slightly worn</td><td class="bl right">25.1</td><td class="bl right">28.0</td></tr>
+<tr><td class="left">Granite block with cement joints</td><td class="bl left">Good</td><td class="bl right">25.5</td><td class="bl right">30.2</td></tr>
+<tr><td class="left">Macadam, water bonded</td><td class="bl left">Dry and hard</td><td class="bl right">23.3</td><td class="bl right">25.8</td></tr>
+<tr><td class="left">Macadam, water bonded</td><td class="bl left">Fair, heavily oiled</td><td class="bl right">35.9</td><td class="bl right">38.7</td></tr>
+<tr><td class="left">Macadam, water bonded</td><td class="bl left">Poor, damp, some holes</td><td class="bl right">36.3</td><td class="bl right">41.6</td></tr>
+<tr><td class="left">Tar macadam</td><td class="bl left">Good</td><td class="bl right">25.7</td><td class="bl right">28.0</td></tr>
+<tr><td class="left">Tar macadam</td><td class="bl left">Very soft</td><td class="bl right">36.8</td><td class="bl right">38.7</td></tr>
+<tr><td class="left">Tar macadam</td><td class="bl left">Many holes, soft, extremely poor</td><td class="bl right">52.4</td><td class="bl right">60.6</td></tr>
+<tr><td class="left">Cinder</td><td class="bl left">Fair, hard</td><td class="bl right">27.5</td><td class="bl right">30.6</td></tr>
+<tr><td class="bb left">Gravel</td><td class="bb bl left">Fair, dusty</td><td class="bb bl right">30.4</td><td class="bb bl right">33.0</td></tr>
+</table></div>
+
+
+<p><span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span></p>
+
+<div class="figcenter" style="width: 437px;">
+<img src="images/i0065.png" width="437" height="265" alt="Fig. 8" title="" />
+<span class="caption">Fig. 8</span>
+</div>
+
+<p><b>Effect of Grades.</b>&mdash;Grades increase or decrease the resistance to
+translation due to the fact that there is a component of the weight of
+the vehicles parallel to the road surface and opposite in direction to
+the motion when the load is ascending the hill and in the same
+direction when the vehicle is descending. In Fig. 8 <i>W</i> represents the
+weight of the vehicle, acting vertically downward, <i>w</i> is the
+component of the weight perpendicular to the road surface and <i>W</i><sub>2</sub>
+is the component parallel to the road surface.</p>
+
+
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="Formula">
+<tr><td align="right"><i>W</i><sub>2</sub></td><td align="center">=</td><td align="left"><i>W</i> tan <i>&theta;</i>.</td></tr>
+<tr><td align="right">tan <i>&theta;</i></td><td align="center">=</td><td align="left">0.01 × per cent of grade.</td></tr>
+<tr><td align="right"><i>W</i><sub>2</sub></td><td align="center">=</td><td align="left">0.01 <i>W</i> × per cent grade.</td></tr>
+<tr><td align="right"><i>W</i><sub>2</sub></td><td align="center">=</td><td align="left">0.01 × 2000 × per cent of grade, for each ton of weight of vehicle.</td></tr>
+<tr><td align="right">Hence <i>W</i><sub>2</sub></td><td align="center">=</td><td align="left">20 lbs. per ton of load for each one per cent of grade.</td></tr>
+</table></div>
+
+<p>The gravity force acting upon a vehicle parallel to the surface on a
+grade is therefore 20 lbs. per ton for each one per cent of grade and
+this force tends either to retard or to accelerate the movement of the
+vehicle.<span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span></p>
+
+<p>Let <i>F</i> = the sum of all forces opposing the translation of a vehicle.</p>
+
+<p class="center">
+<i>F = f<sub>r</sub> + f<sub>i</sub> + f<sub>p</sub> + f<sub>a</sub> + f<sub>g</sub></i>&nbsp;&nbsp;&nbsp;&nbsp;  (1)
+</p>
+
+<p>where</p>
+
+<p>
+<span style="margin-left: 1em;"><i>f<sub>r</sub></i> = rolling resistance of road surface.</span><br />
+<span style="margin-left: 1em;"><i>f<sub>i</sub></i> = resistance due to internal friction in the vehicle.</span><br />
+<span style="margin-left: 1em;"><i>f<sub>p</sub></i> = resistance due to impact of the road surface.</span><br />
+<span style="margin-left: 1em;"><i>f<sub>a</sub></i> = resistance due to air.</span><br />
+<span style="margin-left: 1em;"><i>f<sub>g</sub></i> = resistance due to grade, which is positive when
+ascending and negative when descending.</span><br />
+</p>
+
+<p>All of the above in pounds per ton of 2000 lbs.</p>
+
+<p>Let <i>T</i> = the tractive effort applied to the vehicle by any means.</p>
+
+<p><i>T</i> &gt;= must be greater than <i>F</i> in order to move the vehicle.</p>
+
+<p>By an inspection of (1), it will be seen that for a given vehicle and
+any type of road surface, all terms are constant except <i>f<sub>a</sub></i> and
+<i>f<sub>g</sub></i>. <i>f<sub>a</sub></i> varies as the speed of the vehicle and the driver can
+materially decrease <i>f<sub>a</sub></i> by reducing speed. <i>f<sub>g</sub></i> varies with the
+rate of grade. For any vehicle loaded for satisfactory operation on a
+level road with the power available, the limiting condition is the
+factor <i>f<sub>g</sub></i>. If the load is such as barely to permit motion on a
+level road, any hill will stall the vehicle. Therefore, in practice
+the load is always so adjusted that there is an excess of power on a
+level road. If draft animals are employed the load is usually about
+one fourth of that which the animals could actually move by their
+maximum effort for a short period. With motor vehicles, the excess
+power is provided for by gearing.</p>
+
+<p>If it be assured a load of convenient size is being moved on a level
+road by draft animals, there is a limit to the rate of grade up which
+the load can be drawn by the maximum effort of the animals.</p>
+
+<p>Tests indicate that the horse can pull at a speed of 2&frac12;<span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span> miles per
+hour, an amount equal to 1/8 to 1/10 of its weight, and for short
+intervals can pull &frac34; of its weight. The maximum effort possible is
+therefore six times the average pull, but this is possible for only
+short intervals. A very short steep hill would afford a condition
+where such effort would be utilized. But for hills of any length, that
+is, one hundred feet or more but not to exceed five hundred feet, it
+is safe to count on the draft animal pulling three times his normal
+pulling power for sustained effort.</p>
+
+<p>The limiting grade for the horse drawn vehicle is therefore one
+requiring, to overcome the effect of grade, or <i>f<sub>g</sub></i>, a pull in
+excess of three times that exerted on the level.</p>
+
+<p>A team of draft animals weighing 1800 lbs. each could exert a
+continuous pull of about 1/10 of their weight or 360 lbs. If it be
+assumed that the character of the vehicle and the road surface is such
+that <i>f<sub>r</sub></i> + <i>f<sub>i</sub></i> + <i>f<sub>p</sub></i> + <i>f<sub>a</sub></i> = 100 lbs. per gross ton on
+a level section of road, then the gross load for the team would be 3.6
+tons. The same team could for a short time exert an additional pull of
+three times 360 lbs. or 1080 lbs. For each 1 per cent of grade a pull
+of 20 lbs. per ton would be required or <i>f<sub>g</sub></i> for the 3.6 tons load
+would be 72 lbs. for each per cent of grade. At that rate, the
+limiting grade for the team would be fifteen per cent.</p>
+
+<p>If, however, the character of the vehicle and the road surface were
+such that <i>f<sub>r</sub></i> + <i>f<sub>i</sub></i> + <i>f<sub>p</sub></i> + <i>f<sub>a</sub></i> = 60 lbs. per gross
+ton on a level section of road, the gross load for the team on the
+level would be 6 tons, and the limiting grade 9 per cent.</p>
+
+<p>The above discussion serves to illustrate the desirability of adopting
+a low ruling or limiting grade for roads to be surfaced with a
+material having low tractive resistance and the poor economy of
+adopting a low ruling grade for earth roads or roads to be surfaced
+with material of high tractive resistance.</p>
+
+<p>It may be questioned whether horse drawn traffic should be the
+limiting consideration for main trunk line highways,<span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span> but it is
+certain that for a number of years horse drawn traffic will be a
+factor on secondary roads.</p>
+
+<p>In the case of motor vehicles, excess power is provided by means of
+gears and no difficulty is encountered in moving vehicles over grades
+up to 12 or 15 per cent, so that any grade that would ordinarily be
+tolerated on a main highway will present no obstacle to motor
+vehicles, but the economy of such design is yet to be investigated.</p>
+
+<p><b>Energy Loss on Account of Grades.</b>&mdash;Whether a vehicle is horse drawn or
+motor driven, energy has been expended in moving it up a hill. A part
+of this energy has been required to overcome the various resistances
+other than grade, and that has been dissipated, but the energy
+required to translate the vehicle against the resistance due to grade
+has been transformed into potential energy and can be partially or
+wholly recovered when the vehicle descends a grade, provided the
+physical conditions permit its utilization. If the grade is so steep
+as to cause the vehicle to accelerate rapidly, the brakes must be
+applied and loss of energy results. The coasting grade is dependent
+upon the character of the surface and the nature of the vehicle. In
+the cases discussed in the preceding paragraph, the coasting grades
+would be five per cent and three per cent respectively. For horse
+drawn vehicles then the economical grades would be three and five per
+cent, which again emphasizes the necessity of lower grades on roads
+that are surfaced than on roads with no wearing surface other than the
+natural soil.</p>
+
+<p>The theory of grades is somewhat different when motor vehicles are
+considered, since it is allowable to permit considerably higher speed
+than with horse drawn vehicles before applying the brakes and the
+effect of grade can be utilized not only in translating the vehicle
+down the grade, but also in overcoming resistances due to mechanical
+friction and the air. On long grades, a speed might be attained that
+would require the use of the brake or the same<span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span> condition might apply
+on very steep short grades. There is at present insufficient data on
+the tractive resistance and air resistance with motor vehicles to
+permit the establishing of rules relative to grade, but experience
+indicates a few general principles that may be accepted.</p>
+
+<p>If a hill is of such rate of grade and of such length that it is not
+necessary to use the brake it may be assumed that no energy loss
+results so far as motor vehicles are concerned. Where there is no turn
+at the bottom of the hill and the physical condition of the road
+permits speeds up to thirty-five or forty miles per hour grades of
+five per cent are permissible if the length does not exceed five
+hundred feet and grades of three per cent one thousand feet long are
+allowable. It is a rather settled conviction among highway engineers
+that on trunk line highways the maximum grade should be six per cent,
+unless a very large amount of grading is necessary to reach that
+grade.</p>
+
+<p><b>Undulating Roads.</b>&mdash;Many hills exist upon highways, the grade of which
+is much below the maximum permissible. If there are grades ranging
+from 0 to 4 per cent, with a few hills upon which it is impracticable
+to reach a grade of less than six per cent, it is questionable economy
+to reduce the grades that are already lower than the allowable
+maximum. It is especially unjustifiable to incur expense in reducing a
+grade from two per cent to one and one-half per cent on a road upon
+which there are also grades in excess of that amount. The undulating
+road is not uneconomical unless the grades are above the allowable
+maximum or are exceptionally long or the alignment follows short
+radius curves.</p>
+
+<p><b>Safety Considerations.</b>&mdash;On hills it is especially desirable to provide
+for safety and curves on hills are always more dangerous than on level
+sections of road. Therefore, it is desirable to provide as flat grades
+as possible at the curves and to cut away the berm at the side of the
+road so as to give a view ahead for about three hundred feet.<span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span> Whether
+a road be level or on a hill, safety should always be considered and
+the most important safety precaution is to provide a clear view ahead
+for a sufficient distance to enable motor vehicle drivers to avoid
+accidents.</p>
+
+<div class="figcenter" style="width: 474px;">
+<img src="images/i0070.png" width="474" height="167" alt="Fig. 9.&mdash;Types of Guard Rails" title="" />
+<span class="caption">Fig. 9.&mdash;Types of Guard Rails</span>
+</div>
+
+<p><b>Guard Railing.</b>&mdash;When a section of road is on an embankment, guard
+rails are provided at the top of the side slope to serve as warnings
+of danger, and to prevent vehicles from actually going over the
+embankment in case of skidding, or if for any reason the driver loses
+control. These are usually strongly built, but would hardly restrain a
+vehicle which struck at high speed. But they are adequate for the
+protection of a driver who uses reasonable care. A typical guard rail
+is shown in Fig. 9, but many other designs of similar nature are
+employed. At very dangerous turns a solid plank wall six or eight feet
+high is sometimes built of such substantial construction as to
+withstand the severest shock without being displaced.</p>
+
+<p>Trees, shrubs and the berms at the side of the road in cuts are
+particularly likely to obstruct the view and should be cleared or cut
+back so far as is necessary to provide the proper sight distance.</p>
+
+<p><b>Width of Roadway.</b>&mdash;For roads carrying mixed traffic, 9 feet of width
+is needed for a single line of vehicles and 18 feet for 2 lines of
+vehicles. In accordance with the above, secondary roads, carrying
+perhaps 25 to 50 vehicles<span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span> per day, may have an available traveled way
+18 feet wide. Those more heavily traveled may require room for three
+vehicles to pass at any place and therefore have an available traveled
+way 30 feet wide. Greater width is seldom required on rural highways,
+and 20 feet is the prevailing width for main highways.</p>
+
+<p><b>Cross Section.</b>&mdash;The cross section of the road is designed to give the
+required width of traveled way, and, in addition, provide the drainage
+channels that may be needed. In regions of small rainfall the side
+ditches will be of small capacity or may be entirely omitted, but
+usually some ditch is provided. The transition from the traveled way
+to ditch should be a gradual slope so as to avoid the danger incident
+to abrupt change in the shape of the cross section. The depth of ditch
+may be varied without changing to width or slope of the traveled part
+of the road as shown in Fig. 10.</p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/i0071.png" width="500" height="376" alt="Fig. 10" title="" />
+<span class="caption">Fig. 10</span>
+</div>
+
+<p><span class="pagenum"><a name="Page_61" id="Page_61">[Pg 61]</a></span></p>
+
+<p><b>Control of Erosion.</b>&mdash;The construction of a highway may be utilized to
+control general erosion to some extent, particularly when public
+highways exist every mile or two and are laid out on a gridiron
+system, as is the case in many of the prairie states. The streams
+cross the highways at frequent intervals and the culverts can be
+placed so as effectually to prevent an increase in depth of the
+stream. This will to some extent limit the erosion above the culvert
+and if such culverts are built every mile or two along the stream,
+considerable effect is produced.</p>
+
+<p>Where small streams have their origin a short distance from a culvert
+under which they pass, it is sometimes advisable to provide tile for
+carrying the water under the road, instead of the culvert, and, by
+continuing the tile into the drainage area of the culvert, eliminate
+the flow of surface water and reclaim considerable areas of land.</p>
+
+<p>Erosion in the ditches along a highway can be prevented by
+constructing weirs across the ditch at frequent intervals, thus
+effectually preventing an increase in the depth of the ditch.</p>
+
+<p>Wherever water flows at a velocity sufficient to produce erosion or
+where the drainage channel changes abruptly from a higher to a lower
+level, paved gutters, tile or pipe channels should be employed to
+prevent erosion.</p>
+
+<p><b>Private Entrances.</b>&mdash;Entrance to private property along the highway is
+by means of driveways leading off the main road. These should always
+be provided for in the design so as to insure easy and convenient
+access to the property. The driveways will usually cross the side
+ditch along the road and culverts will be required to carry the water
+under the driveway. Driveways that cross a gutter by means of a
+pavement in the gutter are usually unsatisfactory, and to cross the
+gutter without providing a pavement is to insure stoppage of the flow
+at the crossing. The culvert at a driveway entrance must be large
+enough to take the ditch water readily or it will divert the water to
+the roadway<span class="pagenum"><a name="Page_62" id="Page_62">[Pg 62]</a></span> itself. Generally end walls on such culverts are not
+required as in the case of culverts across a highway.</p>
+
+<p><b>Aesthetics.</b>&mdash;Much of the traffic on the public highways is for
+pleasure and relaxation and anything that tends to increase the
+attractiveness of the highways is to be encouraged. Usually the
+roadside is a mass of bloom in the fall, goldenrod, asters and other
+hardy annuals being especially beautiful. In some states wild roses
+and other low bushes are planted to serve the two-fold purpose of
+assisting to prevent erosion and to beautify the roadside. In humid
+areas trees of any considerable size shade the road surface and are a
+distinct disadvantage to roads surfaced with the less durable
+materials such as sand-clay or gravel. It is doubtful if the same is
+true of paved surfaces, but the trees should be far enough back from
+the traveled way to afford a clear view ahead. Shrubs are not
+objectionable from any view-point and are to be encouraged for their
+beauty, so long as they do not obstruct the view at turns.</p>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_63" id="Page_63">[Pg 63]</a></span></p>
+<h2><a name="Chapter_V" id="Chapter_V"></a><span class="smcap">Chapter V</span></h2>
+
+<h3>EARTH ROADS</h3>
+
+
+<p>Highways constructed without the addition of surfacing material to the
+natural soil of the right-of-way are usually called earth roads. But
+if the natural soil exhibits peculiar characteristics or is of a
+distinct type, the road may be referred to by some distinctive name
+indicating that fact. Hence, roads are referred to as clay, gumbo,
+sandy or caliche roads as local custom may elect. In each case,
+however, the wearing surface consists of the natural soil, which may
+have been shaped and smoothed for traffic or may be in its natural
+state except for a trackway formed by the vehicles that have used it.</p>
+
+<p><b>Variations in Soils.</b>&mdash;The nature of the existing soil will obviously
+determine the serviceability and physical characteristics of the road
+surface it affords. That is to say that even under the most favorable
+conditions some earth roads will be much more serviceable than others,
+due to the better stability of the natural soil. Some soils are dense
+and somewhat tough when dry and therefore resist to a degree the
+tendency of vehicles to grind away the particles and dissipate them in
+the form of dust. Such soils retain a reasonably smooth trackway in
+dry weather even when subjected to considerable traffic. Other soils
+do not possess the inherent tenacity and stability to enable them to
+resist the action of wheels and consequently grind away rapidly. Roads
+on such soils become very dusty. These are the extremes and between
+them are many types of soils or mixtures of soils possessing varying
+degrees of stability, and, in consequence, differing rates of wear.<span class="pagenum"><a name="Page_64" id="Page_64">[Pg 64]</a></span>
+Similarly the various soils exhibit different degrees of stability
+when wet.</p>
+
+<p>It is to be expected that soils will differ with the geographical
+location, for it is well known that there is a great variation in
+soils in the various parts of the world. But wide differences are also
+encountered in the soil on roads very near each other and even on
+successive stretches of the same road. It is for this reason that
+earth roads often exhibit great differences in serviceability even in
+a restricted area.</p>
+
+<p><b>Variation in Rainfall.</b>&mdash;The stability of a soil and its ability to
+support the weight of vehicles varies greatly with the amount of water
+in the soil. A certain small amount of moisture in the soil is
+beneficial in that practically every soil compacts more readily when
+moist than when dry because the moisture aids in binding together the
+particles. But most soils also become unstable when the amount of
+water present is in excess of that small amount referred to above and
+the stability decreases very rapidly as the amount of water in the
+soil increases.</p>
+
+<p>The serviceability of an earth road will change continually as the
+moisture content of the soil changes and consequently the general
+utility of the earth road system in any locality is dependent to a
+considerable extent upon the amount and seasonal distribution of
+precipitation. The methods of maintaining earth roads appropriate to
+any locality must of necessity be adapted to the climatic conditions,
+and the amount of work required to give the highest possible degree of
+serviceability will be exceedingly variable from season to season and
+from place to place. In regions of great humidity, earth roads may be
+expected to have a low average of serviceability, while in arid
+regions they may possess sufficient durability for a considerable
+volume of traffic. The design adopted for earth roads and the methods
+of maintenance followed should therefore be carefully evolved to meet
+the soil and climate conditions<span class="pagenum"><a name="Page_65" id="Page_65">[Pg 65]</a></span> where the roads are located. These
+will differ greatly throughout a state or even a county.</p>
+
+<p><b>Cross Sections.</b>&mdash;The general principles of road design were set forth
+in Chapter IV. In Fig. 11 are shown typical cross sections for earth
+roads adapted to various conditions as indicated. It is not apparent
+that one form of ditch is particularly preferable to the other and
+since some engineers prefer the V section and others the trapezoidal
+section both are shown. It would appear that the V shaped ditch is
+somewhat the easier to construct with the blade grader while the
+trapezoidal is readily excavated with the slip or fresno scraper. The
+ditch capacity required and consequently the dimensions will depend
+upon the drainage requirements, as was pointed out in Chapter III.</p>
+
+<div class="figcenter" style="width: 511px;">
+<img src="images/i0076.png" width="511" height="240" alt="Fig. 11. Cross Section for Earth Roads" title="" />
+<span class="caption">Fig. 11. Cross Section for Earth Roads</span>
+</div>
+
+
+<h4 class="sc">Earth Roads in Regions of Considerable Rainfall</h4>
+
+<p>In the zones where the annual precipitation exceeds 30 inches
+distributed over several months, earth roads will be unserviceable for
+a considerable period each year unless they are constructed so as to
+minimize the effect of water. This is done by providing for the best
+possible drainage<span class="pagenum"><a name="Page_66" id="Page_66">[Pg 66]</a></span> and by adopting a method of maintenance that will
+restore the surface to a smooth condition as quickly as possible after
+a period of rainy weather or after the "frost comes out" in the
+spring.</p>
+
+<p>Before the construction of the desired cross section is undertaken,
+all of the grade reduction should be completed, except for minor cuts
+which can be handled with the elevating grader in the manner that will
+be described presently.</p>
+
+<p>Where any considerable change in grade is to be effected, the earth
+can be moved in several ways and of these the most economical cannot
+be readily determined. Ordinarily a contractor or a county will use
+the equipment that happens to be at hand even though some other might
+be more advantageous.</p>
+
+<p><b>Elevating Grader.</b>&mdash;Where the topography is such as to permit its use,
+the elevating grader is employed in grade reduction to load the earth
+into dump wagons in which it is hauled to the fill or waste bank. The
+elevating grader consists essentially of a heavy shear plow or disc
+plow which loosens the earth and deposits it on a moving canvas apron.
+The apron carries the material up an incline and deposits it into a
+wagon which is driven along under the end of the apron. When the wagon
+is loaded, the grader is stopped while the loaded wagon is hauled out
+and an empty one drawn into position. The motive power for the
+elevating grader is either a tractor or five or six teams of mules.
+For many kinds of work, particularly where frequent turning is
+necessary or where the ground is yielding, mules are preferable to a
+tractor. The apron is operated by gearing from the rear wheels of the
+grader. Generally four mules are hitched to a pusher in the rear of
+the grader and six or eight in the lead. This method of grade
+reduction is particularly advantageous when the material must be
+hauled a distance of 500 yards or more, because wagon hauling in such
+cases is the most economical method to employ. A tractor may be used
+to draw the elevating<span class="pagenum"><a name="Page_67" id="Page_67">[Pg 67]</a></span> grader and one having a commercial rating of 30
+to 45 horsepower is required.</p>
+
+<p><b>Maney Grader.</b>&mdash;If the haul is long and the nature of the cut will not
+permit the use of the elevating grader because of excessive grades or
+lack of room for turning, a grader of the Maney type may be used. This
+consists of a scoop of about one cubic yard capacity, suspended from a
+four-wheel wagon gear. When loading, the scoop is let down and filled
+in the same manner as a two-wheeled scraper or "wheeler." The pull
+required to fill a Maney grader is so great that a tractor is
+ordinarily employed in place of a "snap" team. The tractor is hitched
+at the end of the tongue, without interfering with the team drawing
+the grader. One team readily handles the grader after it is loaded.
+For this service a tractor having a commercial rationing of 25 to 30
+horsepower is required.</p>
+
+<p><b>Wheel Scraper.</b>&mdash;For moving earth for distances between 150 and 500
+yards, the wheel scraper of a capacity of about 1&frac12; yards is quite
+generally employed. The soil must be loosened with a plow before it
+can conveniently be loaded into the wheeler and a heavy plow is
+ordinarily employed for that purpose. Two furrows with the plow will
+loosen a strip of earth about as wide as the scoop of the scraper and
+if more is loosened it will be packed down by the scrapers wheeling in
+place to load. A helper or "snap" team is employed to assist in
+loading, after which the wheel scraper is handled by one team.</p>
+
+<p><b>Slip Scraper.</b>&mdash;The slip scraper differs from the wheel scraper in that
+the scoop is not suspended from wheels but is dragged along the
+ground. It is drawn by one team and the capacity is two to five cubic
+feet, but the material spills out to some extent as the scraper is
+dragged along and the method is not suitable for long hauls, 100 feet
+being about the economical limit.</p>
+
+<p><b>Fresno Scraper.</b>&mdash;The Fresno scraper is one form of slip scraper
+requiring four horses or mules for efficient<span class="pagenum"><a name="Page_68" id="Page_68">[Pg 68]</a></span> work. It differs
+somewhat from the ordinary slip scraper in shape and is of larger
+capacity, but is a drag type of scraper much favored in the western
+states.</p>
+
+
+<h4 class="sc">Shaping To Proper Cross Section</h4>
+
+<p>If a road has been graded so that the profile is satisfactory or if
+the existing profile of the location is satisfactory, and the surface
+is to be shaped to a prescribed cross section, either the elevating
+grader or the blade grader may be employed.</p>
+
+<p><b>Elevating Grader Work.</b>&mdash;If the elevating grader is used in shaping the
+earth road, the apron will be lowered and the material will be
+excavated at the sides of the road and deposited on the middle
+portion. If slight changes in grade are desired, wagons will accompany
+the grader and catch under the apron at the high places and haul the
+material to the low places. After the earth has been deposited it must
+be worked over to secure the correct cross section and be made
+passable for vehicles. This requires that clods be broken, weeds and
+grass that are mixed with the earth be removed by harrowing and
+forking and that the surface be carefully smoothed with a blade
+grader. This latter operation will have to be repeated several times
+before a satisfactory surface is secured. But this miscellaneous work
+is highly important and under no circumstances ought to be neglected.
+Nothing so detracts from an otherwise creditable piece of work as
+failure to provide a smooth surface for the use of vehicles. It is
+especially uncomfortable for the users of a highway if sods and weeds
+in quantity are left in the road after it has been graded. The humus
+that will be left in the soil as the vegetable matter decays increases
+the porosity of the road surface making it more absorbent than soil
+without humus. This increases the susceptibility to softening from
+storm water or ground water.<span class="pagenum"><a name="Page_69" id="Page_69">[Pg 69]</a></span></p>
+
+<p>The tractor can advantageously be used to draw the elevating grader on
+this class of work, but will be greatly handicapped if there are wet
+sections along the road, through which the tractor must be driven. In
+many cases its use is prohibited by such conditions and for all-round
+service of this character, mules are preferred for motive power.</p>
+
+<div class="figcenter" style="width: 414px;">
+<img src="images/i0080.png" width="414" height="220" alt="Fig. 12.&mdash;Tractor-grader Outfit" title="" />
+<span class="caption">Fig. 12.&mdash;Tractor-grader Outfit</span>
+</div>
+
+<p><b>Use of Blade Grader.</b>&mdash;Heavy blade graders designed to be drawn by a
+tractor are suitable for shaping the earth road. Some of these have
+blades 12 feet long and excellent control for regulating the depth of
+cutting. Often two such graders are operated tandem. These machines
+have a device which permits the operator to steer the grader
+independently of the tractor. Thus the grader can be steered off to
+the side to cut out the ditches, while the tractor continues to travel
+on the firm part of the road. Earth moved with the blade grader is
+usually fairly free from large lumps and can readily be smoothed to a
+satisfactory surface for the use of traffic. The sods and weeds will
+be drawn into the road along with the earth just as they are when the
+elevating grader is employed. Precaution must therefore be taken to
+eliminate them before the vegetable<span class="pagenum"><a name="Page_70" id="Page_70">[Pg 70]</a></span> matter decays, and to smooth the
+surface for the use of traffic.</p>
+
+<p><b>Costs.</b>&mdash;The cost of shaping an earth road in the manner described
+above will vary through rather wide limits because the nature and
+amount of work to be done varies so greatly. Some roads can be graded
+satisfactorily for $300.00 per mile, while others will cost $700.00.
+But $425.00 per mile may be taken as an average for blade or elevating
+grader work plus a moderate amount of grade reduction in the way of
+removing slight knolls. For the amount of grade reduction necessary in
+rolling country, followed by grader shaping, $1000.00 to $1800.00 per
+mile will be required. The method is not adapted to rolling country
+where the roads are undulating and require some grade reduction on
+every hill. For hilly roads one of the methods described for grade
+reduction will be required and the cost will obviously depend upon the
+amount of earth moved. Averages of cost figures mean nothing in such
+cases as the cost may reach $10,000.00 per mile, or may be as low as
+$2000.00 per mile.</p>
+
+<p><b>Maintenance.</b>&mdash;Regardless of the care with which an earth road has been
+graded, it will be yielding and will readily absorb water for a long
+time after the completion of the work. The condition of the surface
+will naturally deteriorate rapidly during the first season it is used
+unless the road receives the constant maintenance that is a
+prerequisite to satisfactory serviceability. The road drag is
+generally recommended for this purpose, and if a drag is properly used
+it will serve to restore the shape of the surface as fast as it is
+destroyed by traffic.</p>
+
+<p>Good results with the drag depend upon choosing the proper time to
+drag and upon doing the work in the right way when using the drag. The
+best time to drag is as soon after a rain as the road has dried out
+enough to pack under traffic. If the work is done while the road is
+too wet, the first vehicles traveling the road after it has been
+dragged<span class="pagenum"><a name="Page_71" id="Page_71">[Pg 71]</a></span> will make ruts and to a considerable extent offset the good
+done by the drag. If the road is too dry, the drag will not smooth the
+irregularities. A little observation will be required to determine the
+proper time for dragging on any particular soil, but usually after a
+rain or thaw there is a period lasting a day or two when conditions
+are about right.</p>
+
+<div class="figcenter" style="width: 472px;">
+<img src="images/i0082.png" width="472" height="253" alt="Fig. 13.&mdash;Road Drag" title="" />
+<span class="caption">Fig. 13.&mdash;Road Drag</span>
+</div>
+
+<p>The drag is used merely to restore the shape of the surface and to do
+so a small amount of material is drawn toward the middle of the road.
+But there must not be a ridge of loose material left in the middle
+after the work is completed. Some patrolmen start at one side of the
+road and gradually work across the road on successive trips, finally
+finishing up at the side opposite that at which the start was made.
+The next dragging should start on the opposite side from the first if
+that method is followed.</p>
+
+<p>By shifting his weight on the drag, the operator can adjust the
+cutting edge so that very little loose material is moved crosswise of
+the road and that is the proper method to pursue. In that case no
+ridge will remain at the middle<span class="pagenum"><a name="Page_72" id="Page_72">[Pg 72]</a></span> of the road. If a slight one is left
+it should be removed by a final trip with the drag.</p>
+
+<p>In addition to the dragging, weeds must be cut along the road about
+twice a year, the ditches must be kept cleaned out and culverts open.</p>
+
+<p>All of the maintenance for 10 miles of earth road can be accomplished
+by one man giving his entire time to the work, and that is the only
+method that has proven adequate to the problem.</p>
+
+
+<h4 class="sc">Earth Roads in Arid Regions</h4>
+
+<p>In areas where the rainfall is less than 18 inches per year, and
+especially where it is 10 inches or less, an entirely different road
+problem exists. The effect of precipitation is of significance
+primarily from the standpoint of erosion, and the design of cross
+section and ditches and the culvert provisions are entirely different
+from those necessary in humid regions.</p>
+
+<p>Frequently the rainfall in semi-arid regions will be seasonal and
+provision must be made to care for a large volume of water during the
+rainy season, but, in general, road design is adapted to prevention of
+erosion rather than to elimination of ground water effects, or the
+softening effects of surface water. Generally the rainy period does
+not last long enough to warrant expensive construction to eliminate
+its general effects. In fact, the saturation of the soil is more
+likely to be a benefit than otherwise.</p>
+
+<p>Earth roads are likely to be satisfactory except where the traffic is
+sufficient to grind the surface into dust to such an extent that an
+excessive dust layer is produced. In such locations the problem is one
+of providing a durable surface unaffected by long continued dry
+weather.</p>
+
+<p>Grade reduction will have the same importance as in humid areas and
+will be carried out in the same way.</p>
+
+<p>Maintenance will consist in repairing the damage from occasional
+floods and in removing or preventing accumulations<span class="pagenum"><a name="Page_73" id="Page_73">[Pg 73]</a></span> of drifting sand
+or dust. Crude petroleum oils have been satisfactory for maintenance
+in such locations when used on stable soils.</p>
+
+<p><b>Value of Earth Roads.</b>&mdash;The serviceability of the earth road depends to
+a large extent upon the care exercised in its maintenance. The only
+part of earth road construction that is permanent is the grade
+reduction. The cross section that is so carefully shaped at
+considerable cost may flatten out in one or two years, especially if
+the road goes through unusually wet periods. Traffic will continually
+seek a new track during the period when the road is muddy and is as
+likely to cross the ditch to the sod near the fence as to use any
+other part of the road. Continual and persistent maintenance is
+therefore essential to even reasonable serviceability. At best the
+earth road will be a poor facility for a considerable period each year
+in the regions of year-around rainfall. In most localities, roads of
+distinctly minor importance are of necessity only earth roads and for
+the comparatively small territory they serve and the small amount of
+traffic, they probably serve the purpose. For roads of any importance
+in the humid areas of the United States, the earth road cannot carry
+satisfactorily the traffic of a prosperous and busy community.</p>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_74" id="Page_74">[Pg 74]</a></span></p>
+<h2><a name="Chapter_VI" id="Chapter_VI"></a><span class="smcap">Chapter VI</span></h2>
+
+<h3>SAND-CLAY AND GRAVEL ROADS</h3>
+
+
+<p>In Chapter IV, mention was made of the variation in serviceability of
+road surfaces composed of the natural soil existing on the
+right-of-way of the road. It has been found that soils of a clayey
+nature in which there is a considerable percentage of sand usually
+afford a serviceable road surface for light or moderate traffic,
+especially in areas where climatic conditions are favorable. A study
+of these soils, together with the construction of experimental roads
+of various mixtures of sand and clay, has led to a fairly
+comprehensive understanding of the principles of construction and
+range of capacity of this type of road surface, which is known as the
+sand-clay road.</p>
+
+<p>The sand-clay road surface consists of a natural or artificial mixture
+of sand and clay, in which the amount of clay is somewhat greater than
+sufficient to fill the voids in the dry sand. It may be assumed that
+the sand contains 40 per cent of voids and that at least 45 per cent
+of clay is required to fill the voids and bind the sand grains
+together, because the clay spreads the sand grains apart during the
+mixing, thus having the effect of increasing the voids. As a matter of
+experiment, it is found to be impractical to secure by available
+construction methods mixtures of sufficient uniformity to render it
+necessary to exercise great exactness in proportioning the components,
+but reasonable care in proportioning the materials is desirable.</p>
+
+<p>Successful utilization of this type of surface requires considerable
+study of available materials and investigations of their behavior when
+combined. Extensive and exhaustive<span class="pagenum"><a name="Page_75" id="Page_75">[Pg 75]</a></span> experiments have been conducted
+with sand-clay mixtures in various places where they are widely used
+for road surfaces and the following general principles have been
+deduced.</p>
+
+<p><b>The Binder.</b>&mdash;In the sand-clay road, stability is obtained by utilizing
+the bonding properties possessed to some degree by all soils.
+Naturally this characteristic may be expected to vary widely with the
+several types of soil. It is generally considered to be a common
+property of clay, but the term clay is a general one that is often
+applied to soils differing greatly in physical characteristics and the
+term therefore loses its significance in this connection. Those soils
+that are properly and technically called clay are decidedly sticky
+when wet and are the best materials for sand-clay construction. Of the
+clays, those that produce a tough sticky mud are best. This can be
+tested by mixing a small quantity into a stiff mud and molding it into
+a ball and immersing in water. If the ball retains its shape for some
+little time, it is likely to prove a very satisfactory binder, but, if
+it becomes plastic and loses its shape, it will be an inferior binder,
+as a general rule. The ball clay, as the former is called, may be of
+any color common to soils, not necessarily yellow or reddish as is
+sometimes supposed. Likewise, balls of mixtures containing varying
+percentages of sand and the binder to be used may be made up and
+immersed in water. The mixture that holds its shape longest is of
+course the best combination of the materials and indicates the mixture
+to use in the construction.</p>
+
+<p>An ideal, or even a fairly satisfactory soil for a binder may not
+exist in the vicinity of a proposed improvement, and consequently an
+inferior binder is frequently the only material available.</p>
+
+<p>Sometimes deposits of clay or gravel contain a considerable percentage
+of gypsum which serves as a binder and is particularly effective when
+used in combination with clay and sand or gravel.<span class="pagenum"><a name="Page_76" id="Page_76">[Pg 76]</a></span></p>
+
+<p>In many places a soil of the type used for adobe and called "caliche"
+may be found and this is an excellent binder for sand or gravel.</p>
+
+<p><b>Top-Soil or Natural Mixtures.</b>&mdash;Deposits consisting of a natural
+mixture of sand and clay in which the ingredients happen to exist in
+about the correct relative proportions for sand-clay road surfaces are
+found in many localities. These mixtures are commonly referred to as
+top-soil. If the deposits are somewhat deficient either in sand or
+clay, they can be utilized if the proper corrections in the
+proportions are made during construction. Very satisfactory road
+surfaces are sometimes constructed with mixtures that appear to be far
+from ideal in composition, but experience and frequent trials are
+needed to determine the best way in which to handle these mixtures.</p>
+
+<p><b>Sand-Clay Surfaces on Sandy Roads.</b>&mdash;Sand-clay surfaces may be
+constructed on naturally sandy roads either by adding clay and mixing
+it with the sand to secure the desired composition, or a layer of a
+natural sand-clay mixture, caliche or sand-clay-gypsum may be placed
+on top of the sand.</p>
+
+<p>The most widely used method is to mix clay or other binder with the
+sand. Since there is no need to provide for ditches to carry storm
+water on a deep sand soil, the sand is graded off nearly flat across
+the road and no ditches are provided. The clay is dumped on the road
+in a layer about 8 inches thick and is then mixed into the sand. It is
+desired to mix enough sand with the clay to produce a mixture composed
+of approximately 1/3 clay and 2/3 sand. The mixing is accomplished in
+various ways, the most common being to use a heavy plow at first and
+to follow this with a heavy disc harrow. The mixing is a tedious and
+disagreeable process, but its thorough accomplishment is
+indispensable. The mixing is most readily done when the materials are
+saturated with water and in practice it is customary to depend upon
+rain for the water, although in<span class="pagenum"><a name="Page_77" id="Page_77">[Pg 77]</a></span> the final stages water may be hauled
+and sprinkled on the road to facilitate final completion of the
+mixing. After the mixing has been completed, the surface is smoothed
+with the blade grader and is kept smooth until it dries out. Repeated
+dragging will be required, during the first year especially, and to
+some extent each year in order to keep the surface smooth, but the
+dragging can be successfully accomplished only when the road is wet.</p>
+
+<div class="figcenter" style="width: 494px;">
+<img src="images/i0088.png" width="494" height="279" alt="Fig. 14.&mdash;Cross Sections for Sand-Clay Roads" title="" />
+<span class="caption">Fig. 14.&mdash;Cross Sections for Sand-Clay Roads</span>
+</div>
+
+<p>In regions where several months of continued hot, dry weather is to be
+expected each year, the sand-clay mixture is likely to break through
+unless it is of considerable thickness and generally the surface layer
+is made much thicker than for regions where the annual rainfall is
+fairly well distributed. This is especially necessary when the binder
+is of inferior quality. It is not uncommon in such cases to make the
+sand-clay surface as much as two feet thick.</p>
+
+<p>As the mixing progresses it may appear that patches here and there are
+deficient in either clay or sand and the mixture in these places is
+corrected by the addition of a little sand or clay as may be
+required.<span class="pagenum"><a name="Page_78" id="Page_78">[Pg 78]</a></span></p>
+
+<p>If the top-soil is used it is deposited on the sand in the required
+quantity and is remixed in place to insure uniformity. If either sand
+or clay is needed to give a satisfactory mixture, the proper material
+is added and mixed in as the work progresses. The surface is finally
+smoothed by means of the grader and drag.</p>
+
+<p><b>Sand-Clay on Clay or Loam.</b>&mdash;If the existing road is of clay or loam,
+ample drainage will be required as discussed in Chapter IV. The
+surface may be constructed of a natural sand-clay mixture or of a sand
+mixed with the natural soil. If the former, the surface of the
+existing road is prepared by grading so as to insure good drainage and
+the natural mixture is then deposited and the surface completed as
+described in the preceding section.</p>
+
+<p>If the surface is formed by mixing sand with the existing soil, the
+sands may be deposited in a layer about six inches thick which will
+gradually mix with the soil as the road is used. A second application
+of sand may follow in a year or two if it is needed. Such a road
+surface will lack uniformity of composition and it seems preferable to
+mix the sand with the soil by plowing and discing as previously
+described.</p>
+
+<p><b>Characteristics.</b>&mdash;Sand-clay road surfaces do not have sufficient
+durability for heavily traveled highways, but will be satisfactory for
+a moderate amount of traffic. These surfaces have maximum
+serviceability when moist, not wet, and consequently are not as
+durable in dry climates as in humid areas. They are likely to become
+sticky and unstable in continued wet weather and to become friable and
+wear into chuck holes in long continued dry weather. At their best,
+they are dustless, somewhat resilient and of low tractive resistance.<span class="pagenum"><a name="Page_79" id="Page_79">[Pg 79]</a></span></p>
+
+<h4 class="sc">Gravel Road Surfaces</h4>
+
+<div class="figcenter" style="width: 492px;">
+<img src="images/i0090.png" width="492" height="287" alt="Fig. 15.&mdash;Cross Sections for Gravel Highways" title="" />
+<span class="caption">Fig. 15.&mdash;Cross Sections for Gravel Highways</span>
+</div>
+
+<p><b>Natural Gravel.</b>&mdash;Gravel is the name given to a material consisting of
+a mixture of more or less rounded stones, sand and earthy material,
+which is found in natural deposits. These deposits exist in almost
+every part of North America, being especially numerous in the
+glaciated areas, but by no means confined to them. Gravel deposits
+consist of pieces of rock varying in size from those of a cubic yard
+or more in volume to the finest stone dust, but with pieces ranging in
+size from that which will pass a 3-inch ring down to fine sand
+predominating. The larger pieces are usually more or less rounded and
+the finer particles may be rounded or may be angular. Many varieties
+of rocks are to be found among the gravel pebbles, but the rocks of
+igneous origin and possessing a considerable degree of hardness
+generally predominate. Intermixed with the pieces of rock there is
+likely to be clay or other soil, the quantity varying greatly in
+different deposits and even in various places in the same deposits.<span class="pagenum"><a name="Page_80" id="Page_80">[Pg 80]</a></span></p>
+
+<p>Often there are found deposits of material which are by the layman
+termed gravel, which are really clayey sand or sand containing a few
+pebbles, but which are of value to the road builder for the sand clay
+type of surfacing. The term gravel is exceedingly general and unless
+specifically defined, gives little indication of the exact nature of
+to which it is applied.</p>
+
+<h4 class="sc">Table 7</h4>
+<h4 class="sc">Showing Cementing Properties of Several Samples of
+Gravel</h4>
+
+
+<div class="center">
+<table summary="Cementing Properties of Gravel">
+<tr><td rowspan="2" class="bt bb center">Per Cent Clay<br />by Weight</td><td colspan="2" class="bt bb bl center">Cementing Value</td></tr>
+<tr><td class="bb bl center">As Received</td><td class="bb bl center">Washed</td></tr>
+<tr><td class="right">4.4</td><td class="bl right">276</td><td class="bl right">43</td></tr>
+<tr><td class="right">6.4</td><td class="bl right">105</td><td class="bl right">285</td></tr>
+<tr><td class="right">5.1</td><td class="bl right">241</td><td class="bl right">70</td></tr>
+<tr><td class="right">14.5</td><td class="bl right">500</td><td class="bl right">279</td></tr>
+<tr><td class="right">8.5</td><td class="bl right">500</td><td class="bl right">112</td></tr>
+<tr><td class="right">10.1</td><td class="bl right">300</td><td class="bl right">267</td></tr>
+<tr><td class="right">14.8</td><td class="bl right">500</td><td class="bl right">107</td></tr>
+<tr><td class="right">7.5</td><td class="bl right">184</td><td class="bl right">198</td></tr>
+<tr><td class="right">16.5</td><td class="bl right">500</td><td class="bl right">428</td></tr>
+<tr><td class="right">2.0</td><td class="bl right">185</td><td class="bl right">239</td></tr>
+<tr><td class="right">1.5</td><td class="bl right">500</td><td class="bl right">500</td></tr>
+<tr><td class="right">4.5</td><td class="bl right">212</td><td class="bl right">204</td></tr>
+<tr><td class="bb right">2.5</td><td class="bb bl right">116</td><td class="bb bl right">363</td></tr>
+</table></div>
+
+
+<p>The value of any gravel for road surfacing depends upon the degree to
+which it possesses the properties of an ideal gravel for road
+surfacing. Ideal gravel is seldom encountered, but a consideration of
+its characteristics serves to establish a measure by which to estimate
+the probable value of any deposit.</p>
+
+<p><b>The Ideal Road Gravel.</b>&mdash;The ideal road gravel is a mixture of pebbles,
+sand and earthy material, the pieces varying from coarse to fine in
+such a manner that when the gravel is compacted into a road surface
+the spaces<span class="pagenum"><a name="Page_81" id="Page_81">[Pg 81]</a></span> between the larger pebbles are filled with the finer
+material. The pebbles are of a variety of rock that is highly
+resistant to wear so that the road surface made from the gravel will
+have the quality of durability. The gravel possesses good cementing
+properties, insuring that the pieces will hold together in the road
+surface. The cementing property may be due to the rock powder in the
+deposit or to earthy material mixed with the rock particles, or to
+both. Table 7 shows the results of a number of tests made upon gravels
+and indicates that the cementing property of the gravel does not
+always depend upon the clay content.</p>
+
+<p><b>Permissible Size of Pebbles.</b>&mdash;The larger pebbles in the gravel are
+less likely to crush under loads than smaller pebbles of the same sort
+of rock, but if the rock is of some of the tougher varieties such as
+trap, there is very little likelihood of even the smaller pebbles
+crushing. If the pebbles are of rock of medium toughness, the smaller
+pebbles might be crushed under the heavier loads. It is the usual
+practice to permit gravel to be used for the foundation course in
+which the pebbles are as large as will pass a 3&frac12;-inch circular
+screen opening, and for the wearing course, as large as will pass a
+2&frac12;-inch circular screen opening. If larger pebbles are allowed in
+the wearing course, the surface is certain to become rough after a
+time. If the gravel is to be placed in a single course as is a very
+common practice, then the maximum size should not exceed that which
+will pass a 2&frac12;-inch circular screen opening.</p>
+
+<p>The Wisconsin Highway Commission has constructed a very large mileage
+of excellent gravel roads and the sizes specified for their roads are
+as follows:</p>
+
+<blockquote><p>"<i>Bottom Course Gravel</i>.&mdash;Bottom course shall consist of a
+mixture of gravel, sand and clay with the proportions and various
+sizes as follows:</p>
+
+<p>"All to pass a two-inch screen and to have at least sixty and not
+more than seventy-five per cent retained on a quarter-inch
+screen; at least twenty-five and not more than seventy-five per
+cent of the total coarse aggregate to be retained on a one-inch
+screen; at least sixty-five and not<span class="pagenum"><a name="Page_82" id="Page_82">[Pg 82]</a></span> more than eighty-five per
+cent of the total fine aggregate to be retained on a two
+hundred-mesh sieve."</p>
+
+<p>"<i>Top Course Gravel</i>.&mdash;Top course shall consist of a mixture of
+gravel, sand and clay with the proportions of the various sizes
+as follows:</p>
+
+<p>"All to pass a one-inch screen and to have at least fifty and not
+more than seventy-five per cent retained on a quarter-inch
+screen; at least twenty-five and not more than seventy-five per
+cent of the total coarse aggregate (material over one-fourth inch
+in size) to be retained on a one-half-inch screen; at least
+sixty-five and not more than eighty-five per cent of the total
+fine aggregate (material under one-fourth inch in size) to be
+retained on a two hundred-mesh sieve."</p>
+
+<p>"<i>Screened Gravel and Sand Mixtures</i>.&mdash;Where it is impossible to
+obtain run of bank gravel containing the necessary binder in its
+natural state, screened gravel shall be used and the necessary
+sand and clay binder added as directed by the engineer. Gravel
+and sand shall be delivered on the work separately. Clay binder
+shall be obtained from approved pits and added as directed by the
+engineer."</p>
+
+<p>"<i>Run of Bank Gravel</i>.&mdash;When run of bank gravel is permitted
+either for one course or two course work, the size shall not
+exceed that specified for bottom or top course. If necessary, the
+contractor shall pass all the material through a two-inch screen
+for the bottom course, and through a one-inch screen for the top
+course. When the work consists of only one course, the material
+shall be of the sizes as specified for the top course. The
+necessary binder shall be contained in the material in its
+natural state, excepting that a small percentage of clay binder
+may be added as directed by the Engineer."</p></blockquote>
+
+<p><b>Wearing Properties.</b>&mdash;A certain amount of grinding action takes place
+on the road surface under the direct action of wheels, especially
+those with steel tires. Where rubber tired traffic predominates, this
+action is much less severe than where steel tired vehicles
+predominate, but the tendency exists on all roads. In addition, there
+is distortion of the layer of gravel under heavy loads which causes
+the pieces of stone in the surface to rub against each other and to
+wear away slowly.</p>
+
+<p>The gravel road in the very best condition is slightly uneven but
+there is comparatively little jar imparted to vehicles, and,
+consequently, little impact on the surface. When somewhat worn, the
+impact becomes a factor of some<span class="pagenum"><a name="Page_83" id="Page_83">[Pg 83]</a></span> importance and the pounding of
+vehicles has a very destructive action on the surface. Soft pebbles
+will be reduced to dust in a comparatively short time.</p>
+
+<p>The degree to which any gravel resists the destructive action of
+traffic depends upon the varieties of rock represented by the pebbles
+in the gravel. If the pebbles are mostly from rocks of good wearing
+properties, that quality will be imparted to the road surface. If
+mostly from rocks of little durability, the same characteristic will
+be imparted to the road surface. A very good general notion of the
+probable durability of gravel can therefore be obtained by a careful
+visual examination of the material and classification of the rock
+varieties represented by the pebbles.</p>
+
+<p><b>Utilizing Natural Gravels.</b>&mdash;Gravel road construction is advantageous
+only when it can be accomplished at low first cost. This usually
+presupposes a local supply of gravel that can be utilized, or at any
+rate a supply that need not be shipped a long distance. In the nature
+of things, such deposits are likely to be deficient in some of the
+desirable characteristics, and may be deficient in most of them. By
+various means, the defects in the materials can be partially corrected
+while constructing the road.</p>
+
+<p>If the gravel deposit consists of layers of varying composition as
+regards size and clay content, the material may be loosened from the
+exposed face and allowed to fall to the bottom of the pit thereby
+becoming mixed to a sufficient extent to produce a reasonably uniform
+product. If deficient in clay, it often proves feasible to add a small
+part of the clay over-burden, thereby insuring enough binder.
+Sometimes adjoining deposits will consist one of relatively fine
+material, the other of relatively coarse. These may be mixed on the
+work by first placing the coarse material in a layer about 5 inches
+thick and adding the finer material in a similar layer. The two will
+mix very rapidly during the operations of spreading and shaping.<span class="pagenum"><a name="Page_84" id="Page_84">[Pg 84]</a></span></p>
+
+<p>When deposits contain pebbles larger than will pass a 3&frac12;-inch ring,
+these larger stones will prove to be undesirable if placed on the
+road, as they are almost sure to work to the surface of the gravel
+layer and become a source of annoyance to the users of the road.
+Oversize stone can be removed while loading the gravel or while
+spreading it, if care is exercised and not too large a proportion is
+oversize. It is preferable however to remove the oversize by means of
+screens at the pit. Usually on large jobs the oversize is crushed and
+mixed with the supply so as to utilize what is really the best part of
+the material.</p>
+
+<p>Gravels deficient in bonding material are often encountered in
+deposits where there is insufficient overburden to give enough
+additional binder or where the overburden is of a material unsuitable
+for binder. Such materials may be utilized by adding binder in the
+form of clay after the gravel has been placed on the road.</p>
+
+<p>Almost any gravel deposit can be utilized in some way if the material
+is of a durable nature, regardless of other characteristics. The
+serviceability of a gravel road will depend largely on how nearly the
+gravel approaches the ideal, but variations in the manipulations will
+do much to overcome deficiencies in materials.</p>
+
+<p><b>Thickness of Layer.</b>&mdash;The thickness of the layer of gravel required
+depends both upon the type of soil upon which it is placed and the
+nature of the traffic to which the road will be subjected. Gravel
+surfaces should not ordinarily be constructed on highways carrying
+heavy truck traffic, but if gross loads of three or four tons are the
+heaviest anticipated, the gravel will be reasonably stable. On such
+roads, a layer of well compacted gravel ten inches thick will support
+the loads if a well drained earth foundation is provided. If but
+little truck traffic is anticipated and loads up to three tons on
+steel tires are the average, a layer 8 inches thick will be
+sufficient. In dry climates, a<span class="pagenum"><a name="Page_85" id="Page_85">[Pg 85]</a></span> layer six inches thick will be
+adequate if it can be kept from raveling.</p>
+
+<p>On secondary roads, carrying principally farm-to-market traffic, and
+not a great volume of that, the above thicknesses may be reduced about
+one-fourth.</p>
+
+<p>The exact thickness needed for any particular road is a matter for
+special study on account of the variations in the gravels and in the
+supporting power of the soil upon which they are placed.</p>
+
+
+<h4 class="sc">Placing Gravel</h4>
+
+<p><b>Preparation of the Road.</b>&mdash;The roadway that is to be surfaced with
+gravel is first brought to the desired grade and cross section. It
+would be advantageous if this could be done a year before the gravel
+is placed so that no settlement of the earth foundation would occur
+after the gravel surface is completed. But if that is impractical, the
+grading may be done just prior to placing the gravel, providing
+appropriate methods are adopted for securing compacted fills.</p>
+
+<p><b>Trench Method.</b>&mdash;Two distinct methods of placing the gravel are in
+general use, known as the trench method and the surface or feather
+edge method respectively. The method to adopt for any particular road
+will depend largely on certain conditions that will be explained
+later.</p>
+
+<p>In the trench method, a trench of the proper width and depth for
+receiving the gravel is excavated in the earth road surface and the
+gravel is placed therein.</p>
+
+<p>The trench is formed by plowing a few furrows and scraping out the
+loosened earth with a blade grader. The loose material is generally
+moved out laterally to build up earth berms or "shoulders" alongside
+the gravel. Into this trench the gravel is dumped in the proper
+quantity to give the required thickness after being compacted.</p>
+
+<p>The greatest care must be exercised in spreading the<span class="pagenum"><a name="Page_86" id="Page_86">[Pg 86]</a></span> gravel to
+eliminate unevenness where the loads were deposited. An ordinary blade
+grader is one of the best and most economical implements to use for
+spreading the gravel. When the gravel has been deposited in the trench
+for a distance of a thousand feet or more, the spreading is
+accomplished by dragging the surface repeatedly with the blade grader,
+the work being continued until all waviness disappears. The gravel is
+then thoroughly and repeatedly harrowed with a heavy stiff tooth
+harrow to mix thoroughly the fine and coarse gravel so as to produce
+as nearly a uniform mixture as may be. The gravel is then finally
+smoothed with the blade grader.</p>
+
+<p>The gravel may be compacted by rolling or may be allowed to pack from
+the action of traffic. The former is greatly to be preferred where
+practicable. The rolling is performed with a three-wheeled
+self-propelled roller weighing about 8 tons and must be done while the
+gravel is wet. Generally a sprinkling wagon is used to wet down the
+gravel, but advantage is always taken of rains to facilitate the work.
+The gravel must be spread in layers not over 5 or 6 inches thick to
+get the desired results, which means that for an ordinary gravel road
+about 10 inches thick, the gravel will be placed in two layers of
+about equal thickness, each of which will be rolled.</p>
+
+<p>The gravel will compact slowly even if it is not rolled, but generally
+does not become stable until the material is thoroughly soaked by
+rains. Then it will begin to pack, but will become badly rutted and
+uneven during the process. During this period the surface must be kept
+smooth by means of the blade grader. The drag does not suffice for
+this purpose, tending to accentuate the unevenness rather than to
+correct it.</p>
+
+<p>If gravel is placed in a trench in dense soil and rainy weather
+ensues, sufficient water will be held in the trench to cause
+unevenness from foundation settlement and the gravel will become mixed
+with the soil to some extent and<span class="pagenum"><a name="Page_87" id="Page_87">[Pg 87]</a></span> be thereby wasted. Trenches cut from
+the road bed upon which the gravel is placed, to the side ditches,
+will relieve this condition by affording an outlet for the surplus
+water. Nevertheless some difficulty may be expected if the trench
+method is used and wet weather prevails. If it is possible to close
+the road against traffic until the road is dry the method is
+applicable. Moreover, in long-continued dry weather, the dispersion
+and loss of considerable gravel from the action of automobile traffic
+is avoided because the gravel is held between substantial earth berms
+and the gravel will pack better and hold its shape longer when
+constructed by the trench method than otherwise.</p>
+
+<p><b>Surface Method.</b>&mdash;The surface method is one in which the gravel is
+placed on the graded earth road surface without earth shoulders to
+hold the gravel in place. It is also sometimes called the feather-edge
+method. Except for the manner of placing as just mentioned, the
+several operations are conducted in the same general manner as for the
+trench method. The gravel does not compact as quickly as in the trench
+method and a considerable loss of material is likely to result from
+the effect of automobile traffic while the gravel is loose. But it has
+the advantage of being free from difficulties in wet weather and in
+some locations is therefore preferable to the trench method. It is
+particularly applicable to those projects on which the placing of
+gravel continues throughout the winter, the gravel being dumped and
+spread, to be finally smoothed and finished in the early summer.</p>
+
+<p><b>Bonding.</b>&mdash;Where gravels deficient in binder are utilized, clay for
+binder is sometimes added as the gravel is placed on the road. This
+may be done by spreading the clay on top of the lower course of
+gravel, placing the upper layer and sprinkling and rolling until the
+clay squeezes up through the surface layer. It may also be
+accomplished by spreading dry clay on the upper course before it is
+harrowed and then harrowing to mix it with the gravel. Both<span class="pagenum"><a name="Page_88" id="Page_88">[Pg 88]</a></span> methods
+are practiced, but the former is believed to be preferable. A third
+method is to separate the sand and pebbles and to mix the clay binder
+with the sand and then spread the sand on top of the pebbles and mix
+by harrowing.</p>
+
+<p><b>Maintenance.</b>&mdash;Gravel surfaces require careful maintenance, especially
+during the first season the road is used. The gravel will compact
+slowly and during the process will be rutted and otherwise disturbed
+by traffic. It is important during this period to restore the shape
+once a week or at least twice a month. The light blade grader is
+usually employed for the purpose so long as the gravel is somewhat
+loose. Later a drag of the type known as the planer will prove to be
+the most effective. Figure 16 shows a type of drag that is very
+satisfactory for use on gravel roads.</p>
+
+<div class="figcenter" style="width: 511px;">
+<img src="images/i0099.png" width="511" height="241" alt="Fig. 16.&mdash;Road Planer" title="" />
+<span class="caption">Fig. 16.&mdash;Road Planer</span>
+</div>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_89" id="Page_89">[Pg 89]</a></span></p>
+<h2><a name="Chapter_VII" id="Chapter_VII"></a><span class="smcap">Chapter VII</span></h2>
+
+<h3>BROKEN STONE ROAD SURFACES</h3>
+
+
+<p>The broken stone road surface, or macadam road as it is usually
+termed, consists of a layer of broken stone, bonded or cemented
+together by means of stone dust and water. The surface may or may not
+be coated with some bituminous material.</p>
+
+<p><b>Design.</b>&mdash;It has been an accepted assumption that the macadam road
+surface is somewhat more stable than the gravel road surface of equal
+thickness, and since this is probably the consensus of opinion of
+engineers familiar with both types, it may be accepted until
+experimental data are available on the subject.</p>
+
+<p>The thickness of the layer of macadam required for a road will depend
+upon the same factors that were considered in connection with the
+thickness of the gravel surface, i.e., kind of stone used, character
+of earth foundation and nature of the traffic.</p>
+
+<p>The standard macadam surface where good earth foundation is to be had
+and where the loads do not exceed about four tons has for years been
+eight inches thick. For heavier loads or inferior foundation, a
+somewhat greater thickness would be employed, but the best practice
+would probably provide a foundation course of the Telford type for
+doubtful foundation conditions, especially for the extremely uncertain
+cases. For soils of very good supporting strength such as very sandy
+loam or deep sand or for arid regions where stable foundation is
+always assured the thickness of the macadam might be reduced to six
+inches. It should be borne in mind that the broken stone road is not
+adapted<span class="pagenum"><a name="Page_90" id="Page_90">[Pg 90]</a></span> to the traffic carried by trunk line highways in populous
+districts, but is rather a type permissible on secondary roads and
+usually adequate for local roads. It should never be employed for
+roads carrying any considerable volume of passenger automobile traffic
+or motor truck traffic. If surfaced with a bituminous material it will
+carry up to 1200 passenger automobiles per day, but not to exceed
+fifty trucks.</p>
+
+<p><b>Properties of the Stone.</b>&mdash;The stone employed for the broken stone road
+should possess the qualities of hardness and toughness and should be
+capable of resisting abrasion sufficiently well to have reasonable
+life under the traffic to which it is subjected. Since the traffic may
+vary from very light on some roads to far beyond the limit of the
+economical capacity of this type of pavement on others, it follows
+that any particular deposit of stone might be durable enough for some
+roads, while for others it might be entirely inadequate. As a general
+rule it has been found that stone that wears away at a moderate rate
+will, when used for water-bound macadam surface, result in a smoother
+trackway than one that will wear very slowly. It is not therefore
+altogether certain that the most durable stone to be had should be
+selected for a particular road. This is especially true now that the
+water-bound macadam surface has been largely superseded for trunk line
+highways and other heavily traveled roads, and is employed in
+locations where service conditions are not severe.</p>
+
+<p>The stone employed for the water-bound macadam surface must possess
+good cementing properties, because the surface depends for stability
+primarily upon the bonding action of the dust from the broken stone.
+This is in contrast to the gravel road, where little dependence is
+placed upon the bonding effect of the rock dust. In preparing the
+stone for macadam surfaces, the ledge rock is crushed and screened,
+and in that way a supply of the finer particles, which are a part of
+the output of the crusher, is obtained<span class="pagenum"><a name="Page_91" id="Page_91">[Pg 91]</a></span> for use in bonding the
+surface. This finely broken material, usually called screenings, is
+essential to the construction of the water-bound type of surface.
+Rocks vary considerably in the cementing properties of the dust, but
+usually the rocks classed as "trap," such as andesite, gabbro and
+rhyolite, and schist and basalt possess good cementing properties.
+Limestones usually possess good cementing properties, but some of the
+dolomitic limestones are of low cementing value. Quartz, sandstone and
+the granites are of low cementing value.</p>
+
+<p><b>Kinds of Rocks Used for Macadam.</b>&mdash;Limestone and chert are the two
+sedimentary rocks, employed most extensively for broken stone roads.
+These rocks are found in widely distributed areas and vary in physical
+characteristics from very soft material of no use to the road builder
+to materials possessing considerable durability. It is desirable to
+carefully test out the deposits of these materials before using to
+ascertain the probable value of the rock, for the construction of the
+road surface.</p>
+
+<p>Of the igneous rocks, those classed as trap are best known to the road
+builder and many of the deposits of trap rock afford an excellent
+material for broken stone roads where the severest conditions of
+traffic are encountered. The trap rocks are tough and durable and
+generally possess excellent cementing properties.</p>
+
+<p>Granite and sandstone are seldom used for water-bound macadam as they
+possess poor cementing properties and a binder of some kind must be
+added to cement the pieces together. For this purpose clay or the
+screenings from some other variety of stone may be utilized.</p>
+
+<p>Some other materials are occasionally employed for the construction of
+macadam surfaces. Of these, oyster or marine shells, burnt shale, and
+slag are most common.</p>
+
+<p>Shells and slag are of rather low durability but possess good
+cementing properties. Shale is a makeshift suitable only for very
+light traffic roads.<span class="pagenum"><a name="Page_92" id="Page_92">[Pg 92]</a></span></p>
+
+<p><b>Sizes of Stone.</b>&mdash;The stone for the wearing course of a macadam road
+should be as large as practicable, because the larger the pieces the
+more durable the surface. If the individual stones are too large it is
+difficult to secure a smooth surface, and large stones will be readily
+loosened by tipping as the wheels roll over them. These considerations
+limit the size to a maximum of that which will pass a 2&frac12;-inch
+screen. Stone of excellent wearing qualities may be somewhat smaller,
+but never less than that which will just pass a 1&frac12;-inch screen.</p>
+
+<p>For the lower course, the size is not particularly important except
+where the earth foundation is such as to require special construction.
+It is not uncommon to use the same size of stone for both upper and
+lower course and yet in many instances stone up to that which will
+just pass a 3&frac12;-inch screen is used for the lower course. Stone much
+smaller in size may also be used successfully, but if the stone is
+broken to a smaller size than is required, unnecessary expense is
+incurred.</p>
+
+<p>The bonding material is the finer portion of the product of the
+crusher, which is called screenings. This material may be so finely
+crushed as to pass a one-fourth inch screen, or may be so coarse as to
+just pass a one-half inch screen, but in any case must contain all of
+the dust and fine material produced by the crusher.</p>
+
+<p>Where the soil and drainage conditions demand an especially stable
+foundation course, the Telford type is used. The Telford foundation
+consists of a layer of stones of various dimensions that can be laid
+so as to give a thickness of 8 inches. These large stones are placed
+by hand and therefore the size requirements are not rigid. Stones
+having one dimension about 8 inches and the others not over 10 or 12
+inches are satisfactory.</p>
+
+<p><b>Earth Work.</b>&mdash;A thoroughly drained and stable earth foundation is
+essential to success with the macadam type of surface. Before placing
+the stone, the road must be<span class="pagenum"><a name="Page_93" id="Page_93">[Pg 93]</a></span> shaped to the proper cross section and
+all grade reduction work completed. Preferably heavy fills should have
+a year to settle before the macadam surface is placed. Side ditches,
+necessary culverts and tile drains should be constructed as required
+for drainage. The earth work is often carried out in connection with
+the construction of the macadam surface, being completed just ahead of
+the surfacing. In that case, the fills must be carefully rolled as
+they are placed. The road bed may be shaped in connection with the
+other earthwork. If the road has been brought to a satisfactory grade
+some time prior to placing the macadam, the road bed for the broken
+stone will be prepared as needed for placing the stone.</p>
+
+<p><b>Foundation for the Macadam.</b>&mdash;Macadam surfaces are quite generally
+placed in a trench as described in the trench method for placing
+gravel. It is an almost universal practice to compact the layer of
+stone by rolling with an 8- or 10-ton power roller, and if the stone
+is not held between substantial earth berms or shoulders, the rolling
+merely serves to spread the stone out over the road bed instead of
+compacting it. If an attempt is made to roll broken stone which has
+been placed on a yielding foundation, no benefit results, but on the
+contrary the stone is likely to be forced down into the soil. To
+insure that the layer of broken stone can be compacted by rolling, it
+is first necessary to roll the earth foundation until it becomes hard
+and unyielding. If soft or yielding places appear during the rolling
+these should be corrected by tile drains or by removing the earth from
+the spongy place and back-filling with material that will compact when
+rolled.</p>
+
+<p>It is not always easy to determine why these soft places exist in what
+appears to be a well drained roadway, especially since they are as
+likely to be found on fills as anywhere else. Apparently they are due
+to local pockets of porous soil held by denser soil so that the water
+does not readily drain away. It is usually true that such places<span class="pagenum"><a name="Page_94" id="Page_94">[Pg 94]</a></span> are
+observed during the season of frequent precipitation more often than
+during other seasons of the year.</p>
+
+<p>In dry climates, the difficulties of securing suitable foundations for
+the broken stone road are largely eliminated, but it may be observed
+that this type of surface is not suitable for such climates unless
+some sort of bituminous binder is employed to hold the stones in
+place. The cementing power of the stone dust is inadequate when the
+surface is continually dry.</p>
+
+<div class="figcenter" style="width: 502px;">
+<img src="images/i0105.png" width="502" height="218" alt="Fig. 17.&mdash;Cross Section for Macadam" title="" />
+<span class="caption">Fig. 17.&mdash;Cross Section for Macadam</span>
+</div>
+
+<p><b>Telford Foundation.</b>&mdash;When the Telford type of foundation is employed,
+the earth subgrade is prepared and then the Telford stone placed
+carefully by hand. The spaces between the large stones are filled with
+the spalls broken from the larger stones in fitting them in place.
+When completed the base is rolled with a heavy roller to secure a firm
+unyielding layer. The thickness is generally about eight inches. Any
+fairly sound stone may be used for the Telford base.</p>
+
+<p><b>Placing the Broken Stone.</b>&mdash;It has been found impracticable properly to
+roll a greater thickness than about 5 or 6 inches of loose stone,
+therefore, the stone for the macadam surface is usually placed in two
+layers, the first or lower layer being rolled before the next layer is
+placed.<span class="pagenum"><a name="Page_95" id="Page_95">[Pg 95]</a></span> The stone is hauled in dump wagons, trucks or dump cars,
+dumped on the road bed and spread by hand rakes or by means of a blade
+grader and is then rolled. To insure the proper thickness the loads
+are accurately spaced to spread to the proper thickness.</p>
+
+<p><b>Rolling.</b>&mdash;A three-wheeled or "macadam" type of roller, of the
+self-propelled type, is best for compacting the broken stone road. The
+weight varies from eight to fifteen tons, but for most conditions the
+ten or twelve ton size seems to be preferable. On Telford base
+construction, a heavier machine is desirable and for very hard stone
+it may be successfully employed.</p>
+
+<p>The first trip with the roller is made along the edge of the stone and
+each successive trip is made a little nearer the middle until finally
+one half of the strip of stone has been rolled. The roller is then
+taken to the opposite side of the roadway and the operation repeated
+on the other half. The rolling is continued until the stone is
+thoroughly compacted, which is evidenced by the fact that the roller
+makes but a slight track in the surface.</p>
+
+<p>The second layer of stone is then placed and rolled in the same manner
+as the first.</p>
+
+<p><b>Spreading Screenings.</b>&mdash;After the upper course has been rolled, the
+screenings are spread on it from piles alongside the road, enough
+being used to fill the voids in the layer of stone and furnish a
+slight excess. As the screenings are spread they are rolled to work
+them into the voids. When these are filled, the surface is sprinkled
+thoroughly by means of an ordinary street sprinkling cart and again
+rolled. In this way the dust and water are mixed into a mortar which
+fills the crevices between the stones. This mortar hardens in a few
+days, giving a bond that is weak, but sufficient for the purpose if
+the traffic is not too heavy. A broken stone road finished in this way
+is called a water-bound macadam, and is ready for traffic in three or
+four days after completion.<span class="pagenum"><a name="Page_96" id="Page_96">[Pg 96]</a></span></p>
+
+<p><b>Bituminous Surfaces.</b>&mdash;On account of the inadequacy of the water-bound
+macadam when subjected to motor traffic and to obviate the tendency of
+broken stone surfaces to loosen in dry weather, there has been
+developed a method of covering the surface with a bituminous material
+such as tar or asphalt. This will be described in detail in a later
+chapter.</p>
+
+<p><b>Maintenance.</b>&mdash;Even under favorable conditions as regards kind and
+amount of traffic the macadam road requires constant maintenance. The
+first effect of traffic will be to brush away the fine materials used
+for bonding the surface, thus exposing the larger stones in such a way
+that they are rather easily loosened and removed from the surface by
+wheels and the hoofs of animals. This finer material must be replaced
+as fast as it is removed so as to protect the surface. Either stone
+dust or clayey sand may be used, but clay if used alone is likely to
+be sticky when wet and prove to be worse than the condition it was
+expected to correct. In time, ruts and depressions will appear, either
+as the gradual effect of wear, which will inevitably effect some
+portions of the surface more than others, or on account of subsidence
+of the foundation. Uneven places are repaired by first loosening the
+stone, then restoring the cross section by adding new material and
+tamping or rolling it in place.</p>
+
+<p>If a bituminous coating has been applied, it will eventually peel off
+in places and these places must be recoated as soon as practicable.</p>
+
+<p>Eventually the surface will be worn to such an extent that an entirely
+new wearing surface must be added. This is done by loosening the
+entire surface to a depth of 3 or 4 inches and then adding a new layer
+of broken stone. The loosening is sometimes accomplished by means of
+heavy spikes inserted in the roller wheels, and at others by means of
+a special tool known as a scarifier.</p>
+
+<p>The new surface is placed and rolled in precisely the same<span class="pagenum"><a name="Page_97" id="Page_97">[Pg 97]</a></span> manner as
+the wearing surface of the original construction, but the layer may
+not be as thick as the original wearing course. A new course will not
+bond to the old surface unless the old macadam has been thoroughly
+broken up first.</p>
+
+<p><b>Characteristics.</b>&mdash;The water-bound macadam is a dusty, somewhat rough
+surface of low durability for rubber tired vehicles. It has long been
+the standard rural highway for steel tired vehicles, but cannot carry
+any considerable amount of motor traffic. It is easily repaired. When
+finished with a bituminous surface its durability is greatly increased
+and the dust is eliminated. It does not seem to be sufficiently rigid
+for truck traffic, unless placed on exceptionally good foundation.</p>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_98" id="Page_98">[Pg 98]</a></span></p>
+<h2><a name="Chapter_VIII" id="Chapter_VIII"></a><span class="smcap">Chapter VIII</span></h2>
+
+<h3>CEMENT CONCRETE ROADS</h3>
+
+
+<p>The cement concrete road is one of the later developments in highway
+construction, but the type has had sufficient use to show that it is
+one of the satisfactory types for heavy mixed traffic, and, where the
+proper materials are available, it is one of the economical types of
+construction.</p>
+
+<p><b>Destructive Agencies.</b>&mdash;It is well to have clearly in mind at the
+outset that the concrete in a road surface is subjected to certain
+destructive agencies not usually significant in connection with the
+use of concrete, and these are so often disregarded that the average
+serviceability of the concrete road surface is sometimes much lower
+than it would be if built with due regard for the effect of traffic on
+concrete surfaces. In most structural uses of concrete, its strength
+in compression only is utilized, and the factor of safety is such as
+to eliminate to some extent failures due to inferior materials or
+workmanship.</p>
+
+<p>The concrete road surface is subjected to compression under wheel
+loads, to bending, causing tension in the concrete, to abrasion from
+wheels, and to tension and compression due to effect of temperature.
+The weight of the wheel loads may cause sufficient distortion of the
+road slab to produce rupture. The aggregates may be crushed under
+wheel loads if the material is too soft. Abrasion from steel tired
+vehicles wears away the concrete unless it is hard and durable.
+Changes in dimension due to the effect of change in temperature
+introduce tension or compression into the road slab and may result in
+cracks. Freezing and thawing<span class="pagenum"><a name="Page_99" id="Page_99">[Pg 99]</a></span> in the subgrade subjects the slab to
+vertical movement and discontinuous support with the result that
+longitudinal and transverse cracks occur.</p>
+
+<p>The foregoing indicates the importance of securing good concrete for
+road surfacing, and that is accomplished by using suitable aggregates,
+by proper design of the road surface and by following established
+construction methods.</p>
+
+<p><b>Design.</b>&mdash;The widths usually adopted for concrete roads are: for single
+track roads, 9 or 10 feet, and for double track roads, 18 or 20 feet.
+The thickness is 6 to 8 inches at the middle, varying with climatic
+conditions and with the kind of soil upon which the concrete is laid.
+The thickness at the edge is 1 inch less than at the middle except
+that 6-inch surfaces are usually of uniform thickness, the total crown
+being 2 inches. The thickness of the two course pavement is the same
+as would be used for a single course pavement in the same location.
+The surface of either width has a total crown of one or two inches to
+insure water running off the surface. The earth foundation is often
+flat, the crown being obtained by making the slab thicker at the
+middle than at the edge. Fig. 18 shows cross section for concrete
+roads.</p>
+
+<div class="figcenter" style="width: 513px;">
+<img src="images/i0110.png" width="513" height="91" alt="Fig. 18.&mdash;Cross Section for Concrete Highway" title="" />
+<span class="caption">Fig. 18.&mdash;Cross Section for Concrete Highway</span>
+</div>
+
+<p>In the state of California, concrete roads four or five inches thick
+and surfaced with a bituminous carpet mat have been successfully
+constructed. Similar designs have been used in a few other places, but
+for general practice it is unsafe to depend upon such a thin slab.
+Climatic and soil conditions probably account for the success of the
+thin roads in California.<span class="pagenum"><a name="Page_100" id="Page_100">[Pg 100]</a></span></p>
+
+<p><b>Concrete Materials.</b>&mdash;The coarse aggregate for the concrete may be
+broken stone or pebbles screened from natural gravel. Durability is
+necessary, but it is also important to have uniformity in the concrete
+so that the road surface will wear uniformly and consequently keep
+smooth. Supplies of broken stone are likely to contain a small
+percentage of soft pieces and such of these as are at the surface when
+the concrete is finished will crush under traffic, leaving a pit in
+the surface. Pebbles screened from gravel are also likely to be
+variable in durability and should be carefully inspected if they are
+to be used as aggregate for concrete roads. The harder limestones,
+some sandstones, pebbles from many of the gravel deposits and
+practically all of the igneous rocks make satisfactory aggregates for
+the concrete road.</p>
+
+<p>Sometimes none of the coarse aggregates readily available are
+sufficiently durable or uniform for the wearing surface of the
+concrete road, but a suitable aggregate may be obtained at relatively
+high price by shipping considerable distances. In such cases what is
+known as the two course type of concrete road is employed. The wearing
+course usually is about 2 inches thick and is constructed with
+selected aggregates of good quality shipped in for the purpose. The
+lower course is constructed of aggregates which do not possess the
+desired qualities for a wearing course, but which are satisfactory for
+concrete not subjected to abrasion. The aggregates for the wearing
+course will be selected with the same regard for uniformity and
+durability that would be the case if they were for the one course
+pavement.</p>
+
+<p>Bank run gravel, or run of the crusher stone, is generally not
+sufficiently uniform as regards proportion of fine and coarse material
+to produce uniformity in the concrete, and the use of aggregates of
+that character is not permissible for the wearing course, but under
+proper inspection they may be used for the lower course of two course
+pavements.<span class="pagenum"><a name="Page_101" id="Page_101">[Pg 101]</a></span></p>
+
+<p><b>Fine Aggregate.</b>&mdash;The fine aggregate is generally natural sand, but a
+mixture of natural sand and stone screenings is sometimes employed.
+The fine aggregate of whatever character must be clean, free from
+organic matter and sand, must contain no appreciable amount of mica,
+feldspar, alkali, shale or similar deleterious substances and not
+exceed two and one-half per cent of clay and silt. The sand is of such
+a range of sizes that all will pass the one-fourth-inch sieve and that
+not exceeding about five per cent will pass the 100-mesh sieve.</p>
+
+<p><b>Proportions.</b>&mdash;Various mixtures for the concrete are employed because
+these may properly vary to some extent with the exact character and
+grading of the aggregates. Experience seems to have shown that the
+concrete used for the wearing surface should have a crushing strength
+of at least 2500 pounds per square inch, and the mixture adopted is
+based on the requirements that will give the desired crushing
+strength. The common mixture for the one course pavement is one part
+cement, two parts sand and three and one-half parts coarse aggregate.
+For the wearing course of the two-course type of pavement, a mixture
+of the same kind is very often specified.</p>
+
+<p>While these are perhaps the most widely adopted proportions, many
+others have been used, especially where the aggregates exhibit
+peculiarities or the traffic conditions are unusual. It is desired to
+emphasize that the purpose is to obtain concrete of the desired
+strength and there can be no such thing as "standard" proportions.</p>
+
+<p><b>Measuring Materials.</b>&mdash;In considering the methods employed for
+measuring aggregates, emphasis should be placed on the futility of
+rigid requirements for the aggregates, both as regards quality and
+range of sizes, if the materials are carelessly proportioned at the
+mixer. If even reasonably near uniform wearing qualities are to be
+secured throughout the entire area of the concrete road surface,
+successive batches of concrete must be alike, and<span class="pagenum"><a name="Page_102" id="Page_102">[Pg 102]</a></span> to insure that, the
+aggregates including the water in each batch of concrete must be mixed
+in exactly the same proportions. The aggregates are measured in
+various ways, all essentially alike in that the intent is to insure
+exactly the same amount of each ingredient for each batch of concrete.</p>
+
+<p>One method is to place bottomless boxes in wheelbarrows, fill the
+boxes level full and then lift off the box. Another is to use a
+wheelbarrow with a bed of such shape that the contents will be a
+multiple of 1 cubic foot when level full. For the larger jobs, the
+aggregates are hauled in industrial cars, each having sufficient
+capacity for a batch of concrete. The car body is provided with a
+partition so as to separate the fine and coarse material.</p>
+
+<p>The water is measured in a tank which automatically refills to the
+same level each time it is emptied and when adjusted for a mixture
+will introduce the proper amount of water for each batch. It is highly
+important to use the least amount of water that will produce workable
+concrete.</p>
+
+<p><b>Preparation of the Earth Foundation.</b>&mdash;The concrete road is generally
+placed directly on the natural soil which has been brought to the
+proper cross section. Some engineers advocate that in preparing the
+subgrade, the earth be thoroughly rolled; others prefer not to roll
+the subgrade. If fills of considerable depth are constructed, they
+should either be rolled as built or else should be allowed to settle
+for some months before the concrete road is placed, preferably the
+latter.</p>
+
+<p><b>Placing the Concrete.</b>&mdash;The concrete is placed between substantial side
+forms of a height equal to the thickness of the concrete road slab at
+the edge, and is shaped roughly by means of shovels.</p>
+
+<p>Various methods have been developed for striking the surface to the
+exact shape desired and smoothing it. If hand finishing methods are
+employed, a plank template is cut to the prescribed cross section and
+the concrete is<span class="pagenum"><a name="Page_103" id="Page_103">[Pg 103]</a></span> shaped by drawing the template along the side forms.
+Sometimes the template is used as a tamper, being moved along very
+slowly accompanied by an up and down motion that tends to tamp the
+concrete. The template is then drawn along a second time to smooth the
+surface finally.</p>
+
+<p>After the surface has been struck off by hand, it is finally smoothed,
+first by rolling crosswise with a slight hand roller about 8 inches in
+diameter and 30 inches long. The final finish is effected by dragging
+a piece of web belting back and forth across the surface.</p>
+
+<p>Machines designed to tamp the concrete and strike it off to the
+required cross section are also employed for finishing. The machine is
+power operated and is carried on wheels that run on the side forms,
+and the machine moves slowly along as the tamping progresses. The
+concrete is tamped, struck off to shape and smoothed with the belt at
+one operation. This method of finishing produces denser and stronger
+concrete than can be produced by hand finishing methods.</p>
+
+<p><b>Placing Concrete for Two-course Road.</b>&mdash;The methods employed for the
+two-course concrete road are much the same as for the one-course road.
+The concrete for the lower course is placed and struck off by means of
+hand tools, and after that course has progressed a few feet, the upper
+course is placed and finished as has been described for the one-course
+road.</p>
+
+<p><b>Curing the Concrete.</b>&mdash;The setting action of cement is a chemical
+process, not merely a drying out of the water introduced in mixing the
+concrete. The chemical action is progressive for a long time, but is
+more rapid during the first few hours than during the later periods,
+and the concrete reaches about three-fourths of its maximum strength
+at the end of seven days. During the setting period and particularly
+during the first few days, plenty of water must be available to the
+cement.<span class="pagenum"><a name="Page_104" id="Page_104">[Pg 104]</a></span></p>
+
+<p>To prevent too rapid loss of water from the concrete during the
+setting period, the surface must be protected from the wind and sun.
+This is accomplished by first covering with canvas as soon as the
+concrete has hardened sufficiently and by later covering with earth,
+to a depth of two inches. The earth covering is kept wet for about ten
+days and is left in place for about one month.</p>
+
+<p>In some places the ponding method of curing is adopted. The surface is
+divided into sections by earthen dikes and the space inside the dikes
+filled with water to a depth of two or three inches. The water
+covering is maintained for two weeks or longer.</p>
+
+<p>No traffic is permitted on the surface for one month, and in cold
+weather traffic may be kept off the surface for a longer period.</p>
+
+<p><b>Expansion Joints.</b>&mdash;To permit the concrete slab to accommodate itself
+to changes in dimension due to temperature changes, expansion joints
+&frac12; inch wide are placed about every thirty feet. These consist of a
+sheet of some prepared bituminous material placed in position as the
+concrete is poured.</p>
+
+<p>Experience seems to indicate that in spite of the expansion joints,
+the concrete will crack more or less and many engineers think it
+advisable to omit expansion joints in constructing the pavement and
+when cracks develop to pour bituminous material into them, thus
+forming expansion joints.</p>
+
+<p>The prevailing practice in rural highway construction is to omit the
+expansion joints, but they are commonly adopted in city pavements.</p>
+
+<p><b>Reinforcing.</b>&mdash;To minimize the cracking, either bar or wire mesh
+reinforcing is used in the concrete. If bars are used they are placed
+in the concrete as it is poured so as to form a belt around each
+section about 15 feet square. If the mesh type is employed, a part of
+the layer of concrete is placed and smoothed off and a strip of the
+mesh<span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span> laid in place. Additional concrete is then poured on top of the
+mesh to bring the slab to the required thickness.</p>
+
+<p><b>Bituminous Coatings on Concrete Surfaces.</b>&mdash;The concrete road surface
+is sometimes coated with a layer of bituminous material and stone
+chips or gravel pebbles. This is particularly advisable where no
+really satisfactory aggregates are available and the concrete surface
+would not possess sufficient durability. The bituminous material is
+applied hot to the surface and is then covered with stone chips or
+gravel pebbles, ranging in size from &frac34; inch down to &frac14; inch, the
+resulting coating being about &frac34; inch thick. Many failures of this
+type of surface have been recorded due to the difficulty of securing
+adhesion to the concrete. This seems to be due in part to inability to
+get the proper bituminous materials and in part to climatic effects.
+Considerable progress has been made in developing this type of surface
+and it may eventually become a satisfactory maintenance method.</p>
+
+<p><b>Characteristics.</b>&mdash;The concrete road is of a granular texture and is
+not slippery. It is of course rigid and noisy for steel tired
+vehicles. It is an excellent automobile road and its low tractive
+resistance makes it a desirable surface for horse drawn vehicles. It
+possesses a high degree of durability if properly constructed. It is
+likely to crack indiscriminately but as a general rule the cracks are
+not a serious defect.</p>
+
+<p><b>Maintenance.</b>&mdash;The cracks that appear in the concrete surface are
+filled once or twice a year, tar or asphalt being employed. The dust
+and detritus is cleaned out of the cracks and the hot filler poured
+in, with enough excess overflowing to protect the edges.</p>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span></p>
+<h2><a name="Chapter_IX" id="Chapter_IX"></a><span class="smcap">Chapter IX</span></h2>
+
+<h3>VITRIFIED BRICK ROADS</h3>
+
+
+<p>Vitrified brick roads consist of a foundation course of Portland
+cement concrete, broken stone or slag macadam, or of brick laid flat,
+the first named being by far the most generally used, and a wearing
+course of vitrified brick.</p>
+
+<p><b>Vitrified Brick.</b>&mdash;Vitrified brick are made from clay of such a
+character that when heated to the required temperature they will fuse
+into a glassy texture. Brick roads are constructed on roads carrying
+the severest of traffic and the brick must therefore be tough and of
+high resistance to wear.</p>
+
+<p>Not all of the clays from which brick may be manufactured will produce
+a product suitable for road construction, and paving brick, even
+though truly vitrified, are of different degrees of durability,
+depending upon the nature of the clay and the care exercised in the
+manufacture.</p>
+
+<p>Paving brick are manufactured by the stiff mud process, which means
+that the clay is molded into form in a relatively dry condition. To
+accomplish this, considerable pressure is exerted in forcing the
+column of clay through the dies, which form the prism from which the
+brick are cut. If the clay is unsuitable in character or is not
+properly ground and mixed, the brick will possess planes of weakness
+between the various layers of clay which have been pressed together,
+and these planes, called laminations, are a source of weakness if too
+marked. It is usual to specify that the brick used for road surfaces
+shall be free from marked laminations.<span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span></p>
+
+<p>If the brick is not properly burned it will be only partly vitrified
+and therefore not of maximum durability. It is customary to specify
+that the brick shall show a glassy fracture indicating complete
+vitrification.</p>
+
+<p>Various defects of a minor nature occasionally develop in the brick
+during the successive steps in the manufacturing process. Check cracks
+resulting from the burning or from too rapid cooling are often
+encountered, but unless these are deep, that is 3/16 inch or more,
+they do not impair the wearing quality of the brick, nor indicate
+structural weakness. Kiln marks are formed on some of the brick due to
+the weight of the brick above in the kiln. These depressions are not
+objectionable unless the brick are so distorted that they will not lie
+evenly in the pavement.</p>
+
+<p>Spacing lugs or raised letters are formed on one face of the brick to
+insure sufficient space between the brick for the filler. These lugs
+or letters are not less than 1/8 inch nor more than &frac14; inch high and
+of such design that they will not obstruct the free flow of filler
+into the joints between the brick.</p>
+
+<p>Several varieties of paving brick are to be had, the difference being
+principally in the design or size.</p>
+
+<p><b>Repressed Brick.</b>&mdash;In this type of brick the spacing lugs are formed by
+pressing the green brick, after it has been cut to size, into a mold
+on one face of which are recessed letters or other devices into which
+the clay is pressed, thus forming the spacing lugs.</p>
+
+<p><b>Vertical Fiber Brick.</b>&mdash;These brick are designed to be laid with one
+wire-cut face up and spacing is provided by two or more beads on the
+side of the brick. Sometimes the vertical fiber brick has no spacing
+lug, it being contended that the irregularities of the brick are such
+as to provide all of the space required. In practice this does not
+always work out, as the brick are so regular in shape that when laid
+there is too little space between the brick to permit the introduction
+of a suitable filler. The use of brick<span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span> without spacing lugs is just
+beginning and is not yet a generally accepted practice.</p>
+
+<p><b>Wire-cut-lug Brick.</b>&mdash;This is a type of non-repressed brick which has
+spacing lugs provided by cutting one face in a special manner which
+provided lugs for spacing. In this type the wire cut face is the one
+between the brick as they are laid in the pavement.</p>
+
+<p><b>Tests for Quality.</b>&mdash;The standard test for quality of paving brick is
+the rattler test. The brick rattler consists of a barrel of 14 sides
+24 inches long, mounted so as to rotate at a speed between 29.5 and
+30.5 revolutions per minute. The duration of a test is 1800
+revolutions. Ten brick constitute a charge and these are placed in the
+rattler along with 300 lbs. of cast iron spheres. The spheres are of
+two sizes, the smaller being 1-7/8 inch in diameter when new, and the
+larger 3&frac34; inches in diameter when new. Ten of the larger spheres
+are used and the balance of the charge is made up of the small size.</p>
+
+<p>When tested in the standard manner the loss allowable for the several
+classes of service are as follows:</p>
+
+
+
+
+<div class="center">
+<table  summary="Loss Allowable">
+<tr><td class="bt bb center">Traffic</td><td class="bt bb bl center">Average Loss</td><td class="bt bb bl center">Maximum Loss<br />for any Brick</td></tr>
+<tr><td class="left">Heavy</td><td class="bl center">20 per cent</td><td class="bl center">24 per cent</td></tr>
+<tr><td class="left">Medium</td><td class="bl center">22 per cent</td><td class="bl center">26 per cent</td></tr>
+<tr><td class="bb left">Light</td><td class="bb bl center">25 per cent</td><td class="bb bl center">28 per cent</td></tr>
+</table></div>
+
+
+<p><b>Other Tests.</b>&mdash;Sometimes the absorption test is specified for paving
+brick, but it is rarely a vitrified brick that will pass the rattler
+tests which fails to pass a reasonable absorption test. Absorption of
+water in an amount exceeding 4 per cent indicates incomplete
+vitrification and failure of such brick is almost certain during the
+rattler tests.</p>
+
+<p>The cross breaking test is also sometimes employed, but<span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span> generally
+only to check the general quality of the brick. Failure in service
+more frequently occurs from excessive wear than from any other cause
+and the cross breaking test has little significance, except for brick
+less than 3 inches thick, which are to be laid on a sand bedding
+course.</p>
+
+<p><b>Foundation.</b>&mdash;The foundation for brick roads is usually of Portland
+cement concrete, the thickness varying with the nature of the traffic
+and the kind of soil upon which the pavement is built. For well
+drained soils and normal highway traffic, 5 inches is the ordinary
+thickness of foundation. Under favorable conditions such as locations
+with sandy soils or in semi-arid or arid regions where the soil is
+always stable, the foundation may be four inches thick, and a
+considerable mileage of brick road has been built with concrete
+foundations less than four inches thick.</p>
+
+<p>In other locations the soil and traffic conditions require a base six
+inches or more in thickness, and the proper thickness can be
+determined only after all of the factors involved are known and have
+been analyzed. It is impractical to adopt a standard thickness of
+foundation that will be equally economical for all locations and all
+kinds of traffic. As the brick pavement is essentially a heavy traffic
+type of surface, the design cannot be varied greatly with similar
+foundation conditions because the weight of individual loads is the
+significant factor and this does not vary so much as the volume of
+traffic. A variation in volume of traffic may be compensated for by a
+variation in the quality of the brick as already set forth.</p>
+
+<p>The mixtures for the concrete foundation vary widely because of the
+variation in the aggregates employed. If the fine and coarse aggregate
+for the concrete are of good quality a mixture of one part cement, two
+and one-half parts sand and five parts of coarse aggregate would
+insure concrete of adequate strength. A somewhat leaner mixture is
+sometimes employed and would be satisfactory if the aggregates were of
+exceptional concrete making quality.<span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span> Mixtures of sand and pebbles
+(unscreened gravel) may also be used if care is exercised to secure a
+mixture of adequate strength. The proportion will of necessity vary
+with each particular material and the discussion of the various
+considerations involved may be obtained from various standard works on
+concrete and concrete materials.</p>
+
+<p>Broken stone macadam is sometimes utilized for the foundation course
+of the brick pavement and such foundations are constructed as
+water-bound, which is described in a previous chapter. The thickness,
+like that of the concrete foundation, varies with the soil conditions
+and the weight of the loads that are expected to use the road. The
+macadam is placed in a single layer and is rolled and bonded with
+screenings as described in the chapter dealing with water-bound
+macadam. Six inches is a common thickness for the macadam base. This
+type of foundation should be employed only where the soil is quite
+stable and where material costs are such as to insure that the macadam
+base is materially cheaper than one of concrete. This would usually be
+in locations where the cost of cement is high because of long hauls
+and where suitable macadam materials may be obtained close at hand.</p>
+
+<p>Old macadam roads are sometimes utilized for the foundation for the
+brick surface, but the instances where this is permissible are
+comparatively few in number. When an old macadam is to be used it is
+reshaped to the proper cross section and re-rolled and bonded so as to
+afford a stable foundation of the proper cross slope.</p>
+
+
+<h4 class="sc">Bedding Course for Brick Surfaces</h4>
+
+<p>In order to equalize the variations in size and shape of the brick,
+they are laid on a bedding course composed of material into which the
+brick may be forced by rolling. In this way the upper surfaces of all
+brick can be brought to the proper elevation to insure smoothness and
+easy riding<span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span> qualities. Several kinds of bedding course are now
+employed.</p>
+
+<p><b>Sand Bedding Course.</b>&mdash;The sand bedding course has been referred to as
+a sand cushion, but as a matter of experience the cushion effect is
+slight, although sometimes pavements have become uneven because the
+brick have pushed down into the sand after the pavement was used for a
+time. The sand for the bedding course should preferably be fine
+grained, all particles passing the eight mesh sieve, but ordinary
+concrete sand is satisfactory. The sand need not be clean, as a
+comparatively large percentage of silt or clay does not impair the
+usefulness of the material.</p>
+
+<div class="figcenter" style="width: 496px;">
+<img src="images/i0122.png" width="496" height="232" alt="Fig. 19.&mdash;Cross Sections for Brick Highways" title="" />
+<span class="caption">Fig. 19.&mdash;Cross Sections for Brick Highways</span>
+</div>
+
+<p><b>Sand Mortar Bedding Course.</b>&mdash;In order to eliminate the tendency for
+the straight sand bedding course to shift because of the impact of
+traffic on the brick, a lean cement mortar is sometimes employed
+rather than the straight sand. Sand and cement in the ratio of one
+part cement to four or five parts of sand are mixed dry, and after the
+brick have been rolled, is moistened to furnish water to hydrate the
+cement. The sand employed is ordinary clean concrete sand.</p>
+
+<p><b>Green Concrete Bedding Course.</b>&mdash;In the monolithic<span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span> type of brick road
+construction, the brick are laid directly on the green concrete base
+before the concrete has taken a set and the irregularities of the
+brick are taken up by rolling them until bedded in concrete.</p>
+
+
+<h4 class="sc">Fillers for Brick Surfaces</h4>
+
+<p>The spaces between the brick are filled with some material that will
+prevent the brick from being displaced and prevent water getting to
+the bedding course. A suitable filler must adhere to the brick and
+fill completely the spaces between them. It must withstand traffic so
+as to remain intact in the joints and when in place it must be rigid
+enough to prevent displacement of the brick.</p>
+
+<p><b>Cement Grout Filler.</b>&mdash;One of the most commonly used fillers for brick
+pavements consists of a grout composed of Portland cement and fine
+sand. When properly mixed and applied the grout filler meets all
+requirements for a filler except that it is non-elastic and some means
+must be adopted for caring for pavement expansion.</p>
+
+<p><b>Bituminous Fillers.</b>&mdash;Asphaltic materials and tars are widely used as
+fillers for brick pavements. Such fillers are of high melting point
+and consequently solid at ordinary temperature. They are poured into
+the joints hot and when they cool are firm enough to comply with the
+requirements for a filler. In addition, they have enough ductility to
+accommodate the expansion of the pavement due to temperature changes.</p>
+
+<p><b>Mastic Fillers.</b>&mdash;Mastic consists of a mixture of about equal volumes
+of fine sand and a solid bituminous material. The mixture is prepared
+at high temperature and is worked into the joints between the brick
+while hot. When cool it resembles the straight bituminous filler
+except that the mastic is somewhat more resistant to wear than the
+straight bituminous filler.<span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span></p>
+
+<h4 class="sc">Expansion Joints</h4>
+
+<p>It is recognized that brick will expand and contract with changes in
+temperature. When a bituminous or mastic filler is employed there is
+sufficient yield to the filler to accommodate the change in dimension
+in the brick, but when the grout filler is used either the expansion
+joint must be provided or the pavement must be designed to withstand
+the compression due to expansion of the brick. Expansion joints may
+consist of a sheet of bituminous mastic prepared for the purpose and
+set in place in the pavement. The sheet of joint material is simply
+inserted between courses of brick at the proper place.</p>
+
+<p>Another method of forming an expansion joint consists in placing a
+strip of wood between courses of brick at the place where a joint is
+required. After the pavement has been grouted, the wooden strip is
+pulled out and the joint is filled with a suitable bituminous filler.</p>
+
+<p><b>Marginal Curb.</b>&mdash;If the sand bedding course is employed, it is
+necessary to provide curbing along the sides of the brick to hold the
+bedding course in place. The curb is usually constructed integral with
+the base and of concrete of the same mixture as the base. The width of
+the curb is usually six inches and the top of the curb is at the same
+elevation as the edge of brick surface.</p>
+
+
+<h4 class="sc">Construction of the Surface</h4>
+
+<p>Before the construction of a brick surface should be undertaken on a
+road, the drainage should be provided for even more completely than
+for a less costly type of surface since it does not pay to jeopardize
+the stability of the pavement by failure to provide adequately for the
+stability of the supporting soil. Grades should also be reduced to the
+economical limit.</p>
+
+<p>The earth subgrade is brought to the proper elevation<span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span> and cross
+section and is thoroughly rolled. If there are places where the soil
+will not compact properly under rolling, these places are corrected by
+taking out the material and back filling with new material that will
+properly compact under the roller.</p>
+
+<p>The aggregates for the concrete may be distributed along on the
+prepared subgrade or may be stored in stock piles or bins at
+convenient points. If stored on the subgrade, a traction mixer is
+employed which is drawn along the road as the work progresses, the
+materials being placed directly in the mixer. If stored at a central
+point, they may be transported to the mixer on the road and dumped
+directly into the mixer, or the mixer may be set up at the storage
+piles and the concrete hauled in trucks to the road where it is
+deposited and shaped.</p>
+
+<p>The concrete is spread to the proper thickness and tamped either by
+hand or by machinery. If the marginal curb is to be employed, it is
+constructed immediately after the concrete for the base has been
+finished but before the cement begins to set.</p>
+
+<p>After the foundation concrete has set, the bedding course is spread
+and struck off to the proper thickness. When the bedding course
+consists of sand-cement mortar, the sand and cement are mixed dry and
+spread to prescribed thickness. It is considered to be desirable to
+roll the sand bedding course with a light hand roller before the brick
+are placed, but the sand-cement bedding course is not rolled. The
+bedding course must be carefully shaped by means of a templet or
+strike board before the brick are placed.</p>
+
+<p>The brick are laid in straight courses across the pavement, with the
+spacing lugs all in the same direction if brick with spacing lugs are
+employed, and with the lugs in contact with the brick of adjoining
+courses. If brick without spacing lugs are used they are laid loosely
+so that there will be room for the filler between the brick of
+adjoining courses.<span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span></p>
+
+<p>After the brick have been laid they are rolled to bed them in the sand
+or sand-mortar bedding course and thus secure a smooth surface. For
+this purpose a light, power driven, tandem roller is used and the
+rolling is continued until the brick are thoroughly bedded. Any
+defective brick that are noted are removed and replaced with good
+brick and after this culling has been completed the surface is once
+more thoroughly rolled. If a cement-sand bedding course is employed,
+the surface is sprinkled just after the final rolling so that water
+will flow down between the brick and moisten the bedding course
+sufficiently to cause the cement to set. In some cases, the
+sand-cement bedding course is sprinkled just before the brick are laid
+but in warm weather the setting would take place before the brick
+could be rolled if that were done. In cool weather the setting is
+sufficiently slow to permit rolling before the bedding course hardens.</p>
+
+<p>The filler is applied to the surface after the rolling. If the
+bituminous type of filler is employed, the hot filler is poured onto
+the surface and worked into the joints by means of squeegees, with
+comparatively little material left on the surface. In some instances
+cone-shaped pouring pots are employed and the material is poured
+directly into the joints.</p>
+
+<p>The cement grout filler is applied in the same general manner as the
+bituminous filler. The grout, consisting of equal parts of sand and
+cement, is mixed to a thin consistency and poured onto the surface and
+is then worked into the joints with squeegees. Two or more
+applications are usually required to effect a complete filling of the
+joints. The surface should be covered with sand and be kept moist
+until the cement grout has set.</p>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span></p>
+<h2><a name="Chapter_X" id="Chapter_X"></a><span class="smcap">Chapter X</span></h2>
+
+<h3>BITUMINOUS ROAD MATERIALS AND THEIR USE</h3>
+
+
+<p>Tars and asphaltic materials of various kinds are widely used for road
+construction and maintenance, especially for road surfaces subjected
+to motor traffic. Materials of this character that are employed in
+highway work possess varying degrees of adhesiveness, and while they
+may be semi-solid or viscous liquids at air temperature, they melt on
+the application of heat and can be made sufficiently fluid to mix with
+the mineral aggregates that may be used in the road surface. Upon
+cooling, the bituminous materials return to the previous state and
+impart a certain amount of plasticity to the mixture, at the same time
+serving as a binding or cementing agent, which is sufficiently stable
+for many classes of road construction.</p>
+
+<p><b>Classes of Bituminous Materials.</b>&mdash;Bituminous materials may be
+classified, according to the source from which they are obtained, as
+coal tars, water gas tars, native or natural asphalts and oil or
+petroleum asphalts.</p>
+
+<p><b>Coal Tar.</b>&mdash;Coal tar is obtained as a by-product in the manufacture of
+illuminating gas from coal. It is also obtained in the manufacture of
+coke from coal. The tar thus obtained is manufactured into products
+that are used for dust layers on gravel or macadam roads, binders for
+macadam and gravel surfaces, fillers for brick, wood block and stone
+block pavements and for expansion joints. These various materials
+differ mainly in their consistency at air temperature. (They may
+differ widely in chemical composition, but that need not be considered
+herein.)<span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span></p>
+
+<p><b>Water Gas Tar.</b>&mdash;Water gas tar is obtained as a by-product in the
+manufacture of illuminating gas from crude petroleum. It is used for
+the same kinds of construction as coal tar, and the products utilized
+for the several purposes, like the coal tars, differ mainly in
+consistency.</p>
+
+<p><b>Natural Asphalt.</b>&mdash;Natural asphalt is found in deposits at many places
+in the world, existing in beds or pools where it has exuded from the
+earth or as veins in cavities in the rocks. It is of varying
+composition and consistency, but those kinds in most general use are
+solid or very viscous liquids at air temperature. Of the deposits that
+have been developed on a commercial scale, the Trinidad lake in the
+British West Indies and Bermudez deposit in Venezuela are best known.
+Both of these materials are too hard in the natural state to be used
+for road construction, and are softened, or fluxed as it is called,
+with fluid petroleum oil before being used.</p>
+
+<p><b>Petroleum Asphalt.</b>&mdash;Petroleum asphalt is a residue remaining after the
+fluid products have been distilled from petroleum. Residues of this
+sort are not always suitable for road construction, but a number of
+brands of road material are obtained from this source. Oil asphalts
+are used for dust layers, for binders for macadam roads, for asphalt
+cements for sheet pavement surfaces, and for fillers for block
+pavements and expansion joints.</p>
+
+<p><b>Mixtures.</b>&mdash;Water gas tars and asphalts are sometimes mixed to produce
+road materials, and likewise native asphalts and residues obtained
+from petroleum are sometimes mixed to produce asphalt cements for
+paving mixtures.</p>
+
+<p><b>Classification according to Consistency.</b>&mdash;The various bituminous
+materials may be classified according to consistency in discussing the
+various uses to which they may be put.</p>
+
+<p><b>Road Oils.</b>&mdash;Road oils are fluid petroleum oils of such consistency
+that they may be applied cold or by heating<span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span> slightly. They are used
+as dust layers on earth, gravel and macadam surfaces. Their efficacy
+depends upon the binding properties of the small amount of asphaltic
+material that is contained in the oil.</p>
+
+<p><b>Liquid Asphalts.</b>&mdash;These are somewhat less fluid than the road oils,
+and must always be heated before application, but are viscous liquids
+at ordinary temperature. These materials are obtained from crude
+petroleum or semi-solid native bitumens, in which case they are
+usually called malthas. Both coal tars and water gas tars of
+semi-solid consistency are also employed for the same class of
+construction as the liquid asphalts.</p>
+
+<p>These materials are used for carpeting mediums on macadam roads and as
+cementing agents in the construction of hot-mixed macadam.</p>
+
+<p><b>Asphalt Cements.</b>&mdash;The solid asphaltic materials used for hot-mixed
+types of construction are called asphalt cements. They may be
+petroleum residues or native asphalts fluxed with petroleum oils. They
+are solids at ordinary temperature and must be heated to a temperature
+in excess of two hundred and fifty degrees before they are
+sufficiently fluid to use. Asphalt cements are used for sheet asphalt
+and asphaltic concrete construction and for hot-mixed bituminous
+macadam.</p>
+
+<p><b>Fillers.</b>&mdash;Fillers are solid asphalts or tars that are used for filling
+expansion joints in rigid pavements and for filling the spaces between
+the blocks in brick, wood block and stone block pavements.</p>
+
+<p><b>Bitumen.</b>&mdash;Bituminous materials are all soluble to a greater or lesser
+extent in carbon disulphide and the soluble portion is called bitumen.
+It is the bitumen that gives to the materials the cementing properties
+utilized in road construction. Mixtures of mineral aggregates and
+bituminous materials for various purposes are proportioned with
+bitumen as a basis. Therefore, less of an asphalt containing one
+hundred per cent bitumen will be used than<span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span> of one containing less
+than one hundred per cent of bitumen.</p>
+
+<h4 class="sc">Table 8</h4>
+<h4 class="sc">Properties of Asphaltic Road Materials</h4>
+
+<div class="center">
+<table class="dense" summary="Properties of Asphaltic Road Materials">
+<tr><td class="bt bb bl center">Material</td><td class="bt bb center">Specific Gravity</td><td class="bt bb center">Consistency</td><td class="bt bb center">Solubility<br />in CS<sub>2</sub>,<br />Per Cent</td><td class="bt bb center">Solubility of<br />Bitumen<br />in CCl<sub>4</sub>,<br />Per Cent</td><td class="bt bb center">Solubility<br />of Bitumen<br />in 86° Naphtha,<br />Per Cent</td><td class="bt bb center">Fixed Carbon,<br />Per Cent</td><td class="bt bb center">Flash Point</td><td class="bt bb center">Ductility</td></tr>
+<tr><td class="hang bl left">Mexican&nbsp;oil asphalts</td><td class="right">1.03-1.05</td><td class="right">As&nbsp;desired</td><td class="right">99.5-99.9</td><td class="right">99.5-99.9</td><td class="right">70-80</td><td class="right">13-16</td><td class="right">200°C.&nbsp;up</td><td class="right">60-100</td></tr>
+<tr><td class="hang bl left">California oil asphalts</td><td class="right">1.02-1.04</td><td class="right">As desired</td><td class="right">99.9</td><td class="right">99.9</td><td class="right">75-80</td><td class="right">10-12</td><td class="right">200°C. up</td><td class="right">100+</td></tr>
+<tr><td class="hang bl left">Texas oil asphalts</td><td class="right">1.01-1.03</td><td class="right">As desired</td><td class="right">99.9</td><td class="right">99.9</td><td class="right">75-80</td><td class="right">12-14</td><td class="right">200°C. up</td><td class="right">50-100</td></tr>
+<tr><td class="hang bl left">Bermudez natural asphalt</td><td class="right">1.07</td><td class="right">25</td><td class="right">95</td><td class="right">99+</td><td class="right">68-70</td><td class="right">13-14</td><td class="right">...</td><td class="right">...</td></tr>
+<tr><td class="hang bl left">Trinidad natural asphalt</td><td class="right">1.40</td><td class="right">7</td><td class="right">56-57</td><td class="right">100</td><td class="right">64-65</td><td class="right">10-11</td><td class="right">...</td><td class="right">...</td></tr>
+<tr><td class="bb bl hang left">Bermudez asphalt cement</td><td class="bb right">1.04-1.06</td><td class="bb right">Up to 135</td><td class="bb right">95-97</td><td class="bb right">99.5&nbsp;or&nbsp;more</td><td class="bb right">77-80</td><td class="bb right">11-12</td><td class="bb right">175-200</td><td class="bb right">25-50</td></tr>
+</table></div>
+
+
+<p><b>Specifications.</b>&mdash;Some properties of bituminous materials can be varied
+in the process of manufacture, while others are inherent in the
+material and cannot be changed in the process of manufacture.
+Specifications must therefore be drawn with care to insure that the
+requirements can be met by satisfactory materials. But certain
+properties, such as specific gravity, may vary greatly among materials
+equally satisfactory for construction purposes. One should not be
+misled by apparent differences in the characteristics of materials,
+because these may simply be natural peculiarities which have no
+bearing on the usefulness of the material. There are given in Table 8
+the properties of some of the commonly used bituminous materials and
+the<span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span> properties that can be varied in the process of manufacture are
+indicated with an asterisk. A variation in these properties will
+usually result in some change of other properties, but generally not a
+great change.</p>
+
+
+<h4 class="sc">Surfaces in which Bituminous Materials are Utilized</h4>
+
+<h5>I. Surface Treatments</h5>
+
+<p>Attention has been directed to the rapid deterioration of water-bound
+macadam when subjected to passenger automobile traffic.</p>
+
+<p>In water-bound macadam the stones are held in place by a weak cement
+composed of stone dust and water, and this cement is not sufficiently
+strong to hold the stones in place when they are subjected to the
+shear of automobile tires. In finishing the water-bound macadam
+surface, the spaces between the stones are filled with screening and
+in addition a layer about one-fourth inch thick is left on the
+surface.</p>
+
+<p>The automobile traffic first brushes aside all of the screenings and
+smaller particles of rock, exposing the larger stones. These gradually
+loosen as the road is used and are brushed aside. When this effect
+begins, the road is said to be raveling. Various lengths of time may
+elapse from the time the road is first finished until raveling begins,
+depending upon the character of the stone, the weather and the amount
+of motor traffic. During the period before raveling starts, it is
+comparatively easy to restore the road surface at any time by the
+addition of screenings or clay and sand. Usually there will be a few
+small areas of the surface that, on account of faulty construction,
+will ravel or become rutted much earlier than the remainder of the
+surface. These can be repaired by the methods described in the chapter
+on "Water-bound Macadam Construction." When the surface begins to
+ravel seriously, maintenance becomes much more difficult and in order
+to<span class="pagenum"><a name="Page_121" id="Page_121">[Pg 121]</a></span> prevent raveling and the difficulties of maintenance thereafter,
+the macadam surface is often coated with a bituminous material.</p>
+
+<div class="figcenter" style="width: 471px;">
+<img src="images/i0132.png" width="471" height="279" alt="Fig. 20.&mdash;Oiling a Gravel Road" title="" />
+<span class="caption">Fig. 20.&mdash;Oiling a Gravel Road</span>
+</div>
+
+<p>If there is any dust or screenings on the road surface, the bituminous
+material will not adhere to the stones and will soon flake off under
+traffic. The surface of the macadam must therefore be thoroughly
+cleaned before the bituminous material is applied. The usual practice
+is to finish the road as water-bound macadam, and permit traffic on it
+for a sufficient length of time to show any weak places in the surface
+and at the same time thoroughly to season the surface. If any
+defective places appear, they are repaired and when the surface
+exhibits satisfactory stability, but before it begins to ravel, the
+bituminous surface is applied. There will ordinarily be some stone
+dust and some screenings remaining on the surface at the time
+bituminous treatment is undertaken, and there may also be some caked
+mud or other foreign material. All of this must be removed so as to
+expose the stones throughout.<span class="pagenum"><a name="Page_122" id="Page_122">[Pg 122]</a></span></p>
+
+<p><b>Applying the Bituminous Binder.</b>&mdash;The bituminous binder may be
+delivered in tank cars, which is desirable if the work is near a
+railroad siding, or ample tank wagon service is available for long
+hauls so that the tank will not be held up too long. Often it is
+desirable to purchase the binder in barrels and haul these to the site
+of the work in advance of beginning the construction of the surface.</p>
+
+<p>The bituminous material may be applied by means of hand spreading cans
+not unlike an ordinary garden watering pot, except that a slotted
+nozzle is substituted for the ordinary perforated one. If hand methods
+are employed for spreading, the bituminous material is heated in open
+kettles and then spread on the surface, the quantity required usually
+being about one-half gallon per square yard of surface. The
+temperature of the binder should be great enough to insure fluidity
+and the road should be dry at the time of the application. As soon as
+the material has been spread, the surface is finished with a dressing
+of chips.</p>
+
+<p><b>Finishing the Surface.</b>&mdash;For surface dressing the best material is
+stone chips ranging in size from about 1 inch down to one-fourth inch.
+But the chips must be of durable material, or they will quickly grind
+into dust. They must be free from dust when applied, as the presence
+of any considerable amount of dust interferes with the proper
+finishing of the surface. The stone chips are rolled into the surface,
+a sufficient quantity being used to just cover the surface.</p>
+
+<p><b>Patching.</b>&mdash;It almost always happens that some small areas will not be
+properly cleaned or that for some unknown reason the coating peels off
+the surface. Such places must be promptly patched to prevent them
+enlarging under the action of traffic. This work is usually done by
+patrolmen, who inspect the road at frequent intervals and make the
+necessary repairs. The patrolman is equipped with a small heating
+kettle, a spreading can and the necessary<span class="pagenum"><a name="Page_123" id="Page_123">[Pg 123]</a></span> brushes, tampers and
+miscellaneous tools needed for the repair work. The place to be
+patched is carefully cleaned, coated with bituminous binder and stone
+chips and tamped until dense and solid. Repairs made in this way are
+exceedingly important in that they arrest deterioration in its early
+stages and maintain a high degree of serviceability.</p>
+
+
+<h5>II. Penetration Macadam</h5>
+
+<p>A considerable mileage of macadam has been constructed in which an
+attempt was made to eliminate the difficulties of maintenance by a
+method of construction that involves applying a bituminous binder in
+such a manner as to permit it to penetrate two inches or more into the
+surface. It is expected that the binder will coat the stones to such
+an extent as to increase materially the stability of the bituminous
+macadam over the surface treated one. It is also expected that less
+difficulty will be encountered in maintaining a surface of bituminous
+material and stone chips on this type of road than on the water-bound
+macadam. The extent to which these expectations have been realized has
+varied to a marked degree and although some excellent surfaces have
+been constructed by this method, the results have as a rule been
+neither uniform nor entirely satisfactory. It seems to be apparent
+that good results cannot be obtained unless the materials are entirely
+suitable and the construction is carried out with unusual skill.</p>
+
+<p><b>Foundation.</b>&mdash;The foundation or lower course consists of a layer of
+broken stone six inches thick placed on a well drained and thoroughly
+rolled earth subgrade. In exceptional cases, the Telford type of
+foundation might be employed.</p>
+
+<p>The lower course of broken stone is finished in the same manner as
+water-bound macadam, being bonded with stone screenings or with fine
+gravel of high clay content.</p>
+
+<p>Since this course is in reality the foundation of the surface,<span class="pagenum"><a name="Page_124" id="Page_124">[Pg 124]</a></span> it is
+necessary to secure stability by appropriate construction methods,
+exactly as in constructing water-bound macadam.</p>
+
+<div class="figcenter" style="width: 352px;">
+<img src="images/i0135.png" width="352" height="335" alt="Fig. 21.&mdash;Type of Roller used on Gravel and Macadam
+Roads" title="" />
+<span class="caption">Fig. 21.&mdash;Type of Roller used on Gravel and Macadam
+Roads</span>
+</div>
+
+<p><b>Upper or Wearing Course.</b>&mdash;The wearing course consists of a layer of
+stone about two and one-half inches thick. The stone is placed and
+rolled and the spaces between the stones partially filled with some
+suitable bituminous material. The bituminous material is usually
+applied by means of a mechanical spreading device connected to a tank
+wagon. The bituminous materials employed for this class of
+construction are semi-solid in character and must be heated to give
+them sufficient fluidity for application. They may be heated in the
+tank wagon which is used for the application or they may be heated in
+separate tanks and transferred to the distributing wagon for
+spreading. Some kind of a nozzle or group of nozzles is employed for
+spreading the material so that it can be delivered in the<span class="pagenum"><a name="Page_125" id="Page_125">[Pg 125]</a></span> form of a
+spray or at least in a thin fan-shaped stream and can be distributed
+in a fairly uniform layer over the stone. The binder will cool rather
+rapidly after it is applied, but meanwhile will flow into the openings
+between the stones and will form over the surface stones a coating of
+slight thickness.</p>
+
+<p>The surface of the macadam is next covered with a layer of chips of
+tough rock, similar to the material used for the final dressing in
+surface treatments. These are carefully brushed into the openings
+between the larger stones by means of heavy brush brooms. This is an
+exceedingly important part of the work and often a much neglected part
+of the construction.</p>
+
+<p>The surface is then covered with a second application of bituminous
+material, somewhat less in quantity than required for the first
+treatment and the surface again covered with stone chips and brushed.</p>
+
+<p>The surface is then thoroughly rolled and is ready for traffic.</p>
+
+<p><b>Patching.</b>&mdash;As in the case of surface treatments, there are likely to
+be places that, on account of defects in the construction, will fail
+soon after the road is placed under traffic. These will quickly
+enlarge unless they are repaired promptly. The repairs are made by
+loosening the stone in the area affected and adding new stone as
+needed and then pouring on the necessary amount of bituminous material
+to coat the stones. Allowance must be made for the compression of the
+material by tamping so that a depression does not result. The stones
+are carefully tamped to place and covered with chips which are also
+tamped.</p>
+
+<p><b>Characteristics.</b>&mdash;The penetration macadam is a surface well adapted to
+motor traffic if the individual vehicles are not too heavy. It is
+likely to squeeze out of shape under motor truck traffic, becoming
+seriously uneven and uncomfortable for traffic. Its durability is
+materially affected by the construction methods followed.<span class="pagenum"><a name="Page_126" id="Page_126">[Pg 126]</a></span></p>
+
+
+<h5>III. Hot Mixed Macadam</h5>
+
+<p>The wearing course of the mixed macadam is composed of graded broken
+stone or gravel and a bituminous binder. Usually the bituminous
+material only is heated prior to the mixing, but sometimes the stone
+is also heated.</p>
+
+<p><b>Foundation.</b>&mdash;The lower course, which serves as the foundation, is
+either broken stone macadam, gravel or concrete.</p>
+
+<p>Where a foundation of broken stone is used, it is constructed of the
+materials and in the manner described for the foundation of the
+penetration macadam. Quite often a badly worn macadam or gravel road
+is used for the foundation and a new wearing course provided by adding
+a mixed macadam surface. If such is the case, the old surface is
+worked over so as to restore the shape sufficiently and to insure that
+it is everywhere of sufficient thickness.</p>
+
+<p>Portland cement concrete is sometimes used as a foundation for the
+mixed macadam, but not often. Usually if the traffic is of a character
+requiring a concrete foundation, it is desirable to use a better
+wearing course than the mixed macadam, and the asphaltic concrete or
+sheet asphalt type of surface is employed. It is necessary to finish
+the surface of the concrete base with some device that will leave the
+surface rough to prevent the macadam from creeping. A knobbed tamper
+which leaves numerous irregular depressions about 2 inches in diameter
+and three-fourths inch deep is often employed.</p>
+
+<p><b>Sizes of Stone.</b>&mdash;For the wearing surface, stone ranging in size from 2
+inches down to one-fourth inch is usually employed. If the stone is of
+good quality the maximum size may be but 1&frac12; inches, but soft or
+even medium stone of that size are likely to crush under traffic. The
+stone for the base course should preferably be from 3 inches down, but
+any available size will be satisfactory if the layer is well rolled
+and bonded. The base course is constructed<span class="pagenum"><a name="Page_127" id="Page_127">[Pg 127]</a></span> in the same manner as
+water-bound macadam and any material satisfactory for the base course
+of macadam will serve for the base course of mixed macadam. Screenings
+having good bonding properties will also be required for the base
+course.</p>
+
+<p><b>Mixing and Wearing Surface.</b>&mdash;Several methods are employed in mixing
+the wearing surface. The simplest is to mix by hand with shovels. The
+aggregates are heated in improvised heaters which may consist of
+nothing more than a metal pipe two or three feet in diameter, around
+which the stone is piled. The mixing platform is usually a metal plate
+sometimes arranged so that it can be heated by means of a fire
+underneath. The bituminous material is heated in kettles. For some
+mixtures, the stone is not heated, but the bituminous material is
+always heated. The batch of stone is placed on the mixing platform,
+the bituminous material added and the materials mixed by hand.</p>
+
+<p>Machine mixing is practiced much more extensively than hand mixing,
+being both more rapid and cheaper. The mixer is similar to a concrete
+mixer except that the drum is arranged so that it can be heated. The
+hot stone and the bituminous binder are put into the drum and mixed
+for the requisite length of time. Sometimes the stone is mixed cold,
+the bituminous material only being heated.</p>
+
+<p><b>Placing the Wearing Surface.</b>&mdash;The hot mixture is carted to the road
+and spread to such thickness that after rolling the wearing surface
+will be not less than two inches thick. The hot mixture is dumped and
+then spread by means of shovels to the approximate thickness and the
+spreading completed by means of rakes. The surface is then rolled
+either with a tandem or a three-wheeled roller until thoroughly
+compressed.</p>
+
+<p><b>Seal Coat.</b>&mdash;After the rolling has been completed, the surface is
+covered with hot bituminous cement and dressed with pea gravel or
+stone chips and again rolled. Traffic may be permitted in twenty-four
+hours.<span class="pagenum"><a name="Page_128" id="Page_128">[Pg 128]</a></span></p>
+
+<p><b>Characteristics.</b>&mdash;The mixed macadam is a somewhat resilient surface of
+excellent riding qualities and considerable durability for medium
+traffic. It is likely to creep and become uneven when subjected to
+heavy loads. The seal coat will wear off in two or three years and
+will require replacing.</p>
+
+
+<h5>IV. Asphaltic Concrete</h5>
+
+<p>Asphaltic concrete is a name given to a road surface mixture which is
+composed of graded stone, graded sand and asphalt cement. This type is
+designated as asphaltic concrete because of the analogy of the mixture
+to Portland cement concrete.</p>
+
+<p>Asphaltic concrete is of two general types known as bitulithic, or
+Warrenite, and Topeka asphaltic concrete, respectively, the
+differences being in the nature of the mixture.</p>
+
+<p><b>Bitulithic or Warrenite.</b>&mdash;The stone employed for these types is graded
+down from a size about equal to one-half of the thickness of the
+wearing course, and stone passing a 1&frac14; or 1&frac12;-inch screen is
+usually specified. From the maximum size the stone is graded down to
+the finest particles produced by the crusher. The range of sizes of
+stone will vary with the source of the supply, and in order to secure
+the desired density in the mixture, varying amounts of graded sand and
+mineral dust, such as ground limestone or Portland cement, are added
+to the broken stone. Usually the resulting mixture contains less than
+fifteen per cent of voids, and to this carefully graded mineral
+aggregate there is added enough asphalt cement to bind together the
+particles.</p>
+
+<p><b>Topeka Asphaltic Concrete.</b>&mdash;In this type of asphaltic concrete, the
+mineral aggregate consists of a mixture of carefully graded sand and
+of broken stone of such size that all will pass a one-half-inch screen
+and graded down to the fine dust produced by the crusher. To this
+mixture is added about nine per cent of Portland cement or limestone
+dust.<span class="pagenum"><a name="Page_129" id="Page_129">[Pg 129]</a></span> The voids in the mixture are usually about twenty-five per
+cent.</p>
+
+<p>It will be seen that the essential differences between the Bitulithic
+and Topeka types are these: the Topeka type contains a larger
+percentage of voids and stone of a smaller maximum size than the
+Bitulithic. Both types have been extensively employed for city paving,
+but the Bitulithic and Warrenite types have also been used to some
+extent for rural highways. The Topeka type has been used but little
+for rural highways.</p>
+
+<p><b>Foundation.</b>&mdash;The foundation for the asphaltic concrete may be an old
+macadam road, a base course constructed of broken stone or Portland
+cement concrete, the latter being used much more extensively than
+either of the other types.</p>
+
+<p>Sometimes asphaltic concrete is used for resurfacing water-bound
+macadam or gravel roads when the traffic has increased to the point
+where the cost of maintenance of the water-bound macadam has become
+excessive. The existing surface is repaired and the cross section is
+restored, or possibly flattened somewhat.</p>
+
+<p><b>Placing the Surface.</b>&mdash;The stone, sand and asphalt cement are heated to
+the required temperature and combined in the proper proportions and
+are then thoroughly mixed by a mechanical mixer. The mixture is hauled
+directly to the road and is dumped and spread by means of rakes. It is
+then rolled thoroughly while still hot, a three-wheeled roller being
+most satisfactory. After rolling, a seal coat of hot asphalt cement is
+spread over the surface and covered with hot stone chips about &frac14;
+inch in size. The surface can be opened to traffic immediately after
+the surface has been completed.</p>
+
+<p><b>Characteristics.</b>&mdash;The asphaltic concrete surface is of excellent
+riding properties, is easily repaired and of moderate durability. It
+is a particularly desirable surface for pleasure automobile riding and
+for horse drawn traffic.</p>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_130" id="Page_130">[Pg 130]</a></span></p>
+<h2><a name="Chapter_XI" id="Chapter_XI"></a><span class="smcap">Chapter XI</span></h2>
+
+<h3>MAINTENANCE OF HIGHWAYS</h3>
+
+
+<p>Proper maintenance of highways is equally important with proper
+construction. With nearly all types of road construction, the need for
+maintenance arises soon after the surface is placed under traffic and
+is continuous thereafter. The nature and amount of maintenance work
+varies greatly among the several types of surface and the organization
+suitable for a system of highways will depend to a considerable extent
+upon the kinds of surfaces that are to be maintained.</p>
+
+<p>The upkeep of a road may be conveniently considered as of two kinds,
+viz., (1) that which has to do with the wearing surface and earth
+shoulders or berms upon which there is some traffic and (2) that which
+has to do with the side ditches and drainage structures and keeping
+the roadside in presentable condition. Both kinds of work are usually
+carried out by the same organization, but whereas the nature of the
+work indicated under (1) will vary with the type of wearing surface
+and with all variations in traffic, that which is indicated under (2)
+will be nearly constant in any locality.</p>
+
+
+<h4 class="sc">Organization for Maintenance</h4>
+
+<p>Maintenance of highways is preferably under the administration of the
+same authority as construction and when an improvement is undertaken
+under the jurisdiction of a State Highway Department, the completed
+improvement is ordinarily maintained under the state<span class="pagenum"><a name="Page_131" id="Page_131">[Pg 131]</a></span> authority. If
+the improvement is made by county authorities, the maintenance is also
+carried out under county authority.</p>
+
+<p>The nature of the organization of maintenance forces is dependent upon
+the kind of roads to be cared for and must of necessity be varied in
+any instance as conditions demand. In general, either maintenance
+gangs or patrolmen are employed and often both are used on the same
+road system.</p>
+
+<p><b>Patrol Maintenance.</b>&mdash;Where this system is in operation, the highway
+system is divided into patrol districts of from six to eighteen miles
+of highway and a single patrolman is placed in charge of each
+district. He is provided with all of the necessary tools and materials
+required in his district and performs all of the work required in the
+ordinary upkeep of the highway. He should work under the direction of
+the county engineer or the district engineer for the state highway
+department, because his work involves the use of materials and
+processes requiring technical supervision.</p>
+
+<p><b>Gang Maintenance.</b>&mdash;The maintenance gang may be employed for some types
+of road surface in lieu of the patrolman or with other types of
+surface may be employed to supplement the work of the patrolman. The
+maintenance gang consists of three to ten men and is furnished all of
+the tools and materials required for the particular kind of work they
+do. Ordinarily the gang goes over the roads assigned to it once each
+season and performs those repair operations requiring more work than
+the patrolman can find time for. The work of the maintenance gang like
+that of the patrolman should be under engineering supervision.</p>
+
+<p><b>Maintenance of Earth, Sand-clay, Gravel and Macadam Roads.</b>&mdash;The
+ordinary upkeep of earth, sand-clay, gravel and macadam surfaces is
+most readily accomplished by the patrol method, since constant care is
+required to keep the roads in a condition of maximum service ability.<span class="pagenum"><a name="Page_132" id="Page_132">[Pg 132]</a></span></p>
+
+<p>The tools required for each patrolman may include the following:</p>
+
+
+<div class="center">
+<table summary="Tools">
+<tr><td class="left">1 shovel</td><td class="left">1 spade</td></tr>
+<tr><td class="left">1 stone rake</td><td class="left">1 pick</td></tr>
+<tr><td class="left">1 scythe</td><td class="left">1 tamper</td></tr>
+<tr><td class="left">1 or more road drags</td><td class="left">1 mowing machine for cutting weeds (sometimes)</td></tr>
+<tr><td class="left">1 wheelbarrow</td><td class="left">1 small kit carpenter's tools</td></tr>
+<tr><td class="left">1 light truck</td></tr>
+</table></div>
+
+
+<p>The work of the patrolman consists in keeping the surface of the road
+smooth by dragging, repairing chuck holes by tamping in fresh material
+of the appropriate kind, keeping the ditches and culverts free from
+obstruction, cutting weeds and repairing bridge floors if they are of
+plank construction. Removal of snow drifts is sometimes a part of the
+patrolman's duty, but more often that is done by special gangs.
+Usually the patrolman is authorized to hire teams for dragging and
+cutting weeds.</p>
+
+<p>When an earth road requires to be re-graded so as to restore the
+cross-section and deepen the ditches, a gang is sent in to perform
+that work, as it is obviously impossible for the patrolman to perform
+work, of that kind.</p>
+
+<p>If the gravel road is being maintained with a bituminous carpet coat,
+the patrolman will be furnished the necessary tools to enable him to
+patch the surface with bituminous material as necessity requires.</p>
+
+<p>When the surface deteriorates to such an extent that a new carpet coat
+is required, the gang system is employed for all work connected with
+resurfacing, instead of attempting to have the work done by patrolmen.</p>
+
+<p>The maintenance of the macadam road is carried out in much the same
+manner as that of the gravel road. The binder of stone dust or clayey
+sand is renewed as often as it is swept off by traffic. Depressions or
+ruts are repaired by first loosening the surface with a pick and then
+adding broken stone and screenings to restore the surface.</p>
+
+<p>When the macadam reaches the stage where entire resurfacing<span class="pagenum"><a name="Page_133" id="Page_133">[Pg 133]</a></span> is
+needed, the work is performed by gangs organized and equipped for the
+purpose; and likewise when the surface is being maintained with a
+bituminous carpet, the renewal of the carpet coat is performed by
+special gangs, but the ordinary upkeep of the surface by patching is
+handled by a patrolman.</p>
+
+
+<h4 class="sc">Maintenance of Mixed Bituminous Surfaces</h4>
+
+<div class="figcenter" style="width: 411px;">
+<img src="images/i0144.png" width="411" height="330" alt="Fig. 22.&mdash;Scarafier used in Gravel Road Maintenance" title="" />
+<span class="caption">Fig. 22.&mdash;Scarafier used in Gravel Road Maintenance</span>
+</div>
+
+<p>These types of surface can be kept in satisfactory condition if they
+are carefully repaired once or twice each season. This work requires
+considerable experience and some special equipment, not ordinarily
+supplied to patrolmen. A gang is organized for the work and supplied
+with the proper equipment. They go over the roads and patch all worn
+places, generally first removing the wearing surface entirely in the
+area affected.<span class="pagenum"><a name="Page_134" id="Page_134">[Pg 134]</a></span></p>
+
+<p>The wearing surface mixture is then prepared and tamped or rolled into
+place. If the area affected is small, tamping is satisfactory, and
+when the area is considerable, rolling is employed. The upkeep of the
+side roads may be accomplished by the same gang but is preferably
+taken care of by patrolmen, who do not attempt any but minor repairs
+to the wearing surface.</p>
+
+
+<h4 class="sc">Maintenance of Brick and Concrete Roads</h4>
+
+<p>On brick and concrete roads, the principal work on the wearing surface
+consists in filling the cracks with a suitable bituminous material.
+This work is done by patrolmen or by special gangs and generally will
+be done once each year. The upkeep of the side roads is cared for by
+patrolmen who drag the side roads and cut the weeds as occasion
+requires.</p>
+
+
+
+<hr />
+<p><span class="pagenum"><a name="Page_135" id="Page_135">[Pg 135]</a></span></p>
+<a name="INDEX" id="INDEX"></a>
+<h2>INDEX</h2>
+
+
+<div class="index">
+<ul class="IX">
+<li><a id="IX_A" name="IX_A"></a>Administration county; <a href="#Page_15">15</a>
+  <ul class="IX">
+  <li>federal; <a href="#Page_17">17</a></li>
+  <li>highway; <a href="#Page_13">13</a></li>
+  <li>state; <a href="#Page_16">16</a></li>
+  <li>township; <a href="#Page_13">13</a></li>
+  </ul></li>
+<li>Aesthetics; <a href="#Page_62">62</a></li>
+<li>Aggregate, fine; <a href="#Page_101">101</a></li>
+<li>Aggregate, coarse; <a href="#Page_100">100</a></li>
+<li>Air resistance; <a href="#Page_51">51</a></li>
+<li>Alignment; <a href="#Page_46">46</a></li>
+<li>Applying bituminous binder; <a href="#Page_122">122</a></li>
+<li>Asphaltic concrete; <a href="#Page_128">128</a></li>
+<li>Asphalt, natural; <a href="#Page_117">117</a>
+  <ul class="IX">
+  <li>liquid; <a href="#Page_118">118</a></li>
+  <li>petroleum; <a href="#Page_117">117</a></li>
+  </ul></li>
+<li>Assessments, special; <a href="#Page_19">19</a>
+  <ul class="IX">
+  <li>zone method; <a href="#Page_20">20</a></li>
+  </ul></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_B" name="IX_B"></a>Bedding course, green mortar; <a href="#Page_111">111</a>
+  <ul class="IX">
+  <li>sand mortar; <a href="#Page_111">111</a></li>
+  <li>sand bedding mortar; <a href="#Page_111">111</a></li>
+  </ul></li>
+<li>Binder for gravel; <a href="#Page_75">75</a></li>
+<li>Bitulithic or warrenite; <a href="#Page_128">128</a></li>
+<li>Bitumen; <a href="#Page_118">118</a></li>
+<li>Bituminous coatings on concrete; <a href="#Page_105">105</a></li>
+<li>Bituminous fillers; <a href="#Page_112">112</a></li>
+<li>Bituminous road materials and their use; <a href="#Page_116">116</a></li>
+<li>Bituminous surfaces; <a href="#Page_96">96</a>, 120</li>
+<li>Blade grader; <a href="#Page_69">69</a></li>
+<li>Bonding; <a href="#Page_87">87</a></li>
+<li>Bonds, annuity; <a href="#Page_26">26</a>
+  <ul class="IX">
+  <li>serial; <a href="#Page_27">27</a></li>
+  <li>sinking fund; <a href="#Page_25">25</a></li>
+  </ul></li>
+<li>Box culverts; <a href="#Page_39">39</a></li>
+<li>Brick roads; <a href="#Page_113">113</a></li>
+<li>Brick, repressed; <a href="#Page_107">107</a>
+  <ul class="IX">
+  <li>tests of 108;</li>
+  <li>vertical fiber; <a href="#Page_107">107</a></li>
+  <li>vitrified; <a href="#Page_106">106</a></li>
+  <li>wire-cut-lug; <a href="#Page_108">108</a></li>
+  </ul></li>
+<li>Broken stone road surfaces; <a href="#Page_89">89</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_C" name="IX_C"></a>Cement, asphaltic; <a href="#Page_118">118</a><span class="pagenum"><a name="Page_136" id="Page_136">[Pg 136]</a></span></li>
+<li>Cement concrete roads; <a href="#Page_98">98</a></li>
+<li>Cement grout filler; <a href="#Page_112">112</a></li>
+<li>Characteristics, asphaltic concrete; <a href="#Page_129">129</a>
+  <ul class="IX">
+  <li>bituminous macadam; <a href="#Page_125">125</a></li>
+  <li>broken stone; <a href="#Page_97">97</a></li>
+  <li>concrete; <a href="#Page_105">105</a></li>
+  <li>mixed macadam; <a href="#Page_128">128</a></li>
+  <li>sand clay; <a href="#Page_78">78</a></li>
+  </ul></li>
+<li>Classes of bituminous materials; <a href="#Page_116">116</a></li>
+<li>Classification according to consistency; <a href="#Page_117">117</a></li>
+<li>Clay and cement concrete pipe; <a href="#Page_39">39</a></li>
+<li>Coal tar; <a href="#Page_116">116</a></li>
+<li>Concrete, asphaltic; <a href="#Page_128">128</a></li>
+<li>Concrete materials; <a href="#Page_100">100</a></li>
+<li>Concrete pipe; <a href="#Page_39">39</a></li>
+<li>Control of erosion; <a href="#Page_61">61</a></li>
+<li>Costs; <a href="#Page_70">70</a></li>
+<li>County administration; <a href="#Page_15">15</a></li>
+<li>Cross sections; <a href="#Page_60">60</a>, <a href="#Page_65">65</a></li>
+<li>Culverts; <a href="#Page_56">56</a></li>
+<li>Curing concrete; <a href="#Page_103">103</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_D" name="IX_D"></a>Design, broken stone roads; <a href="#Page_89">89</a>
+  <ul class="IX">
+  <li>concrete roads; <a href="#Page_99">99</a></li>
+  <li>earth roads; <a href="#Page_42">42</a></li>
+  </ul></li>
+<li>Desirability of road bonds; <a href="#Page_27">27</a></li>
+<li>Development of traffic; <a href="#Page_2">2</a></li>
+<li>Drainage, necessity of; <a href="#Page_29">29</a></li>
+<li>Drainage of roads; <a href="#Page_29">29</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_E" name="IX_E"></a>Earth roads, in arid regions; <a href="#Page_72">72</a>
+  <ul class="IX">
+  <li>humid regions; <a href="#Page_65">65</a></li>
+  <li>value of; <a href="#Page_73">73</a></li>
+  </ul></li>
+<li>Earth works; <a href="#Page_92">92</a></li>
+<li>Education, rural; <a href="#Page_6">6</a></li>
+<li>Effect of grades; <a href="#Page_54">54</a></li>
+<li>Elevating grader; <a href="#Page_66">66</a></li>
+<li>Elevating grader work; <a href="#Page_68">68</a></li>
+<li>End walls for culverts; <a href="#Page_39">39</a></li>
+<li>Energy loss on account of grades; <a href="#Page_57">57</a></li>
+<li>Entrances, farm; <a href="#Page_37">37</a>, <a href="#Page_61">61</a></li>
+<li>Expansion joints; <a href="#Page_104">104</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_F" name="IX_F"></a>Farm entrance culverts; <a href="#Page_37">37</a></li>
+<li>Federal administration; <a href="#Page_17">17</a></li>
+<li>Fillers; <a href="#Page_118">118</a></li>
+<li>Finance, highway; <a href="#Page_19">19</a><span class="pagenum"><a name="Page_137" id="Page_137">[Pg 137]</a></span></li>
+<li>Fine aggregate; <a href="#Page_101">101</a></li>
+<li>Finishing surface of concrete; <a href="#Page_122">122</a></li>
+<li>Foundation, asphaltic concrete; <a href="#Page_129">129</a>
+  <ul class="IX">
+  <li>brick; <a href="#Page_109">109</a></li>
+  <li>macadam; <a href="#Page_93">93</a></li>
+  <li>mixed macadam; <a href="#Page_126">126</a></li>
+  <li>penetration macadam; <a href="#Page_123">123</a></li>
+  <li>Telford; <a href="#Page_94">94</a></li>
+  </ul></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_G" name="IX_G"></a>Gang maintenance; <a href="#Page_131">131</a></li>
+<li>Grader, Maney; <a href="#Page_67">67</a>
+  <ul class="IX">
+  <li>use of; <a href="#Page_69">69</a></li>
+  </ul></li>
+<li>Gravel, ideal; <a href="#Page_81">81</a>
+  <ul class="IX">
+  <li>natural; <a href="#Page_83">83</a></li>
+  <li>roads; <a href="#Page_74">74</a></li>
+  </ul></li>
+<li>General taxation; <a href="#Page_24">24</a></li>
+<li>Good roads and commerce; <a href="#Page_7">7</a></li>
+<li>Green concrete bedding course; <a href="#Page_111">111</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_H" name="IX_H"></a>Highway administration; <a href="#Page_13">13</a></li>
+<li>Highway finance; <a href="#Page_19">19</a>
+  <ul class="IX">
+  <li>maintenance; <a href="#Page_130">130</a></li>
+  </ul></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_I" name="IX_I"></a>Importance of design; <a href="#Page_30">30</a></li>
+<li>Ideal road gravel; <a href="#Page_81">81</a></li>
+<li>Inter-city traffic; <a href="#Page_5">5</a></li>
+<li>Inter-county and inter-state traffic; <a href="#Page_5">5</a></li>
+<li>Internal resistance; <a href="#Page_50">50</a></li>
+<li>Intersections; <a href="#Page_46">46</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_L" name="IX_L"></a>Laying tile; <a href="#Page_35">35</a></li>
+<li>Length of culvert; <a href="#Page_37">37</a></li>
+<li>Liquid asphalt; <a href="#Page_118">118</a></li>
+<li>Local farm to market traffic; <a href="#Page_4">4</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_M" name="IX_M"></a>Macadam; <a href="#Page_89">89</a></li>
+<li>Maintenance, concrete; <a href="#Page_105">105</a>
+  <ul class="IX">
+  <li>earth roads; <a href="#Page_70">70</a></li>
+  <li>general; <a href="#Page_131">131</a></li>
+  <li>gravel roads; <a href="#Page_88">88</a></li>
+  <li>macadam; <a href="#Page_96">96</a></li>
+  <li>of highways; <a href="#Page_130">130</a></li>
+  <li>patrol; <a href="#Page_131">131</a></li>
+  </ul></li>
+<li>Maney grader; <a href="#Page_67">67</a></li>
+<li>Marginal curb; <a href="#Page_113">113</a></li>
+<li>Measuring materials; <a href="#Page_101">101</a><span class="pagenum"><a name="Page_138" id="Page_138">[Pg 138]</a></span></li>
+<li>Metal pipe; <a href="#Page_38">38</a></li>
+<li>Mixing wearing surface; <a href="#Page_127">127</a></li>
+<li>Mixtures; <a href="#Page_117">117</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_N" name="IX_N"></a>Natural asphalt; <a href="#Page_117">117</a>
+  <ul class="IX">
+  <li>gravel; <a href="#Page_79">79</a></li>
+  </ul></li>
+<li>Necessity for planning; <a href="#Page_42">42</a>
+  <ul class="IX">
+  <li>drainage; <a href="#Page_29">29</a></li>
+  </ul></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_P" name="IX_P"></a>Patching; <a href="#Page_122">122</a>, 125</li>
+<li>Patrol maintenance; <a href="#Page_131">131</a></li>
+<li>Pebbles, size of; <a href="#Page_80">80</a></li>
+<li>Petroleum asphalt; <a href="#Page_117">117</a></li>
+<li>Placing asphaltic concrete; <a href="#Page_129">129</a></li>
+<li>Placing broken stone; <a href="#Page_94">94</a></li>
+<li>Placing concrete; <a href="#Page_102">102</a>, 103
+  <ul class="IX">
+  <li>mixed macadam; <a href="#Page_127">127</a></li>
+  </ul></li>
+<li>Plans for roads; <a href="#Page_43">43</a></li>
+<li>Preliminary investigation; <a href="#Page_44">44</a></li>
+<li>Preparation of earth foundation; <a href="#Page_102">102</a>
+  <ul class="IX">
+  <li>of road; <a href="#Page_85">85</a></li>
+  </ul></li>
+<li>Private entrances; <a href="#Page_61">61</a></li>
+<li>Properties of stone; <a href="#Page_90">90</a></li>
+<li>Proportions for concrete roads; <a href="#Page_101">101</a></li>
+<li>Purpose of highways; <a href="#Page_1">1</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_R" name="IX_R"></a>Reinforced concrete box culverts; <a href="#Page_39">39</a></li>
+<li>Reinforcing; <a href="#Page_104">104</a></li>
+<li>Repressed brick; <a href="#Page_107">107</a></li>
+<li>Road oils; <a href="#Page_117">117</a></li>
+<li>Road plans; <a href="#Page_43">43</a></li>
+<li>Rocks, kind of, for macadam; <a href="#Page_91">91</a></li>
+<li>Rolling, macadam; <a href="#Page_95">95</a></li>
+<li>Rolling resistance; <a href="#Page_50">50</a></li>
+<li>Run-off; <a href="#Page_31">31</a></li>
+<li>Rural education; <a href="#Page_6">6</a></li>
+<li>Rural social life; <a href="#Page_7">7</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_S" name="IX_S"></a>Safety consideration; <a href="#Page_58">58</a></li>
+<li>Sand bedding course; <a href="#Page_111">111</a></li>
+<li>Sand clay and gravel road; <a href="#Page_74">74</a></li>
+<li>Sand mortar bedding course; <a href="#Page_111">111</a></li>
+<li>Seal coat; <a href="#Page_127">127</a></li>
+<li>Serial bonds; <a href="#Page_27">27</a></li>
+<li>Sinking fund bond; <a href="#Page_25">25</a></li>
+<li>Slip scraper; <a href="#Page_67">67</a><span class="pagenum"><a name="Page_139" id="Page_139">[Pg 139]</a></span></li>
+<li>Special assessments; <a href="#Page_19">19</a></li>
+<li>Specifications; <a href="#Page_119">119</a></li>
+<li>Spreading screenings; <a href="#Page_95">95</a></li>
+<li>State administration; <a href="#Page_16">16</a></li>
+<li>Stone, use of; <a href="#Page_92">92</a></li>
+<li>Surface drainage; <a href="#Page_30">30</a></li>
+<li>Surfaces, bituminous; <a href="#Page_120">120</a></li>
+<li>Surface method; <a href="#Page_87">87</a></li>
+<li>Superelevation; <a href="#Page_47">47</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_T" name="IX_T"></a>Tests, brick; <a href="#Page_108">108</a></li>
+<li>Tile drains; <a href="#Page_35">35</a></li>
+<li>Topeka asphaltic concrete; <a href="#Page_128">128</a></li>
+<li>Tractive resistance; <a href="#Page_52">52</a></li>
+<li>Trench method; <a href="#Page_85">85</a></li>
+<li>Truck operation costs; <a href="#Page_9">9</a></li>
+<li>Types of culverts; <a href="#Page_38">38</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_U" name="IX_U"></a>Underground water; <a href="#Page_34">34</a></li>
+<li>Undulating roads; <a href="#Page_58">58</a></li>
+<li>Use of blade grader; <a href="#Page_69">69</a></li>
+<li>Utilizing natural gravels; <a href="#Page_83">83</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_V" name="IX_V"></a>Value of earth roads; <a href="#Page_73">73</a></li>
+<li>Variation in rainfall; <a href="#Page_64">64</a></li>
+<li>Variation in soils; <a href="#Page_63">63</a></li>
+<li>Vehicle taxes; <a href="#Page_24">24</a></li>
+<li>Vertical fiber brick; <a href="#Page_107">107</a></li>
+<li>Vitrified brick roads; <a href="#Page_106">106</a></li>
+<li>Vitrified brick; <a href="#Page_106">106</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_W" name="IX_W"></a>Water gas tar; <a href="#Page_117">117</a></li>
+<li>Width of roadway; <a href="#Page_59">59</a></li>
+<li>Wire-cut-lug brick; <a href="#Page_108">108</a></li>
+</ul>
+
+<ul class="IX">
+<li><a id="IX_Z" name="IX_Z"></a>Zone method of assessing; <a href="#Page_20">20</a></li>
+</ul>
+
+</div>
+
+
+<hr class="full" />
+
+<div class="trans-note">
+<a name="END" id="END"></a>
+<p class="heading">Transcriber's Notes</p>
+
+<p>The transcriber made these changes to the text to correct obvious errors:</p>
+
+<pre class="note">
+   1. p.   5, accomodate --> accommodate
+   2. p.  39, guage --> gauge
+   3. p.  46, enbankment --> embankment
+   4. p.  63, tought --> tough
+   5. p.  68, absorbant --> absorbent
+   6. p.  73, persistant --> persistent
+   7. p.  77, indispensible --> indispensable
+   8. p. 119, aspealt --> asphalt
+   9. p. 127, repaid --> rapid
+  10. p. 130, Vetrified brick; 105 -->
+                           Vitrified brick; 106
+  11. p. 130, Virtical --> Vertical
+</pre>
+
+</div>
+
+<hr class="full" />
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
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+The Project Gutenberg EBook of American Rural Highways, by T. R. Agg
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: American Rural Highways
+
+Author: T. R. Agg
+
+Release Date: July 16, 2009 [EBook #29420]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK AMERICAN RURAL HIGHWAYS ***
+
+
+
+
+Produced by Tom Roch, Richard J. Shiffer and the Online
+Distributed Proofreading Team at https://www.pgdp.net (This
+file was produced from images produced by Core Historical
+Literature in Agriculture (CHLA), Cornell University)
+
+
+
+
+
+[Transcriber's Note: Every effort has been made to replicate
+this text as faithfully as possible, including obsolete and
+variant spellings and other inconsistencies. Text that has been
+changed to correct an obvious error is noted at the end of this
+ebook.
+
+Also, on pages 47-48, the Greek letter theta is represented by
+THETA. In chemical and mathematical notations, a subscript is
+enclosed in braces and preceded by an underscore (e.g., H_{2}O.)]
+
+
+
+
+  AGRICULTURAL ENGINEERING SERIES
+
+  E. B. MCCORMICK, CONSULTING EDITOR
+
+
+  FORMERLY DEAN OF ENGINEERING DIVISION
+  KANSAS STATE AGRICULTURAL COLLEGE
+
+
+
+
+  AMERICAN
+
+  RURAL HIGHWAYS
+
+
+
+  _McGraw-Hill Book Co. Inc._
+
+  PUBLISHERS OF BOOKS FOR
+
+
+  Coal Age -- Electric Railway Journal
+  Electrical World -- Engineering News-Record
+  American Machinist -- Ingenieria Internacional
+  Engineering & Mining Journal -- Power
+  Chemical & Metallurgical Engineering
+  Electrical Merchandising
+
+
+  [Illustration: _Frontispiece_]
+
+
+
+
+  AMERICAN
+  RURAL HIGHWAYS
+
+
+  BY
+
+  T. R. AGG, C.E.
+
+
+  PROFESSOR OF HIGHWAY ENGINEERING
+  IOWA STATE COLLEGE
+
+
+
+  FIRST EDITION
+
+
+
+  MCGRAW-HILL BOOK COMPANY, INC.
+  NEW YORK: 239 WEST 39TH STREET
+  LONDON: 6 & 8 BOUVERIE ST., E. C. 4
+  1920
+
+
+  COPYRIGHT, 1920, BY THE
+  McGRAW-HILL BOOK COMPANY, INC.
+
+
+
+
+PREFACE
+
+
+AMERICAN RURAL HIGHWAYS was written for use as a text or reference in
+courses dealing with rural highways and intended for agricultural
+engineers, students in agriculture and for short courses and extension
+courses. The reader is assumed to have familiarity with drawing and
+surveying, but the text is adapted primarily for students who do not
+receive training along the lines of the usual course in Highway or
+Civil Engineering.
+
+The text is intended to familiarize the student with the relation of
+highway improvement to national progress, to indicate the various
+problems of highway administration and to set forth the usual methods
+of design and construction for rural highways in sufficient detail to
+establish a clear understanding of the distinguishing characteristics
+and relative serviceability of each of the common types of roadway
+surface.
+
+Experience with classes made up of students in agriculture or
+agricultural engineering and with trade school students in road making
+served as a guide in the selection and arrangement of the material.
+Detailed discussion of tests of materials and of the theory of design
+has to a considerable extent been eliminated as being outside of the
+scope of the course for which the text is intended.
+
+In the preparation of American Rural Highways reference was had to
+many books on highway subjects and to current periodical literature.
+Wherever direct extracts were made from such source, appropriate
+acknowledgment appears in the text.
+
+                                             T. R. AGG
+
+  AMES, IOWA,
+  AUGUST 18, 1920.
+
+
+
+
+CONTENTS
+
+
+PREFACE                                                            vii
+
+
+CHAPTER I
+
+THE PURPOSE AND UTILITY OF HIGHWAYS
+
+Transportation Problem--National in Scope--Development in
+Traffic--Location or Farm to Market Traffic--Farm to Farm
+Traffic--Inter-City Traffic--Inter-County and Inter-State
+Traffic--Rural Education--Rural Social Life--Good Roads and
+Commerce                                                          1-12
+
+
+CHAPTER II
+
+HIGHWAY ADMINISTRATION
+
+Township Administration--County Administration--State
+Administration--Federal Administration--Special Assessments--Zone
+Method of Assessing--General Taxation--Vehicle Taxes--Sinking
+Fund Bonds--Annuity Bonds--Serial Bonds--Comparison of Methods
+of Issuing Bonds--Desirability of Road Bonds                      13-28
+
+
+CHAPTER III
+
+DRAINAGE OF ROADS
+
+The Necessity for Drainage--Importance of Design--Surface
+Drainage--Run-off--Ordinary Design of Ditches--Underground
+Water--Tile Drains--Lying Tile--Culverts--Length of Culvert--
+Farm Entrance Culverts--Metal Pipe--Clay and Cement Concrete
+Pipe--Concrete Pipe--Endwalls for Culverts--Reinforced Concrete
+Box Culverts--Drop Inlet Culverts                                29-41
+
+
+CHAPTER IV
+
+ROAD DESIGN
+
+Necessity for Planning--Road Plans--Problems of Design--
+Preliminary Investigations--Road Surveys--Alignment--
+Intersections--Superelevation--Tractive Resistance--Rolling
+Resistance--Internal Resistance--Air Resistance--Effect of
+Trades--Energy Loss on Account of Grades--Undulating Roads--
+Guard Railing--Width of Roadway--Cross Section--Control of
+Erosion--Private Entrances--AEsthetics                            42-62
+
+
+CHAPTER V
+
+EARTH ROADS
+
+Variations in Soils--Variation in Rainfall--Cross Sections
+Elevating Grader--Maney Grader--Slip Scraper--Fresno
+Scraper--Elevating Grader Work--Use of Blade Grader--
+Costs--Maintenance--Value of Earth Roads                         63-73
+
+
+CHAPTER VI
+
+SAND-CLAY AND GRAVEL ROADS
+
+The Binder--Top-soil or Natural Mixtures--Sand-clay on Sandy
+Roads--Sand-clay on Clay or Loam--Characteristics--Natural
+Gravel--The Ideal Road Gravel--Permissible Size of Pebbles--
+Wearing Properties--Utilizing Natural Gravels--Thickness
+of Layer--Preparation of the Road--Trench Method--Surface
+Method--Maintenance                                              74-88
+
+
+CHAPTER VII
+
+BROKEN STONE ROAD SURFACES
+
+Design--Properties of the Stone--Kinds of Rocks used for
+Macadam--Sizes of Stone--Earth Work--Foundation for the
+Macadam--Telford Foundation--Placing the Broken Stone--
+Rolling--Spreading Screenings--Bituminous Surfaces--Maintenance
+Characteristics                                                  89-97
+
+
+CHAPTER VIII
+
+CEMENT CONCRETE ROADS
+
+Destructive Agencies--Design--Concrete Materials--Fine
+Aggregate--Proportions--Measuring Materials--Preparation of the
+Earth Foundation--Placing Concrete for Two-course Road--Curing
+the Concrete--Expansion Joints--Reinforcing--Bituminous Coatings
+on Concrete Surfaces--Characteristics--Maintenance              98-105
+
+
+CHAPTER IX
+
+VITRIFIED BRICK ROADS
+
+Vitrified Brick--Paving Brick--Repressed Brick--Vitrified Fiber
+Brick--Wire-cut-lug Brick--Tests for Quality--Other Tests--
+Foundation--Sand Bedding Course--Sand Mortar Bedding Course--
+Green Concrete Bedding Course--Bituminous Fillers--Mastic
+Fillers--Marginal Curb                                         106-115
+
+
+CHAPTER X
+
+BITUMINOUS ROAD MATERIALS AND THEIR USE
+
+Classes of Bituminous Materials--Coal Tar--Water Gas Tar--Natural
+Asphalt--Petroleum Asphalt--Mixtures--Classification According to
+Consistency--Road Oils--Liquid Asphalts--Asphalt Cements--
+Fillers--Bitumen--Specifications--Surface Treatments--Applying
+the Bituminous Binder--Finishing the Surface--Patching--
+Penetration Macadam--Foundation--Upper or Wearing Course--
+Patching Characteristics--Hot Mixed Macadam--Foundation--Sizes
+of Stone--Mixing the Wearing Stone--Placing and Wearing
+Surface--Seal Coat--Characteristics--Asphaltic Concrete--
+Bitulithic or Warrenite--Topeka Asphaltic Concrete--Foundation
+--Placing the Surface--Characteristics                         116-129
+
+
+CHAPTER XI
+
+MAINTENANCE OF HIGHWAYS
+
+Petrol Maintenance--Gang Maintenance--Maintenance of Earth,
+Sand-clay, Gravel and Macadam Roads                            130-134
+
+
+Index                                                              135
+
+
+
+
+AMERICAN RURAL HIGHWAYS
+
+
+
+
+CHAPTER I
+
+THE PURPOSE AND UTILITY OF HIGHWAYS
+
+
+THE DEVELOPMENT OF HIGHWAY SYSTEMS
+
+=Transportation Problem.=--Public highways, like many other familiar
+things, are utilized constantly with little thought of how
+indispensable they are to the conduct of the business of a nation or
+of the intimate relation they bear to the everyday life of any
+community. The degree to which a nation or a community perfects its
+transportation facilities is an index of its industrial progress and
+public highways constitute an important element in the national
+transportation system. It is to be expected that the average citizen
+will think of the public highway only when it affects his own
+activities and that he will concern himself but little with the broad
+problem of highway improvement unless it be brought forcibly to his
+attention through taxation or by publicity connected with the
+advancement of specific projects.
+
+=National in Scope.=--The improvement and extension of the highway
+system is of national importance just as is development and extension
+of railways, and concerted action throughout a nation is a
+prerequisite to an adequate policy in regard to either. It is
+inconceivable that any community in a nation can prosper greatly
+without some benefit accruing to many other parts of the country.
+Increased consumption, which always accompanies material prosperity,
+means increased production somewhere, and people purchase from many
+varied sources to supply the things that they want. Good
+transportation facilities contribute greatly to community prosperity
+and indirectly to national prosperity, and the benefits of highly
+improved public highways are therefore national in scope. This fact
+has been recognized in Europe, notably in England, France and Belgium,
+where the public highways are administered largely as national
+utilities.
+
+Until recent years, highway improvement in the United States has been
+subordinated to other more pressing public improvements, but during
+the World War the inadequacy of the transportation system of the
+United States became apparent. While such an unprecedented load upon
+transportation facilities may not recur for many years, it has become
+apparent that more rapid progress in highway improvement is necessary
+and in the United States the subject is now likely to receive
+attention commensurate with its importance.
+
+=Development of Traffic.=--The character and extent of the highway
+improvement needed in any locality is dependent entirely on the
+demands of traffic. In sparsely settled areas, particularly those that
+are semi-arid or arid, the amount of traffic on local roads is likely
+to be small and the unimproved trails or natural roads adequate. But
+as an area develops either on account of agricultural progress or the
+establishment of industrial enterprises, the use of the public
+highways both for business and for pleasure increases and the old
+trails are gradually improved to meet, at least to some degree, the
+new demands of traffic. In sparsely settled areas, it is possible for
+the public to accommodate its use of the highways to the physical
+condition thereof, and business is more or less regulated according to
+the condition of the roads. This is not always pleasant or economical
+but is the only possible arrangement. In populous districts, with
+diversified activities, it becomes imperative to have year-round
+usable roads in order to transact with reasonable dispatch the regular
+business of the industries. Anything less will handicap normal
+community progress.
+
+The advent of the motor driven vehicle in the United States has
+resulted in a greatly increased use of the public highways of
+agricultural areas, even of those that are sparsely populated, because
+of the convenience of the motor vehicle both for passenger and for
+freight service. Probably in excess of 90 per cent of the tonnage
+passing over the rural highways in the United States is carried by
+motor vehicles. This class of traffic has really just developed and no
+one can predict what it will be in ten years, yet it has already
+introduced into the highway problem an element that has revolutionized
+methods of construction and maintenance.
+
+A different set of traffic conditions exists in those parts of the
+United States where large areas are devoted primarily to industrial
+pursuits, the agricultural development being of secondary importance.
+Public highways connecting the industrial centers are indispensable
+adjuncts to the business facilities in such communities and are
+ordinarily subjected to a very large volume and tonnage of traffic
+consisting principally of motor vehicles. The roads first selected for
+improvement will not be those serving the agricultural interests of
+the district, but rather those serving the industrial centers.
+Inter-city roads of great durability and relatively high cost are
+necessary for such traffic conditions.
+
+Not infrequently the transportation needs will require a system of
+both inter-city and rural highways in the same community. There are
+few areas in the United States where there is no agricultural
+development. It is apparent therefore that the nature of the highway
+systems and the administrative organization under which they are built
+and maintained will differ in various states or areas according to
+the nature of development of that area agriculturally and
+industrially. In planning improvements of highway systems, it is
+recognized that one or more of several groups of traffic may be
+encountered and that the extent and nature of the improvement must be
+such as will meet the requirements of all classes of traffic, the most
+important being first provided for, and that of lesser importance as
+rapidly as finances permit.
+
+
+KINDS OF TRAFFIC ON PUBLIC HIGHWAYS
+
+=Local or Farm to Market Traffic.=--In strictly agricultural
+communities the principal use of the highways will pertain to
+agricultural activities and most of it will be between the farm and
+the most convenient market center. In the ordinary state, the number
+of rural families will not average more than six to eight per square
+mile, but in some districts it may reach twenty families per square
+mile. The travel from the district around a market center will
+originate in this rather sparsely populated area and converge onto a
+few main roads leading to market. The outlying or feeder roads will be
+used by only a few families, but the density of traffic will increase
+nearer the market centers and consequently the roads nearer town will
+be much more heavily traveled than the outlying ones. It is apparent
+therefore that considerable difference may exist in the kind of
+construction adequate for the various sections of road where farm
+traffic is the principal consideration. This traffic is made up of
+horse drawn wagons, transporting farm products and of horse drawn and
+motor passenger vehicles, the motor traffic comprising 80 per cent or
+more of the volume of traffic and a greater per cent of the tonnage.
+Motor trucks are now employed to some extent for marketing farm
+products and, where surfaced highways have been provided, this class
+of traffic is superseding horse drawn traffic.
+
+=Farm to Farm Traffic.=--In the ordinary prosecution of farming
+operations, a considerable amount of neighborhood travel is
+inevitable. Farmers help each other with certain kinds of work,
+exchange commodities such as seed, machinery and farm animals and
+visit back and forth both for business and pleasure. To accommodate
+this traffic, it is desirable to provide good neighborhood roads.
+Traffic of this sort follows no particular route and can to some
+extent accommodate itself to the condition of the highways without
+entailing financial loss, although some discomfort and some
+inconvenience may result from inadequate highway facilities. This
+traffic will be partly motor and partly horse drawn, but the
+proportion of motor driven is large.
+
+=Inter-city Traffic.=--In strictly agricultural districts there is a
+large amount of travel between towns, both for business and for
+pleasure. The pleasure travel is mostly in motor vehicles and a
+considerable part of the business traffic is the same, although horse
+drawn vehicles are employed to some extent.
+
+In industrial districts there is a large volume of this class of
+traffic consisting of motor passenger vehicles used for business and
+for pleasure and of motor freight vehicles used for general business
+purposes. In addition, there is certain to be a large amount of motor
+truck freight traffic incident to the particular industrial pursuits
+of the cities. Where adequate public highways connect industrial
+centers, there is invariably a very large amount of inter-city
+traffic, due in part to the needs of industry and in part to
+concentration of population in industrial centers.
+
+=Inter-County and Inter-State Traffic.=--Automobile touring is a
+popular means of relaxation, especially on the part of those who live
+in the cities, although it is by no means confined to them. Traffic of
+this kind follows the routes where roads are best and passes entirely
+across a county, attracted by some public gathering. Often it is
+inter-state in character, made up of tourists who are traveling to
+distant pleasure resorts. Such traffic at present constitutes a
+relatively small part of the travel on public highways, except on
+certain favorable routes, but as the wealth of the country increases
+and good touring roads are numerous, long distance travel will
+increase and will eventually necessitate the construction of a number
+of well maintained national highways, located with reference to the
+convenience of the automobile tourist.
+
+
+PUBLIC HIGHWAYS AND COMMUNITY LIFE
+
+It is well to recognize the intimate relation public highways bear to
+the economic progress of a nation. Normal development of all of the
+diverse activities of a people depends very largely upon the highway
+policy that is adopted and whether the actual construction of
+serviceable roads keeps pace with transportation needs.
+
+=Rural Education.=--It has become increasingly apparent during the
+World War that the demand upon North America for food stuffs is to
+become more and more insistent as the years pass. Already the
+consumption in the United States has approached quite closely to the
+average production and yet the population is constantly increasing.
+The time is not far distant when greater production will be required
+of the agricultural area in North America in order to meet the home
+demand for foodstuffs, and many thousands of tons will be needed for
+export. This need can only be met by agricultural methods that will
+increase greatly the present yield of the soil. The adoption of better
+agricultural methods must of necessity be preceded by the technical
+training of the school children who will be the farmers of the next
+generation, which can best be accomplished in graded schools with well
+equipped laboratories and with suitably trained teachers. The problem
+of providing such schools in rural communities has, in some instances,
+been solved by consolidating a number of rural school districts and
+constructing a well equipped building to accommodate the students from
+an area several miles square. An educational system of this sort can
+reach its highest usefulness only when adequate public highways
+facilitate attendance of pupils. The whole trend of rural educational
+progress is toward a system which is predicated upon a comprehensive
+highway policy in the district.
+
+=Rural Social Life.=--Closely allied to the rural educational problem
+is the rural social problem. Motor cars and good roads do a great deal
+to eliminate the isolation and lack of social opportunity that has
+characterized rural life in the United States. A high order of
+citizenship in rural communities is essential to the solution of many
+problems of rural economics, and such citizens will not live away from
+the social opportunities of modern life. The rural school house and
+the rural church may become social centers and local plays, moving
+picture shows and lectures and entertainments of other kinds made
+available to those who live in the country. Their enjoyment of these
+social opportunities will be much more general if the public highways
+are at all times in a condition to be traveled in comfort. Good homes
+and good schools on good roads are prerequisites to the solution of
+many rural problems.
+
+If there is opportunity for those who live in the cities to get some
+adequate idea of rural life and the conditions under which farming
+operations are carried on it will correct many misunderstandings of
+the broad problems of food production and distribution. Reference has
+frequently been made to the seeming desire on the part of city people
+to get into the country, and, by facilitating the realization of this
+desire, a great social service is rendered.
+
+=Good Roads and Commerce.=--That good highways are almost as necessary
+as are railroads to the commercial development of a nation is
+recognized but, unlike the railroads, the highways are not operated
+for direct profit and the responsibility of securing consideration of
+the demand for improvements is not centralized. Therefore, sentiment
+for road improvement has been of slow growth, and important projects
+are often delayed until long after the need for them was manifest.
+Movements to secure financial support for highway improvement must go
+through the slow process of legislative enactment, encountering all of
+the uncertainties of political action, and the resulting financial
+plan is likely to be inadequate and often inequitable.
+
+The whole commercial structure of a nation rests upon transportation,
+and the highways are a part of the transportation system. The highway
+problem can never receive adequate consideration until public highways
+are recognized as an indispensable element in the business equipment
+of a nation.
+
+During the World War all transportation facilities were taxed to the
+limit, and motor trucks were utilized for long distance freight
+haulage to an extent not previously considered practicable. As a
+result, the interest in the motor truck as an addition to the
+transportation equipment of the nation, has been greatly stimulated.
+Many haulage companies have entered the freight transportation field,
+delivering commodities by truck to distances of a hundred miles or
+more.
+
+The part the motor truck will play in the future can only be
+estimated, but it seems clear that the most promising field is for
+shipments destined to or originating in a city of some size and a
+warehouse or store not on a railroad spur, and especially when the
+shipments are less than car load lots. The delays and expense incident
+to handling small shipments of freight through the terminals of a
+large city and carting from the unloading station to the warehouse or
+other destination constitute a considerable item in the cost of
+transportation.
+
+Mr. Charles Whiting Baker, Consulting Editor of _Engineering
+News-Record_, states:[1]
+
+     [1] Engineering News Record, July 10, 1919.
+
+     "It costs today as much to haul a ton of farm produce ten miles
+     to a railway station as it does to haul it a thousand miles over
+     a heavy-traffic trunk-line railway. It often costs more today to
+     transport a ton of merchandise from its arrival in a long train
+     in the freight yard on the outskirts of a great city to its
+     deposit in the warehouse of a merchant four or five miles away
+     than it has cost to haul it over a thousand miles of railway
+     line."
+
+Nevertheless it seems probable that new methods of operating the motor
+truck transport, and possibly new types of trucks or trucks and
+trailers will be developed so that freight traffic over many roads
+will be of considerable tonnage and an established part of the
+transportation system of the nation. In the article above referred to
+are given the following data relative to the cost of hauling on
+improved roads by motor truck and these cost estimates are based on
+the best information available at this time. They should be considered
+as approximate only, but serve to indicate the limitations of the
+truck as a competitor of the steam railway.
+
+  TABLE 1
+
+  TRUCK OPERATION COSTS, FROM REPORTS BY SIX MOTOR TRUCK
+  OPERATORS, DIRECT CHARGES PER DAY
+
+  +---------+-------+-------+-------+-------+-------+-------+-----------
+            |   A   |   B   |   C   |   D   |   E   |   F   | Average
+            |       |       |       |       |       |       |     Total
+  +---------+-------+-------+-------+-------+-------+-------+-----------
+  Driver    | $5.00 | $5.20 | $5.00 | $5.00 | $5.17 | $5.50 |  $5.13
+  Tires     |  3.00 |  3.75 |  2.00 |  2.00 |  2.00 |  3.00 |   2.68
+  Oil, etc. |   .30 |  ...  |   .30 |   .50 |   .25 |   .25 |    .35
+  Gasoline  |  3.00 |  4.00 |  3.50 |  4.65 |  2.08 |  3.75 |   3.50
+            |       |       |       |       |       |       | ------
+            |       |       |       |       |       |       |     $11.66
+  +---------+-------+-------+-------+-------+-------+-------+-----------
+
+
+  INDIRECT CHARGES PER DAY
+
+  -------------+------+------+------+------+------+------+------------
+               |      |      |      |      |      |      | Average
+               |   A  |   B  |   C  |   D      E  |   F  |      Total
+  -------------+------+------+------+------+------+------+------------
+  Depreciation | $3.50| $4.19| $3.60| $3.40| $3.67| $4.00| $3.77
+  Interest     |  1.20|  1.26|  1.08|  1.22|  1.10|  1.00|  1.15
+  Insurance    |  1.50|  2.54|  1.26|  2.10|   .86|   .50|  1.47
+  Garage       |  1.00|  1.20|  1.00|  1.00|   .89|  1.00|  1.01
+  Maintenance  |   .50|   ...|   .50|   ...|  1.00|   ...|   .75
+  Overhaul     |  1.33|  2.75|  1.80|  1.60|  2.00|  3.00|  2.07
+  License      |   .17|   .27|   .20|   .20|   .20|   .20|   .20
+  Body upkeep  |   .25|   ...|   .30|   .10|   .40|   ...|   .27
+               |      |      |      |      |      |      | ----
+               |      |      |      |      |      |      |      $10.69
+  Supervision  |   .50|  2.93|  2.05|  1.90|  ... |  ... |  1.90  1.90
+  Lost time    |  2.20|  ... |  1.67|  3.40|  2.50|  1.97|  2.57  2.57
+               | -----| -----| -----| -----| -----| -----| -----------
+               | 23.45| 28.09| 24.26| 28.07| 22.12| 24.17|       26.82
+  -------------+------+------+------+------+------+------+------------
+
+  TABLE 2
+
+  OVERHEAD CHARGES PER YEAR FOR A 5-TON CAPACITY GASOLINE
+  MOTOR TRUCK RUNNING AN AVERAGE OF 50 MILES PER DAY
+  FOR 240 DAYS PER YEAR
+
+  Driver's wages[1]                                               $1500
+  Depreciation (20% on $6000 investment)                           1200
+  Interest (6% on $6000 investment)                                 360
+  Insurance                                                         450
+  Garage (rental, upkeep, etc.)                                     300
+  Maintenance, minor repairs and supplies, tire chains, tools,
+  lamps, springs, equipment, etc. (estimated)                       300
+  Complete overhaul once a year                                     600
+  License fee                                                        60
+  Body upkeep, repairs, painting, etc.                               90
+  Supervision                                                       696
+                                                                  -----
+  Total per annum                                                 $5556
+
+  Overhead charges per day for 240 days in the year,
+  actual operation                                            $23.15
+  Overhead charges per mile for 50 miles per day                 .463
+
+    [1] In the above table the driver's wages have been placed under
+    overhead charges because the driver is paid by the month and his
+    wages continue even though the truck is idle because of repairs,
+    bad weather or lack of business, unless, of course, the idleness
+    should be of long duration, when the driver might be laid off.
+
+  DIRECT CHARGES PER DAY AND PER MILE FOR 5-TON TRUCK
+  OPERATED AS ABOVE
+
+  ------------------------------------------------+---------+---------
+                                                  |  Cost   |  Cost
+                                                  | per day | per mile
+  ------------------------------------------------+---------+---------
+  Tires (based on present tire guarantee)         |  $3.00  |  $0.06
+  Lubricants                                      |    .50  |    .01
+  Gasoline (3-1/2 miles per gal., 14 gal. at 25c) |   3.50  |    .07
+                                                  |  -----  |  -----
+                                                  |   7.00  |   0.14
+  ------------------------------------------------+---------+---------
+
+  Total of overhead and direct charges for 240 days per year operation,
+      per day                                                    $30.15
+  Per mile                                                          .603
+  Cost per ton-mile for full loads one way and empty returning      .2412
+  Cost per ton-mile for full loads one way and half load returning  .16
+
+The significance of these figures becomes apparent when they are
+compared with the cost of hauling freight over trunk-line railways
+with heavy traffic where the cost per ton-mile, including terminal
+charges, ranges from 1.7 _mills_ per ton-mile to 4.4 _mills_ per
+ton-mile.
+
+In view of these facts it seems reasonable to suppose that motor
+vehicles for use on the public highways are more likely to be employed
+to supplement the rail transport than to compete with it. To the
+actual cost of operation of motor trucks given in Table 2, there
+should be added the proportionate cost of maintaining the highway for
+the use of the truck, which is partly covered by the item "License
+Fee" in the table. The license fee would necessarily be considerably
+larger if it were to compensate adequately for the wear on the
+highways over which the trucks operate. This will still further
+increase the cost of hauling by motor truck.
+
+Motor trucks are employed for many kinds of hauling where their speed
+and consequently their daily capacity is an advantage over team
+hauling that is decidedly worth while. It probably could be shown
+that for many kinds of hauling, teams are more economical than motor
+trucks, but when promptness and speed and the consequent effect on
+dependent activities are considered, the motor truck often has a
+distinct advantage, and the use of the truck to replace horse drawn
+vans is progressing rapidly. This is true not only in the cities, but
+also in the smaller towns and in the country. Motor trucks have been
+adopted in a great many communities for delivery of farm products to
+market, and this use of the truck is certain to increase rapidly. But
+trucks in this service will use the secondary roads as well as the
+main or primary roads.
+
+These observations emphasize the extent to which the highway policy of
+the nation must be predicated on the use of the highways by motor
+vehicles.
+
+
+
+
+CHAPTER II
+
+HIGHWAY ADMINISTRATION
+
+
+The systems of highway administration extant in the various political
+units in the United States present a patchwork of overlapping
+authority and undetermined responsibility. Highway laws are being
+constantly revised by state legislatures and with each revision there
+is some change in administrative methods and often the changes are
+revolutionary in character. In most states, the trend is away from
+county and township administration and toward state administration,
+with provision for considerable participation by the federal
+government.
+
+It will be pertinent to consider briefly the present functions of each
+of the administrative authorities having duties in connection with
+highway work in the United States, although these duties vary greatly
+in the several states and change periodically with the action of
+legislatures.
+
+=Township Administration.=--Township or "Town" authority is a survival
+of the old New England town government and the town board consists of
+three or more trustees who hold office for fixed terms. The usual term
+is three years, but is less in some states. The incumbent is generally
+a man who has other responsibilities of a public or private nature and
+who gives but little of his time to highway matters. In some states
+the pay is a fixed annual salary and in others a per diem with some
+limitation on the amount that may be drawn in any one year, which
+limitation may be statutory or may be by common consent.
+
+The township highway commissioners or trustees have jurisdiction over
+certain of the roads in the township, usually best described as all
+roads not by law placed under the jurisdiction of some other
+authority. In certain instances, the township authorities have charge
+of all of the roads in the township, which would mean that no "county"
+or "state" roads happened to be laid out in that township. It is a
+matter of general observation that the trend of legislation is toward
+removing from the jurisdiction of the township officials all roads
+except those upon which the traffic is principally local in character.
+The actual mileage of roads in the United States that is at present
+administered by township officials is large, probably constituting not
+less than seventy per cent of the total mileage.
+
+In most states the township officials are responsible for the
+maintenance of the roads under their jurisdiction and also supervise
+such new construction as is undertaken. This includes the construction
+of culverts and bridges as a rule, but in some states the county board
+of supervisors is responsible for all of the bridge and culvert work
+on the township roads. In other states, the township board is
+responsible only for bridges or culverts that cost less than a certain
+amount specified by law (usually about $1000) and the county board
+provides for the construction and upkeep of the more expensive bridges
+and culverts.
+
+Funds for the work carried out by the township road officials are
+obtained by general taxation, the amount that may be levied being
+limited by statute and the actual levy being any amount up to the
+maximum that the township board deems necessary for its purposes. It
+is the general observation that the tax levy is usually the maximum
+permitted by law.
+
+In many states, township officials are permitted to issue bonds for
+road construction, almost invariably, however, with the restriction
+that each issue must be approved by the voters of the township. There
+is always a provision that the total amount of bonds outstanding must
+not exceed the constitutional limit in force in the state. In several
+states, the townships have large amounts of road bonds outstanding.
+
+=County Administration.=--In some states the county is the smallest
+administrative unit in the road system. A county board, called the
+board of county supervisors or board of county commissioners
+consisting of from three to fifteen members, is the administrative
+authority. Its members are elected for fixed terms which vary in
+length from one to five years. The county board usually has many
+public responsibilities other than highway administration, and is
+generally made up of men with considerably more business ability than
+the average township board.
+
+The county board has jurisdiction over all of the highways in the
+county in some states, and in others it has charge of only the more
+important highways. In most states, the laws set forth specifically
+what highways shall be under the jurisdiction of the county
+authorities.
+
+In addition to having direct supervision of the improvement and
+maintenance of the roads assigned to county administration, the county
+boards in some states arrange for the construction of all culverts and
+bridges on the roads that are under township supervision, or at least
+the more expensive bridges and culverts on such roads. Sometimes this
+is accomplished by granting county aid for township bridges, under
+which system the county pays a part of the cost of the construction of
+bridges on the township roads. The amount of aid varies, but is
+generally about one-half of the cost, and the township and county
+officials jointly assume the responsibility of arranging for the
+construction by contract or otherwise.
+
+The county board obtains funds for road work through a direct tax on
+all property in the county, the maximum rate being limited by statute.
+County boards are also authorized to issue bonds for road construction
+under statutory restrictions and limitations similar to those
+effective in the township as to total amount issued, and many
+millions of dollars' worth of highway bonds have been issued by
+county authorities in the United States.
+
+=State Administration.=--In a state, the administrative authority in
+highway matters is vested in a board of commissioners usually
+consisting of three or more members. In a few states, the
+administrative authority is delegated to a single commissioner. Where
+the authority is vested in a board, that board is usually appointed by
+the governor. In several states one or more members of the commission
+hold that position _ex officio_; for example, in several states the
+governor is by law a member of the commission, in others the secretary
+of state or the dean of engineering at the State University or the
+state geologist is a member of the commission. Where the
+administrative authority is a single commissioner he may be elected
+along with other state officers, but this is the case in only a few
+states.
+
+The authority of the state highway department varies in the several
+states, but in general the departments serve in the dual capacity of
+general advisers to the county and township authorities on road
+matters and as the executive authority responsible for the
+construction of those highways that are built entirely or in part from
+state or federal funds.
+
+State highway departments consist of the commission or commissioner,
+and the technical and clerical staff required to perform the duties
+imposed on the state organization. To some extent the state highway
+departments are able to encourage economical and correct construction
+of highways by the township and county authorities by furnishing them
+standard plans and specifications and by formulating regulations to
+govern the character of construction, but such efforts are likely to
+be more or less ineffective unless the state authority has supervision
+of the allotment of state or federal funds to the various counties and
+townships. Nevertheless, most state highway departments do a great
+deal of advisory work in connection with the highway construction
+carried out by county and township authorities.
+
+State highway departments are supported by funds obtained in various
+ways, laws differing greatly in this respect. The necessary support is
+in some states appropriated from funds obtained by general taxation,
+and is in others obtained from automobile license fees. In still
+others, the funds are secured by a combination of the two methods
+mentioned above. In addition to these support funds, a certain part of
+the money obtained as federal aid may be employed for the engineering
+and inspection costs on federal aid roads. The above mentioned funds
+are required to maintain the state highway department. In addition,
+the departments have supervision of the expenditures of construction
+funds which can be used for road construction and maintenance, and may
+not be expended for salaries or other overhead expense.
+
+In a number of states, automobile license fees are set aside for
+financing road construction and maintenance, and the work paid for
+from the fees is carried out under the supervision of the state
+highway department.
+
+In a number of instances, state bonds have been issued for road
+construction, and the expenditure of the proceeds of the sale of road
+bonds has usually been supervised by the state highway department.
+
+All federal aid funds allotted to a state must be expended under the
+direction of the state highway department.
+
+=Federal Administration.=--Federal authority in highway work is vested
+in the Bureau of Public Roads of the United States Department of
+Agriculture. The official head is the Secretary of Agriculture, but
+the administrative head is the Director of the Bureau. In this Bureau
+are the various instrumentalities needed for carrying on
+investigations and furnishing information to the various states on
+highway subjects. The Bureau also supervises the construction of
+federal aid roads in a general way through district engineers, each
+of whom looks after the work in several states.
+
+Funds for the support of the Bureau of Public Roads are obtained from
+congressional appropriations to the Department of Agriculture and from
+a percentage of the funds appropriated for federal aid.
+
+Federal aid is money appropriated by Congress to be distributed to the
+various states to stimulate road construction. It is granted to the
+states on the condition that the states will expend at least an equal
+amount on the projects involved. The states in turn usually give a
+suitable part of the state allotment to each county. There are various
+limitations as to the amount of federal aid per mile of road and the
+type of construction that may be employed, but these are matters of
+regulation that change from time to time.
+
+It will be seen that each of the administrative authorities, except
+the Bureau of Public Roads, is to some extent subservient to a higher
+authority, and the Bureau of Public Roads is supervised by the United
+States Congress. Considerable diplomacy is required on the part of any
+administrative authority if his contact with other officials is to be
+without friction. This is especially true in connection with the
+formulation of a policy regarding the types of construction to be
+adopted for an improvement. The responsibility for the selection is
+variously placed on the township, county or state authority, the laws
+not being uniform in this respect. If state or federal funds are
+allotted to an improvement, the state authority either makes the
+selection of the type of construction or the selection is made by some
+subordinate authority subject to the approval of the state highway
+department. Where the improvement is paid for exclusively with
+township or county funds, the selection is often made by the township
+or county authority without review by higher authority. Many abuses
+have crept into highway administration through the unscrupulous
+methods of promoters of the sale of road materials or road machinery.
+A great deal of the selling activity of the agents for these
+commodities is entirely irreproachable, but it is well known that such
+is not always the case. As a result, the tendency of legislation is to
+require the state highway department to approve contracts for
+materials or construction entered into by the township or county
+authorities. The state highway departments can secure the requisite
+technical experts to determine the merits of materials and equipment
+and, in spite of some glaring examples of inefficiency or worse, have
+made a good record for impartiality and integrity as custodians of the
+funds for which they are responsible.
+
+
+HIGHWAY FINANCE
+
+The paramount problem in highway administration is the development of
+an adequate financial plan for carrying on road improvement. The
+necessary expenditures are enormous, although the money so expended is
+probably much less than the actual benefit resulting from the
+improvements.
+
+=Special Assessments.=--There is presumed to be a direct and
+recognized benefit conferred on farm lands by the construction of
+improved highways adjacent thereto. Therefore, it is equitable to
+charge a part of the cost against the lands so benefited.
+
+The principle of paying for public improvements by a special
+assessment upon private property has been long established and a large
+proportion of the public improvements in the cities and towns have
+been made financially possible through the medium of special
+assessments on abutting and adjacent property. The same principle has
+been applied to the financing of drainage projects for reclaiming farm
+lands. Recently the special assessment method has come into limited
+use in financing rural highway improvements. The policy in such cases
+is to assess the abutting and adjacent property in a zone along the
+improved road for a percentage of the cost of the improvement. The
+amount so assessed does not ordinarily exceed one-fourth of the total
+cost of the improvement and may be considerably less. The assessment
+is spread over an area extending back from one to six miles from the
+improved road. The assessment area is generally divided into about
+four zones parallel to the road. The zone next the road is assessed at
+a rate arbitrarily determined as a fair measure of the benefit, and
+each succeeding zone is assessed at a somewhat lower rate. Generally
+about three-fourths of the total assessment is placed on the half of
+the assessment area lying next to the road.
+
+Many systems of making assessments have been proposed which are
+mechanical in application after the area and rate of distribution of
+benefit have been established, but in practice it is always found
+necessary to make adjustments on individual parcels of land because of
+variation in benefits received and it is impossible to eliminate the
+exercise of human judgment in equalizing the assessments.
+
+=Zone Method of Assessing.=--The area to be assessed on each side of
+the improved road is divided into zones usually four in number, but a
+larger or smaller number of zones may be adopted. The rate for each
+zone is then arbitrarily determined. For a typical case, the first of
+four zones would receive an assessment of 50 per cent of the amount to
+be borne by the area; the second zone 25 per cent, the third 15 per
+cent and the fourth 10 per cent. Other percentages sometimes adopted
+are 45, 25, 20 and 10 and 60, 20, 15 and 5. The set of percentages
+first mentioned seems to insure the most equitable distribution for an
+area all of which is substantially equally productive.
+
+When a road, for the improvement of which an assessment is being made,
+lies on two or more sides of a parcel of land all of which is within
+the assessment area, the rate is arbitrarily reduced to relieve that
+parcel of land somewhat, or the assessment is first spread as above
+outlined and afterward equalized as judgment dictates.
+
+In applying the zone method some difficulty is encountered in
+determining an equitable distribution on those parcels of land lying
+partly in one zone and partly in another, but the rate may be arrived
+at with reasonable accuracy by pro-rating in accordance with the exact
+conditions.
+
+In. Fig. 1, let it be assumed that the assessment area is to be two
+miles wide, one mile on each side of the road and the various
+ownerships to be indicated by the parcels of land numbered 1 to 8, as
+shown. Each zone for the assessment of the 3-1/4 mile section is 1/4
+mile wide and the rates for the several zones are 50, 25, 15 and 10
+per cent respectively. Let it be assumed that the portion of the cost
+of the 3-1/4 miles of road to be assessed on the area shown is
+$20,000. The assessment would then be as follows:
+
+  ------+-------+----------------------+------------+-------------
+        |       |  Rate x frontage on  | Amount of  |
+  Parcel|  Rate |  improved road =     | Assessment |  Assessment
+        |       |  assessment units    | per unit[1]|
+    1   |    2  |         3            |     4      |      5
+  ------+-------+----------------------+------------+-------------
+    1   |  a 50 |  50 x 2640 = 132,000 | $0.016655  |  $1558.46
+        |  b 75 |  75 x 1320 =  99,000 |            |   1153.90
+    2   |    40 |  40 x 2640 = 105,600 |            |   1230.77
+    3   |    10 |  10 x 2640 =  26,400 |            |    307.69
+    4   |    25 |  25 x 1320 =  33,000 |            |    384.66
+    5   | [2]85 |  85 x 5280 = 448,800 |            |   5230.88
+    6   |    15 |  15 x 5280 =  79,200 |            |   923.08
+    7   | [2]65 |  65 x 7920 = 514,800 |            |   6000.00
+    8   |    35 |  35 x 7920 = 277,200 |            |   3230.77
+        |       |  ------------------- |            | -----------
+        |       |            1,716,000 |            | $20000.00
+  ------+-------+----------------------+------------+-------------
+
+    [1] The assessment per unit is obtained by dividing the total
+    assessment by the total of column three.
+
+    [2] On these two parcels, it is decided that more than half of
+    the zone rate should apply to the half of the zone toward the
+    improved road, but some modification of the rates adopted might be
+    justified.
+
+[Illustration: Fig. 1]
+
+The assessment of the cost of the east and west one-mile section of
+road is made up in like manner, and let it be assumed that the portion
+of the cost of this road that is to be assessed on the area shown is
+$5500. The assessment area will be one mile wide and each zone
+one-fourth mile in width and the rates for each zone the same as
+before.
+
+  ------+-------+----------------------+------------+-------------
+        |       |  Rate x frontage on  | Amount of  |
+  Parcel| Rate  |  improved road =     | Assessment | Assessment
+        |       |  assessment units    | per unit   |
+  ------|-------+----------------------+------------+-------------
+  1     | a 75  |  75 x 1320 =  99,000 | $0.010417  |  $1031.25
+        | b 15  |  15 x 2640 =  39,600 |            |    412.49
+  2     |   75  |  75 x 2640 = 198,000 |            |   2062.53
+  3     |   50  |  50 x 1320 =  66,000 |            |    687.51
+  4     | a 25  |  25 x 1320 =  33,000 |            |    756.25
+        | b 15  |  15 x 2640 =  39,600 |            |
+  5     |   10  |  10 x 3300 =  33,000 |            |    343.73
+  6     |   10  |  10 x 1980 =  19,800 |            |    206.24
+  ------|-------|                      |            |-------------
+        |       |              528,000 |            |   5500.00
+  ------+-------+----------------------+------------+-------------
+
+It will be noted that the combined assessment for the two sections of
+road is especially heavy on parcels 1, 2 and 3. In order to prevent
+unjust charges against such properties, laws usually limit the total
+assessment against any parcel of land to a fixed percentage of a fair
+market value or of the assessed value. The assessment on these parcels
+would be reduced as seemed expedient and the deficit would be
+distributed over the remainder of the area in the same manner as the
+original assessment was spread. In practice such re-distribution is
+ordinarily made by the arbitrary adjustment in accordance with what
+the authorized officials consider to be fair and equitable. The method
+outlined is merely a mechanical means of securing distribution and
+must not be considered as an infallible method of making the
+assessment. It is always necessary to review the results in the light
+of the actual benefits to be presumed for each parcel of land.
+Nevertheless, the method outlined will prove equitable in a majority
+of cases.
+
+=General Taxation.=--There is a general community benefit derived from
+the construction of good roads in that the actual cost of marketing
+farm products is lessened with a resulting lowering of the price to
+the consumer. The benefit also accrues from the greater facility with
+which all community business may be conducted. The introduction of
+better opportunities for social, religious and educational activities
+in the rural districts which results from improved highways is also a
+community benefit of no mean importance. A part of the cost of road
+improvement may therefore be equitably paid from funds obtained by
+general taxation.
+
+A considerable portion of the current expense of maintaining the
+township and county highway work and at least a part of the cost of
+maintaining state highway activities is met from funds obtained by
+general taxation. Likewise, the funds required for the amortization of
+bond issues are often obtained from general taxation although vehicle
+license fees are sometimes used for that purpose.
+
+General taxes are levied on all taxable property in a political unit
+under statutory provisions regulating the amount of the levy and the
+purpose for which the revenue is to be used. In the aggregate, the
+road taxes are large but in the township or county the rate is
+generally small compared to some other taxes, such as the school tax.
+
+=Vehicle Taxes.=--The great direct benefit derived by those who
+actually operate vehicles over the roads justifies the policy of
+requiring a vehicle to pay a license fee in lieu of other taxes, the
+funds so obtained to be used for the construction and maintenance of
+public highways. In practice, this method has already been applied to
+motor vehicles in most states and has proven to be an important source
+of revenue. Its application to horse-drawn vehicles has not been
+attempted, due probably to the fact that such horse-drawn vehicles as
+use the public highways are also employed about the farm or in the
+towns and the determination of an equitable basis for taxation
+involves many difficulties.
+
+The rate of the fee for motor vehicles should be based on their
+destructive effect on the road so far as that is possible. The scale
+of fees should therefore take account of weight and speed of vehicle
+and if the license is in lieu of all other taxes, it should also be
+graduated with the cost of the vehicle.
+
+When funds are thus derived, every precaution should be taken to
+insure that the money is used judiciously for construction and
+especially for maintenance on those roads most useful to motor
+traffic.
+
+=Highway Bonds.=--Bond issues for road improvement afford a means of
+constructing roads and paying for them while they are being used. A
+very large volume of such bonds are outstanding in the United States.
+Road bonds should be issued only for durable types of improvement and
+the life of the bond should be well within the probable useful life of
+the road surface. It is customary and highly desirable that the
+general nature and extent of the improvement be established before the
+bonds are issued. It is desirable that bond issues be subject to
+approval by referendum before issue and that is provided in every
+instance.
+
+Highway bonds are of three classes known as Sinking Fund, Annuity and
+Serial Bonds, respectively. The earlier bonds issued were almost all
+of the sinking fund class, but in recent years the serial bond has
+been widely employed and is probably the most satisfactory to
+administer.
+
+=Sinking Fund Bonds.=[1]--When this type of bond is employed, the
+amount of the expenditure for road improvement is determined upon and
+the length of the period during which tax payments shall be made is
+settled. To employ a concrete example, it may be assumed that $100,000
+is to be expended for road work and is to be paid at the end of ten
+years. The interest rate on the bonds will vary with the condition of
+the bond market and the stability of the political unit issuing the
+bonds, but is usually about 5 per cent. Knowing these factors, the
+amount to be added to the sinking fund each year is computed. In order
+to pay the interest on the bonds, a tax of suitable rate is levied,
+and in order to retire the bonds at the end of the period, a sum is
+set aside each year which is supposed to be invested and draw interest
+which will be added to the principle, and the principle and interest
+comprise the sinking fund. The principle of the sinking fund is
+obtained by tax levies, a sum being added to the principle of the
+sinking fund each year.
+
+    [1] For a more detailed discussion of highway bonds see Bulletin
+    136, U. S. Dept. of Agriculture, which is the basis of this
+    discussion.
+
+The success of this method of financing depends upon the proper
+administration of the sinking fund. It must be invested with fidelity
+and the fund be kept intact. Usually the sinking fund cannot be
+invested at as high a rate of interest as the bonds bear and there is
+some loss as a result. Road bonds bearing 5 per cent interest can
+usually be sold at par while the sinking fund will usually net about 3
+or 3-1/2 per cent interest. The total cost of a bond issue will be
+greater by the sinking fund method than by either of the other methods
+described.
+
+=Annuity Bonds.=--Annuity bonds are drawn in such a manner that the
+amount of the payment for principle and interest is the same each year
+during the life of the bond. When the amount of the issue and the rate
+of interest has been determined and the amount of the desired annual
+payment has been determined, the number of years the bonds must run is
+computed.
+
+This method is convenient in that the amount of the tax to be levied
+each year remains constant.
+
+=Serial Bonds.=--Serial bonds are drawn so that a uniform amount of
+the principle is retired each year after retirement starts and the
+total interest payments decrease each year after the first bonds are
+retired. The first bond may not be retired for a number of years after
+the issue of the bonds, but when it once starts retirement proceeds at
+a constant rate annually.
+
+=Comparison of Methods of Issuing Bonds.=--The relative costs of
+financing by either of the three methods depends upon the rate of
+interest in each case and the net rate secured on the sinking fund
+provided for retiring sinking fund bonds.
+
+For comparative purposes, some typical examples are given in Table 3.
+These illustrate the differences in total cost of securing $100,000 by
+each of the three methods at various interest rates.
+
+  TABLE 3
+
+  TOTAL COST OF A LOAN OF $100,000 FOR 20 YEARS, INTEREST
+  COMPOUNDED ANNUALLY
+
+  ---------+---------------------------------------+---------+---------
+  Annual   |        Sinking Fund Compounded        |         |
+  Interest |              Annually at              |         |
+  on Bonds +----------+----------------+-----------+ Annuity |  Serial
+           |3 per cent| 3-1/2 per cent | 4 per cent|         |
+  ---------+----------+----------------+-----------+---------+---------
+  4        | $154,431 | $150,722       | $147,163  |$147,163 | $142,000
+  4-1/2    |  164,431 |  160,722       |  157,163  | 153,752 |  147,250
+  5        |  174,431 |  170,722       |  167,163  | 160,485 |  152,500
+  5-1/2    |  184,431 |  180,722       |  177,163  | 167,359 |  157,750
+  6        |  194,431 |  190,722       |  187,163  | 174,369 |  163,000
+  ---------+----------+----------------+-----------+---------+---------
+
+=Desirability of Road Bonds.=--In theory the bond method of financing
+enables the highway authorities to construct a large mileage of roads
+in a few years and spreads the cost over the period during which the
+public is being benefited. Better prices are obtained on contracts for
+a large mileage than for smaller jobs, and the community can receive
+the benefit more quickly than where construction proceeds piecemeal
+with current funds. The vital consideration is to insure that the term
+of the bonds is well within the useful life of the road, and that
+ample provision is made to maintain the roads during that period.
+Under proper restrictions the bond method of financing is to be
+commended. The bonds are an attractive investment and readily
+marketable on satisfactory terms.
+
+
+
+
+CHAPTER III
+
+DRAINAGE OF ROADS
+
+
+=The Necessity for Drainage.=--The importance of drainage for all
+roads subject to the effects of storm or underground water has always
+been recognized by road builders, but during recent years constantly
+increasing attention has been given to this phase of road
+construction. It is unfortunate that there has in the past been some
+tendency to consider elaborate drainage provisions less necessary
+where rigid types of surfaces were employed. It has become apparent,
+from the nature of the defects observed in all sorts of road surfaces,
+that to neglect or minimize the importance of drainage in connection
+with either earth roads or any class of surfaced roads is to invite
+rapid deterioration of some sections of the roadway surface and to add
+to maintenance costs.
+
+The degree to which lack of drainage provisions affect the
+serviceability of the road surface varies with the amount of
+precipitation in the locality and the manner in which it is
+distributed throughout the year. In the humid areas of the United
+States, which are, roughly, those portions east of a north and south
+line passing through Omaha and Kansas City, together with the northern
+part of the Pacific slope, precipitation is generally in excess of 30
+inches per year and fairly well distributed throughout the year, but
+with seasonal variations in rate. In these areas, the effect of the
+precipitation, both as regards its tendency to lower the stability of
+soils and as an eroding agent, must be carefully provided against in
+highway design.
+
+Outside of the areas mentioned above, the precipitation is much less
+than 30 inches per year and its effect as an agent of erosion is of
+greatest significance, although in restricted areas there may be short
+periods when the soil is made unstable by ground water.
+
+=Importance of Design.=--The drainage system for a proposed road
+improvement ought to be designed with as much care as any other
+element, and, to do so, a study must be made of all factors that have
+any bearing on the drainage requirements and the probable
+effectiveness of the proposed drainage system. The well established
+principles of land drainage should be followed so far as applicable.
+
+The basic principle of road drainage is to minimize the effect of
+water to such an extent that there will always be a layer of
+comparatively dry soil of appreciable thickness under the traveled
+part of the road. This layer should probably never be less than two
+feet thick and for soils of a structure favorable to capillary action
+it should be at least three feet thick. The means employed to
+accomplish the requisite drainage will be as various as the conditions
+encountered.
+
+=Surface Drainage.=--The drainage method which is by far the most
+nearly general in application is that which utilizes open ditches, and
+the system which employs these ditches is usually referred to as
+surface drainage. The full possibilities of this method of minimizing
+the effects of storm water are rarely fully utilized in road
+construction. Very frequently, deterioration of a road surface is
+directly attributable to failure to provide adequately for the removal
+of the storm water or water from the melting of snow that has fallen
+on the road, or water that flows to the road from land adjacent
+thereto. Surface water can usually most cheaply and expeditiously be
+carried away in open ditches, although special conditions are
+occasionally encountered which require supplementary tile drains. The
+cross section commonly adopted for roads lends itself naturally to the
+construction of drainage ditches at the sides of the traveled way, and
+these are usually the principal dependence for the disposal of storm
+water.
+
+=Run-off.=--The capacity required of side ditches to insure
+satisfactory surface drainage will be affected by the amount and
+nature of the precipitation in the region where the road is built. The
+annual rainfall in a region may amount to several feet, but may be
+well distributed throughout the year with an absence of excessive
+rainfall for short periods, that is, flood conditions may rarely
+occur. In other areas, the annual rainfall may be comparatively small
+but the precipitation occurs at a very high rate, that is, flood
+conditions may be common, or it may be at a low rate extending over a
+considerable period. These peculiarities must be known before an
+adequate drainage system can be planned.
+
+It is almost universally true in the United States that precipitation
+at a very high rate will be for a relatively short duration, and
+during these short periods, which usually do not exceed thirty
+minutes, a portion of the water that falls on the areas adjacent to
+the road and that drains to the road ditches will soak into the soil
+and therefore not reach the ditches along the road. The extent to
+which the water is taken up by the soil will vary with the porosity
+and slope of the land and the character of the growth thereon.
+Cultivated land will absorb nearly all of the water from showers up to
+fifteen or twenty minutes duration; grass land a somewhat smaller
+percentage; and hard baked or other impervious soil will absorb a
+comparatively small amount. Rocky ground and steep slopes will absorb
+very little storm water.
+
+The surface of the road is designed to turn water rapidly to the
+ditches, but when the material is the natural soil, there is always
+considerable absorption of storm water. Surfaces such as sandclay,
+gravel and macadam do not absorb to exceed 10 per cent of the
+precipitation during short showers. Bituminous surfaces, brick and
+concrete pavements, do not absorb an appreciable amount of storm
+water.
+
+Generally it is best to assume that if a rain lasts for forty-five
+minutes or more, all of the water will run off, as the soil will reach
+a state of saturation in that time. This is not true of deep sand, but
+is for nearly all other soils.
+
+The ditch capacity needed will therefore depend upon the area drained,
+the character of the soil, the slopes and the rainfall characteristics
+of the region, and upon the nature of the road surface.
+
+For a required capacity, the cross section area of the ditch will vary
+inversely as the grade, because the velocity of flow increases with an
+increase in the grade of the ditch. If the surface water must be
+carried along the road for distances exceeding five or six hundred
+feet, the ditch must be constructed of increasing capacity toward the
+outlet in order to accommodate the accumulated volume of water.
+
+The velocity of flow varies not only with the grade, but with the
+shape of the cross section, cleanness of the channel, the depth of the
+water in the channel, alignment of the channel and the kind of
+material in which the channel is formed. It is not necessary to go to
+great refinement in the design of the side ditches for the ordinary
+case where the water is carried along the road for only a few hundred
+feet. The ditches are made of ample capacity by using the commonly
+accepted cross section for a road, which will be discussed in a later
+paragraph. But where large areas must be drained by the road ditches,
+it is desirable carefully to design the side ditches. The basis for
+that design is too lengthy to be included herein, and reference should
+be made to a standard treatise on the subject.
+
+=Ordinary Design of Ditches.=--For grades of one per cent or less on
+roads in the humid area, the bottom of the ditch should be at least
+three and one-half feet lower than the traveled surface of the road,
+except for very sandy soil. For grades greater than one per cent, this
+depth may be decreased one foot, and for grades of four per cent and
+upward, the depth may be still less. These general rules for depth are
+susceptible of variation but are believed to be the minimum except in
+arid or semi-arid climates. It is far better to be too liberal in
+ditch allowance than to be too conservative. In arid or semi-arid
+regions, the ditch design will be based on the necessity of providing
+for flood flow and preventing damage through erosion. Ordinary
+drainage requirements will be satisfactory with the ditch about one
+foot deep.
+
+If the topography is such that it is evident considerable storm water
+will flow from the adjacent land to the road ditches, the design must
+be modified to take this into account. Sometimes such water can be
+diverted by ditches well back from the road, and thus prevented from
+flowing into the side ditches along the roadway. It is especially
+desirable to divert water, which would otherwise flow down the slope
+of a cut, by means of a ditch on the hill-side above the upper edge of
+the slope of the cut.
+
+Ditches are not effective unless they afford a free flow throughout
+their length and have an outlet to a drainage channel of ample
+capacity. Therefore, ditch grades should be established by survey,
+especially if the gradient is less than one per cent, and the
+construction work should be checked to insure that the ditch is
+actually constructed as planned. A few high places in the ditch will
+greatly reduce the effectiveness, although these may appear at the
+time of construction to be slight. Constricted places, such as might
+be due to a small amount of loose earth left in the ditch, are always
+to be avoided.
+
+Where the side ditch passes from a cut to the berm alongside a fill,
+the ditch should be excavated throughout in the undisturbed natural
+soil, five feet or more from the toe of the slope of the fill, and
+along the filled portion of the road there should be a berm of three
+or four feet between the toe of the slope of the fill and the near
+edge of the ditch.
+
+=Underground Water.=--In a preceding paragraph, mention was made of
+the fact that only a part of the storm water runs off over the surface
+of the ground, the larger part being absorbed by the soil. The water
+thus absorbed flows downward through the pores in the soil until it is
+deflected laterally by some physical characteristic of the soil
+structure. The movement of underground water is affected by many
+circumstances, but only two conditions need be discussed herein.
+
+Underground water, like surface water, tends to attain a level
+surface, but in so doing it may need to flow long distances through
+the pores of the soil, and to overcome the resistance incident to so
+doing some head will be required. That is to say, the water will be
+higher at some places than at others. If a cut is made in grading the
+road, the road surface may actually be lower than the ground water
+level in the land adjoining the road. As a result, the water will seep
+out of the side slopes in the cut and keep the ditches wet, or even
+furnish enough water to occasion a flow in the ditch. Similarly, the
+higher head of the underground water near the top of a hill may result
+in ground water coming quite close to the surface some distance down
+the hill. The remedy in both cases is tile underdrains alongside the
+road to lower the ground water level so that it cannot affect the road
+surface.
+
+Sometimes the ground water encounters an impervious stratum as it
+flows downward through the soil, or one that is less pervious than the
+surface soil. When such is the case, the water will follow along this
+stratum, and should there be an outcrop of the dense stratum, a spring
+will be found at that place. This may be on a highway. The impervious
+stratum may not actually outcrop but may lie only a few feet under the
+surface of the road, in which case, the road surface will be so water
+soaked as to be unstable. The so-called "seepy places" so often noted
+along a road are generally the result of this condition. This
+condition can be corrected by tile laid so as to intercept the flow at
+a depth that precludes damage to the road. Commonly, the tile will be
+laid diagonally across the road some distance above the section where
+the effect of the water is noted, and will be turned parallel to the
+road at the ditch line and carried under one of the side ditches to an
+outlet.
+
+=Tile Drains.=--Where the soil and climatic conditions are such that
+the roadway at times becomes unstable because of underground water
+rising to a level not far below the road surface, the ground water
+level is lowered by means of tile underdrains. The function of the
+tile drains in such cases is precisely the same as when employed in
+land drainage; to lower the ground water level.
+
+=Laying Tile.=--The tile lines are usually laid in trenches parallel
+to the center line of the road near the ditch line and at least 4 feet
+deep so as to keep the ground water level well down. They must be
+carefully laid to line and grade. A good outlet must be provided and
+the last few joints of pipe should be bell-and-spigot sewer pipe with
+the joints filled with cement mortar. The opening of the tile should
+be covered with a coarse screen to prevent animals from nesting in the
+tile.
+
+It is frequently necessary to lay a line of tile at the toe of the
+slope in cuts to intercept water that will percolate under the road
+from the banks at the sides. In some cases, it is desirable to
+back-fill the tile trench with gravel or broken stone to insure rapid
+penetration of surface water to the tile. In other instances, it is
+advantageous to place catch basins about every three or four hundred
+feet. These may be of concrete or of tile placed on end or may be
+blind catch basins formed by filling a section of the trench with
+broken stone. When a blind catch basin is used, the top should be
+built up into a mound, and for a tile or concrete catch basin, a
+grating of the beehive type should be used, so that flow to the tile
+will not be obstructed by weeds and other trash that is carried to the
+catch basin.
+
+=Culverts.=--Culverts and bridges are a part of the drainage system
+and the distinction between the two is merely a matter of size.
+Generally, structures of spans less than about eight feet are classed
+as culverts, but the practice is not uniform. In this discussion
+culverts will be defined as of spans of 8 feet or less.
+
+Numerous culverts are required to afford passage for storm water and
+small streams crosswise of the road, and their aggregate cost is a
+large item in the cost of road improvement. The size of the waterway
+of a culvert required in any location will be estimated by an
+inspection of the stream and existing structure, and by determining
+the extent and physical characteristics of the drainage area.
+Sometimes there is sufficient evidence at the site to indicate quite
+closely the size required, but this should always be checked by
+run-off computations. The drainage area contributing water to the
+stream passing through the culvert under consideration is computed
+from contour maps or from a survey of the ground, and the size of
+culvert determined by one of the empirical formulas applicable to that
+purpose. In these formulas, the solution depends upon the proper
+selection of a factor "C" which varies in accordance with the nature
+of the drainage area. Two of these that are quite widely used are as
+follows:
+
+  _Myers' Formula: a = CA_
+
+Where _a_ = area of cross section of culvert in square feet. _A_ =
+area in acres of the drainage area above culvert. _C_ a factor varying
+from 1 for flat country to 4 for mountainous country or rocky soil,
+the exact value to be selected after an inspection of the drainage
+area.
+
+_Talbot's Formula_: Area of waterway in square feet =
+
+  _C_ [Square root of] ((Drainage area in acres)^3)
+
+     Transcriber's Note: The above formula used the mathematical
+     square root symbol in the original. One should read it as "C
+     times the square root of the Drainage area in acres cubed."
+
+_C_ being variable according to circumstances thus:
+
+"For steep and rocky ground _C_ varies from 2/3 to 1. For rolling
+agricultural country, subject to floods at times of melting snow, and
+with length of valley three or four times its width, _C_ is about 1/3,
+and if stream is longer in proportion to the area, decrease _C_. In
+districts not affected by accumulated snow, and where the length of
+valley is several times its width, 1/5 or 1/6 or even less may be
+used. _C_ should be increased for steep side slopes, especially if the
+upper part of the valley has a much greater fall than the channel at
+the culvert. The value of _C_ to be used in any case is determined
+after an inspection of the drainage area."
+
+[Illustration: Fig. 2. Design of Pipe Culvert and Bulkhead]
+
+=Length of Culvert.=--The clear length between end walls on a culvert
+should be at least equal to the width of the roadway between ditches.
+This is a minimum of 20 feet for secondary roads and ranges from 24 to
+30 feet for main roads. The headwall to the culvert should not be a
+monument, but should be no higher than needed to prevent vehicles from
+leaving the roadway at the culvert.
+
+=Farm Entrance Culverts.=--At farm entrances, culverts are required to
+carry the farm driveway across the side ditch of the road. These
+culverts are usually about 16 feet along, and should be of a size
+adequate to take the flow of the side ditch. The farm entrance culvert
+should be of such design that it can be easily removed to permit
+cleaning out the ditches with a road grader.
+
+
+TYPES OF CULVERTS
+
+Culverts constructed of concrete and poured in place are called box
+culverts because of the rectangular form of the cross section.
+Culverts of pre-cast pipe are known as pipe culverts. Several forms of
+pipe culvert are in general use.
+
+[Illustration: Fig. 3.--Typical Concrete Box Culvert]
+
+=Metal Pipe.=--These may be of cast iron, steel or wrought iron. The
+cast iron pipe is very durable but expensive and heavy to handle and
+is not widely used in highway construction. Steel pipe has been
+employed to a limited extent but its durability is questioned. At
+least it is known that the pipe made from uncoated, light sheet steel
+is not very durable. Sheet iron and sheets made from alloy iron
+coated with spelter have been extensively used and seem to be durable,
+especially when laid deep enough to eliminate possibility of damage
+from heavy loads. To insure reasonable resistance to corrosion, the
+metal sheets should be coated with at least one and one-half ounces of
+spelter per square foot of sheet and the sheets should not be lighter
+than 16 gauge for small sizes and should be heavier for the larger
+sizes.
+
+=Clay and Cement Concrete Pipe.=--The ordinary burned clay bell and
+spigot pipe that is employed for sewer construction is sometimes used
+for culverts. It must be very carefully bedded, preferably on a
+concrete cradle and the joints filled with cement mortar. Culverts of
+this type have a tendency to break under unusual loads, such as
+traction engines or trucks. They may be damaged by the pressure from
+freezing water, particularly when successive freezing and thawing
+results in the culvert filling with mushy snow, which subsequently
+freezes.
+
+=Concrete Pipe.=--Reinforced concrete pipe is a satisfactory material
+for culverts, if the pipe is properly designed. The pipe should be
+carefully laid on a firm earth bed with earth carefully back-filled
+and tamped around the pipe. The joints in the pipe should be filled
+with cement mortar, or should be of a design that will be tight.
+
+=Endwalls for Culverts.=--A substantial retaining wall is placed at
+each end of the culvert barrel, whatever the type. This is to prevent
+the end of the culvert from becoming choked with earth and to retain
+the roadway at the culvert. It also indicates to the drivers the
+location of the end of the culvert. The endwall extends a foot or more
+below the floor of the culvert to prevent water from cutting under the
+barrel. Plain concrete or stone masonry are most commonly used for
+culvert endwalls.
+
+[Illustration: Fig. 4.--Two Types of Drop Inlet Culvert]
+
+=Reinforced Concrete Box Culverts.=--The pipe culvert is limited in
+application to the smaller waterways. Reinforced concrete is
+extensively used for culverts of all sizes, but especially for the
+larger ones. These are usually constructed with endwalls integral with
+the barrel of the culvert. Culverts of this type must be designed for
+the loads anticipated to insure suitable strength and stability, and
+must be constructed of a good quality of concrete. Figs. 2 and 3 show
+designs for pipe and box culverts.
+
+[Illustration: Fig. 5.--Drop Inlet Culvert]
+
+=Drop Inlet Culverts.=--In some locations erosion has begun in the
+fields adjacent to a culvert and it will probably continue until the
+stream above the culvert has eroded to about the level of the floor of
+the culvert. This is a reason for placing the culvert as high as the
+roadway will permit, so long as the area above the culvert will be
+properly drained. Considerable reclamation of land is possible if the
+culvert is constructed with a box at the inlet and as shown in Fig. 4.
+The area up-stream from the culvert will not erode below the level of
+the top of the box at the inlet end.
+
+Where the stream crossing the road has eroded to considerable depth or
+has considerable fall, as would sometimes be the case on side hill
+roads, the culvert barrel would follow the general slope of the ditch
+but should have a drop inlet. This type of culvert is shown in Fig.
+5.
+
+
+
+
+CHAPTER IV
+
+ROAD DESIGN
+
+
+=Necessity for Planning.=--Sometimes highway improvement is the result
+of spasmodic and carelessly directed work carried out at odd times on
+various sections of a road, finally resulting in the worst places
+being at least temporarily bettered. The grade on the steepest hills
+is probably reduced somewhat and some of the worst of the low lying
+sections are filled in and thereby raised. Short sections of surfacing
+such as gravel or broken stone may be placed here and there. From the
+standpoint of the responsible official, the road has been "improved,"
+but too often such work does not produce an improvement that lasts,
+and sometimes it is not even of any great immediate benefit to those
+who use the roads. In nearly every instance such work costs more in
+money and labor that it is worth.
+
+Lasting improvement of public highways can be brought about only
+through systematic and correlated construction carried on for a series
+of years. In other words, there must be a road improvement policy
+which will be made effective through some agency that is so organized
+that its policies will be perpetuated and is clothed with enough
+authority to be capable of enforcing the essential features of good
+design and of securing the proper construction of improvements.
+
+Details of highway construction and design must vary with many local
+conditions and types of surface. The limits of grades and the many
+other details of design may properly be adopted for a specific piece
+of work only after an adequate investigation of the local requirements
+and in the light of wide experience in supervising road improvement.
+
+New ideas are constantly being injected into the art of road building,
+but these are disseminated somewhat slowly, so that valuable devices
+and improvements in methods remain long unknown except to the
+comparatively few who have the means for informing themselves of all
+such developments.
+
+It follows then that the logical system of conducting road improvement
+is through an agency of continuing personnel which will supervise the
+preparation of suitable plans and direct the construction in
+accordance with the most recent experience.
+
+=Road Plans.=--The information shown on the plans prepared for road
+improvement varies somewhat with the design and with the ideas of the
+engineer as to what constitutes necessary information, but in general
+the plans show the existing road and the new construction contemplated
+in an amount of detail depending principally upon the character of the
+construction. Simple plans suffice for grade reduction or reshaping an
+earth road surface, while for the construction of paved roads, the
+plans must be worked out in considerable detail. The essential
+requirement is that there be given on the plans all information
+necessary to enable the construction to be carried out according to
+the intentions of the engineer, that all parts of the work fit
+together, that the culverts are of the proper size and located at the
+proper places, ditches drain properly, grades are reduced to the
+predetermined rate, that excavated material is utilized and that an
+exact record of the work done is retained. Plans are indispensable to
+economical road construction and the preparation of the plans is the
+work of the expert in road design, that is, the highway engineer.
+
+=Problem of Design.=--The problem of road design is to prepare plans
+for a road improvement with the various details so correlated as to
+insure in the road constructed in accordance therewith the maximum of
+safety, convenience and economy to the users thereof. The degree to
+which the design will be effective will depend to a considerable
+extent upon the financial limitations imposed upon the engineer, but
+skill and effort on the plans will do a great deal to offset financial
+handicap and no pains should be spared in the preparation of the
+plans. Moreover, the plans must afford all of the information needed
+by the contractor in preparing a bid for the work.
+
+=Preliminary Investigation.=--The first step in road improvement is to
+secure an adequate idea of the existing conditions on the road or
+roads involved. The detail to which this information need go will
+depend entirely upon the purpose of the preliminary investigation, for
+before a definite plan is prepared, it may be necessary to choose the
+best from among several available routes. For this purpose, it is not
+always necessary to make an actual instrument survey of the several
+routes. A hasty reconnaissance will usually be sufficient. This is
+made by walking or riding over the road and noting, in a suitable book
+or upon prepared blanks, the information needed. The items of
+information recorded will usually be as follows: distances, grades,
+type of soil on the road and nature of existing surface, character of
+drainage, location of bridges and culverts and the type of each with
+notes as to its condition, location of railway crossings and notes as
+to type, location of intersecting roads, farm entrances, and all
+similar features that have a bearing on the choice of routes. These
+data can be obtained in a comparatively short time by a skilled
+observer who may drive over the road in a motor car. Sometimes it may
+be desirable to make a more careful study of some certain sections of
+road and this may be done by waking over the section in question in
+order to make a more deliberate survey of the features to be
+considered than is possible when riding in a motor car.
+
+Factors other than relative lengths of routes will obviously determine
+the cost of improvement and the comparative merits of the improved
+roads. Some special characteristic of a road, such as bad railroad
+crossings or a few bad hills, may eliminate a route, or availability
+of materials along a route may offset disadvantages of alignment or
+grade.
+
+In special cases, complete surveys of routes may be required finally
+to select the best route, but these instances are few in number.
+
+=Road Surveys.=--When a road has been definitely selected for
+improvement, a careful survey is made to furnish information for the
+preparation of the plans. This will consist of a transit survey and a
+level survey.
+
+The transit survey is made by running a line between established
+corners following the recorded route of the road, or if no records are
+available or the road is irregular in alignment, by establishing
+arbitrary reference points and running a line along the center line of
+the existing road or parallel thereto. The topography is referenced to
+this line in such completeness that it can be reproduced on the plans.
+The level survey consists in taking levels on cross sections of the
+road at one hundred foot intervals, and oftener if there are abrupt
+changes in grade. Special level determinations are made at streams,
+railroad crossings, intersecting roads or lanes and wherever it
+appears some special features of the terrain should be recorded.
+
+From the surveys and such other information as has been assembled
+relative to the project, a plan is prepared which embodies a design
+presumed to provide for an improvement in accordance with the best
+highway practice.
+
+
+THE PROBLEM OF DESIGN
+
+It will be convenient to consider separately the components of a road
+design, although in the actual design the consideration of these
+cannot be separated because all parts of the plan must fit together.
+
+=Alignment.=--The alignment of the road is determined to a
+considerable extent by the existing right-of-way, which may follow
+section lines, regardless of topography, as is the case with many
+roads in the prairie states, or it may follow the valleys, ridges, or
+other favorable location in hilly country. In many places the roads of
+necessity wind around among the hills in order to avoid excessive
+grades. In designing an improvement, it is generally desirable to
+follow the existing right-of-way so far as possible. But the element
+of safety must not be lost sight of, and curves should not preclude a
+view ahead for sufficient distance to insure safety to vehicles. The
+necessary length of clear view ahead is usually assumed to be 250
+feet, but probably 200 feet is a satisfactory compromise distance when
+a greater distance cannot be obtained at reasonable cost. To secure
+suitable sight distance, the curves must be of long radii, and where
+possible the right-of-way on the inside of the curve should be cleared
+of trees or brush that will obstruct the view. Where the topography
+will not permit a long radius curve and the view is obstructed by an
+embankment or by growing crops or other growth, it is desirable to
+separate the tracks around the curve to eliminate the possibility of
+accidents on the curve. This is readily accomplished if the road is
+surfaced, but if it is not surfaced, the same end is accomplished by
+making the earth road of ample width at the curve.
+
+Relocations should be resorted to whenever they shorten distances or
+reduce grades sufficiently to compensate for the cost.
+
+=Intersections.=--At road intersections, it is always difficult to
+design a curve that entirely meets the requirements of safety because
+there is not enough room in the right-of-way, and enough additional
+right-of-way must be secured to permit the proper design. It is not
+necessary to provide an intersection that is adapted to high speed
+traffic, where main roads cross, but, on the contrary, a design that
+automatically causes traffic to slow up has distinct advantages.
+
+Where a main route, improved with a hard surface, crosses secondary
+roads, it is satisfactory to continue the paved surface across the
+intersecting road at normal width and make no provision for the
+intersecting road traffic other than a properly graded approach at the
+intersection.
+
+=Superelevation.=--On all curved sections of road, other than
+intersections, account is taken of the tendency of motor cars to skid
+toward the outside of the curve. This tendency is counteracted by
+designing the cross section with superelevation.
+
+[Illustration: Fig. 6]
+
+In Fig. 6, _F_ represents the tangential force that tends to cause
+skidding. _W_ represents the weight of the vehicle in pounds, THETA
+= the angle of superelevated surface _c-d_, with the horizontal _c-a_.
+_R_ represents the radius of the curve upon which the vehicle is
+moving. _w_ is the component of the weight parallel to the surface
+_c-d_, _v_ = velocity of the vehicle in feet per second. _m_ = mass
+of vehicle = _W/g  THETA_
+
+
+                  _w_ = _W_ tan _THETA_
+
+
+               _mv^2_     _wv^2_
+       _F_ =  -------  =  ------
+                _R_        _gR_
+
+If _F_ = _w_ there will be no tendency to skid; hence the rate of
+superelevation necessary in any case is as follows:
+
+
+                         _Wv^2_
+      _W_ tan _THETA_ = -------
+                          _gR_
+
+
+                          _v^2_
+          tan _THETA_ = -------
+                          _gR_
+
+
+The amount of superelevation required, therefore, varies as the square
+of the velocity and inversely as the radius of the curve.
+
+Theoretically, the amount of the superelevation should increase with a
+decrease in the radius of the curve and should also increase as the
+square of the speed of the vehicle. On account of the variation in
+speeds of the vehicles, the superelevation for curves on a highway can
+only be designed to suit the average speed. At turns approaching
+ninety degrees, the curve is likely to be of such short radius that it
+is impossible to maintain the ordinary road speed around the curve,
+even with the maximum superelevation permissible. It is good practice
+to provide the theoretical superelevation on all curves having radii
+greater than 300 feet for vehicle speeds of the maximum allowed by
+law, which is generally about 25 miles per hour. Where the radii are
+less than 300 feet, the theoretical superelevation for the maximum
+vehicle speeds gives a superelevation too great for motor trucks and
+horse drawn vehicles and generally no charge is made in superelevation
+for radii less than 300 feet, but all such curves are constructed with
+the same superelevation as the curve with 300 foot radius.
+
+The diagram in Fig. 7 shows the theoretical superelevation for various
+curve radii.
+
+[Illustration: Fig. 7. Curves showing Theoretical Superelevation for
+Various Degrees of Curve for Various Speeds of Vehicle]
+
+At the intersection of important highways, the problem is complicated
+by the necessity for providing for through traffic in both directions
+and for traffic which may turn in either direction and the engineer
+must provide safe roadways for each class of traffic.
+
+=Tractive Resistance.=--The adoption of a policy regarding the grades
+on a road involves an understanding of the effect of variation in the
+character of the surface and in rate of grade upon the energy required
+to transport a load over the highway. The forces that oppose the
+movement of a horse drawn vehicle are fairly well understood and their
+magnitude has been measured by several observers, but comparatively
+little is known about the forces opposing translation of rubber tired
+self-propelled vehicles.
+
+The resistance to translation of a vehicle is made up of three
+elements: resistance of the road surface to the rolling wheel,
+resistance of the air to the movement of the vehicle and internal
+friction in the vehicle itself.
+
+=Rolling Resistance.=--When the wheel of a vehicle rolls over a road
+surface, both the wheel and the surface are distorted. If the wheel
+has steel tires and the road surface is plastic, there will be
+considerable distortion of the road surface and very little of the
+wheel. A soft rubber tire will be distorted considerably by a brick
+road surface. Between these extremes there are innumerable
+combinations of tire and road surface encountered, but there is always
+a certain amount of distortion of either road surface or wheel, or of
+both, which has the same effect upon the force necessary for
+translation as a slight upward grade. When both the tire and the road
+surface strongly resist distortion (as steel tires on vitrified brick
+paving), the resistance to translation is low but the factor of impact
+is likely to be introduced. Where impact is present, energy is used up
+in the pounding and grinding of the wheels on the surface, and this
+factor increases as the speed of translation, and may be a
+considerable item. Impact is especially significant on rough roads
+with motor vehicles, particularly trucks, traveling at high speed.
+These two factors (impact and rolling resistance) combined constitute
+the major part of the resistance to translation for horse drawn
+vehicles.
+
+=Internal Resistance.=--For horse drawn vehicles, the internal
+resistance consists of axle friction, which is small in amount. For
+self-propelled vehicles, the internal resistance consists of axle
+friction and friction in the driving mechanism, of which gear
+friction and the churning of oil in the gear boxes is a large item.
+Internal friction is of significance in all self-propelled vehicles
+and especially so at high speeds.
+
+=Air Resistance.=--At slow speeds, the resistance of still air to
+translation is small, but as the speed increases, the air resistance
+increases rapidly and at the usual speed of the passenger automobile
+on the road becomes a very considerable part of the total resistance
+to translation. This factor has no significance in connection with
+horse drawn vehicles, but is to be taken into account when dealing
+with self-propelled vehicles at speeds in excess of five miles per
+hour.
+
+Many determinations of tractive resistance with horse drawn vehicles
+have been made from time to time and these show values that are fairly
+consistent when the inevitable variations in surfaces of the same type
+are taken into account. Table 4 is a composite made up of values
+selected from various reliable sources and Table 5 is from experiments
+by Professor J. B. Davidson on California highways.
+
+  TABLE 4
+
+  AVERAGE TRACTIVE RESISTANCE OF ROAD SURFACES TO STEEL TIRED
+  VEHICLES
+
+  Surface               Tractive force per ton
+
+  Earth packed and dry           100
+  Earth dusty                    106
+  Earth muddy                    190
+  Sand loose                     320
+  Gravel good                     51
+  Gravel loose                   147
+  Cinders well-packed             92
+  Oiled road--dry                 61
+  Oiled road--wet                108
+  Macadam--very good              38
+  Macadam--average                46
+  Sheet asphalt                   38
+  Asphaltic concrete              40
+  Vitrified brick--new            56
+  Wood block--good                33
+  Wood block--poor                42
+  Cobblestone                     54
+  Granite tramway                 27
+  Asphalt block                   52
+  Granite block                   47
+
+  TABLE 5
+
+  TRACTIVE RESISTANCES TO STEEL TIRED VEHICLES[1]
+
+  ----------+-----------------+-----------------+-----------+-----------
+            |                 |    Condition    | Tractive  | Resistance
+   Test No. |  Kind of Road   |     of Road     | Total lb. | per ton lb.
+  ----------+-----------------+-----------------+-----------+-----------
+   29-30-31 | Concrete        |Good, excellent  |    83.0   |   27.6
+            |   (unsurfaced)  |                 |           |
+   [2]11-12 | Concrete        |Good, excellent  |    90.0   |   30.0
+            |    (unsurfaced) |                 |           |
+   26-27-28 | Concrete 3/8-in.|Good, excellent  |   147.6   |   49.2
+            |   surface       |                 |           |
+            |   asphaltic oil |                 |           |
+            |   and screenings|                 |           |
+      13-14 | Concrete 3/8-in.|Good, excellent  |   155.0   |   51.6
+            |   surface       |                 |           |
+            |   asphaltic oil |                 |           |
+            |   and screenings|                 |           |
+       9-10 | Macadam,        |Good, excellent  |   193.0   |   64.3
+            |   water-bound   |                 |           |
+      22-23 | Topeka on       |Good, excellent  |   205.5   |   68.5
+            |   concrete      |                 |           |
+          8 | Gravel          |Compact, good    |   225.0   |   75.0
+            |                 |  condition      |           |
+   [3]45-48 | Oil macadam     |Good, new        |   234.5   |   78.2
+   [4]46-47 | Oil macadam     |Good, new        |   244.0   |   81.3
+         38 | Gravel          |Packed, in       |   247.0   |   82.3
+            |                 |  good condition |           |
+   18-19-20 | Topeka on plank |Good condition,  |   265.0   |   88.3
+            |                 |  soft, wagon    |           |
+            |                 |  left marks     |           |
+         34 | Earth road      |Firm, 1-1/2-in.  |   276.0   |   92.0
+            |                 |  fine loose dust|           |
+      24-25 | Topeka on plank |Good condition,  |   278.0   |   92.6
+            |                 |  but soft       |           |
+      1-2-5 | Earth road      |Dust 3/4 to 2 in.|   298.0   |   99.3
+        3-3 | Earth           |Mud, stiff, firm |   654.0   |  218.0
+            |                 |  underneath     |           |
+        6-7 | Gravel          |Loose, not packed|   789.0   |  263.0
+  ----------+-----------------+-----------------+-----------+-----------
+
+    [1] Prof. J. B. Davidson in _Engineering News-Record_, August 17,
+    1918.
+
+    [2] Graphic record indicates that the load was being accelerated
+    when test was started.
+
+    [3] Drawn with motor truck at 2-1/2 miles per hour.
+
+    [4] Drawn with motor truck at 5 miles per hour.
+
+Comparatively few data are available showing the tractive resistance
+of motor vehicles, but the following tables are based on sufficient
+data to serve to illustrate the general trend.
+
+These data on the tractive resistances of an electric truck with solid
+rubber tires on asphalt and bitulithic, wood, brick and granite block,
+water-bonded and tar macadam, cinder and gravel road surfaces were
+obtained by A. E. Kennelly and O. R. Schurig in the research division
+of the electrical engineering department of the Massachusetts
+Institute of Technology, and are published in Bulletin No. 10 of the
+division.
+
+An electric truck was run over measured sections, ranging from 400 to
+2600 feet in length, surfaced with these various materials, at certain
+speeds per hour, ranging from about 8 to about 15.5 miles per hour.
+The result of the observations of speeds, tractive resistances,
+conditions of surfaces, etc., were collected and studied in various
+combinations.
+
+  TABLE 6
+
+  ----------------------+-----------------------+-----------+----------
+                        |                       | Tractive  | Tractive
+                        |                       |Resistance |Resistance
+    Type of Surface     | Condition of Surface  |  in lbs.  |  in lbs.
+                        |                       |  per ton  |  per ton
+                        |                       | 10 miles  |12.4 miles
+                        |                       |  per hr.  |  per hr.
+  ----------------------+-----------------------+-----------+----------
+  Asphalt               | Good                  |   20.4    |
+  Asphalt               | Poor                  |   22.6    |   25.5
+  Wood block            | Good                  |   24.2    |   25.3
+  Brick block           | Good                  |   24.6    |   26.6
+  Granite block         | Good                  |   40.3    |   45.75
+  Brick block           | Slightly worn         |   25.1    |   28.0
+  Granite block with    |                       |           |
+    cement joints       | Good                  |   25.5    |   30.2
+  Macadam, water bonded | Dry and hard          |   23.3    |   25.8
+  Macadam, water bonded | Fair, heavily oiled   |   35.9    |   38.7
+  Macadam, water bonded | Poor, damp, some holes|   36.3    |   41.6
+  Tar macadam           | Good                  |   25.7    |   28.0
+  Tar macadam           | Very soft             |   36.8    |   38.7
+  Tar macadam           | Many holes, soft,     |           |
+                        |  extremely poor       |   52.4    |   60.6
+  Cinder                | Fair, hard            |   27.5    |   30.6
+  Gravel                | Fair, dusty           |   30.4    |   33.0
+  ----------------------+-----------------------+-----------+----------
+
+[Illustration: Fig. 8]
+
+=Effect of Grades.=--Grades increase or decrease the resistance to
+translation due to the fact that there is a component of the weight of
+the vehicles parallel to the road surface and opposite in direction to
+the motion when the load is ascending the hill and in the same
+direction when the vehicle is descending. In Fig. 8 _W_ represents the
+weight of the vehicle, acting vertically downward, _w_ is the
+component of the weight perpendicular to the road surface and _W_{2}_
+is the component parallel to the road surface.
+
+    _W_{2}_     = _W_ tan _THETA_.
+
+    tan _THETA_ = 0.01 x per cent of grade.
+
+    _W_{2}_     = 0.01 _W_ x per cent grade.
+
+    _W_{2}_     = 0.01 x 2000 x per cent of grade, for each ton
+                      of weight of vehicle.
+
+  Hence _W_{2}_ = 20 lbs. per ton of load for each one per cent of
+                      grade.
+
+The gravity force acting upon a vehicle parallel to the surface on a
+grade is therefore 20 lbs. per ton for each one per cent of grade and
+this force tends either to retard or to accelerate the movement of the
+vehicle.
+
+Let _F_ = the sum of all forces opposing the translation of a vehicle.
+
+  _F = f_{r} + f_{i} + f_{p} + f_{a} + f_{g}_     (1)
+
+where
+
+  _f_{r}_ = rolling resistance of road surface.
+  _f_{i}_ = resistance due to internal friction in the vehicle.
+  _f_{p}_ = resistance due to impact of the road surface.
+  _f_{a}_ = resistance due to air.
+  _f_{g}_ = resistance due to grade, which is positive when
+      ascending and negative when descending.
+
+All of the above in pounds per ton of 2000 lbs.
+
+Let _T_ = the tractive effort applied to the vehicle by any means.
+
+_T_ >= must be greater than _F_ in order to move the vehicle.
+
+By an inspection of (1), it will be seen that for a given vehicle and
+any type of road surface, all terms are constant except _f_{a}_ and
+_f_{g}_. _f_{a}_ varies as the speed of the vehicle and the driver can
+materially decrease _f_{a}_ by reducing speed. _f_{g}_ varies with the
+rate of grade. For any vehicle loaded for satisfactory operation on a
+level road with the power available, the limiting condition is the
+factor _f_{g}_. If the load is such as barely to permit motion on a
+level road, any hill will stall the vehicle. Therefore, in practice
+the load is always so adjusted that there is an excess of power on a
+level road. If draft animals are employed the load is usually about
+one fourth of that which the animals could actually move by their
+maximum effort for a short period. With motor vehicles, the excess
+power is provided for by gearing.
+
+If it be assured a load of convenient size is being moved on a level
+road by draft animals, there is a limit to the rate of grade up which
+the load can be drawn by the maximum effort of the animals.
+
+Tests indicate that the horse can pull at a speed of 2-1/2 miles per
+hour, an amount equal to 1/8 to 1/10 of its weight, and for short
+intervals can pull 3/4 of its weight. The maximum effort possible is
+therefore six times the average pull, but this is possible for only
+short intervals. A very short steep hill would afford a condition
+where such effort would be utilized. But for hills of any length, that
+is, one hundred feet or more but not to exceed five hundred feet, it
+is safe to count on the draft animal pulling three times his normal
+pulling power for sustained effort.
+
+The limiting grade for the horse drawn vehicle is therefore one
+requiring, to overcome the effect of grade, or _f_{g}_, a pull in
+excess of three times that exerted on the level.
+
+A team of draft animals weighing 1800 lbs. each could exert a
+continuous pull of about 1/10 of their weight or 360 lbs. If it be
+assumed that the character of the vehicle and the road surface is such
+that _f_{r}_ + _f_{i}_ + _f_{p}_ + _f_{a}_ = 100 lbs. per gross ton on
+a level section of road, then the gross load for the team would be 3.6
+tons. The same team could for a short time exert an additional pull of
+three times 360 lbs. or 1080 lbs. For each 1 per cent of grade a pull
+of 20 lbs. per ton would be required or _f_{g}_ for the 3.6 tons load
+would be 72 lbs. for each per cent of grade. At that rate, the
+limiting grade for the team would be fifteen per cent.
+
+If, however, the character of the vehicle and the road surface were
+such that _f_{r}_ + _f_{i}_ + _f_{p}_ + _f_{a}_ = 60 lbs. per gross
+ton on a level section of road, the gross load for the team on the
+level would be 6 tons, and the limiting grade 9 per cent.
+
+The above discussion serves to illustrate the desirability of adopting
+a low ruling or limiting grade for roads to be surfaced with a
+material having low tractive resistance and the poor economy of
+adopting a low ruling grade for earth roads or roads to be surfaced
+with material of high tractive resistance.
+
+It may be questioned whether horse drawn traffic should be the
+limiting consideration for main trunk line highways, but it is
+certain that for a number of years horse drawn traffic will be a
+factor on secondary roads.
+
+In the case of motor vehicles, excess power is provided by means of
+gears and no difficulty is encountered in moving vehicles over grades
+up to 12 or 15 per cent, so that any grade that would ordinarily be
+tolerated on a main highway will present no obstacle to motor
+vehicles, but the economy of such design is yet to be investigated.
+
+=Energy Loss on Account of Grades.=--Whether a vehicle is horse drawn
+or motor driven, energy has been expended in moving it up a hill. A
+part of this energy has been required to overcome the various
+resistances other than grade, and that has been dissipated, but the
+energy required to translate the vehicle against the resistance due to
+grade has been transformed into potential energy and can be partially
+or wholly recovered when the vehicle descends a grade, provided the
+physical conditions permit its utilization. If the grade is so steep
+as to cause the vehicle to accelerate rapidly, the brakes must be
+applied and loss of energy results. The coasting grade is dependent
+upon the character of the surface and the nature of the vehicle. In
+the cases discussed in the preceding paragraph, the coasting grades
+would be five per cent and three per cent respectively. For horse
+drawn vehicles then the economical grades would be three and five per
+cent, which again emphasizes the necessity of lower grades on roads
+that are surfaced than on roads with no wearing surface other than the
+natural soil.
+
+The theory of grades is somewhat different when motor vehicles are
+considered, since it is allowable to permit considerably higher speed
+than with horse drawn vehicles before applying the brakes and the
+effect of grade can be utilized not only in translating the vehicle
+down the grade, but also in overcoming resistances due to mechanical
+friction and the air. On long grades, a speed might be attained that
+would require the use of the brake or the same condition might apply
+on very steep short grades. There is at present insufficient data on
+the tractive resistance and air resistance with motor vehicles to
+permit the establishing of rules relative to grade, but experience
+indicates a few general principles that may be accepted.
+
+If a hill is of such rate of grade and of such length that it is not
+necessary to use the brake it may be assumed that no energy loss
+results so far as motor vehicles are concerned. Where there is no turn
+at the bottom of the hill and the physical condition of the road
+permits speeds up to thirty-five or forty miles per hour grades of
+five per cent are permissible if the length does not exceed five
+hundred feet and grades of three per cent one thousand feet long are
+allowable. It is a rather settled conviction among highway engineers
+that on trunk line highways the maximum grade should be six per cent,
+unless a very large amount of grading is necessary to reach that
+grade.
+
+=Undulating Roads.=--Many hills exist upon highways, the grade of
+which is much below the maximum permissible. If there are grades
+ranging from 0 to 4 per cent, with a few hills upon which it is
+impracticable to reach a grade of less than six per cent, it is
+questionable economy to reduce the grades that are already lower than
+the allowable maximum. It is especially unjustifiable to incur expense
+in reducing a grade from two per cent to one and one-half per cent on
+a road upon which there are also grades in excess of that amount. The
+undulating road is not uneconomical unless the grades are above the
+allowable maximum or are exceptionally long or the alignment follows
+short radius curves.
+
+=Safety Considerations.=--On hills it is especially desirable to
+provide for safety and curves on hills are always more dangerous than
+on level sections of road. Therefore, it is desirable to provide as
+flat grades as possible at the curves and to cut away the berm at the
+side of the road so as to give a view ahead for about three hundred
+feet. Whether a road be level or on a hill, safety should always be
+considered and the most important safety precaution is to provide a
+clear view ahead for a sufficient distance to enable motor vehicle
+drivers to avoid accidents.
+
+[Illustration: Fig. 9.--Types of Guard Rails]
+
+=Guard Railing.=--When a section of road is on an embankment, guard
+rails are provided at the top of the side slope to serve as warnings
+of danger, and to prevent vehicles from actually going over the
+embankment in case of skidding, or if for any reason the driver loses
+control. These are usually strongly built, but would hardly restrain a
+vehicle which struck at high speed. But they are adequate for the
+protection of a driver who uses reasonable care. A typical guard rail
+is shown in Fig. 9, but many other designs of similar nature are
+employed. At very dangerous turns a solid plank wall six or eight feet
+high is sometimes built of such substantial construction as to
+withstand the severest shock without being displaced.
+
+Trees, shrubs and the berms at the side of the road in cuts are
+particularly likely to obstruct the view and should be cleared or cut
+back so far as is necessary to provide the proper sight distance.
+
+=Width of Roadway.=--For roads carrying mixed traffic, 9 feet of width
+is needed for a single line of vehicles and 18 feet for 2 lines of
+vehicles. In accordance with the above, secondary roads, carrying
+perhaps 25 to 50 vehicles per day, may have an available traveled way
+18 feet wide. Those more heavily traveled may require room for three
+vehicles to pass at any place and therefore have an available traveled
+way 30 feet wide. Greater width is seldom required on rural highways,
+and 20 feet is the prevailing width for main highways.
+
+=Cross Section.=--The cross section of the road is designed to give
+the required width of traveled way, and, in addition, provide the
+drainage channels that may be needed. In regions of small rainfall the
+side ditches will be of small capacity or may be entirely omitted, but
+usually some ditch is provided. The transition from the traveled way
+to ditch should be a gradual slope so as to avoid the danger incident
+to abrupt change in the shape of the cross section. The depth of ditch
+may be varied without changing to width or slope of the traveled part
+of the road as shown in Fig. 10.
+
+[Illustration: Fig. 10]
+
+=Control of Erosion.=--The construction of a highway may be utilized
+to control general erosion to some extent, particularly when public
+highways exist every mile or two and are laid out on a gridiron
+system, as is the case in many of the prairie states. The streams
+cross the highways at frequent intervals and the culverts can be
+placed so as effectually to prevent an increase in depth of the
+stream. This will to some extent limit the erosion above the culvert
+and if such culverts are built every mile or two along the stream,
+considerable effect is produced.
+
+Where small streams have their origin a short distance from a culvert
+under which they pass, it is sometimes advisable to provide tile for
+carrying the water under the road, instead of the culvert, and, by
+continuing the tile into the drainage area of the culvert, eliminate
+the flow of surface water and reclaim considerable areas of land.
+
+Erosion in the ditches along a highway can be prevented by
+constructing weirs across the ditch at frequent intervals, thus
+effectually preventing an increase in the depth of the ditch.
+
+Wherever water flows at a velocity sufficient to produce erosion or
+where the drainage channel changes abruptly from a higher to a lower
+level, paved gutters, tile or pipe channels should be employed to
+prevent erosion.
+
+=Private Entrances.=--Entrance to private property along the highway
+is by means of driveways leading off the main road. These should
+always be provided for in the design so as to insure easy and
+convenient access to the property. The driveways will usually cross
+the side ditch along the road and culverts will be required to carry
+the water under the driveway. Driveways that cross a gutter by means
+of a pavement in the gutter are usually unsatisfactory, and to cross
+the gutter without providing a pavement is to insure stoppage of the
+flow at the crossing. The culvert at a driveway entrance must be large
+enough to take the ditch water readily or it will divert the water to
+the roadway itself. Generally end walls on such culverts are not
+required as in the case of culverts across a highway.
+
+=Aesthetics.=--Much of the traffic on the public highways is for
+pleasure and relaxation and anything that tends to increase the
+attractiveness of the highways is to be encouraged. Usually the
+roadside is a mass of bloom in the fall, goldenrod, asters and other
+hardy annuals being especially beautiful. In some states wild roses
+and other low bushes are planted to serve the two-fold purpose of
+assisting to prevent erosion and to beautify the roadside. In humid
+areas trees of any considerable size shade the road surface and are a
+distinct disadvantage to roads surfaced with the less durable
+materials such as sand-clay or gravel. It is doubtful if the same is
+true of paved surfaces, but the trees should be far enough back from
+the traveled way to afford a clear view ahead. Shrubs are not
+objectionable from any view-point and are to be encouraged for their
+beauty, so long as they do not obstruct the view at turns.
+
+
+
+
+CHAPTER V
+
+EARTH ROADS
+
+
+Highways constructed without the addition of surfacing material to the
+natural soil of the right-of-way are usually called earth roads. But
+if the natural soil exhibits peculiar characteristics or is of a
+distinct type, the road may be referred to by some distinctive name
+indicating that fact. Hence, roads are referred to as clay, gumbo,
+sandy or caliche roads as local custom may elect. In each case,
+however, the wearing surface consists of the natural soil, which may
+have been shaped and smoothed for traffic or may be in its natural
+state except for a trackway formed by the vehicles that have used it.
+
+=Variations in Soils.=--The nature of the existing soil will obviously
+determine the serviceability and physical characteristics of the road
+surface it affords. That is to say that even under the most favorable
+conditions some earth roads will be much more serviceable than others,
+due to the better stability of the natural soil. Some soils are dense
+and somewhat tough when dry and therefore resist to a degree the
+tendency of vehicles to grind away the particles and dissipate them in
+the form of dust. Such soils retain a reasonably smooth trackway in
+dry weather even when subjected to considerable traffic. Other soils
+do not possess the inherent tenacity and stability to enable them to
+resist the action of wheels and consequently grind away rapidly. Roads
+on such soils become very dusty. These are the extremes and between
+them are many types of soils or mixtures of soils possessing varying
+degrees of stability, and, in consequence, differing rates of wear.
+Similarly the various soils exhibit different degrees of stability
+when wet.
+
+It is to be expected that soils will differ with the geographical
+location, for it is well known that there is a great variation in
+soils in the various parts of the world. But wide differences are also
+encountered in the soil on roads very near each other and even on
+successive stretches of the same road. It is for this reason that
+earth roads often exhibit great differences in serviceability even in
+a restricted area.
+
+=Variation in Rainfall.=--The stability of a soil and its ability to
+support the weight of vehicles varies greatly with the amount of water
+in the soil. A certain small amount of moisture in the soil is
+beneficial in that practically every soil compacts more readily when
+moist than when dry because the moisture aids in binding together the
+particles. But most soils also become unstable when the amount of
+water present is in excess of that small amount referred to above and
+the stability decreases very rapidly as the amount of water in the
+soil increases.
+
+The serviceability of an earth road will change continually as the
+moisture content of the soil changes and consequently the general
+utility of the earth road system in any locality is dependent to a
+considerable extent upon the amount and seasonal distribution of
+precipitation. The methods of maintaining earth roads appropriate to
+any locality must of necessity be adapted to the climatic conditions,
+and the amount of work required to give the highest possible degree of
+serviceability will be exceedingly variable from season to season and
+from place to place. In regions of great humidity, earth roads may be
+expected to have a low average of serviceability, while in arid
+regions they may possess sufficient durability for a considerable
+volume of traffic. The design adopted for earth roads and the methods
+of maintenance followed should therefore be carefully evolved to meet
+the soil and climate conditions where the roads are located. These
+will differ greatly throughout a state or even a county.
+
+=Cross Sections.=--The general principles of road design were set
+forth in Chapter IV. In Fig. 11 are shown typical cross sections for
+earth roads adapted to various conditions as indicated. It is not
+apparent that one form of ditch is particularly preferable to the
+other and since some engineers prefer the V section and others the
+trapezoidal section both are shown. It would appear that the V shaped
+ditch is somewhat the easier to construct with the blade grader while
+the trapezoidal is readily excavated with the slip or fresno scraper.
+The ditch capacity required and consequently the dimensions will
+depend upon the drainage requirements, as was pointed out in Chapter
+III.
+
+[Illustration: Fig. 11. Cross Section for Earth Roads]
+
+
+EARTH ROADS IN REGIONS OF CONSIDERABLE RAINFALL
+
+In the zones where the annual precipitation exceeds 30 inches
+distributed over several months, earth roads will be unserviceable for
+a considerable period each year unless they are constructed so as to
+minimize the effect of water. This is done by providing for the best
+possible drainage and by adopting a method of maintenance that will
+restore the surface to a smooth condition as quickly as possible after
+a period of rainy weather or after the "frost comes out" in the
+spring.
+
+Before the construction of the desired cross section is undertaken,
+all of the grade reduction should be completed, except for minor cuts
+which can be handled with the elevating grader in the manner that will
+be described presently.
+
+Where any considerable change in grade is to be effected, the earth
+can be moved in several ways and of these the most economical cannot
+be readily determined. Ordinarily a contractor or a county will use
+the equipment that happens to be at hand even though some other might
+be more advantageous.
+
+=Elevating Grader.=--Where the topography is such as to permit its
+use, the elevating grader is employed in grade reduction to load the
+earth into dump wagons in which it is hauled to the fill or waste
+bank. The elevating grader consists essentially of a heavy shear plow
+or disc plow which loosens the earth and deposits it on a moving
+canvas apron. The apron carries the material up an incline and
+deposits it into a wagon which is driven along under the end of the
+apron. When the wagon is loaded, the grader is stopped while the
+loaded wagon is hauled out and an empty one drawn into position. The
+motive power for the elevating grader is either a tractor or five or
+six teams of mules. For many kinds of work, particularly where
+frequent turning is necessary or where the ground is yielding, mules
+are preferable to a tractor. The apron is operated by gearing from the
+rear wheels of the grader. Generally four mules are hitched to a
+pusher in the rear of the grader and six or eight in the lead. This
+method of grade reduction is particularly advantageous when the
+material must be hauled a distance of 500 yards or more, because wagon
+hauling in such cases is the most economical method to employ. A
+tractor may be used to draw the elevating grader and one having a
+commercial rating of 30 to 45 horsepower is required.
+
+=Maney Grader.=--If the haul is long and the nature of the cut will
+not permit the use of the elevating grader because of excessive grades
+or lack of room for turning, a grader of the Maney type may be used.
+This consists of a scoop of about one cubic yard capacity, suspended
+from a four-wheel wagon gear. When loading, the scoop is let down and
+filled in the same manner as a two-wheeled scraper or "wheeler." The
+pull required to fill a Maney grader is so great that a tractor is
+ordinarily employed in place of a "snap" team. The tractor is hitched
+at the end of the tongue, without interfering with the team drawing
+the grader. One team readily handles the grader after it is loaded.
+For this service a tractor having a commercial rationing of 25 to 30
+horsepower is required.
+
+=Wheel Scraper.=--For moving earth for distances between 150 and 500
+yards, the wheel scraper of a capacity of about 1-1/2 yards is quite
+generally employed. The soil must be loosened with a plow before it
+can conveniently be loaded into the wheeler and a heavy plow is
+ordinarily employed for that purpose. Two furrows with the plow will
+loosen a strip of earth about as wide as the scoop of the scraper and
+if more is loosened it will be packed down by the scrapers wheeling in
+place to load. A helper or "snap" team is employed to assist in
+loading, after which the wheel scraper is handled by one team.
+
+=Slip Scraper.=--The slip scraper differs from the wheel scraper in
+that the scoop is not suspended from wheels but is dragged along the
+ground. It is drawn by one team and the capacity is two to five cubic
+feet, but the material spills out to some extent as the scraper is
+dragged along and the method is not suitable for long hauls, 100 feet
+being about the economical limit.
+
+=Fresno Scraper.=--The Fresno scraper is one form of slip scraper
+requiring four horses or mules for efficient work. It differs
+somewhat from the ordinary slip scraper in shape and is of larger
+capacity, but is a drag type of scraper much favored in the western
+states.
+
+
+SHAPING TO PROPER CROSS SECTION
+
+If a road has been graded so that the profile is satisfactory or if
+the existing profile of the location is satisfactory, and the surface
+is to be shaped to a prescribed cross section, either the elevating
+grader or the blade grader may be employed.
+
+=Elevating Grader Work.=--If the elevating grader is used in shaping
+the earth road, the apron will be lowered and the material will be
+excavated at the sides of the road and deposited on the middle
+portion. If slight changes in grade are desired, wagons will accompany
+the grader and catch under the apron at the high places and haul the
+material to the low places. After the earth has been deposited it must
+be worked over to secure the correct cross section and be made
+passable for vehicles. This requires that clods be broken, weeds and
+grass that are mixed with the earth be removed by harrowing and
+forking and that the surface be carefully smoothed with a blade
+grader. This latter operation will have to be repeated several times
+before a satisfactory surface is secured. But this miscellaneous work
+is highly important and under no circumstances ought to be neglected.
+Nothing so detracts from an otherwise creditable piece of work as
+failure to provide a smooth surface for the use of vehicles. It is
+especially uncomfortable for the users of a highway if sods and weeds
+in quantity are left in the road after it has been graded. The humus
+that will be left in the soil as the vegetable matter decays increases
+the porosity of the road surface making it more absorbent than soil
+without humus. This increases the susceptibility to softening from
+storm water or ground water.
+
+The tractor can advantageously be used to draw the elevating grader on
+this class of work, but will be greatly handicapped if there are wet
+sections along the road, through which the tractor must be driven. In
+many cases its use is prohibited by such conditions and for all-round
+service of this character, mules are preferred for motive power.
+
+[Illustration: Fig. 12.--Tractor-grader Outfit]
+
+=Use of Blade Grader.=--Heavy blade graders designed to be drawn by a
+tractor are suitable for shaping the earth road. Some of these have
+blades 12 feet long and excellent control for regulating the depth of
+cutting. Often two such graders are operated tandem. These machines
+have a device which permits the operator to steer the grader
+independently of the tractor. Thus the grader can be steered off to
+the side to cut out the ditches, while the tractor continues to travel
+on the firm part of the road. Earth moved with the blade grader is
+usually fairly free from large lumps and can readily be smoothed to a
+satisfactory surface for the use of traffic. The sods and weeds will
+be drawn into the road along with the earth just as they are when the
+elevating grader is employed. Precaution must therefore be taken to
+eliminate them before the vegetable matter decays, and to smooth the
+surface for the use of traffic.
+
+=Costs.=--The cost of shaping an earth road in the manner described
+above will vary through rather wide limits because the nature and
+amount of work to be done varies so greatly. Some roads can be graded
+satisfactorily for $300.00 per mile, while others will cost $700.00.
+But $425.00 per mile may be taken as an average for blade or elevating
+grader work plus a moderate amount of grade reduction in the way of
+removing slight knolls. For the amount of grade reduction necessary in
+rolling country, followed by grader shaping, $1000.00 to $1800.00 per
+mile will be required. The method is not adapted to rolling country
+where the roads are undulating and require some grade reduction on
+every hill. For hilly roads one of the methods described for grade
+reduction will be required and the cost will obviously depend upon the
+amount of earth moved. Averages of cost figures mean nothing in such
+cases as the cost may reach $10,000.00 per mile, or may be as low as
+$2000.00 per mile.
+
+=Maintenance.=--Regardless of the care with which an earth road has
+been graded, it will be yielding and will readily absorb water for a
+long time after the completion of the work. The condition of the
+surface will naturally deteriorate rapidly during the first season it
+is used unless the road receives the constant maintenance that is a
+prerequisite to satisfactory serviceability. The road drag is
+generally recommended for this purpose, and if a drag is properly used
+it will serve to restore the shape of the surface as fast as it is
+destroyed by traffic.
+
+Good results with the drag depend upon choosing the proper time to
+drag and upon doing the work in the right way when using the drag. The
+best time to drag is as soon after a rain as the road has dried out
+enough to pack under traffic. If the work is done while the road is
+too wet, the first vehicles traveling the road after it has been
+dragged will make ruts and to a considerable extent offset the good
+done by the drag. If the road is too dry, the drag will not smooth the
+irregularities. A little observation will be required to determine the
+proper time for dragging on any particular soil, but usually after a
+rain or thaw there is a period lasting a day or two when conditions
+are about right.
+
+[Illustration: Fig. 13.--Road Drag]
+
+The drag is used merely to restore the shape of the surface and to do
+so a small amount of material is drawn toward the middle of the road.
+But there must not be a ridge of loose material left in the middle
+after the work is completed. Some patrolmen start at one side of the
+road and gradually work across the road on successive trips, finally
+finishing up at the side opposite that at which the start was made.
+The next dragging should start on the opposite side from the first if
+that method is followed.
+
+By shifting his weight on the drag, the operator can adjust the
+cutting edge so that very little loose material is moved crosswise of
+the road and that is the proper method to pursue. In that case no
+ridge will remain at the middle of the road. If a slight one is left
+it should be removed by a final trip with the drag.
+
+In addition to the dragging, weeds must be cut along the road about
+twice a year, the ditches must be kept cleaned out and culverts open.
+
+All of the maintenance for 10 miles of earth road can be accomplished
+by one man giving his entire time to the work, and that is the only
+method that has proven adequate to the problem.
+
+
+EARTH ROADS IN ARID REGIONS
+
+In areas where the rainfall is less than 18 inches per year, and
+especially where it is 10 inches or less, an entirely different road
+problem exists. The effect of precipitation is of significance
+primarily from the standpoint of erosion, and the design of cross
+section and ditches and the culvert provisions are entirely different
+from those necessary in humid regions.
+
+Frequently the rainfall in semi-arid regions will be seasonal and
+provision must be made to care for a large volume of water during the
+rainy season, but, in general, road design is adapted to prevention of
+erosion rather than to elimination of ground water effects, or the
+softening effects of surface water. Generally the rainy period does
+not last long enough to warrant expensive construction to eliminate
+its general effects. In fact, the saturation of the soil is more
+likely to be a benefit than otherwise.
+
+Earth roads are likely to be satisfactory except where the traffic is
+sufficient to grind the surface into dust to such an extent that an
+excessive dust layer is produced. In such locations the problem is one
+of providing a durable surface unaffected by long continued dry
+weather.
+
+Grade reduction will have the same importance as in humid areas and
+will be carried out in the same way.
+
+Maintenance will consist in repairing the damage from occasional
+floods and in removing or preventing accumulations of drifting sand
+or dust. Crude petroleum oils have been satisfactory for maintenance
+in such locations when used on stable soils.
+
+=Value of Earth Roads.=--The serviceability of the earth road depends
+to a large extent upon the care exercised in its maintenance. The only
+part of earth road construction that is permanent is the grade
+reduction. The cross section that is so carefully shaped at
+considerable cost may flatten out in one or two years, especially if
+the road goes through unusually wet periods. Traffic will continually
+seek a new track during the period when the road is muddy and is as
+likely to cross the ditch to the sod near the fence as to use any
+other part of the road. Continual and persistent maintenance is
+therefore essential to even reasonable serviceability. At best the
+earth road will be a poor facility for a considerable period each year
+in the regions of year-around rainfall. In most localities, roads of
+distinctly minor importance are of necessity only earth roads and for
+the comparatively small territory they serve and the small amount of
+traffic, they probably serve the purpose. For roads of any importance
+in the humid areas of the United States, the earth road cannot carry
+satisfactorily the traffic of a prosperous and busy community.
+
+
+
+
+CHAPTER VI
+
+SAND-CLAY AND GRAVEL ROADS
+
+
+In Chapter IV, mention was made of the variation in serviceability of
+road surfaces composed of the natural soil existing on the
+right-of-way of the road. It has been found that soils of a clayey
+nature in which there is a considerable percentage of sand usually
+afford a serviceable road surface for light or moderate traffic,
+especially in areas where climatic conditions are favorable. A study
+of these soils, together with the construction of experimental roads
+of various mixtures of sand and clay, has led to a fairly
+comprehensive understanding of the principles of construction and
+range of capacity of this type of road surface, which is known as the
+sand-clay road.
+
+The sand-clay road surface consists of a natural or artificial mixture
+of sand and clay, in which the amount of clay is somewhat greater than
+sufficient to fill the voids in the dry sand. It may be assumed that
+the sand contains 40 per cent of voids and that at least 45 per cent
+of clay is required to fill the voids and bind the sand grains
+together, because the clay spreads the sand grains apart during the
+mixing, thus having the effect of increasing the voids. As a matter of
+experiment, it is found to be impractical to secure by available
+construction methods mixtures of sufficient uniformity to render it
+necessary to exercise great exactness in proportioning the components,
+but reasonable care in proportioning the materials is desirable.
+
+Successful utilization of this type of surface requires considerable
+study of available materials and investigations of their behavior when
+combined. Extensive and exhaustive experiments have been conducted
+with sand-clay mixtures in various places where they are widely used
+for road surfaces and the following general principles have been
+deduced.
+
+=The Binder.=--In the sand-clay road, stability is obtained by
+utilizing the bonding properties possessed to some degree by all
+soils. Naturally this characteristic may be expected to vary widely
+with the several types of soil. It is generally considered to be a
+common property of clay, but the term clay is a general one that is
+often applied to soils differing greatly in physical characteristics
+and the term therefore loses its significance in this connection.
+Those soils that are properly and technically called clay are
+decidedly sticky when wet and are the best materials for sand-clay
+construction. Of the clays, those that produce a tough sticky mud are
+best. This can be tested by mixing a small quantity into a stiff mud
+and molding it into a ball and immersing in water. If the ball retains
+its shape for some little time, it is likely to prove a very
+satisfactory binder, but, if it becomes plastic and loses its shape,
+it will be an inferior binder, as a general rule. The ball clay, as
+the former is called, may be of any color common to soils, not
+necessarily yellow or reddish as is sometimes supposed. Likewise,
+balls of mixtures containing varying percentages of sand and the
+binder to be used may be made up and immersed in water. The mixture
+that holds its shape longest is of course the best combination of the
+materials and indicates the mixture to use in the construction.
+
+An ideal, or even a fairly satisfactory soil for a binder may not
+exist in the vicinity of a proposed improvement, and consequently an
+inferior binder is frequently the only material available.
+
+Sometimes deposits of clay or gravel contain a considerable percentage
+of gypsum which serves as a binder and is particularly effective when
+used in combination with clay and sand or gravel.
+
+In many places a soil of the type used for adobe and called "caliche"
+may be found and this is an excellent binder for sand or gravel.
+
+=Top-Soil or Natural Mixtures.=--Deposits consisting of a natural
+mixture of sand and clay in which the ingredients happen to exist in
+about the correct relative proportions for sand-clay road surfaces are
+found in many localities. These mixtures are commonly referred to as
+top-soil. If the deposits are somewhat deficient either in sand or
+clay, they can be utilized if the proper corrections in the
+proportions are made during construction. Very satisfactory road
+surfaces are sometimes constructed with mixtures that appear to be far
+from ideal in composition, but experience and frequent trials are
+needed to determine the best way in which to handle these mixtures.
+
+=Sand-Clay Surfaces on Sandy Roads.=--Sand-clay surfaces may be
+constructed on naturally sandy roads either by adding clay and mixing
+it with the sand to secure the desired composition, or a layer of a
+natural sand-clay mixture, caliche or sand-clay-gypsum may be placed
+on top of the sand.
+
+The most widely used method is to mix clay or other binder with the
+sand. Since there is no need to provide for ditches to carry storm
+water on a deep sand soil, the sand is graded off nearly flat across
+the road and no ditches are provided. The clay is dumped on the road
+in a layer about 8 inches thick and is then mixed into the sand. It is
+desired to mix enough sand with the clay to produce a mixture composed
+of approximately 1/3 clay and 2/3 sand. The mixing is accomplished in
+various ways, the most common being to use a heavy plow at first and
+to follow this with a heavy disc harrow. The mixing is a tedious and
+disagreeable process, but its thorough accomplishment is
+indispensable. The mixing is most readily done when the materials are
+saturated with water and in practice it is customary to depend upon
+rain for the water, although in the final stages water may be hauled
+and sprinkled on the road to facilitate final completion of the
+mixing. After the mixing has been completed, the surface is smoothed
+with the blade grader and is kept smooth until it dries out. Repeated
+dragging will be required, during the first year especially, and to
+some extent each year in order to keep the surface smooth, but the
+dragging can be successfully accomplished only when the road is wet.
+
+[Illustration: Fig. 14.--Cross Sections for Sand-Clay Roads]
+
+In regions where several months of continued hot, dry weather is to be
+expected each year, the sand-clay mixture is likely to break through
+unless it is of considerable thickness and generally the surface layer
+is made much thicker than for regions where the annual rainfall is
+fairly well distributed. This is especially necessary when the binder
+is of inferior quality. It is not uncommon in such cases to make the
+sand-clay surface as much as two feet thick.
+
+As the mixing progresses it may appear that patches here and there are
+deficient in either clay or sand and the mixture in these places is
+corrected by the addition of a little sand or clay as may be
+required.
+
+If the top-soil is used it is deposited on the sand in the required
+quantity and is remixed in place to insure uniformity. If either sand
+or clay is needed to give a satisfactory mixture, the proper material
+is added and mixed in as the work progresses. The surface is finally
+smoothed by means of the grader and drag.
+
+=Sand-Clay on Clay or Loam.=--If the existing road is of clay or loam,
+ample drainage will be required as discussed in Chapter IV. The
+surface may be constructed of a natural sand-clay mixture or of a sand
+mixed with the natural soil. If the former, the surface of the
+existing road is prepared by grading so as to insure good drainage and
+the natural mixture is then deposited and the surface completed as
+described in the preceding section.
+
+If the surface is formed by mixing sand with the existing soil, the
+sands may be deposited in a layer about six inches thick which will
+gradually mix with the soil as the road is used. A second application
+of sand may follow in a year or two if it is needed. Such a road
+surface will lack uniformity of composition and it seems preferable to
+mix the sand with the soil by plowing and discing as previously
+described.
+
+=Characteristics.=--Sand-clay road surfaces do not have sufficient
+durability for heavily traveled highways, but will be satisfactory for
+a moderate amount of traffic. These surfaces have maximum
+serviceability when moist, not wet, and consequently are not as
+durable in dry climates as in humid areas. They are likely to become
+sticky and unstable in continued wet weather and to become friable and
+wear into chuck holes in long continued dry weather. At their best,
+they are dustless, somewhat resilient and of low tractive resistance.
+
+GRAVEL ROAD SURFACES
+
+[Illustration: Fig. 15.--Cross Sections for Gravel Highways]
+
+=Natural Gravel.=--Gravel is the name given to a material consisting
+of a mixture of more or less rounded stones, sand and earthy material,
+which is found in natural deposits. These deposits exist in almost
+every part of North America, being especially numerous in the
+glaciated areas, but by no means confined to them. Gravel deposits
+consist of pieces of rock varying in size from those of a cubic yard
+or more in volume to the finest stone dust, but with pieces ranging in
+size from that which will pass a 3-inch ring down to fine sand
+predominating. The larger pieces are usually more or less rounded and
+the finer particles may be rounded or may be angular. Many varieties
+of rocks are to be found among the gravel pebbles, but the rocks of
+igneous origin and possessing a considerable degree of hardness
+generally predominate. Intermixed with the pieces of rock there is
+likely to be clay or other soil, the quantity varying greatly in
+different deposits and even in various places in the same deposits.
+
+Often there are found deposits of material which are by the layman
+termed gravel, which are really clayey sand or sand containing a few
+pebbles, but which are of value to the road builder for the sand clay
+type of surfacing. The term gravel is exceedingly general and unless
+specifically defined, gives little indication of the exact nature of
+to which it is applied.
+
+  TABLE 7
+
+  SHOWING CEMENTING PROPERTIES OF SEVERAL SAMPLES OF
+  GRAVEL
+
+  -----------------+----------------------------
+                   |       Cementing Value
+  Per Cent Clay by +---------------+------------
+      Weight       | As Received   |  Washed
+  -----------------+---------------+------------
+        4.4        |      276      |      43
+        6.4        |      105      |     285
+        5.1        |      241      |      70
+       14.5        |      500      |     279
+        8.5        |      500      |     112
+       10.1        |      300      |     267
+       14.8        |      500      |     107
+        7.5        |      184      |     198
+       16.5        |      500      |     428
+        2.0        |      185      |     239
+        1.5        |      500      |     500
+        4.5        |      212      |     204
+        2.5        |      116      |     363
+  -----------------+---------------+------------
+
+The value of any gravel for road surfacing depends upon the degree to
+which it possesses the properties of an ideal gravel for road
+surfacing. Ideal gravel is seldom encountered, but a consideration of
+its characteristics serves to establish a measure by which to estimate
+the probable value of any deposit.
+
+=The Ideal Road Gravel.=--The ideal road gravel is a mixture of
+pebbles, sand and earthy material, the pieces varying from coarse to
+fine in such a manner that when the gravel is compacted into a road
+surface the spaces between the larger pebbles are filled with the
+finer material. The pebbles are of a variety of rock that is highly
+resistant to wear so that the road surface made from the gravel will
+have the quality of durability. The gravel possesses good cementing
+properties, insuring that the pieces will hold together in the road
+surface. The cementing property may be due to the rock powder in the
+deposit or to earthy material mixed with the rock particles, or to
+both. Table 7 shows the results of a number of tests made upon gravels
+and indicates that the cementing property of the gravel does not
+always depend upon the clay content.
+
+=Permissible Size of Pebbles.=--The larger pebbles in the gravel are
+less likely to crush under loads than smaller pebbles of the same sort
+of rock, but if the rock is of some of the tougher varieties such as
+trap, there is very little likelihood of even the smaller pebbles
+crushing. If the pebbles are of rock of medium toughness, the smaller
+pebbles might be crushed under the heavier loads. It is the usual
+practice to permit gravel to be used for the foundation course in
+which the pebbles are as large as will pass a 3-1/2-inch circular
+screen opening, and for the wearing course, as large as will pass a
+2-1/2-inch circular screen opening. If larger pebbles are allowed in
+the wearing course, the surface is certain to become rough after a
+time. If the gravel is to be placed in a single course as is a very
+common practice, then the maximum size should not exceed that which
+will pass a 2-1/2-inch circular screen opening.
+
+The Wisconsin Highway Commission has constructed a very large mileage
+of excellent gravel roads and the sizes specified for their roads are
+as follows:
+
+     "_Bottom Course Gravel_.--Bottom course shall consist of a
+     mixture of gravel, sand and clay with the proportions and various
+     sizes as follows:
+
+     "All to pass a two-inch screen and to have at least sixty and not
+     more than seventy-five per cent retained on a quarter-inch
+     screen; at least twenty-five and not more than seventy-five per
+     cent of the total coarse aggregate to be retained on a one-inch
+     screen; at least sixty-five and not more than eighty-five per
+     cent of the total fine aggregate to be retained on a two
+     hundred-mesh sieve."
+
+     "_Top Course Gravel_.--Top course shall consist of a mixture of
+     gravel, sand and clay with the proportions of the various sizes
+     as follows:
+
+     "All to pass a one-inch screen and to have at least fifty and not
+     more than seventy-five per cent retained on a quarter-inch
+     screen; at least twenty-five and not more than seventy-five per
+     cent of the total coarse aggregate (material over one-fourth inch
+     in size) to be retained on a one-half-inch screen; at least
+     sixty-five and not more than eighty-five per cent of the total
+     fine aggregate (material under one-fourth inch in size) to be
+     retained on a two hundred-mesh sieve."
+
+     "_Screened Gravel and Sand Mixtures_.--Where it is impossible to
+     obtain run of bank gravel containing the necessary binder in its
+     natural state, screened gravel shall be used and the necessary
+     sand and clay binder added as directed by the engineer. Gravel
+     and sand shall be delivered on the work separately. Clay binder
+     shall be obtained from approved pits and added as directed by the
+     engineer."
+
+     "_Run of Bank Gravel_.--When run of bank gravel is permitted
+     either for one course or two course work, the size shall not
+     exceed that specified for bottom or top course. If necessary, the
+     contractor shall pass all the material through a two-inch screen
+     for the bottom course, and through a one-inch screen for the top
+     course. When the work consists of only one course, the material
+     shall be of the sizes as specified for the top course. The
+     necessary binder shall be contained in the material in its
+     natural state, excepting that a small percentage of clay binder
+     may be added as directed by the Engineer."
+
+=Wearing Properties.=--A certain amount of grinding action takes place
+on the road surface under the direct action of wheels, especially
+those with steel tires. Where rubber tired traffic predominates, this
+action is much less severe than where steel tired vehicles
+predominate, but the tendency exists on all roads. In addition, there
+is distortion of the layer of gravel under heavy loads which causes
+the pieces of stone in the surface to rub against each other and to
+wear away slowly.
+
+The gravel road in the very best condition is slightly uneven but
+there is comparatively little jar imparted to vehicles, and,
+consequently, little impact on the surface. When somewhat worn, the
+impact becomes a factor of some importance and the pounding of
+vehicles has a very destructive action on the surface. Soft pebbles
+will be reduced to dust in a comparatively short time.
+
+The degree to which any gravel resists the destructive action of
+traffic depends upon the varieties of rock represented by the pebbles
+in the gravel. If the pebbles are mostly from rocks of good wearing
+properties, that quality will be imparted to the road surface. If
+mostly from rocks of little durability, the same characteristic will
+be imparted to the road surface. A very good general notion of the
+probable durability of gravel can therefore be obtained by a careful
+visual examination of the material and classification of the rock
+varieties represented by the pebbles.
+
+=Utilizing Natural Gravels.=--Gravel road construction is advantageous
+only when it can be accomplished at low first cost. This usually
+presupposes a local supply of gravel that can be utilized, or at any
+rate a supply that need not be shipped a long distance. In the nature
+of things, such deposits are likely to be deficient in some of the
+desirable characteristics, and may be deficient in most of them. By
+various means, the defects in the materials can be partially corrected
+while constructing the road.
+
+If the gravel deposit consists of layers of varying composition as
+regards size and clay content, the material may be loosened from the
+exposed face and allowed to fall to the bottom of the pit thereby
+becoming mixed to a sufficient extent to produce a reasonably uniform
+product. If deficient in clay, it often proves feasible to add a small
+part of the clay over-burden, thereby insuring enough binder.
+Sometimes adjoining deposits will consist one of relatively fine
+material, the other of relatively coarse. These may be mixed on the
+work by first placing the coarse material in a layer about 5 inches
+thick and adding the finer material in a similar layer. The two will
+mix very rapidly during the operations of spreading and shaping.
+
+When deposits contain pebbles larger than will pass a 3-1/2-inch ring,
+these larger stones will prove to be undesirable if placed on the
+road, as they are almost sure to work to the surface of the gravel
+layer and become a source of annoyance to the users of the road.
+Oversize stone can be removed while loading the gravel or while
+spreading it, if care is exercised and not too large a proportion is
+oversize. It is preferable however to remove the oversize by means of
+screens at the pit. Usually on large jobs the oversize is crushed and
+mixed with the supply so as to utilize what is really the best part of
+the material.
+
+Gravels deficient in bonding material are often encountered in
+deposits where there is insufficient overburden to give enough
+additional binder or where the overburden is of a material unsuitable
+for binder. Such materials may be utilized by adding binder in the
+form of clay after the gravel has been placed on the road.
+
+Almost any gravel deposit can be utilized in some way if the material
+is of a durable nature, regardless of other characteristics. The
+serviceability of a gravel road will depend largely on how nearly the
+gravel approaches the ideal, but variations in the manipulations will
+do much to overcome deficiencies in materials.
+
+=Thickness of Layer.=--The thickness of the layer of gravel required
+depends both upon the type of soil upon which it is placed and the
+nature of the traffic to which the road will be subjected. Gravel
+surfaces should not ordinarily be constructed on highways carrying
+heavy truck traffic, but if gross loads of three or four tons are the
+heaviest anticipated, the gravel will be reasonably stable. On such
+roads, a layer of well compacted gravel ten inches thick will support
+the loads if a well drained earth foundation is provided. If but
+little truck traffic is anticipated and loads up to three tons on
+steel tires are the average, a layer 8 inches thick will be
+sufficient. In dry climates, a layer six inches thick will be
+adequate if it can be kept from raveling.
+
+On secondary roads, carrying principally farm-to-market traffic, and
+not a great volume of that, the above thicknesses may be reduced about
+one-fourth.
+
+The exact thickness needed for any particular road is a matter for
+special study on account of the variations in the gravels and in the
+supporting power of the soil upon which they are placed.
+
+
+PLACING GRAVEL
+
+=Preparation of the Road.=--The roadway that is to be surfaced with
+gravel is first brought to the desired grade and cross section. It
+would be advantageous if this could be done a year before the gravel
+is placed so that no settlement of the earth foundation would occur
+after the gravel surface is completed. But if that is impractical, the
+grading may be done just prior to placing the gravel, providing
+appropriate methods are adopted for securing compacted fills.
+
+=Trench Method.=--Two distinct methods of placing the gravel are in
+general use, known as the trench method and the surface or feather
+edge method respectively. The method to adopt for any particular road
+will depend largely on certain conditions that will be explained
+later.
+
+In the trench method, a trench of the proper width and depth for
+receiving the gravel is excavated in the earth road surface and the
+gravel is placed therein.
+
+The trench is formed by plowing a few furrows and scraping out the
+loosened earth with a blade grader. The loose material is generally
+moved out laterally to build up earth berms or "shoulders" alongside
+the gravel. Into this trench the gravel is dumped in the proper
+quantity to give the required thickness after being compacted.
+
+The greatest care must be exercised in spreading the gravel to
+eliminate unevenness where the loads were deposited. An ordinary blade
+grader is one of the best and most economical implements to use for
+spreading the gravel. When the gravel has been deposited in the trench
+for a distance of a thousand feet or more, the spreading is
+accomplished by dragging the surface repeatedly with the blade grader,
+the work being continued until all waviness disappears. The gravel is
+then thoroughly and repeatedly harrowed with a heavy stiff tooth
+harrow to mix thoroughly the fine and coarse gravel so as to produce
+as nearly a uniform mixture as may be. The gravel is then finally
+smoothed with the blade grader.
+
+The gravel may be compacted by rolling or may be allowed to pack from
+the action of traffic. The former is greatly to be preferred where
+practicable. The rolling is performed with a three-wheeled
+self-propelled roller weighing about 8 tons and must be done while the
+gravel is wet. Generally a sprinkling wagon is used to wet down the
+gravel, but advantage is always taken of rains to facilitate the work.
+The gravel must be spread in layers not over 5 or 6 inches thick to
+get the desired results, which means that for an ordinary gravel road
+about 10 inches thick, the gravel will be placed in two layers of
+about equal thickness, each of which will be rolled.
+
+The gravel will compact slowly even if it is not rolled, but generally
+does not become stable until the material is thoroughly soaked by
+rains. Then it will begin to pack, but will become badly rutted and
+uneven during the process. During this period the surface must be kept
+smooth by means of the blade grader. The drag does not suffice for
+this purpose, tending to accentuate the unevenness rather than to
+correct it.
+
+If gravel is placed in a trench in dense soil and rainy weather
+ensues, sufficient water will be held in the trench to cause
+unevenness from foundation settlement and the gravel will become mixed
+with the soil to some extent and be thereby wasted. Trenches cut from
+the road bed upon which the gravel is placed, to the side ditches,
+will relieve this condition by affording an outlet for the surplus
+water. Nevertheless some difficulty may be expected if the trench
+method is used and wet weather prevails. If it is possible to close
+the road against traffic until the road is dry the method is
+applicable. Moreover, in long-continued dry weather, the dispersion
+and loss of considerable gravel from the action of automobile traffic
+is avoided because the gravel is held between substantial earth berms
+and the gravel will pack better and hold its shape longer when
+constructed by the trench method than otherwise.
+
+=Surface Method.=--The surface method is one in which the gravel is
+placed on the graded earth road surface without earth shoulders to
+hold the gravel in place. It is also sometimes called the feather-edge
+method. Except for the manner of placing as just mentioned, the
+several operations are conducted in the same general manner as for the
+trench method. The gravel does not compact as quickly as in the trench
+method and a considerable loss of material is likely to result from
+the effect of automobile traffic while the gravel is loose. But it has
+the advantage of being free from difficulties in wet weather and in
+some locations is therefore preferable to the trench method. It is
+particularly applicable to those projects on which the placing of
+gravel continues throughout the winter, the gravel being dumped and
+spread, to be finally smoothed and finished in the early summer.
+
+=Bonding.=--Where gravels deficient in binder are utilized, clay for
+binder is sometimes added as the gravel is placed on the road. This
+may be done by spreading the clay on top of the lower course of
+gravel, placing the upper layer and sprinkling and rolling until the
+clay squeezes up through the surface layer. It may also be
+accomplished by spreading dry clay on the upper course before it is
+harrowed and then harrowing to mix it with the gravel. Both methods
+are practiced, but the former is believed to be preferable. A third
+method is to separate the sand and pebbles and to mix the clay binder
+with the sand and then spread the sand on top of the pebbles and mix
+by harrowing.
+
+=Maintenance.=--Gravel surfaces require careful maintenance,
+especially during the first season the road is used. The gravel will
+compact slowly and during the process will be rutted and otherwise
+disturbed by traffic. It is important during this period to restore
+the shape once a week or at least twice a month. The light blade
+grader is usually employed for the purpose so long as the gravel is
+somewhat loose. Later a drag of the type known as the planer will
+prove to be the most effective. Figure 16 shows a type of drag that is
+very satisfactory for use on gravel roads.
+
+[Illustration: Fig. 16.--Road Planer]
+
+
+
+
+CHAPTER VII
+
+BROKEN STONE ROAD SURFACES
+
+
+The broken stone road surface, or macadam road as it is usually
+termed, consists of a layer of broken stone, bonded or cemented
+together by means of stone dust and water. The surface may or may not
+be coated with some bituminous material.
+
+=Design.=--It has been an accepted assumption that the macadam road
+surface is somewhat more stable than the gravel road surface of equal
+thickness, and since this is probably the consensus of opinion of
+engineers familiar with both types, it may be accepted until
+experimental data are available on the subject.
+
+The thickness of the layer of macadam required for a road will depend
+upon the same factors that were considered in connection with the
+thickness of the gravel surface, i.e., kind of stone used, character
+of earth foundation and nature of the traffic.
+
+The standard macadam surface where good earth foundation is to be had
+and where the loads do not exceed about four tons has for years been
+eight inches thick. For heavier loads or inferior foundation, a
+somewhat greater thickness would be employed, but the best practice
+would probably provide a foundation course of the Telford type for
+doubtful foundation conditions, especially for the extremely uncertain
+cases. For soils of very good supporting strength such as very sandy
+loam or deep sand or for arid regions where stable foundation is
+always assured the thickness of the macadam might be reduced to six
+inches. It should be borne in mind that the broken stone road is not
+adapted to the traffic carried by trunk line highways in populous
+districts, but is rather a type permissible on secondary roads and
+usually adequate for local roads. It should never be employed for
+roads carrying any considerable volume of passenger automobile traffic
+or motor truck traffic. If surfaced with a bituminous material it will
+carry up to 1200 passenger automobiles per day, but not to exceed
+fifty trucks.
+
+=Properties of the Stone.=--The stone employed for the broken stone
+road should possess the qualities of hardness and toughness and should
+be capable of resisting abrasion sufficiently well to have reasonable
+life under the traffic to which it is subjected. Since the traffic may
+vary from very light on some roads to far beyond the limit of the
+economical capacity of this type of pavement on others, it follows
+that any particular deposit of stone might be durable enough for some
+roads, while for others it might be entirely inadequate. As a general
+rule it has been found that stone that wears away at a moderate rate
+will, when used for water-bound macadam surface, result in a smoother
+trackway than one that will wear very slowly. It is not therefore
+altogether certain that the most durable stone to be had should be
+selected for a particular road. This is especially true now that the
+water-bound macadam surface has been largely superseded for trunk line
+highways and other heavily traveled roads, and is employed in
+locations where service conditions are not severe.
+
+The stone employed for the water-bound macadam surface must possess
+good cementing properties, because the surface depends for stability
+primarily upon the bonding action of the dust from the broken stone.
+This is in contrast to the gravel road, where little dependence is
+placed upon the bonding effect of the rock dust. In preparing the
+stone for macadam surfaces, the ledge rock is crushed and screened,
+and in that way a supply of the finer particles, which are a part of
+the output of the crusher, is obtained for use in bonding the
+surface. This finely broken material, usually called screenings, is
+essential to the construction of the water-bound type of surface.
+Rocks vary considerably in the cementing properties of the dust, but
+usually the rocks classed as "trap," such as andesite, gabbro and
+rhyolite, and schist and basalt possess good cementing properties.
+Limestones usually possess good cementing properties, but some of the
+dolomitic limestones are of low cementing value. Quartz, sandstone and
+the granites are of low cementing value.
+
+=Kinds of Rocks Used for Macadam.=--Limestone and chert are the two
+sedimentary rocks, employed most extensively for broken stone roads.
+These rocks are found in widely distributed areas and vary in physical
+characteristics from very soft material of no use to the road builder
+to materials possessing considerable durability. It is desirable to
+carefully test out the deposits of these materials before using to
+ascertain the probable value of the rock, for the construction of the
+road surface.
+
+Of the igneous rocks, those classed as trap are best known to the road
+builder and many of the deposits of trap rock afford an excellent
+material for broken stone roads where the severest conditions of
+traffic are encountered. The trap rocks are tough and durable and
+generally possess excellent cementing properties.
+
+Granite and sandstone are seldom used for water-bound macadam as they
+possess poor cementing properties and a binder of some kind must be
+added to cement the pieces together. For this purpose clay or the
+screenings from some other variety of stone may be utilized.
+
+Some other materials are occasionally employed for the construction of
+macadam surfaces. Of these, oyster or marine shells, burnt shale, and
+slag are most common.
+
+Shells and slag are of rather low durability but possess good
+cementing properties. Shale is a makeshift suitable only for very
+light traffic roads.
+
+=Sizes of Stone.=--The stone for the wearing course of a macadam road
+should be as large as practicable, because the larger the pieces the
+more durable the surface. If the individual stones are too large it is
+difficult to secure a smooth surface, and large stones will be readily
+loosened by tipping as the wheels roll over them. These considerations
+limit the size to a maximum of that which will pass a 2-1/2-inch
+screen. Stone of excellent wearing qualities may be somewhat smaller,
+but never less than that which will just pass a 1-1/2-inch screen.
+
+For the lower course, the size is not particularly important except
+where the earth foundation is such as to require special construction.
+It is not uncommon to use the same size of stone for both upper and
+lower course and yet in many instances stone up to that which will
+just pass a 3-1/2-inch screen is used for the lower course. Stone much
+smaller in size may also be used successfully, but if the stone is
+broken to a smaller size than is required, unnecessary expense is
+incurred.
+
+The bonding material is the finer portion of the product of the
+crusher, which is called screenings. This material may be so finely
+crushed as to pass a one-fourth inch screen, or may be so coarse as to
+just pass a one-half inch screen, but in any case must contain all of
+the dust and fine material produced by the crusher.
+
+Where the soil and drainage conditions demand an especially stable
+foundation course, the Telford type is used. The Telford foundation
+consists of a layer of stones of various dimensions that can be laid
+so as to give a thickness of 8 inches. These large stones are placed
+by hand and therefore the size requirements are not rigid. Stones
+having one dimension about 8 inches and the others not over 10 or 12
+inches are satisfactory.
+
+=Earth Work.=--A thoroughly drained and stable earth foundation is
+essential to success with the macadam type of surface. Before placing
+the stone, the road must be shaped to the proper cross section and
+all grade reduction work completed. Preferably heavy fills should have
+a year to settle before the macadam surface is placed. Side ditches,
+necessary culverts and tile drains should be constructed as required
+for drainage. The earth work is often carried out in connection with
+the construction of the macadam surface, being completed just ahead of
+the surfacing. In that case, the fills must be carefully rolled as
+they are placed. The road bed may be shaped in connection with the
+other earthwork. If the road has been brought to a satisfactory grade
+some time prior to placing the macadam, the road bed for the broken
+stone will be prepared as needed for placing the stone.
+
+=Foundation for the Macadam.=--Macadam surfaces are quite generally
+placed in a trench as described in the trench method for placing
+gravel. It is an almost universal practice to compact the layer of
+stone by rolling with an 8- or 10-ton power roller, and if the stone
+is not held between substantial earth berms or shoulders, the rolling
+merely serves to spread the stone out over the road bed instead of
+compacting it. If an attempt is made to roll broken stone which has
+been placed on a yielding foundation, no benefit results, but on the
+contrary the stone is likely to be forced down into the soil. To
+insure that the layer of broken stone can be compacted by rolling, it
+is first necessary to roll the earth foundation until it becomes hard
+and unyielding. If soft or yielding places appear during the rolling
+these should be corrected by tile drains or by removing the earth from
+the spongy place and back-filling with material that will compact when
+rolled.
+
+It is not always easy to determine why these soft places exist in what
+appears to be a well drained roadway, especially since they are as
+likely to be found on fills as anywhere else. Apparently they are due
+to local pockets of porous soil held by denser soil so that the water
+does not readily drain away. It is usually true that such places are
+observed during the season of frequent precipitation more often than
+during other seasons of the year.
+
+In dry climates, the difficulties of securing suitable foundations for
+the broken stone road are largely eliminated, but it may be observed
+that this type of surface is not suitable for such climates unless
+some sort of bituminous binder is employed to hold the stones in
+place. The cementing power of the stone dust is inadequate when the
+surface is continually dry.
+
+[Illustration: Fig. 17.--Cross Section for Macadam]
+
+=Telford Foundation.=--When the Telford type of foundation is
+employed, the earth subgrade is prepared and then the Telford stone
+placed carefully by hand. The spaces between the large stones are
+filled with the spalls broken from the larger stones in fitting them
+in place. When completed the base is rolled with a heavy roller to
+secure a firm unyielding layer. The thickness is generally about eight
+inches. Any fairly sound stone may be used for the Telford base.
+
+=Placing the Broken Stone.=--It has been found impracticable properly
+to roll a greater thickness than about 5 or 6 inches of loose stone,
+therefore, the stone for the macadam surface is usually placed in two
+layers, the first or lower layer being rolled before the next layer is
+placed. The stone is hauled in dump wagons, trucks or dump cars,
+dumped on the road bed and spread by hand rakes or by means of a blade
+grader and is then rolled. To insure the proper thickness the loads
+are accurately spaced to spread to the proper thickness.
+
+=Rolling.=--A three-wheeled or "macadam" type of roller, of the
+self-propelled type, is best for compacting the broken stone road. The
+weight varies from eight to fifteen tons, but for most conditions the
+ten or twelve ton size seems to be preferable. On Telford base
+construction, a heavier machine is desirable and for very hard stone
+it may be successfully employed.
+
+The first trip with the roller is made along the edge of the stone and
+each successive trip is made a little nearer the middle until finally
+one half of the strip of stone has been rolled. The roller is then
+taken to the opposite side of the roadway and the operation repeated
+on the other half. The rolling is continued until the stone is
+thoroughly compacted, which is evidenced by the fact that the roller
+makes but a slight track in the surface.
+
+The second layer of stone is then placed and rolled in the same manner
+as the first.
+
+=Spreading Screenings.=--After the upper course has been rolled, the
+screenings are spread on it from piles alongside the road, enough
+being used to fill the voids in the layer of stone and furnish a
+slight excess. As the screenings are spread they are rolled to work
+them into the voids. When these are filled, the surface is sprinkled
+thoroughly by means of an ordinary street sprinkling cart and again
+rolled. In this way the dust and water are mixed into a mortar which
+fills the crevices between the stones. This mortar hardens in a few
+days, giving a bond that is weak, but sufficient for the purpose if
+the traffic is not too heavy. A broken stone road finished in this way
+is called a water-bound macadam, and is ready for traffic in three or
+four days after completion.
+
+=Bituminous Surfaces.=--On account of the inadequacy of the
+water-bound macadam when subjected to motor traffic and to obviate the
+tendency of broken stone surfaces to loosen in dry weather, there has
+been developed a method of covering the surface with a bituminous
+material such as tar or asphalt. This will be described in detail in a
+later chapter.
+
+=Maintenance.=--Even under favorable conditions as regards kind and
+amount of traffic the macadam road requires constant maintenance. The
+first effect of traffic will be to brush away the fine materials used
+for bonding the surface, thus exposing the larger stones in such a way
+that they are rather easily loosened and removed from the surface by
+wheels and the hoofs of animals. This finer material must be replaced
+as fast as it is removed so as to protect the surface. Either stone
+dust or clayey sand may be used, but clay if used alone is likely to
+be sticky when wet and prove to be worse than the condition it was
+expected to correct. In time, ruts and depressions will appear, either
+as the gradual effect of wear, which will inevitably effect some
+portions of the surface more than others, or on account of subsidence
+of the foundation. Uneven places are repaired by first loosening the
+stone, then restoring the cross section by adding new material and
+tamping or rolling it in place.
+
+If a bituminous coating has been applied, it will eventually peel off
+in places and these places must be recoated as soon as practicable.
+
+Eventually the surface will be worn to such an extent that an entirely
+new wearing surface must be added. This is done by loosening the
+entire surface to a depth of 3 or 4 inches and then adding a new layer
+of broken stone. The loosening is sometimes accomplished by means of
+heavy spikes inserted in the roller wheels, and at others by means of
+a special tool known as a scarifier.
+
+The new surface is placed and rolled in precisely the same manner as
+the wearing surface of the original construction, but the layer may
+not be as thick as the original wearing course. A new course will not
+bond to the old surface unless the old macadam has been thoroughly
+broken up first.
+
+=Characteristics.=--The water-bound macadam is a dusty, somewhat rough
+surface of low durability for rubber tired vehicles. It has long been
+the standard rural highway for steel tired vehicles, but cannot carry
+any considerable amount of motor traffic. It is easily repaired. When
+finished with a bituminous surface its durability is greatly increased
+and the dust is eliminated. It does not seem to be sufficiently rigid
+for truck traffic, unless placed on exceptionally good foundation.
+
+
+
+
+CHAPTER VIII
+
+CEMENT CONCRETE ROADS
+
+
+The cement concrete road is one of the later developments in highway
+construction, but the type has had sufficient use to show that it is
+one of the satisfactory types for heavy mixed traffic, and, where the
+proper materials are available, it is one of the economical types of
+construction.
+
+=Destructive Agencies.=--It is well to have clearly in mind at the
+outset that the concrete in a road surface is subjected to certain
+destructive agencies not usually significant in connection with the
+use of concrete, and these are so often disregarded that the average
+serviceability of the concrete road surface is sometimes much lower
+than it would be if built with due regard for the effect of traffic on
+concrete surfaces. In most structural uses of concrete, its strength
+in compression only is utilized, and the factor of safety is such as
+to eliminate to some extent failures due to inferior materials or
+workmanship.
+
+The concrete road surface is subjected to compression under wheel
+loads, to bending, causing tension in the concrete, to abrasion from
+wheels, and to tension and compression due to effect of temperature.
+The weight of the wheel loads may cause sufficient distortion of the
+road slab to produce rupture. The aggregates may be crushed under
+wheel loads if the material is too soft. Abrasion from steel tired
+vehicles wears away the concrete unless it is hard and durable.
+Changes in dimension due to the effect of change in temperature
+introduce tension or compression into the road slab and may result in
+cracks. Freezing and thawing in the subgrade subjects the slab to
+vertical movement and discontinuous support with the result that
+longitudinal and transverse cracks occur.
+
+The foregoing indicates the importance of securing good concrete for
+road surfacing, and that is accomplished by using suitable aggregates,
+by proper design of the road surface and by following established
+construction methods.
+
+=Design.=--The widths usually adopted for concrete roads are: for
+single track roads, 9 or 10 feet, and for double track roads, 18 or 20
+feet. The thickness is 6 to 8 inches at the middle, varying with
+climatic conditions and with the kind of soil upon which the concrete
+is laid. The thickness at the edge is 1 inch less than at the middle
+except that 6-inch surfaces are usually of uniform thickness, the
+total crown being 2 inches. The thickness of the two course pavement
+is the same as would be used for a single course pavement in the same
+location. The surface of either width has a total crown of one or two
+inches to insure water running off the surface. The earth foundation
+is often flat, the crown being obtained by making the slab thicker at
+the middle than at the edge. Fig. 18 shows cross section for concrete
+roads.
+
+[Illustration: Fig. 18.--Cross Section for Concrete Highway]
+
+In the state of California, concrete roads four or five inches thick
+and surfaced with a bituminous carpet mat have been successfully
+constructed. Similar designs have been used in a few other places, but
+for general practice it is unsafe to depend upon such a thin slab.
+Climatic and soil conditions probably account for the success of the
+thin roads in California.
+
+=Concrete Materials.=--The coarse aggregate for the concrete may be
+broken stone or pebbles screened from natural gravel. Durability is
+necessary, but it is also important to have uniformity in the concrete
+so that the road surface will wear uniformly and consequently keep
+smooth. Supplies of broken stone are likely to contain a small
+percentage of soft pieces and such of these as are at the surface when
+the concrete is finished will crush under traffic, leaving a pit in
+the surface. Pebbles screened from gravel are also likely to be
+variable in durability and should be carefully inspected if they are
+to be used as aggregate for concrete roads. The harder limestones,
+some sandstones, pebbles from many of the gravel deposits and
+practically all of the igneous rocks make satisfactory aggregates for
+the concrete road.
+
+Sometimes none of the coarse aggregates readily available are
+sufficiently durable or uniform for the wearing surface of the
+concrete road, but a suitable aggregate may be obtained at relatively
+high price by shipping considerable distances. In such cases what is
+known as the two course type of concrete road is employed. The wearing
+course usually is about 2 inches thick and is constructed with
+selected aggregates of good quality shipped in for the purpose. The
+lower course is constructed of aggregates which do not possess the
+desired qualities for a wearing course, but which are satisfactory for
+concrete not subjected to abrasion. The aggregates for the wearing
+course will be selected with the same regard for uniformity and
+durability that would be the case if they were for the one course
+pavement.
+
+Bank run gravel, or run of the crusher stone, is generally not
+sufficiently uniform as regards proportion of fine and coarse material
+to produce uniformity in the concrete, and the use of aggregates of
+that character is not permissible for the wearing course, but under
+proper inspection they may be used for the lower course of two course
+pavements.
+
+=Fine Aggregate.=--The fine aggregate is generally natural sand, but a
+mixture of natural sand and stone screenings is sometimes employed.
+The fine aggregate of whatever character must be clean, free from
+organic matter and sand, must contain no appreciable amount of mica,
+feldspar, alkali, shale or similar deleterious substances and not
+exceed two and one-half per cent of clay and silt. The sand is of such
+a range of sizes that all will pass the one-fourth-inch sieve and that
+not exceeding about five per cent will pass the 100-mesh sieve.
+
+=Proportions.=--Various mixtures for the concrete are employed because
+these may properly vary to some extent with the exact character and
+grading of the aggregates. Experience seems to have shown that the
+concrete used for the wearing surface should have a crushing strength
+of at least 2500 pounds per square inch, and the mixture adopted is
+based on the requirements that will give the desired crushing
+strength. The common mixture for the one course pavement is one part
+cement, two parts sand and three and one-half parts coarse aggregate.
+For the wearing course of the two-course type of pavement, a mixture
+of the same kind is very often specified.
+
+While these are perhaps the most widely adopted proportions, many
+others have been used, especially where the aggregates exhibit
+peculiarities or the traffic conditions are unusual. It is desired to
+emphasize that the purpose is to obtain concrete of the desired
+strength and there can be no such thing as "standard" proportions.
+
+=Measuring Materials.=--In considering the methods employed for
+measuring aggregates, emphasis should be placed on the futility of
+rigid requirements for the aggregates, both as regards quality and
+range of sizes, if the materials are carelessly proportioned at the
+mixer. If even reasonably near uniform wearing qualities are to be
+secured throughout the entire area of the concrete road surface,
+successive batches of concrete must be alike, and to insure that, the
+aggregates including the water in each batch of concrete must be mixed
+in exactly the same proportions. The aggregates are measured in
+various ways, all essentially alike in that the intent is to insure
+exactly the same amount of each ingredient for each batch of concrete.
+
+One method is to place bottomless boxes in wheelbarrows, fill the
+boxes level full and then lift off the box. Another is to use a
+wheelbarrow with a bed of such shape that the contents will be a
+multiple of 1 cubic foot when level full. For the larger jobs, the
+aggregates are hauled in industrial cars, each having sufficient
+capacity for a batch of concrete. The car body is provided with a
+partition so as to separate the fine and coarse material.
+
+The water is measured in a tank which automatically refills to the
+same level each time it is emptied and when adjusted for a mixture
+will introduce the proper amount of water for each batch. It is highly
+important to use the least amount of water that will produce workable
+concrete.
+
+=Preparation of the Earth Foundation.=--The concrete road is generally
+placed directly on the natural soil which has been brought to the
+proper cross section. Some engineers advocate that in preparing the
+subgrade, the earth be thoroughly rolled; others prefer not to roll
+the subgrade. If fills of considerable depth are constructed, they
+should either be rolled as built or else should be allowed to settle
+for some months before the concrete road is placed, preferably the
+latter.
+
+=Placing the Concrete.=--The concrete is placed between substantial
+side forms of a height equal to the thickness of the concrete road
+slab at the edge, and is shaped roughly by means of shovels.
+
+Various methods have been developed for striking the surface to the
+exact shape desired and smoothing it. If hand finishing methods are
+employed, a plank template is cut to the prescribed cross section and
+the concrete is shaped by drawing the template along the side forms.
+Sometimes the template is used as a tamper, being moved along very
+slowly accompanied by an up and down motion that tends to tamp the
+concrete. The template is then drawn along a second time to smooth the
+surface finally.
+
+After the surface has been struck off by hand, it is finally smoothed,
+first by rolling crosswise with a slight hand roller about 8 inches in
+diameter and 30 inches long. The final finish is effected by dragging
+a piece of web belting back and forth across the surface.
+
+Machines designed to tamp the concrete and strike it off to the
+required cross section are also employed for finishing. The machine is
+power operated and is carried on wheels that run on the side forms,
+and the machine moves slowly along as the tamping progresses. The
+concrete is tamped, struck off to shape and smoothed with the belt at
+one operation. This method of finishing produces denser and stronger
+concrete than can be produced by hand finishing methods.
+
+=Placing Concrete for Two-course Road.=--The methods employed for the
+two-course concrete road are much the same as for the one-course road.
+The concrete for the lower course is placed and struck off by means of
+hand tools, and after that course has progressed a few feet, the upper
+course is placed and finished as has been described for the one-course
+road.
+
+=Curing the Concrete.=--The setting action of cement is a chemical
+process, not merely a drying out of the water introduced in mixing the
+concrete. The chemical action is progressive for a long time, but is
+more rapid during the first few hours than during the later periods,
+and the concrete reaches about three-fourths of its maximum strength
+at the end of seven days. During the setting period and particularly
+during the first few days, plenty of water must be available to the
+cement.
+
+To prevent too rapid loss of water from the concrete during the
+setting period, the surface must be protected from the wind and sun.
+This is accomplished by first covering with canvas as soon as the
+concrete has hardened sufficiently and by later covering with earth,
+to a depth of two inches. The earth covering is kept wet for about ten
+days and is left in place for about one month.
+
+In some places the ponding method of curing is adopted. The surface is
+divided into sections by earthen dikes and the space inside the dikes
+filled with water to a depth of two or three inches. The water
+covering is maintained for two weeks or longer.
+
+No traffic is permitted on the surface for one month, and in cold
+weather traffic may be kept off the surface for a longer period.
+
+=Expansion Joints.=--To permit the concrete slab to accommodate itself
+to changes in dimension due to temperature changes, expansion joints
+1/2 inch wide are placed about every thirty feet. These consist of a
+sheet of some prepared bituminous material placed in position as the
+concrete is poured.
+
+Experience seems to indicate that in spite of the expansion joints,
+the concrete will crack more or less and many engineers think it
+advisable to omit expansion joints in constructing the pavement and
+when cracks develop to pour bituminous material into them, thus
+forming expansion joints.
+
+The prevailing practice in rural highway construction is to omit the
+expansion joints, but they are commonly adopted in city pavements.
+
+=Reinforcing.=--To minimize the cracking, either bar or wire mesh
+reinforcing is used in the concrete. If bars are used they are placed
+in the concrete as it is poured so as to form a belt around each
+section about 15 feet square. If the mesh type is employed, a part of
+the layer of concrete is placed and smoothed off and a strip of the
+mesh laid in place. Additional concrete is then poured on top of the
+mesh to bring the slab to the required thickness.
+
+=Bituminous Coatings on Concrete Surfaces.=--The concrete road surface
+is sometimes coated with a layer of bituminous material and stone
+chips or gravel pebbles. This is particularly advisable where no
+really satisfactory aggregates are available and the concrete surface
+would not possess sufficient durability. The bituminous material is
+applied hot to the surface and is then covered with stone chips or
+gravel pebbles, ranging in size from 3/4 inch down to 1/4 inch, the
+resulting coating being about 3/4 inch thick. Many failures of this
+type of surface have been recorded due to the difficulty of securing
+adhesion to the concrete. This seems to be due in part to inability to
+get the proper bituminous materials and in part to climatic effects.
+Considerable progress has been made in developing this type of surface
+and it may eventually become a satisfactory maintenance method.
+
+=Characteristics.=--The concrete road is of a granular texture and is
+not slippery. It is of course rigid and noisy for steel tired
+vehicles. It is an excellent automobile road and its low tractive
+resistance makes it a desirable surface for horse drawn vehicles. It
+possesses a high degree of durability if properly constructed. It is
+likely to crack indiscriminately but as a general rule the cracks are
+not a serious defect.
+
+=Maintenance.=--The cracks that appear in the concrete surface are
+filled once or twice a year, tar or asphalt being employed. The dust
+and detritus is cleaned out of the cracks and the hot filler poured
+in, with enough excess overflowing to protect the edges.
+
+
+
+
+CHAPTER IX
+
+VITRIFIED BRICK ROADS
+
+
+Vitrified brick roads consist of a foundation course of Portland
+cement concrete, broken stone or slag macadam, or of brick laid flat,
+the first named being by far the most generally used, and a wearing
+course of vitrified brick.
+
+=Vitrified Brick.=--Vitrified brick are made from clay of such a
+character that when heated to the required temperature they will fuse
+into a glassy texture. Brick roads are constructed on roads carrying
+the severest of traffic and the brick must therefore be tough and of
+high resistance to wear.
+
+Not all of the clays from which brick may be manufactured will produce
+a product suitable for road construction, and paving brick, even
+though truly vitrified, are of different degrees of durability,
+depending upon the nature of the clay and the care exercised in the
+manufacture.
+
+Paving brick are manufactured by the stiff mud process, which means
+that the clay is molded into form in a relatively dry condition. To
+accomplish this, considerable pressure is exerted in forcing the
+column of clay through the dies, which form the prism from which the
+brick are cut. If the clay is unsuitable in character or is not
+properly ground and mixed, the brick will possess planes of weakness
+between the various layers of clay which have been pressed together,
+and these planes, called laminations, are a source of weakness if too
+marked. It is usual to specify that the brick used for road surfaces
+shall be free from marked laminations.
+
+If the brick is not properly burned it will be only partly vitrified
+and therefore not of maximum durability. It is customary to specify
+that the brick shall show a glassy fracture indicating complete
+vitrification.
+
+Various defects of a minor nature occasionally develop in the brick
+during the successive steps in the manufacturing process. Check cracks
+resulting from the burning or from too rapid cooling are often
+encountered, but unless these are deep, that is 3/16 inch or more,
+they do not impair the wearing quality of the brick, nor indicate
+structural weakness. Kiln marks are formed on some of the brick due to
+the weight of the brick above in the kiln. These depressions are not
+objectionable unless the brick are so distorted that they will not lie
+evenly in the pavement.
+
+Spacing lugs or raised letters are formed on one face of the brick to
+insure sufficient space between the brick for the filler. These lugs
+or letters are not less than 1/8 inch nor more than 1/4 inch high and
+of such design that they will not obstruct the free flow of filler
+into the joints between the brick.
+
+Several varieties of paving brick are to be had, the difference being
+principally in the design or size.
+
+=Repressed Brick.=--In this type of brick the spacing lugs are formed
+by pressing the green brick, after it has been cut to size, into a
+mold on one face of which are recessed letters or other devices into
+which the clay is pressed, thus forming the spacing lugs.
+
+=Vertical Fiber Brick.=--These brick are designed to be laid with one
+wire-cut face up and spacing is provided by two or more beads on the
+side of the brick. Sometimes the vertical fiber brick has no spacing
+lug, it being contended that the irregularities of the brick are such
+as to provide all of the space required. In practice this does not
+always work out, as the brick are so regular in shape that when laid
+there is too little space between the brick to permit the introduction
+of a suitable filler. The use of brick without spacing lugs is just
+beginning and is not yet a generally accepted practice.
+
+=Wire-cut-lug Brick.=--This is a type of non-repressed brick which has
+spacing lugs provided by cutting one face in a special manner which
+provided lugs for spacing. In this type the wire cut face is the one
+between the brick as they are laid in the pavement.
+
+=Tests for Quality.=--The standard test for quality of paving brick is
+the rattler test. The brick rattler consists of a barrel of 14 sides
+24 inches long, mounted so as to rotate at a speed between 29.5 and
+30.5 revolutions per minute. The duration of a test is 1800
+revolutions. Ten brick constitute a charge and these are placed in the
+rattler along with 300 lbs. of cast iron spheres. The spheres are of
+two sizes, the smaller being 1-7/8 inch in diameter when new, and the
+larger 3-3/4 inches in diameter when new. Ten of the larger spheres
+are used and the balance of the charge is made up of the small size.
+
+When tested in the standard manner the loss allowable for the several
+classes of service are as follows:
+
+  ------------+---------------+----------------
+              |               |   Maximum Loss
+    Traffic   |  Average Loss |   for any Brick
+  ------------+---------------+----------------
+    Heavy     |   20 per cent |    24 per cent
+    Medium    |   22 per cent |    26 per cent
+    Light     |   25 per cent |    28 per cent
+  ------------+---------------+----------------
+
+=Other Tests.=--Sometimes the absorption test is specified for paving
+brick, but it is rarely a vitrified brick that will pass the rattler
+tests which fails to pass a reasonable absorption test. Absorption of
+water in an amount exceeding 4 per cent indicates incomplete
+vitrification and failure of such brick is almost certain during the
+rattler tests.
+
+The cross breaking test is also sometimes employed, but generally
+only to check the general quality of the brick. Failure in service
+more frequently occurs from excessive wear than from any other cause
+and the cross breaking test has little significance, except for brick
+less than 3 inches thick, which are to be laid on a sand bedding
+course.
+
+=Foundation.=--The foundation for brick roads is usually of Portland
+cement concrete, the thickness varying with the nature of the traffic
+and the kind of soil upon which the pavement is built. For well
+drained soils and normal highway traffic, 5 inches is the ordinary
+thickness of foundation. Under favorable conditions such as locations
+with sandy soils or in semi-arid or arid regions where the soil is
+always stable, the foundation may be four inches thick, and a
+considerable mileage of brick road has been built with concrete
+foundations less than four inches thick.
+
+In other locations the soil and traffic conditions require a base six
+inches or more in thickness, and the proper thickness can be
+determined only after all of the factors involved are known and have
+been analyzed. It is impractical to adopt a standard thickness of
+foundation that will be equally economical for all locations and all
+kinds of traffic. As the brick pavement is essentially a heavy traffic
+type of surface, the design cannot be varied greatly with similar
+foundation conditions because the weight of individual loads is the
+significant factor and this does not vary so much as the volume of
+traffic. A variation in volume of traffic may be compensated for by a
+variation in the quality of the brick as already set forth.
+
+The mixtures for the concrete foundation vary widely because of the
+variation in the aggregates employed. If the fine and coarse aggregate
+for the concrete are of good quality a mixture of one part cement, two
+and one-half parts sand and five parts of coarse aggregate would
+insure concrete of adequate strength. A somewhat leaner mixture is
+sometimes employed and would be satisfactory if the aggregates were of
+exceptional concrete making quality. Mixtures of sand and pebbles
+(unscreened gravel) may also be used if care is exercised to secure a
+mixture of adequate strength. The proportion will of necessity vary
+with each particular material and the discussion of the various
+considerations involved may be obtained from various standard works on
+concrete and concrete materials.
+
+Broken stone macadam is sometimes utilized for the foundation course
+of the brick pavement and such foundations are constructed as
+water-bound, which is described in a previous chapter. The thickness,
+like that of the concrete foundation, varies with the soil conditions
+and the weight of the loads that are expected to use the road. The
+macadam is placed in a single layer and is rolled and bonded with
+screenings as described in the chapter dealing with water-bound
+macadam. Six inches is a common thickness for the macadam base. This
+type of foundation should be employed only where the soil is quite
+stable and where material costs are such as to insure that the macadam
+base is materially cheaper than one of concrete. This would usually be
+in locations where the cost of cement is high because of long hauls
+and where suitable macadam materials may be obtained close at hand.
+
+Old macadam roads are sometimes utilized for the foundation for the
+brick surface, but the instances where this is permissible are
+comparatively few in number. When an old macadam is to be used it is
+reshaped to the proper cross section and re-rolled and bonded so as to
+afford a stable foundation of the proper cross slope.
+
+
+BEDDING COURSE FOR BRICK SURFACES
+
+In order to equalize the variations in size and shape of the brick,
+they are laid on a bedding course composed of material into which the
+brick may be forced by rolling. In this way the upper surfaces of all
+brick can be brought to the proper elevation to insure smoothness and
+easy riding qualities. Several kinds of bedding course are now
+employed.
+
+=Sand Bedding Course.=--The sand bedding course has been referred to
+as a sand cushion, but as a matter of experience the cushion effect is
+slight, although sometimes pavements have become uneven because the
+brick have pushed down into the sand after the pavement was used for a
+time. The sand for the bedding course should preferably be fine
+grained, all particles passing the eight mesh sieve, but ordinary
+concrete sand is satisfactory. The sand need not be clean, as a
+comparatively large percentage of silt or clay does not impair the
+usefulness of the material.
+
+[Illustration: Fig. 19.--Cross Sections for Brick Highways]
+
+=Sand Mortar Bedding Course.=--In order to eliminate the tendency for
+the straight sand bedding course to shift because of the impact of
+traffic on the brick, a lean cement mortar is sometimes employed
+rather than the straight sand. Sand and cement in the ratio of one
+part cement to four or five parts of sand are mixed dry, and after the
+brick have been rolled, is moistened to furnish water to hydrate the
+cement. The sand employed is ordinary clean concrete sand.
+
+=Green Concrete Bedding Course.=--In the monolithic type of brick
+road construction, the brick are laid directly on the green concrete
+base before the concrete has taken a set and the irregularities of the
+brick are taken up by rolling them until bedded in concrete.
+
+
+FILLERS FOR BRICK SURFACES
+
+The spaces between the brick are filled with some material that will
+prevent the brick from being displaced and prevent water getting to
+the bedding course. A suitable filler must adhere to the brick and
+fill completely the spaces between them. It must withstand traffic so
+as to remain intact in the joints and when in place it must be rigid
+enough to prevent displacement of the brick.
+
+=Cement Grout Filler.=--One of the most commonly used fillers for
+brick pavements consists of a grout composed of Portland cement and
+fine sand. When properly mixed and applied the grout filler meets all
+requirements for a filler except that it is non-elastic and some means
+must be adopted for caring for pavement expansion.
+
+=Bituminous Fillers.=--Asphaltic materials and tars are widely used as
+fillers for brick pavements. Such fillers are of high melting point
+and consequently solid at ordinary temperature. They are poured into
+the joints hot and when they cool are firm enough to comply with the
+requirements for a filler. In addition, they have enough ductility to
+accommodate the expansion of the pavement due to temperature changes.
+
+=Mastic Fillers.=--Mastic consists of a mixture of about equal volumes
+of fine sand and a solid bituminous material. The mixture is prepared
+at high temperature and is worked into the joints between the brick
+while hot. When cool it resembles the straight bituminous filler
+except that the mastic is somewhat more resistant to wear than the
+straight bituminous filler.
+
+EXPANSION JOINTS
+
+It is recognized that brick will expand and contract with changes in
+temperature. When a bituminous or mastic filler is employed there is
+sufficient yield to the filler to accommodate the change in dimension
+in the brick, but when the grout filler is used either the expansion
+joint must be provided or the pavement must be designed to withstand
+the compression due to expansion of the brick. Expansion joints may
+consist of a sheet of bituminous mastic prepared for the purpose and
+set in place in the pavement. The sheet of joint material is simply
+inserted between courses of brick at the proper place.
+
+Another method of forming an expansion joint consists in placing a
+strip of wood between courses of brick at the place where a joint is
+required. After the pavement has been grouted, the wooden strip is
+pulled out and the joint is filled with a suitable bituminous filler.
+
+=Marginal Curb.=--If the sand bedding course is employed, it is
+necessary to provide curbing along the sides of the brick to hold the
+bedding course in place. The curb is usually constructed integral with
+the base and of concrete of the same mixture as the base. The width of
+the curb is usually six inches and the top of the curb is at the same
+elevation as the edge of brick surface.
+
+
+CONSTRUCTION OF THE SURFACE
+
+Before the construction of a brick surface should be undertaken on a
+road, the drainage should be provided for even more completely than
+for a less costly type of surface since it does not pay to jeopardize
+the stability of the pavement by failure to provide adequately for the
+stability of the supporting soil. Grades should also be reduced to the
+economical limit.
+
+The earth subgrade is brought to the proper elevation and cross
+section and is thoroughly rolled. If there are places where the soil
+will not compact properly under rolling, these places are corrected by
+taking out the material and back filling with new material that will
+properly compact under the roller.
+
+The aggregates for the concrete may be distributed along on the
+prepared subgrade or may be stored in stock piles or bins at
+convenient points. If stored on the subgrade, a traction mixer is
+employed which is drawn along the road as the work progresses, the
+materials being placed directly in the mixer. If stored at a central
+point, they may be transported to the mixer on the road and dumped
+directly into the mixer, or the mixer may be set up at the storage
+piles and the concrete hauled in trucks to the road where it is
+deposited and shaped.
+
+The concrete is spread to the proper thickness and tamped either by
+hand or by machinery. If the marginal curb is to be employed, it is
+constructed immediately after the concrete for the base has been
+finished but before the cement begins to set.
+
+After the foundation concrete has set, the bedding course is spread
+and struck off to the proper thickness. When the bedding course
+consists of sand-cement mortar, the sand and cement are mixed dry and
+spread to prescribed thickness. It is considered to be desirable to
+roll the sand bedding course with a light hand roller before the brick
+are placed, but the sand-cement bedding course is not rolled. The
+bedding course must be carefully shaped by means of a templet or
+strike board before the brick are placed.
+
+The brick are laid in straight courses across the pavement, with the
+spacing lugs all in the same direction if brick with spacing lugs are
+employed, and with the lugs in contact with the brick of adjoining
+courses. If brick without spacing lugs are used they are laid loosely
+so that there will be room for the filler between the brick of
+adjoining courses.
+
+After the brick have been laid they are rolled to bed them in the sand
+or sand-mortar bedding course and thus secure a smooth surface. For
+this purpose a light, power driven, tandem roller is used and the
+rolling is continued until the brick are thoroughly bedded. Any
+defective brick that are noted are removed and replaced with good
+brick and after this culling has been completed the surface is once
+more thoroughly rolled. If a cement-sand bedding course is employed,
+the surface is sprinkled just after the final rolling so that water
+will flow down between the brick and moisten the bedding course
+sufficiently to cause the cement to set. In some cases, the
+sand-cement bedding course is sprinkled just before the brick are laid
+but in warm weather the setting would take place before the brick
+could be rolled if that were done. In cool weather the setting is
+sufficiently slow to permit rolling before the bedding course hardens.
+
+The filler is applied to the surface after the rolling. If the
+bituminous type of filler is employed, the hot filler is poured onto
+the surface and worked into the joints by means of squeegees, with
+comparatively little material left on the surface. In some instances
+cone-shaped pouring pots are employed and the material is poured
+directly into the joints.
+
+The cement grout filler is applied in the same general manner as the
+bituminous filler. The grout, consisting of equal parts of sand and
+cement, is mixed to a thin consistency and poured onto the surface and
+is then worked into the joints with squeegees. Two or more
+applications are usually required to effect a complete filling of the
+joints. The surface should be covered with sand and be kept moist
+until the cement grout has set.
+
+
+
+
+CHAPTER X
+
+BITUMINOUS ROAD MATERIALS AND THEIR USE
+
+
+Tars and asphaltic materials of various kinds are widely used for road
+construction and maintenance, especially for road surfaces subjected
+to motor traffic. Materials of this character that are employed in
+highway work possess varying degrees of adhesiveness, and while they
+may be semi-solid or viscous liquids at air temperature, they melt on
+the application of heat and can be made sufficiently fluid to mix with
+the mineral aggregates that may be used in the road surface. Upon
+cooling, the bituminous materials return to the previous state and
+impart a certain amount of plasticity to the mixture, at the same time
+serving as a binding or cementing agent, which is sufficiently stable
+for many classes of road construction.
+
+=Classes of Bituminous Materials.=--Bituminous materials may be
+classified, according to the source from which they are obtained, as
+coal tars, water gas tars, native or natural asphalts and oil or
+petroleum asphalts.
+
+=Coal Tar.=--Coal tar is obtained as a by-product in the manufacture
+of illuminating gas from coal. It is also obtained in the manufacture
+of coke from coal. The tar thus obtained is manufactured into products
+that are used for dust layers on gravel or macadam roads, binders for
+macadam and gravel surfaces, fillers for brick, wood block and stone
+block pavements and for expansion joints. These various materials
+differ mainly in their consistency at air temperature. (They may
+differ widely in chemical composition, but that need not be considered
+herein.)
+
+=Water Gas Tar.=--Water gas tar is obtained as a by-product in the
+manufacture of illuminating gas from crude petroleum. It is used for
+the same kinds of construction as coal tar, and the products utilized
+for the several purposes, like the coal tars, differ mainly in
+consistency.
+
+=Natural Asphalt.=--Natural asphalt is found in deposits at many
+places in the world, existing in beds or pools where it has exuded
+from the earth or as veins in cavities in the rocks. It is of varying
+composition and consistency, but those kinds in most general use are
+solid or very viscous liquids at air temperature. Of the deposits that
+have been developed on a commercial scale, the Trinidad lake in the
+British West Indies and Bermudez deposit in Venezuela are best known.
+Both of these materials are too hard in the natural state to be used
+for road construction, and are softened, or fluxed as it is called,
+with fluid petroleum oil before being used.
+
+=Petroleum Asphalt.=--Petroleum asphalt is a residue remaining after
+the fluid products have been distilled from petroleum. Residues of
+this sort are not always suitable for road construction, but a number
+of brands of road material are obtained from this source. Oil asphalts
+are used for dust layers, for binders for macadam roads, for asphalt
+cements for sheet pavement surfaces, and for fillers for block
+pavements and expansion joints.
+
+=Mixtures.=--Water gas tars and asphalts are sometimes mixed to
+produce road materials, and likewise native asphalts and residues
+obtained from petroleum are sometimes mixed to produce asphalt cements
+for paving mixtures.
+
+=Classification according to Consistency.=--The various bituminous
+materials may be classified according to consistency in discussing the
+various uses to which they may be put.
+
+=Road Oils.=--Road oils are fluid petroleum oils of such consistency
+that they may be applied cold or by heating slightly. They are used
+as dust layers on earth, gravel and macadam surfaces. Their efficacy
+depends upon the binding properties of the small amount of asphaltic
+material that is contained in the oil.
+
+=Liquid Asphalts.=--These are somewhat less fluid than the road oils,
+and must always be heated before application, but are viscous liquids
+at ordinary temperature. These materials are obtained from crude
+petroleum or semi-solid native bitumens, in which case they are
+usually called malthas. Both coal tars and water gas tars of
+semi-solid consistency are also employed for the same class of
+construction as the liquid asphalts.
+
+These materials are used for carpeting mediums on macadam roads and as
+cementing agents in the construction of hot-mixed macadam.
+
+=Asphalt Cements.=--The solid asphaltic materials used for hot-mixed
+types of construction are called asphalt cements. They may be
+petroleum residues or native asphalts fluxed with petroleum oils. They
+are solids at ordinary temperature and must be heated to a temperature
+in excess of two hundred and fifty degrees before they are
+sufficiently fluid to use. Asphalt cements are used for sheet asphalt
+and asphaltic concrete construction and for hot-mixed bituminous
+macadam.
+
+=Fillers.=--Fillers are solid asphalts or tars that are used for
+filling expansion joints in rigid pavements and for filling the spaces
+between the blocks in brick, wood block and stone block pavements.
+
+=Bitumen.=--Bituminous materials are all soluble to a greater or
+lesser extent in carbon disulphide and the soluble portion is called
+bitumen. It is the bitumen that gives to the materials the cementing
+properties utilized in road construction. Mixtures of mineral
+aggregates and bituminous materials for various purposes are
+proportioned with bitumen as a basis. Therefore, less of an asphalt
+containing one hundred per cent bitumen will be used than of one
+containing less than one hundred per cent of bitumen.
+
+  TABLE 8
+
+  PROPERTIES OF ASPHALTIC ROAD MATERIALS
+
+  (A) Material
+  (B) Specific Gravity
+  (C) Consistency
+  (D) Solubility in CS_2, Per Cent
+  (E) Solubility of Bitumen in CCl_4, Per Cent
+  (F) Solubility of Bitumen in 86 deg. Naphtha, Per Cent
+  (G) Fixed Carbon, Per Cent
+  (H) Flash Point
+  (I) Ductility
+  -------------------------+---------+----------+----------+------------
+           (A)             |   (B)   |    (C)   |   (D)    |    (E)
+  -------------------------+---------+----------+----------+------------
+  Mexican oil asphalts     |1.03-1.05|As desired| 99.5-99.9|99.5-99.9
+  California oil asphalts  |1.02-1.04|As desired|   99.9   |    99.9
+  Texas oil asphalts       |1.01-1.03|As desired|   99.9   |    99.9
+  Bermudez  natural asphalt|1.07     |    25    |    95    |     99+
+  Trinidad natural asphalt |1.40     |     7    |  56-57   |     100
+  Bermudez asphalt cement  |1.04-1.06|Up to 135 |  95-97   |99.5 or more
+  -------------------------+---------+----------+----------+------------
+
+  -------------------------+---------+----------+----------+------------
+           (A)             |   (F)   |   (G)    |   (H)    |     (I)
+  -------------------------+---------+----------+----------+------------
+  Mexican oil asphalts     |  70-80  |   13-16  | 200 deg.C. up|   60-100
+  California oil asphalts  |  75-80  |   10-12  | 200 deg.C. up|   100+
+  Texas oil asphalts       |  75-80  |   12-14  | 200 deg.C. up|   50-100
+  Bermudez  natural asphalt|  68-70  |   13-14  |    ...   |    ...
+  Trinidad natural asphalt |  64-65  |   10-11  |    ...   |    ...
+  Bermudez asphalt cement  |  77-80  |   11-12  |  175-200 |   25-50
+  -------------------------+---------+----------+----------+------------
+
+=Specifications.=--Some properties of bituminous materials can be
+varied in the process of manufacture, while others are inherent in the
+material and cannot be changed in the process of manufacture.
+Specifications must therefore be drawn with care to insure that the
+requirements can be met by satisfactory materials. But certain
+properties, such as specific gravity, may vary greatly among materials
+equally satisfactory for construction purposes. One should not be
+misled by apparent differences in the characteristics of materials,
+because these may simply be natural peculiarities which have no
+bearing on the usefulness of the material. There are given in Table 8
+the properties of some of the commonly used bituminous materials and
+the properties that can be varied in the process of manufacture are
+indicated with an asterisk. A variation in these properties will
+usually result in some change of other properties, but generally not a
+great change.
+
+
+SURFACES IN WHICH BITUMINOUS MATERIALS ARE UTILIZED
+
+I. Surface Treatments
+
+Attention has been directed to the rapid deterioration of water-bound
+macadam when subjected to passenger automobile traffic.
+
+In water-bound macadam the stones are held in place by a weak cement
+composed of stone dust and water, and this cement is not sufficiently
+strong to hold the stones in place when they are subjected to the
+shear of automobile tires. In finishing the water-bound macadam
+surface, the spaces between the stones are filled with screening and
+in addition a layer about one-fourth inch thick is left on the
+surface.
+
+The automobile traffic first brushes aside all of the screenings and
+smaller particles of rock, exposing the larger stones. These gradually
+loosen as the road is used and are brushed aside. When this effect
+begins, the road is said to be raveling. Various lengths of time may
+elapse from the time the road is first finished until raveling begins,
+depending upon the character of the stone, the weather and the amount
+of motor traffic. During the period before raveling starts, it is
+comparatively easy to restore the road surface at any time by the
+addition of screenings or clay and sand. Usually there will be a few
+small areas of the surface that, on account of faulty construction,
+will ravel or become rutted much earlier than the remainder of the
+surface. These can be repaired by the methods described in the chapter
+on "Water-bound Macadam Construction." When the surface begins to
+ravel seriously, maintenance becomes much more difficult and in order
+to prevent raveling and the difficulties of maintenance thereafter,
+the macadam surface is often coated with a bituminous material.
+
+[Illustration: Fig. 20.--Oiling a Gravel Road]
+
+If there is any dust or screenings on the road surface, the bituminous
+material will not adhere to the stones and will soon flake off under
+traffic. The surface of the macadam must therefore be thoroughly
+cleaned before the bituminous material is applied. The usual practice
+is to finish the road as water-bound macadam, and permit traffic on it
+for a sufficient length of time to show any weak places in the surface
+and at the same time thoroughly to season the surface. If any
+defective places appear, they are repaired and when the surface
+exhibits satisfactory stability, but before it begins to ravel, the
+bituminous surface is applied. There will ordinarily be some stone
+dust and some screenings remaining on the surface at the time
+bituminous treatment is undertaken, and there may also be some caked
+mud or other foreign material. All of this must be removed so as to
+expose the stones throughout.
+
+=Applying the Bituminous Binder.=--The bituminous binder may be
+delivered in tank cars, which is desirable if the work is near a
+railroad siding, or ample tank wagon service is available for long
+hauls so that the tank will not be held up too long. Often it is
+desirable to purchase the binder in barrels and haul these to the site
+of the work in advance of beginning the construction of the surface.
+
+The bituminous material may be applied by means of hand spreading cans
+not unlike an ordinary garden watering pot, except that a slotted
+nozzle is substituted for the ordinary perforated one. If hand methods
+are employed for spreading, the bituminous material is heated in open
+kettles and then spread on the surface, the quantity required usually
+being about one-half gallon per square yard of surface. The
+temperature of the binder should be great enough to insure fluidity
+and the road should be dry at the time of the application. As soon as
+the material has been spread, the surface is finished with a dressing
+of chips.
+
+=Finishing the Surface.=--For surface dressing the best material is
+stone chips ranging in size from about 1 inch down to one-fourth inch.
+But the chips must be of durable material, or they will quickly grind
+into dust. They must be free from dust when applied, as the presence
+of any considerable amount of dust interferes with the proper
+finishing of the surface. The stone chips are rolled into the surface,
+a sufficient quantity being used to just cover the surface.
+
+=Patching.=--It almost always happens that some small areas will not
+be properly cleaned or that for some unknown reason the coating peels
+off the surface. Such places must be promptly patched to prevent them
+enlarging under the action of traffic. This work is usually done by
+patrolmen, who inspect the road at frequent intervals and make the
+necessary repairs. The patrolman is equipped with a small heating
+kettle, a spreading can and the necessary brushes, tampers and
+miscellaneous tools needed for the repair work. The place to be
+patched is carefully cleaned, coated with bituminous binder and stone
+chips and tamped until dense and solid. Repairs made in this way are
+exceedingly important in that they arrest deterioration in its early
+stages and maintain a high degree of serviceability.
+
+
+II. Penetration Macadam
+
+A considerable mileage of macadam has been constructed in which an
+attempt was made to eliminate the difficulties of maintenance by a
+method of construction that involves applying a bituminous binder in
+such a manner as to permit it to penetrate two inches or more into the
+surface. It is expected that the binder will coat the stones to such
+an extent as to increase materially the stability of the bituminous
+macadam over the surface treated one. It is also expected that less
+difficulty will be encountered in maintaining a surface of bituminous
+material and stone chips on this type of road than on the water-bound
+macadam. The extent to which these expectations have been realized has
+varied to a marked degree and although some excellent surfaces have
+been constructed by this method, the results have as a rule been
+neither uniform nor entirely satisfactory. It seems to be apparent
+that good results cannot be obtained unless the materials are entirely
+suitable and the construction is carried out with unusual skill.
+
+=Foundation.=--The foundation or lower course consists of a layer of
+broken stone six inches thick placed on a well drained and thoroughly
+rolled earth subgrade. In exceptional cases, the Telford type of
+foundation might be employed.
+
+The lower course of broken stone is finished in the same manner as
+water-bound macadam, being bonded with stone screenings or with fine
+gravel of high clay content.
+
+Since this course is in reality the foundation of the surface, it is
+necessary to secure stability by appropriate construction methods,
+exactly as in constructing water-bound macadam.
+
+[Illustration: Fig. 21.--Type of Roller used on Gravel and Macadam
+Roads]
+
+=Upper or Wearing Course.=--The wearing course consists of a layer of
+stone about two and one-half inches thick. The stone is placed and
+rolled and the spaces between the stones partially filled with some
+suitable bituminous material. The bituminous material is usually
+applied by means of a mechanical spreading device connected to a tank
+wagon. The bituminous materials employed for this class of
+construction are semi-solid in character and must be heated to give
+them sufficient fluidity for application. They may be heated in the
+tank wagon which is used for the application or they may be heated in
+separate tanks and transferred to the distributing wagon for
+spreading. Some kind of a nozzle or group of nozzles is employed for
+spreading the material so that it can be delivered in the form of a
+spray or at least in a thin fan-shaped stream and can be distributed
+in a fairly uniform layer over the stone. The binder will cool rather
+rapidly after it is applied, but meanwhile will flow into the openings
+between the stones and will form over the surface stones a coating of
+slight thickness.
+
+The surface of the macadam is next covered with a layer of chips of
+tough rock, similar to the material used for the final dressing in
+surface treatments. These are carefully brushed into the openings
+between the larger stones by means of heavy brush brooms. This is an
+exceedingly important part of the work and often a much neglected part
+of the construction.
+
+The surface is then covered with a second application of bituminous
+material, somewhat less in quantity than required for the first
+treatment and the surface again covered with stone chips and brushed.
+
+The surface is then thoroughly rolled and is ready for traffic.
+
+=Patching.=--As in the case of surface treatments, there are likely to
+be places that, on account of defects in the construction, will fail
+soon after the road is placed under traffic. These will quickly
+enlarge unless they are repaired promptly. The repairs are made by
+loosening the stone in the area affected and adding new stone as
+needed and then pouring on the necessary amount of bituminous material
+to coat the stones. Allowance must be made for the compression of the
+material by tamping so that a depression does not result. The stones
+are carefully tamped to place and covered with chips which are also
+tamped.
+
+=Characteristics.=--The penetration macadam is a surface well adapted
+to motor traffic if the individual vehicles are not too heavy. It is
+likely to squeeze out of shape under motor truck traffic, becoming
+seriously uneven and uncomfortable for traffic. Its durability is
+materially affected by the construction methods followed.
+
+
+III. Hot Mixed Macadam
+
+The wearing course of the mixed macadam is composed of graded broken
+stone or gravel and a bituminous binder. Usually the bituminous
+material only is heated prior to the mixing, but sometimes the stone
+is also heated.
+
+=Foundation.=--The lower course, which serves as the foundation, is
+either broken stone macadam, gravel or concrete.
+
+Where a foundation of broken stone is used, it is constructed of the
+materials and in the manner described for the foundation of the
+penetration macadam. Quite often a badly worn macadam or gravel road
+is used for the foundation and a new wearing course provided by adding
+a mixed macadam surface. If such is the case, the old surface is
+worked over so as to restore the shape sufficiently and to insure that
+it is everywhere of sufficient thickness.
+
+Portland cement concrete is sometimes used as a foundation for the
+mixed macadam, but not often. Usually if the traffic is of a character
+requiring a concrete foundation, it is desirable to use a better
+wearing course than the mixed macadam, and the asphaltic concrete or
+sheet asphalt type of surface is employed. It is necessary to finish
+the surface of the concrete base with some device that will leave the
+surface rough to prevent the macadam from creeping. A knobbed tamper
+which leaves numerous irregular depressions about 2 inches in diameter
+and three-fourths inch deep is often employed.
+
+=Sizes of Stone.=--For the wearing surface, stone ranging in size from
+2 inches down to one-fourth inch is usually employed. If the stone is
+of good quality the maximum size may be but 1-1/2 inches, but soft or
+even medium stone of that size are likely to crush under traffic. The
+stone for the base course should preferably be from 3 inches down, but
+any available size will be satisfactory if the layer is well rolled
+and bonded. The base course is constructed in the same manner as
+water-bound macadam and any material satisfactory for the base course
+of macadam will serve for the base course of mixed macadam. Screenings
+having good bonding properties will also be required for the base
+course.
+
+=Mixing and Wearing Surface.=--Several methods are employed in mixing
+the wearing surface. The simplest is to mix by hand with shovels. The
+aggregates are heated in improvised heaters which may consist of
+nothing more than a metal pipe two or three feet in diameter, around
+which the stone is piled. The mixing platform is usually a metal plate
+sometimes arranged so that it can be heated by means of a fire
+underneath. The bituminous material is heated in kettles. For some
+mixtures, the stone is not heated, but the bituminous material is
+always heated. The batch of stone is placed on the mixing platform,
+the bituminous material added and the materials mixed by hand.
+
+Machine mixing is practiced much more extensively than hand mixing,
+being both more rapid and cheaper. The mixer is similar to a concrete
+mixer except that the drum is arranged so that it can be heated. The
+hot stone and the bituminous binder are put into the drum and mixed
+for the requisite length of time. Sometimes the stone is mixed cold,
+the bituminous material only being heated.
+
+=Placing the Wearing Surface.=--The hot mixture is carted to the road
+and spread to such thickness that after rolling the wearing surface
+will be not less than two inches thick. The hot mixture is dumped and
+then spread by means of shovels to the approximate thickness and the
+spreading completed by means of rakes. The surface is then rolled
+either with a tandem or a three-wheeled roller until thoroughly
+compressed.
+
+=Seal Coat.=--After the rolling has been completed, the surface is
+covered with hot bituminous cement and dressed with pea gravel or
+stone chips and again rolled. Traffic may be permitted in twenty-four
+hours.
+
+=Characteristics.=--The mixed macadam is a somewhat resilient surface
+of excellent riding qualities and considerable durability for medium
+traffic. It is likely to creep and become uneven when subjected to
+heavy loads. The seal coat will wear off in two or three years and
+will require replacing.
+
+
+IV. Asphaltic Concrete
+
+Asphaltic concrete is a name given to a road surface mixture which is
+composed of graded stone, graded sand and asphalt cement. This type is
+designated as asphaltic concrete because of the analogy of the mixture
+to Portland cement concrete.
+
+Asphaltic concrete is of two general types known as bitulithic, or
+Warrenite, and Topeka asphaltic concrete, respectively, the
+differences being in the nature of the mixture.
+
+=Bitulithic or Warrenite.=--The stone employed for these types is
+graded down from a size about equal to one-half of the thickness of
+the wearing course, and stone passing a 1-1/4 or 1-1/2-inch screen is
+usually specified. From the maximum size the stone is graded down to
+the finest particles produced by the crusher. The range of sizes of
+stone will vary with the source of the supply, and in order to secure
+the desired density in the mixture, varying amounts of graded sand and
+mineral dust, such as ground limestone or Portland cement, are added
+to the broken stone. Usually the resulting mixture contains less than
+fifteen per cent of voids, and to this carefully graded mineral
+aggregate there is added enough asphalt cement to bind together the
+particles.
+
+=Topeka Asphaltic Concrete.=--In this type of asphaltic concrete, the
+mineral aggregate consists of a mixture of carefully graded sand and
+of broken stone of such size that all will pass a one-half-inch screen
+and graded down to the fine dust produced by the crusher. To this
+mixture is added about nine per cent of Portland cement or limestone
+dust. The voids in the mixture are usually about twenty-five per
+cent.
+
+It will be seen that the essential differences between the Bitulithic
+and Topeka types are these: the Topeka type contains a larger
+percentage of voids and stone of a smaller maximum size than the
+Bitulithic. Both types have been extensively employed for city paving,
+but the Bitulithic and Warrenite types have also been used to some
+extent for rural highways. The Topeka type has been used but little
+for rural highways.
+
+=Foundation.=--The foundation for the asphaltic concrete may be an old
+macadam road, a base course constructed of broken stone or Portland
+cement concrete, the latter being used much more extensively than
+either of the other types.
+
+Sometimes asphaltic concrete is used for resurfacing water-bound
+macadam or gravel roads when the traffic has increased to the point
+where the cost of maintenance of the water-bound macadam has become
+excessive. The existing surface is repaired and the cross section is
+restored, or possibly flattened somewhat.
+
+=Placing the Surface.=--The stone, sand and asphalt cement are heated
+to the required temperature and combined in the proper proportions and
+are then thoroughly mixed by a mechanical mixer. The mixture is hauled
+directly to the road and is dumped and spread by means of rakes. It is
+then rolled thoroughly while still hot, a three-wheeled roller being
+most satisfactory. After rolling, a seal coat of hot asphalt cement is
+spread over the surface and covered with hot stone chips about 1/4
+inch in size. The surface can be opened to traffic immediately after
+the surface has been completed.
+
+=Characteristics.=--The asphaltic concrete surface is of excellent
+riding properties, is easily repaired and of moderate durability. It
+is a particularly desirable surface for pleasure automobile riding and
+for horse drawn traffic.
+
+
+
+
+CHAPTER XI
+
+MAINTENANCE OF HIGHWAYS
+
+
+Proper maintenance of highways is equally important with proper
+construction. With nearly all types of road construction, the need for
+maintenance arises soon after the surface is placed under traffic and
+is continuous thereafter. The nature and amount of maintenance work
+varies greatly among the several types of surface and the organization
+suitable for a system of highways will depend to a considerable extent
+upon the kinds of surfaces that are to be maintained.
+
+The upkeep of a road may be conveniently considered as of two kinds,
+viz., (1) that which has to do with the wearing surface and earth
+shoulders or berms upon which there is some traffic and (2) that which
+has to do with the side ditches and drainage structures and keeping
+the roadside in presentable condition. Both kinds of work are usually
+carried out by the same organization, but whereas the nature of the
+work indicated under (1) will vary with the type of wearing surface
+and with all variations in traffic, that which is indicated under (2)
+will be nearly constant in any locality.
+
+
+ORGANIZATION FOR MAINTENANCE
+
+Maintenance of highways is preferably under the administration of the
+same authority as construction and when an improvement is undertaken
+under the jurisdiction of a State Highway Department, the completed
+improvement is ordinarily maintained under the state authority. If
+the improvement is made by county authorities, the maintenance is also
+carried out under county authority.
+
+The nature of the organization of maintenance forces is dependent upon
+the kind of roads to be cared for and must of necessity be varied in
+any instance as conditions demand. In general, either maintenance
+gangs or patrolmen are employed and often both are used on the same
+road system.
+
+=Patrol Maintenance.=--Where this system is in operation, the highway
+system is divided into patrol districts of from six to eighteen miles
+of highway and a single patrolman is placed in charge of each
+district. He is provided with all of the necessary tools and materials
+required in his district and performs all of the work required in the
+ordinary upkeep of the highway. He should work under the direction of
+the county engineer or the district engineer for the state highway
+department, because his work involves the use of materials and
+processes requiring technical supervision.
+
+=Gang Maintenance.=--The maintenance gang may be employed for some
+types of road surface in lieu of the patrolman or with other types of
+surface may be employed to supplement the work of the patrolman. The
+maintenance gang consists of three to ten men and is furnished all of
+the tools and materials required for the particular kind of work they
+do. Ordinarily the gang goes over the roads assigned to it once each
+season and performs those repair operations requiring more work than
+the patrolman can find time for. The work of the maintenance gang like
+that of the patrolman should be under engineering supervision.
+
+=Maintenance of Earth, Sand-clay, Gravel and Macadam Roads.=--The
+ordinary upkeep of earth, sand-clay, gravel and macadam surfaces is
+most readily accomplished by the patrol method, since constant care is
+required to keep the roads in a condition of maximum service ability.
+
+The tools required for each patrolman may include the following:
+
+  1 shovel              1 spade
+  1 stone rake          1 pick
+  1 scythe              1 tamper
+  1 or more road drags  1 mowing machine for cutting weeds
+  1 wheelbarrow           (sometimes)
+  1 light truck         1 small kit carpenter's tools
+
+The work of the patrolman consists in keeping the surface of the road
+smooth by dragging, repairing chuck holes by tamping in fresh material
+of the appropriate kind, keeping the ditches and culverts free from
+obstruction, cutting weeds and repairing bridge floors if they are of
+plank construction. Removal of snow drifts is sometimes a part of the
+patrolman's duty, but more often that is done by special gangs.
+Usually the patrolman is authorized to hire teams for dragging and
+cutting weeds.
+
+When an earth road requires to be re-graded so as to restore the
+cross-section and deepen the ditches, a gang is sent in to perform
+that work, as it is obviously impossible for the patrolman to perform
+work, of that kind.
+
+If the gravel road is being maintained with a bituminous carpet coat,
+the patrolman will be furnished the necessary tools to enable him to
+patch the surface with bituminous material as necessity requires.
+
+When the surface deteriorates to such an extent that a new carpet coat
+is required, the gang system is employed for all work connected with
+resurfacing, instead of attempting to have the work done by patrolmen.
+
+The maintenance of the macadam road is carried out in much the same
+manner as that of the gravel road. The binder of stone dust or clayey
+sand is renewed as often as it is swept off by traffic. Depressions or
+ruts are repaired by first loosening the surface with a pick and then
+adding broken stone and screenings to restore the surface.
+
+When the macadam reaches the stage where entire resurfacing is
+needed, the work is performed by gangs organized and equipped for the
+purpose; and likewise when the surface is being maintained with a
+bituminous carpet, the renewal of the carpet coat is performed by
+special gangs, but the ordinary upkeep of the surface by patching is
+handled by a patrolman.
+
+
+MAINTENANCE OF MIXED BITUMINOUS SURFACES
+
+[Illustration: Fig. 22.--Scarafier used in Gravel Road Maintenance]
+
+These types of surface can be kept in satisfactory condition if they
+are carefully repaired once or twice each season. This work requires
+considerable experience and some special equipment, not ordinarily
+supplied to patrolmen. A gang is organized for the work and supplied
+with the proper equipment. They go over the roads and patch all worn
+places, generally first removing the wearing surface entirely in the
+area affected.
+
+The wearing surface mixture is then prepared and tamped or rolled into
+place. If the area affected is small, tamping is satisfactory, and
+when the area is considerable, rolling is employed. The upkeep of the
+side roads may be accomplished by the same gang but is preferably
+taken care of by patrolmen, who do not attempt any but minor repairs
+to the wearing surface.
+
+
+MAINTENANCE OF BRICK AND CONCRETE ROADS
+
+On brick and concrete roads, the principal work on the wearing surface
+consists in filling the cracks with a suitable bituminous material.
+This work is done by patrolmen or by special gangs and generally will
+be done once each year. The upkeep of the side roads is cared for by
+patrolmen who drag the side roads and cut the weeds as occasion
+requires.
+
+
+
+
+INDEX
+
+
+  Administration county; 15
+    federal; 17
+    highway; 13
+    state; 16
+    township; 13
+
+  Aesthetics; 62
+
+  Aggregate, fine; 101
+
+  Aggregate, coarse; 100
+
+  Air resistance; 51
+
+  Alignment; 46
+
+  Applying bituminous binder; 122
+
+  Asphaltic concrete; 128
+
+  Asphalt, natural; 117
+    liquid; 118
+    petroleum; 117
+
+  Assessments, special; 19
+    zone method; 20
+
+
+  Bedding course, green mortar; 111
+    sand mortar; 111
+    sand bedding mortar; 111
+
+  Binder for gravel; 75
+
+  Bitulithic or warrenite; 128
+
+  Bitumen; 118
+
+  Bituminous coatings on concrete; 105
+
+  Bituminous fillers; 112
+
+  Bituminous road materials and their use; 116
+
+  Bituminous surfaces; 96, 120
+
+  Blade grader; 69
+
+  Bonding; 87
+
+  Bonds, annuity; 26
+    serial; 27
+    sinking fund; 25
+
+  Box culverts; 39
+
+  Brick roads; 113
+
+  Brick, repressed; 107
+    tests of 108;
+    vertical fiber; 107
+    vitrified; 106
+    wire-cut-lug; 108
+
+  Broken stone road surfaces; 89
+
+
+  Cement, asphaltic; 118
+
+  Cement concrete roads; 98
+
+  Cement grout filler; 112
+
+  Characteristics, asphaltic concrete; 129
+    bituminous macadam; 125
+    broken stone; 97
+    concrete; 105
+    mixed macadam; 128
+    sand clay; 78
+
+  Classes of bituminous materials; 116
+
+  Classification according to consistency; 117
+
+  Clay and cement concrete pipe; 39
+
+  Coal tar; 116
+
+  Concrete, asphaltic; 128
+
+  Concrete materials; 100
+
+  Concrete pipe; 39
+
+  Control of erosion; 61
+
+  Costs; 70
+
+  County administration; 15
+
+  Cross sections; 60, 65
+
+  Culverts; 56
+
+  Curing concrete; 103
+
+
+  Design, broken stone roads; 89
+    concrete roads; 99
+    earth roads; 42
+
+  Desirability of road bonds; 27
+
+  Development of traffic; 2
+
+  Drainage, necessity of; 29
+
+  Drainage of roads; 29
+
+
+  Earth roads, in arid regions; 72
+    humid regions; 65
+    value of; 73
+
+  Earth works; 92
+
+  Education, rural; 6
+
+  Effect of grades; 54
+
+  Elevating grader; 66
+
+  Elevating grader work; 68
+
+  End walls for culverts; 39
+
+  Energy loss on account of grades; 57
+
+  Entrances, farm; 37, 61
+
+  Expansion joints; 104
+
+
+  Farm entrance culverts; 37
+
+  Federal administration; 17
+
+  Fillers; 118
+
+  Finance, highway; 19
+
+  Fine aggregate; 101
+
+  Finishing surface of concrete; 122
+
+  Foundation, asphaltic concrete; 129
+    brick; 109
+    macadam; 93
+    mixed macadam; 126
+    penetration macadam; 123
+    Telford; 94
+
+
+  Gang maintenance; 131
+
+  Grader, Maney; 67
+    use of; 69
+
+  Gravel, ideal; 81
+    natural; 83
+    roads; 74
+
+  General taxation; 24
+
+  Good roads and commerce; 7
+
+  Green concrete bedding course; 111
+
+
+  Highway administration; 13
+
+  Highway finance; 19
+    maintenance; 130
+
+
+  Importance of design; 30
+
+  Ideal road gravel; 81
+
+  Inter-city traffic; 5
+
+  Inter-county and inter-state traffic; 5
+
+  Internal resistance; 50
+
+  Intersections; 46
+
+
+  Laying tile; 35
+
+  Length of culvert; 37
+
+  Liquid asphalt; 118
+
+  Local farm to market traffic; 4
+
+
+  Macadam; 89
+
+  Maintenance, concrete; 105
+    earth roads; 70
+    general; 131
+    gravel roads; 88
+    macadam; 96
+    of highways; 130
+    patrol; 131
+
+  Maney grader; 67
+
+  Marginal curb; 113
+
+  Measuring materials; 101
+
+  Metal pipe; 38
+
+  Mixing wearing surface; 127
+
+  Mixtures; 117
+
+
+  Natural asphalt; 117
+    gravel; 79
+
+  Necessity for planning; 42
+    drainage; 29
+
+
+  Patching; 122, 125
+
+  Patrol maintenance; 131
+
+  Pebbles, size of; 80
+
+  Petroleum asphalt; 117
+
+  Placing asphaltic concrete; 129
+
+  Placing broken stone; 94
+
+  Placing concrete; 102, 103
+    mixed macadam; 127
+
+  Plans for roads; 43
+
+  Preliminary investigation; 44
+
+  Preparation of earth foundation; 102
+    of road; 85
+
+  Private entrances; 61
+
+  Properties of stone; 90
+
+  Proportions for concrete roads; 101
+
+  Purpose of highways; 1
+
+
+  Reinforced concrete box culverts; 39
+
+  Reinforcing; 104
+
+  Repressed brick; 107
+
+  Road oils; 117
+
+  Road plans; 43
+
+  Rocks, kind of, for macadam; 91
+
+  Rolling, macadam; 95
+
+  Rolling resistance; 50
+
+  Run-off; 31
+
+  Rural education; 6
+
+  Rural social life; 7
+
+
+  Safety consideration; 58
+
+  Sand bedding course; 111
+
+  Sand clay and gravel road; 74
+
+  Sand mortar bedding course; 111
+
+  Seal coat; 127
+
+  Serial bonds; 27
+
+  Sinking fund bond; 25
+
+  Slip scraper; 67
+
+  Special assessments; 19
+
+  Specifications; 119
+
+  Spreading screenings; 95
+
+  State administration; 16
+
+  Stone, use of; 92
+
+  Surface drainage; 30
+
+  Surfaces, bituminous; 120
+
+  Surface method; 87
+
+  Superelevation; 47
+
+
+  Tests, brick; 108
+
+  Tile drains; 35
+
+  Topeka asphaltic concrete; 128
+
+  Tractive resistance; 52
+
+  Trench method; 85
+
+  Truck operation costs; 9
+
+  Types of culverts; 38
+
+
+  Underground water; 34
+
+  Undulating roads; 58
+
+  Use of blade grader; 69
+
+  Utilizing natural gravels; 83
+
+
+  Value of earth roads; 73
+
+  Variation in rainfall; 64
+
+  Variation in soils; 63
+
+  Vehicle taxes; 24
+
+  Vertical fiber brick; 107
+
+  Vitrified brick roads; 106
+
+  Vitrified brick; 106
+
+
+  Water gas tar; 117
+
+  Width of roadway; 59
+
+  Wire-cut-lug brick; 108
+
+
+  Zone method of assessing; 20
+
+       *       *       *       *       *
+
+[Transcriber's Notes:
+
+The transcriber made these changes to the text to correct obvious
+errors:
+
+   1. p.   5, accomodate --> accommodate
+   2. p.  39, guage --> gauge
+   3. p.  46, enbankment --> embankment
+   4. p.  63, tought --> tough
+   5. p.  68, absorbant --> absorbent
+   6. p.  73, persistant --> persistent
+   7. p.  77, indispensible --> indispensable
+   8. p. 119, aspealt --> asphalt
+   9. p. 127, repaid --> rapid
+  10. p. 130, Vetrified brick; 105 --> Vitrified brick; 106
+  11. p. 130, Virtical --> Vertical
+
+End of Transcriber's Notes]
+
+
+
+
+
+End of the Project Gutenberg EBook of American Rural Highways, by T. R. Agg
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