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.