U. S. D. A.
Exhibit of the Office of
Public RoadB%
AlaflkcuYukon^Pacific
Expos it ion, 190$
U. S. DEPARTMENT OF AGRICULTURE,
OFFICE OF PUBLIC ROAD8,
LOG;LN WALLER PAGE, DIRBCTOK.
EXHIBIT OF THE
OFFICE OF PUBLIC ROADS
AI^\SKA-YUKO:s -PACIFIC EXPOSITION.
WASHINGTOl
GOVERNMENT i . FICE
19"
OFFICE OF PUBLIC ROADS.
LOGAN WALLER PAGE, Director.
ALLEBTON S. CUSHMAN, Assistant Director and Chemist.
W. GAEL WYATT, Chief Clerk.
VEENON M. PEISCE, Chief Engineer.
J. E. PENNYBACKER, Jr., Chief of Road Management.
MAUBICE O. ELDBIDGE, Assistant Chief of Road Management.
PHILIP L. WOBMELEY, Testing Engineer.
EI>WIN C. E. LORD, Petrographer.
BENJAMIN F. HEIDEL, Assistant Engineer.
PBEVOST HUBBAED, Assistant Chemist.
WM. W. SNIFFIN, Editor and Librarian.
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1 909.
PLATE I.
Issued September 10, 1909.
U. S. DEPARTMENT OF AGRICULTURE,
OFFICE OF PUBLIC ROADS,
LOGAN WALLER PAGE, DIRECTOR.
EXHIBIT OF THE
OFFICE OF PUBLIC ROADS.
ALASKA- YUKON -PACIFIC EXPOSITION.
WASHINGTON:
GOVERNMENT PRINTING OFFICE
1909.
At
LETTER OE TRANSMITTAI.
U. S. DEPARTMENT OF AGRICULTURE,
OFFICE OF PUBLIC ROADS,
Washington, D. C., July lJ h 1909.
SIR: I have the honor to transmit herewith a manuscript con-
taining data explaining the exhibit of this office at the Alaska-
Yukon-Pacific Exposition. The models of the various kinds of
roads are explained in detail, and information is included about
several different road machines also. I believe that this publication
will be of a highly instructive nature, and it is therefore requested
that it be printed as a separate bulletin of this office.
Respectfully,
L. W. PAGE, Director.
Hon. JAMES WILSON,
Secretary of Agriculture.
CONTENTS.
Page.
Introduction 5
Earth roads 5
Sand-clay roads 7
Gravel roads 8
Telford roads 9
Macadam roads 10
Completed macadam road 12
Gravel macadam roads 12
Macadam roads with V-shaped foundation 13
Burnt-clay roads 14
Oiled earth roads 15
Treated macadam roads .- 16
Tarred or oiled roads 16
Tarred roads penetration method ^ 16
Tarred roads Glad well method 17
Tar, oil, or asphalt roads 17
Tar-slag roads 18
Roads in Rock Creek Park, District of Columbia 18
Road machinery 19
Crushing plants 19
Wheeled scrapers 21
Road machines or graders 21
Elevating graders 23
3
ILLUSTRATIONS.
PLATES.
Page.
PLATE I. Macadam road, Rock Creek Park, District of Columbia Frontispiece.
II. Fig. 1. Model of earth road, showing split-log drag and road grader
in operation. Fig. 2. Model of sand-clay road 8
III. Fig. 1 .Model of gravel road. Fig. 2. Model of Telford road 8
IV. Gravel road in park, Richmond, Ind 8
V. Fig. 1. Model of macadam road. Fig. 2. Model of gravel macadam
road 8
VI. Model of macadam road with exact model of road roller in operation. 16
VII. Fig. 1. Model of macadam road with V-shaped foundation.
Fig. 2. Model of burnt-clay road : 16
VIII. Macadam road with V-shaped foundation at Russell, Mass 16
IX. Fig. 1. Model of oiled earth road. Fig. 2. Model of tarred mac-
adam road. 16
X. Fig. 1. Model of tarred macadam road penetration method.
Fig. 2. Model of tarred macadam road Glad well method 18
XI. Fig. 1. Model of sand-bituminous macadam road. Fig. 2. Model
of tar-slag macadam road 18
XII. Fig. 1. Model of section of Rock Creek Park, District of Columbia.
Fig. 2. Model of quarry 18
TEXT FIGURES.
FIG. 1 . Exact model of portable crushing plant in operation 20
2. Exact model of wheeled road scraper 21
3. Exact model of road grader 22
4. Exact model of elevating road grader 23
4
EXHIBIT OF OFFICE OF PUBLIC ROADS.
ALASKA- YUKON-PACIFIC EXPOSITION,
INTRODUCTION.
In assembling the very complete exhibit shown by the Office of
Public Roads of the United States Department of Agriculture, those
rr-ponsible for this feature of the Federal Government's contribu-
tion to the Alaska- Yukon-Pacific Exposition have sought to put on
view such striking examples in miniature of model roads that visitors
will not merely immediately appreciate the beneficent effects of
perfected highways, but will at the same time be able to understand
the methods of their construction.
Visitors will probably decide that the most striking feature of the
display is the miniature model of a section of Rock Creek Park
the most beautiful of the many breathing spots in the District of
Columbia. In this handsome miniature is shown not only some of
Rock Creek Park's most picturesque landscape features but also
some of the best examples obtainable of scientific road construction.
The model includes the famous Bowlder Bridge, the Pebble
Bridge, and one other, with Rock Creek passing beneath them and
winding in and out among the hills.
Picturesque, and yet practical, as is this handsome centerpiece of
the exhibit, it will not attract as much attention from scientific road
builders as will the miniature sections illustrating every type of road
now in use.
Among the types thus illustrated, built to exact scale, are macadam,
bituminous maoadam, tarred macadam, Telford, slag asphalt, slag
tar, oiled macadam, oiled earth, sand clay, burnt clay, and dragged
earth.
Inasmuch as there are approximately 1,975,000 miles of earth road
in the United States out of a total mileage of 2,150,000, a model of
an earth road is appropriately first described.
EARTH ROADS.
(Platell, fig. 1.)
This model illustrates the construction and maintenance of an
earth road, and is built on a scale of 1J inches to the foot, or one-
eighth full size, the various sections which go to make up the com-
OK PUBLIC ROADS.
plete model showing the roadbed and each succeeding step in the
construction of this type of highway.
It will be noted that Section A shows the old and unimproved road-
bed.
Section B illustrates a section of earth road under improvement
with a road machine or grader, the width of the section shown being
equivalent to 20 feet of finished surface.
Section C illustrates an earth road which, though surfaced by a
road machine, has rutted under heavy traffic and is being maintained
by the use of the split-log drag.
In the road illustrated by Sections B and C, the crown, or slope
from center to sides, is equivalent to 1 inch to the foot. The surface of
the section labeled "A" is characteristic of altogether too many earth
roads, the center being several inches lower than the sides. This
faulty condition makes it impossible for the water to run from the
surface; and even if this were possible there are no roadside ditches
to carry it away. In consequence, the road is usually full of puddles
and cut up with ruts and mud holes.
Section B illustrates the use of a road machine or grader in open-
ing roadside ditches and in shaping the road surface so it will shed
water. This machine is equivalent to the labor of many men, and it
does the work far better than can be done with shovels and picks.
The road machine should be used when the ground is damp and
soft. In dry weather far more power is required to draw it than in
wet, and clods when placed on the road in a dry condition make a
most unsatisfactory surface, turning to mud with the first heavy rain.
Because of these conditions, the road should be shaped in the spring
or early summer, thus permitting the roadbed to pack and bake dur-
ing the heated period in order that it may better hold up traffic
during the winter rains.
An earth road should have a width of at least 20 feet better still,
24 or 30. If the road be narrow there is a tendency to use but the
narrow central portion, and wagons running in " the same old rut "
soon create a water-holding depression. The surface drainage can be
provided for by giving the road an average crown or slope from
center to sides of 1 inch to the foot. On some soils the crown could
be even less than that, but seldom greater. Unless the road runs
through swampy or wet districts, side ditches, as shown in Model B,
should be built. They can be made and maintained with a road
machine, but care should be taken that they have a fall sufficient to
carry the water along the side of the road. One use of the road
machine will not keep the ordinary earth road in permanent repair.
The machine should be used several times during the spring and early
summer.
EXHIBIT OF OFFICE OF PUBLIC ROADS. 7
For continuous maintenance the split-log drag shown in Section C
has been devised. This little model has been built to the same scale
as the road model 1J inches to the foot. It can be best made from
a log 7 or 8 inches in diameter and from 6 to 8 feet long. The log
>hould be carefully split and the halves fastened together with stakes,
the flat sides vertical and facing to the front. The logs, though of
the same length, are attached so that the end of the rear log is from
16 to 20 inches nearer to the" center of the road than the first one.
An ordinary trace chain and set of doubletrees is then attached.
When the horses move forward the drag should slide along the road
at an angle of about 45, the forward end being nearest to the ditch
and thereby moving the earth toward the road center.
In the construction of this implement care should be taken to make
it so light that one man can lift it. The best material is a dry red
cedar log, though red elm and walnut are excellent, and box elder, soft
maple, or elm willow are superior to oak, hickory, or ash. A board
platform is usually placed on the cross stakes, helping to strengthen
the implement and giving a place for the driver to stand. After a
little practice a man will learn how to best distribute his weight so as
to make the drag cut, spread, and pack the earth properly.
Dragging up one side of the road and down the other across the ruts
is all that should be undertaken the first time, but this should be re-
peated after each heavy rain. As a mile of road can be dragged in a
few minutes, the split-log drag provides a simple and inexpensive
method of road maintenance. If it be used in conjunction with the
road machine, fairly good earth roads can be secured at a nominal
expense. If 50 cents a mile for dragging be considered a fair figure,
and if the road be dragged a dozen times a year, it follows that road
maintenance by this method will not cost more than $6 per mile per
annum. Some really remarkable results have been accomplished
with the drag without the aid of the scraper. Farmers' Bulletin 321,
" The Use of the Split-log Drag on Earth Roads," deals fully with
this subject.
SAND-CLAY ROADS.
(Plate II, fig. 2.)
This model shows the sand-clay road construction and, like all
other models, is on the scale of 1J inches to the foot.
Section A represents an unimproved sand road about 22 feet wide.
Section B represents an old sand road slightly rounded up to re-
ceive the clay, the center being 4 inches higher than the sides.
Farmers' bulletins will be sent free to any address in the United States on
application to a Senator or Representative in Congress or to the Secretary of
Agriculture, Washington, D. C.
8 EXHIBIT OF OFFICE OF PUBLIC ROADS.
Section C shows a portion of road covered with clay to a depth of 6
inches.
Section D illustrates the harrowing or mixing process.
Section E shows the completed road.
An inspection of this model shows that the bottom of the ditch of
a completed road of this type would be about 1 foot lower than the
road at the center, this giving an average slope of 1J inches to the
foot.
In a generality of cases sand-clay roads are built on sandy founda-
tions, and it is usually the practice to place the clay on the unim-
proved foundation, but better results will be obtained if the sandy
foundation is given a slight crown; making the center from 4 to 6
inches higher than the side ditches. If this is neglected," more clay
will be necessary to give the road the needed crown and that is ex-
pensive, especially if the material has to be hauled a considerable
distance.
If the foundation is of clay the process may be reversed with sat-
isfactory results, the clay road being plowed and harrowed, covered
with from 4 to 6 inches of sand, and worked with a disk or tooth
harrow when the ground is wet until both have been thoroughly
mixed. When the mixing has been done the surface is brought to
a crown with a road machine and covered with a thin layer of sand.
After the first two or three rains another sand coat should be applied,
this method producing a smooth, cheap, and satisfactory road suit-
able for light traffic.
Farmers' Bulletin No. 311, " Sand-clay and Burnt-clay Koads,"
gives full information on this subject, if more be desired.
GRAVEL ROADS.
(Plate III, fig. 1; Plate IV.)
The construction of a gravel road having shoulders is illustrated
by this model. The model, being 30 inches wide between ditches, is
equivalent to a 20-foot road, the traveled way representing a width
of 12 feet.
Section A represents the prepared earth roadbed, showing a sub-
grade with the center 10 inches higher than the bottoms of the side
ditches and illustrating at the same time the method of constructing
the shoulders so as to hold the gravel roadbed in position. These
shoulders should be built upon the subgrade to a depth of about 4
inches.
Section B shows the first course of gravel, laid to a depth of 4
inches in the center and about 3 inches at the sides.
Section C represents the second course, the material being about
2 inches in depth at the center and 1J inches at the sides. The crown
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1909.
PLATE
FIG. 1. MODEL OF EARTH ROAD, SHOWING SPLIT-LOG DRAG AND ROAD GRADER IN
OPERATION.
FIG. 2. MODEL OF SAND-CLAY ROAD.
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1909.
PLATE
FIG. 1. MODEL OF GRAVEL ROAD.
FIG. 2. MODEL OF TELFORD ROAD.
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1909.
PLATE IV.
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1909.
PLATE V.
FIG. 1. MODEL OF MACADAM ROAD.
FIQ. 2. MODEL OF GRAVEL MACADAM ROAD.
EXHIBIT OF OFFICE OF PUBLIC ROADS. 9
01 eeiiler nf the road thus represented i> about () inches higher than
the surface of the road G feet from the center, which gives an average
-lope of 1 inch to the foot.
There is financial wisdom in thu> preparing a foundation for a
irravel road, because- it >aves material. If the gravel is simply spread
on the unimproved roadbed far more will be required, and if it is
-pread without having shoulders constructed to hold it in place
wagons will rut it and horses kick it away until in a short time the
ditches will be full of gravel and the denuded road surface will be
cut up with ruts.
With plenty of gravel available, it is wise to build shoulders from
: to *\ feet in width and with a depth of from 4 to 6 inches at the
inside edge, the depth of the gravel diminishing toward the side
ditches. In some cases thin boards from 4 to 6 inches wide are
placed along the inner edge of the shoulder to hold it in position until
it i> packed and the material has been spread. The material for the
foundation course is then spread to a depth of from 4 to 8 inches in
the center and from 4 to G inches at the sides. Creek or river gravel
may be used for this course, but it is better to use bank or pit gravel,
which possesses sufficient clay or earthy matter to bind it together.
When the foundation course has been prepared, the surface course
>hould fa spread to a depth of from 3 to 4 inches in the center and 2 to
o inches at the sides. It should be of the very best quality and free
from large pieces. In some instances it is advisable to screen the
gravel into two or three sizes, using the larger sizes for the founda-
tion course. All sand, clay, or earthy matter should be removed.
The l>est and cheapest method of screening gravel is by the rotary
M-reen having holes of 2^, H. and f inches. The best season for build-
ing gravel roads is in the spring, as they will then consolidate during
the summer and be in better condition to withstand the fall and
winter rains.
TELFORD ROADS.
Plate III, fig. 2.)
Here is illustrated the construction of a Telford road having a
width of 12 feet, with shoulders 4 feet in width, or 5 feet from the
edge of the stone surface to the bottom of the side ditches.
Section A illustrates the prepared subgrade, 12 feet wide and
excavated to a depth of 14 inches. The foundation being 5 inches
higher in the center than at the sides gives the same crown as the
finished surface.
Section B represents the Telford ba>e. the depth of material being
7 inche.-.
Section C illu>trate- the No. 1 course of broken stone, laid to a
depth of 4 inche-
380009 2
10 EXHIBIT OF OFFICE OF PUBLIC ROADS.
Section D illustrates the No. '2 or second course, 3 inches deep.
Section E illustrates the finished road after being surfaced with
screenings and stone dust, this last course adding nothing to the
thickness of the road, as the fine material is washed and rolled
firmly into the No. 2 course of broken stone.
In the preparation for a Telford road, the bed is excavated from
the earth surface, as in the macadam road, side ditches and shoulder
drains being built the same.
The radical difference between the Telforcl and the macadam road
lies in the paved or hand-laid foundation of the first named, the
stones forming a base from 5 to 8 inches thick.
The model of which this treats illustrates a Telford road with a
base 7 inches thick, the paved foundation being about two-thirds the
road's total thickness.
Telford's original method provided for a flat foundation, his pave-
ments being deeper in the middle than at the sides, the stone in a
16-foot road being 8 inches deep in the middle and 5 inches deep at
the sides. Modern practice, however, calls for stone of uniform
depth, the surface of the base being parallel to the surface of the
finished road.
In the construction of such a base as that illustrated, the various
stones should be of the following sizes : Length, from 8 to 12 inches ;
depth, from 5 to 8 inches ; thickness, at the base from 3 to 6 inches
and at the top from 1 to 3 inches. They are to be laid lengthwise
across the road on their broadest bases, every other course breaking
joints as nearly as possible. Uneven points must be broken off and
spalls used to wedge the surface together until a firm foundation has
been secured.
Sections C, D 5 and E are built in the same manner as the macadam
road, though not so thick, for roads possessing a Telford base do not
require a macadam surface of more than from 4 to 6 inches after
consolidation.
MACADAM ROADS.
(Plate V, tig. 1.)
This model illustrates a macadam road 12 feet wide and surfaced
with 8 inches of consolidated stone, the shoulders being equivalent to
4 feet 4 inches.
Section A represents the prepared subgrade.
Section B represents the first course of broken stone, spread to a
depth of about 5 inches.
Section C represents the second course, spread to a depth of 3
inches.
EXHIBIT OF OFFICE OF PUBLIC ROADS. 11
Iii the model the crown or slope of the foundation is the same as in
the finished road. giving an average fall of three-fourths of an inch
to the foot from center to sides.
In preparing for the construction of a road of this type it is ad-
visable to roll the foundation thoroughly when the soil is damp so
that all soft spots may be found and filled and the ground firmly and
smoothly prepared for the first layer of stone. Shoulders are built
on either side to hold the macadam in place, either by excavating the
body of the old roadbed or by piling up the earth as the work pro-
gresses. The shoulders should never be less than 3 or 4 feet wide, if
possible 6 or 8. If sufficiently wide and having a slope of not more
than 1 inch to the foot, they will be used in dry weather for light
traffic, thus relieving the macadam of fast travel, which causes it to
ravel.
In every case the bottoms of the side ditches should be lower than
the road foundation to insure speedy drainage. If the road is built
of clay or heavy soil shoulder drains should be built at low places
to lead water from the foundation. The drains are filled with
crushed rock or gravel and the side ditches should be shallow, but
wide, their construction being based on the volume of water they
may be expected to carry.
The Xo. 1 crushed rock for the foundation course may vary in
size from 1J to 2^ inches in diameter, but never larger. The depth
of this course must depend upon conditions. If built on light grav-
elly soil where light traffic may be looked for, a depth of 3 or 4 inches
is sufficient, but for heavy soils and heavy traffic the course should
be from 4 to 6 inches deep after rolling. For roads 12 feet wide
or less the depth of material should be uniform throughout, but if
the road be from 14 to 16 feet the total depth of both courses may be
reduced to 6 inches for an 8-inch road and 4 inches for a 6-inch road.
After the foundation course has been thoroughly rolled from the
sides to the center, the second course, varying in size from J to 1^
inches, is applied. While rock of inferior quality may be used for
the foundation course, nothing but the best hard and tough rock
should be used for the surface. It should not only be able to resist
the pounding and grinding of traffic, but should have a high cement-
ing value so that the fine particles will bind the surface into a water -
ahedding cru>t.
The final course of screenings does not add to the depth of the
road, which when completed should be flush with the earth shoulders.
The total depth of roads of this type should vary from 4 to 12 inches,
construction being governed by local conditions, but the average
depth of such roads in the United States is not more than 6 inches.
12 EXHIBIT OF OFFICE OF PUBLIC ROADS.
COMPLETED MACADAM ROAD.
(Plate VI.)
By this model is illustrated a completed macadam road with a 12-
foot macadam surface and shoulders 4 feet 4 inches wide, to total
road width of 20 feet 8 inches.
There is wisdom in building wide roads, for they expose a larger
surface to traffic and require less care than narrow ones, the traffic
being more evenly spread because of the greater area of road surface.
The initial cost of wide roads is of course greater than that of narrow
ones, but there is a saving in maintenance, especially if the narrow
road be so scant that teams can not pass and must travel in the
same rut.
In spreading the No. 2 or surface-bonding course, the stone may
vary from three-fourths of an inch down to dust. It is not necessary
to separate the dust from the screenings unless there be an excess of
dust. If too much is used the road will be sloppy in wet weather and
dusty in dry, and if there is not a sufficient quantity of screenings the
road will quickly ravel, especially under fast automobile traffic.
Care and judgment must be exercised in determining the proper
amount of screenings and also in spreading them. One thin layer
should be spread and rolled, and after it has been thoroughly
sprinkled and rolled another should be spread. By continuing this
process until all voids are filled and the surface has been thoroughly
consolidated a waterproof surface will be secured.
On this model is shown a miniature steam roller, the presence of
this tiny facsimile of its gigantic prototype emphasizing the impor-
tance of road rolling. In the long run better aiid cheaper work can
be done v, ith a steam than with a horse roller, and one may also be
used to advantage in road repair w^ork.
If the road surface becomes uneven or rutted it can be spiked by
teeth placed in the wheels of the roller. Then the surface can be
leveled off and resurfaced with another course of No. 2 stone, after
which it may be rolled and again treated with screenings.
Farmers' Bulletin No. 338, " Macadam Roads,'' gives much addi-
tional information on this subject.
GRAVEL MACADAM ROADS.
(Plate V. fig. 2.)
This model illustrates the construction of a gravel macadam road,
built in layers after the macadam method, the miniature represent-
ing a 12-foot road with 4-foot shoulders on either side, the shoulder
depth being 4 inches.
KX II I HIT OF OFFICE OF PUBLIC ROADS. 13
Section .V >hm\> the prepared subgrade, the excavation represent-
ing a width of \'2 feet and a depth of 8 inches.
Section IS represents the first course of gravel, spread to a depth
nf :> inches.
Section C shows the >econd course of h'ner gravel, equivalent to a
depth of 3 inches in the completed road, the shoulders represented
being equivalent to a width of 4i feet. The crown or slope of the
foundation is 5 inches higher in the center than at the sides, an aver-
age of three- fourths of an inch to the foot.
In constructing this type the foundation should be thoroughly
rolled before any gravel i- spread, in order that all depressions may
be found and filled.
Side ditches should be lower than the lowest part of the road
foundation, and drains should be cut through the shoulder and filled
with gravel if the road be built of clay or other heavy soil. They
should be placed 200 or 300 feet apart, or at all low places, their loca-
tions being governed by conditions. Creek or river gravel from
which clay or soil has been removed may be used for the foundation
course, provided gravel possessing sufficient binding clay is used for
the surface course.
In frequent instances good results are secured by separating the
gravel into three sizes, as for a macadam road, using the larger sizes
for the foundation and the finer for the second and the binder course^
The gravel should be wet when spread and rolled. The surface course
should be composed of material not larger than from 1 to H inches
in diameter, and enough clay or fine gravel should be added to it to
bind it together. If too much clay be present, however, the road will
be muddy and sticky in wet weather and dusty in dry.
A judicious use of the split-log drag will keep this type of road
in repair at a small cost.
.MACADAM ROADS WITH VSIIAI'KD FOTNDATIOX.
Plate VII. fig. 1 : Plate VIII.
Here is illustrated a 12- foot macadam road with a V-shaped foun-
dation which is constructed of field stones or bowlders.
Section A shows the prepared subgrade ready to receive the foun-
dation stone. The depth of shoulders is 1 foot and the center of
the foundation is 10 inches below the bottom of these shoulders.
tin* slope toward the center being equivalent to 1^ inches to the foot.
Section B represents the completed foundation.
Section (' represents the first course of macadam.
Section I) represents the regular Xo. '2 course of macadam laid
to a depth of 3 inches.
14 EXHIBIT OF OFFICE OF PUBLIC ROADS.
Section E shows the completed surface of a macadam road bonded
with screenings and dust.
The V-shaped macadam road has been constructed by the Massa-
chusetts Highway Commission as a substitute for the Telford
method. It is especially good in heavy clay soils or in low swampy
places where .the foundation can not be depended upon to hold up
the regular macadam road.
In this type of road the foundation is sloped from the sides to the
center rather than from center to sides, as in all other methods of road
construction, and shoulder drains are cut at low places and filled with
bowlders or gravel. Through these drains the water which makes its
way to the foundation is conveyed to the side ditches.
Field stones, bowlders, or broken stone secured from excavations in
the road are used in building the foundation, the larger pieces being
placed in the bottom and the smaller ones on the surface. The total
depth of the foundation is from 18 inches to 2 feet in the center and
from 4 to 8 inches at the sides. The foundation is given a slope or
crown and the crushed stone is then placed on the road, as illustrated
by Plate Y, figure 1, and Plate VI.
In the completed road the crown appears to be higher than in the
ordinary macadam road, but this is on account of the deep side
ditches, the crown really being only about 5 inches higher at the
center than at the sides an average of about three-fourths of an inch
to the foot.
In the model the depth of the first and second courses is equivalent
to 8 inches, but in actual construction the depth of these two courses
frequently amounts to no more than 4 to 6 inches.
BURNT-CLAY ROADS.
(Plate VII, fig. 2.)
This model illustrates the building of a burnt-clay road, the model
being the equivalent of a road 20 feet between ditches, with a burnt -
clay surface 16 feet wide.
Section A shows the old roadbed plowed up and after ridges 18
inches high and 4 feet apart have been thrown across the road.
Section B shows the method of stacking the clay and wood pre-
paratory to burning. A layer of 4-foot cord wood is placed across
the ridges and lengthwise of the road. Then a second layer is laid
across the road, and on this a few clods of clay are placed. A third
layer of wood is then placed with the sticks running lengthwise
along the highway, and 18 inches of clay from the roadside ditches
is placed upon it. Then the flues between the ridges are filled with
bark and light wood and fire is applied. It will require from twenty-
four to thirty-six hours to complete the burning of one section.
KXHIBIT OF OFFICE OF PUBLIC ROADS. 15
Section C shows a piece of road after it has been burned and
before being spread and roiled. It will be noted that the burning
removes the stickiness or plasticity of the clay and leaves it in hard
clinker-like lumps.
Section D illustrates the finished road, smooth and firm and well
crowned, the slope being 1 inch to the foot.
The burnt-clay road, which is confined to the Mississippi Delta
States where stone and gravel is scarce and " gumbo " or " buckshot "
< Inv plentiful, is never muddy in winter unless mud be carried to it
from other roads.
Farmers' Bulletin No. 311, " Sand-clay and Burnt-clay Roads,"
gives full information about this type of highway, if more be
desired.
OILED EARTH ROADS.
< Plate IX. fi. 1.)
This model shows the construction of an oiled earth road, the type
now popular in the California orange belt.
Section A shows the dusty road before improvement.
Section B shows the road plowed to a depth of 6 inches.
Section C illustrates the application of oil to the plowed road.
Section D shows the road after being harrowed and the oil worked
into the loose soil.
Section E shows the completed road after having been thorough!}-
rolled, the crown representing a slope of three-fourths inch to the
foot.
In preparing this road for its final treatment it is necessary first to
bring the surface to the same general crown as for an ordinary earth
road and then to plow and harrow it until all clods, are broken up.
After that has been done the hot oil is applied from a tank wagon at
the proportion of 1 gallon to the square yard, the oil being thor-
oughly mixed with the earth by means of a harrow and a road grader.
To facilitate proper mixing it is frequently advantageous to apply a
considerable quantity of water.
After this first mixing the road is again plowed and a second and
then a third application of oil is made. If, when the finished road is
being rolled and compacted, any excess oil shows on the surface, it
should be taken up with fresh earth. In compacting the oiled earth
road it is wise to use a tamping roller, which consists of a drum car-
rying a large number of blunt-headed spikes in its circumference.
This device compacts the road from the bottom up rather than from
the top down, as is done by an ordinarv roller.
16 EXHIBIT OF OFFICE OF PUBLIC ROADS.
TREATED MACADAM ROADS.
TARRED OR OILED ROADS.
(Plate IX. fix. 2.)
The surface treatment of an old macadam road with tar or oil is
shown by this model.
Section A shows the macadam surface before treatment.
Section B shows the surface swept free from dust and detritus.
Section C shows the application of hot tar to the swept surface at
a ratio of from three-tenths to seven-tenths gallon per square yard.
Section D shows the final application of sand to the tarred surface,
thus completing the treatment.
In applying the tar or oil a number of methods may be adopted-
pouring by hand or through the use of a sprinkling wagon. The
liquid should be thoroughly broomed into the old surface before the
sand is applied to insure perfect cohesion. Before any application
of oil or tar be made all loose material should be removed and the
road surface be absolutely dry. Enough sand should be applied to
take up what excess of tar may be left on the surface.
TARRED ROADS PENETRATION METHOD.
(Plate X, fig. 1.)
The construction of a tar macadam road built according to the
penetration method is here shown the model being equivalent to
a macadam surface 12 feet wide.
Section A represents the prepared subgrade, excavated to a width
of 12 feet and a depth of 6 inches.
Section B represents the first course of No. 1 stone, placed to a depth
of 4 inches.
Section C represents the second course of No. 2 stone, spread to a
depth of 2 inches.
Section D shows the application of tar to the No. 2 course.
Section E shows the application of screenings, which completes
the road surface, the crown of the finished road representing an
average fall of one-half inch to the foot.
The construction of this road, to a certain point, is the same as
an ordinary macadam road Nos. 1 and 2 courses being so built.
Before the screenings are applied, however, hot tar is flushed into
the No. 2 course at the ratio of from 1 to 1^ gallons to the square yard.
When the screenings have been spread the road is rolled until thor-
oughly compacted and it is then ready for traffic.
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1909.
PLATE VI.
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1909.
PLATE VII.
FIG. 1. MODEL OF MACADAM ROAD WITH V-SHAPED FOUNDATION.
FIG. 2. MODEL OF BURNT-CLAY ROAD.
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1909.
PLATE VIII.
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1909.
PLATE IX.
FIG. 1. MODEL OF OILED EARTH ROAD.
FIG. 2. MODEL OF TARRED MACADAM ROAD.
EXHIBIT OF OFFICE OF PUBLIC ROADS. 17
TARRED ROADS GLADWELL METHOD.
(Plate X, fig. 2.)
This model illustrates a tarred macadam road built according to
the Gladwell method and, like the other models, is on a scale of 1J
inches to the foot, the macadam surface being equivalent to a width
of 12 feet.
Section A shows a No. 1 course of stone which has been placed on
the subgrade as in the ordinary macadam construction.
Section B represents the application of 1 inch of tarred screenings.
Section C represents the application of 2 inches of No. 2 stones.
Section D shows that layer painted with hot tar.
Section E shows the application of a final coat of screenings. These
being rolled down add nothing to the thickness of the road, which,
when thus completed, is crowned with a slope of one-half inch to
the foot.
The peculiar departure that makes this road distinctive begins
after the first course of No. 1 stone the foundation course has been
laid. On that the course of tarred screenings is spread and then the
layer of No. 2 stone, and when rolled the screenings are forced down-
ward into the foundation course and upward into the surface course,
thus binding both together. Rolling should be continued until the
tarred screenings appear on the surface, and then a light sprinkling
of screenings or tarred sand may be applied to fill the surface voids.
The final operation is the painting of the No. 2 course with hot
tar at the ratio of from one-half to seven-tenths gallon a square yard
and the application of dry screenings to take up all excess of tar
and to give a proper finish.
TAR, OIL, OR ASPHALT ROADS.
(Plate XI, fig. 1.)
This model illustrates the construction of a tar, oil, or asphalt mac-
adam road, having a macadam surface 12 feet wide.
Section A illustrates the prepared subgrade excavated to a depth of
6 inches and a width of 12 feet.
Section B represents the first course of No. 1 stone, placed to a
depth of 4 inches.
Section C represents the second course of bitumen-covered stone,
spread to a depth of about 2 inches.
Section D represents the application of about a one-fourth-inch
layer of bitumen-covered sand, which being rolled firmly into the sur-
face voids adds nothing to the thickness of the road.
Section E shows the application of an extremely light coat of stone
dust, which is the finished application and which should leave the
road with a sloping crown of one-half inch to the foot.
18 EXHIBIT OF OFFICE OF PUBLIC EOADS.
The subgrade is as in other macadam roads, the course of bitumen-
covered stones being prepared by applying sufficient hot bitumen to
cover a graded mineral aggregate when mixed. This graded aggre-
gate is composed of No. 2 stone and stone ranging in size from three-
fourths of an inch to dust in proportions of 960 pounds to 350 pounds.
Before applying the bitumen-covered sand, this course must be
thoroughly rolled and the sand then applied in such quantities that
it will fill the surface voids and bring the surface to a smooth and even
condition.
The final coat of stone dust is merely applied for the purpose of
taking up any excess of bitumen and of giving the road a pleasing
appearance.
TAR-SLAG ROADS.
(Plate XI, fig. 2.)
This model shows the construction of a tar-slag macadam road, the
slag surface being equivalent to a width of 12 feet.
Section A represents the subgrade, prepared as for the ordinary
macadam road, being excavated to a width of 12 feet and a depth of
6 inches.
Section B represents the first course of broken slag, placed to a
depth of 4 inches.
Section C represents the second course of broken slag, the slag
being the regular No. 2 size, coated with tar before spreading, and
placed to a depth of 2 inches.
Section D represents the No. 2 slag, which has been rolled and
painted with tar.
Section E shows the application of a light covering of slag screen-
ings which, being rolled into the surface voids of Section D, adds
nothing to the road thickness, the road crown when finished repre-
senting an average slope of about one-half inch to the foot.
The method employed in making this road is similar to that in an
ordinary macadam road except that no water is used and the second
course is covered with hot tar before being applied, the slag and tar
being mixed either by machinery or by hand. The amount of tar
will vary with the quantity of slag, though usually averaging about
5 per cent of the weight of the slag.
When the course represented by Section D has been rolled, it is
painted with a light coat of tar to insure a perfect adhesion of the
coat of screenings, which is last applied and thoroughly rolled.
ROADS IN BOCK CREEK PARK, DISTRICT OF COLUMBIA.
(Plate I; Plate XII, fig. 1.)
This is a model in miniature of a portion of the handsome Kock
Creek P5rk at the National Capital, and it shows the relationship of
roads and bridges to rugged topography.
Exhibit Office of Public Roads, U. S. Dept. of Agr , 1909.
PLATE X.
FIG. 1. MODEL OF TARRED MACADAM ROAD PENETRATION METHOD.
FIQ. 2. MODEL OF TARRED MACADAM ROAD GLADWELL METHOD.
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1909.
PLATE XI.
FIG. 1. MODEL OF SAND-BITUMINOUS MACADAM ROAD.
FIG. 2. MODEL OF TAR-SLAG MACADAM ROAD.
Exhibit Office of Public Roads, U. S. Dept. of Agr., 1909.
PLATE XII.
FIG. 1. MODEL OF SECTION OF ROCK CREEK PARK, DISTRICT OF COLUMBIA.
FIG. 2. MODEL OF QUARRY.
EXHIBIT OF OFFICE OF PUBLIC ROADS. 19
The model is on the scale of 1 inch to 20 feet, and it represents a
rectangle about 1,000 feet wkle and 2,500 feet long. The highways
which cut the park are splendid examples of the road-builder's art,
the grades being eas^ and the roadbeds being surfaced with trap rock
of the best quality. Bowlder Bridge and Pebble Bridge, which are
shown in the model, are picturesque ornaments, Bowlder Bridge,
which fits harmoniously into the scene, being especially attractive in
coloring, as it was constructed from bowlders picked from the bed
of the stream.
Of all its attractive features, visitors to Rock Creek Park will find
none more pleasing than the section of road which runs past Pierce's
old vine-covered mill with its broken wheel and shimmering mill
pond. For 7 miles this road follows the tortuous windings of Rock
Creek, each twist and turn revealing a new vista of wild and pictur-
esque beauty.
Passing from the gorge through which the stream flows, this road
branches into others, which by slight detours and gentle inclines lead
to high plateaus from which the stately Capitol may be seen in the
distance.
KOAD MACHINERY.
CRUSHING PLANTS.
This model (fig. 1) represents a portable stone-crushing plant, an
indispensable adjunct to the building of first-class stone roads, for
if such work is to be well and cheaply done, it follows that the plant
must be complete and conveniently arranged.
When possible the crusher should be so near the quarry that the
rock may be sent down grade in tram cars and delivered to the
crusher's mouth by gravity, thus rendering lifting it by hand un-
necessary. The crusher should be provided with an elevator and with
screens for separating the material into proper sizes. The screens
should be divided so that through the section near the upper end
fragments not exceeding one-half inch will pass, the second section
allowing the passage of stones of 1J inches, and the third section
permitting stones 2^ inches to make their way. Any larger stones will
be forced through the open end of the screen, from which they will
drop into the tailings conveyor, being finally crushed or eliminated
from the work. The jaws of the crusher should be set so as to make
as few tailings as possible, and the lengths of the screen sections
should be adjusted to the same purpose.
When soft stones are being crushed a dust jacket, having one-half
inch mesh, may be placed over the first section to eliminate dust from
the screenings.
20
EXHIBIT OF OFFICE OF PUBLIC KOADS.
For receiving the various sizes of crushed rock, bins with slanting
metal bottoms and sliding doors should be provided, so that the ma-
terial can be loaded into wagons by gravity.
Two types of crusher are now commonly used, one the jaw crusher,
as shown in figure 1, and the gyratory crusher. The jaw crusher is
generally used for portable plants.
In this machine one of the jaw r s moves backward and forward by
means of a toggle joint and an eccentric, the stone descending as the
jaw recedes. As it returns, it catches the stone and crushes it. The
FIG. 1. Exact model of portable crushing plant in operation.
maximum size of the product is determined by the distance the jaw
plates are apart at the lower edge.
The gyratory crusher consists of a solid conical iron shaft, sup-
ported with a heavy mass somewhat like an inverted bell. By means
of an eccentric a rotary motion is given the shaft so that every point
of its surface is successively brought near the surface of the " bell,"
the rock caught between shaft and bell being crushed.
The gyratory crusher will not produce as many flat pieces or tail-
ings as the jaw crusher, because the stones have to come in contact
with two curved surfaces at the same time before they are broken.
EXHIBIT OF OFFICE OF PUBLIC ROADS. 21
WHEELED SCRAPERS.
This model (fig. 2) illustrates a wheeled scraper, which consists of
a steel box mounted on wheels, provided with levers for raising,
lowering, and dumping, all of these movements being made without
stopping the team.
Wheeled scrapers are made in three sizes, having capacities of 9, 12,
and 16 cubic feet, respectively. They are used in building earth
roads, or in preparing the subgrade for macadam roads, especially
FIG. 2. Exact model of wheeled road scraper.
where cuts and fills are to be made and where the material can not be
conveniently handled with drag scrapers.
ROAD MACHINES OR GRADERS.
This model (fig. 3) shows in miniature a machine which is exten-
sively used in building and in preparing the subgrade for macadam
roads. As will be noted, it consists of a frame carried on wheels
which support an adjustable scraper blade, the front end of which
plows a furrow, while the rear end pushes the earth toward the center
or distributes it smoothly. The blade may be set at any angle or
tilted either backward or forward.
In building the earth road with the road machine a furrow is first
plowed with the point of the blade \vhere the outside of the ditch
22
EXHIBIT OF OFFICE OF PUBLIC ROADS.
is to be located. The blade may be made to penetrate hard or stony
ground by elevating the rear end considerably and by using only
the point of the blade for such plowing.
On the second round, with the front and rear wheels in line, the
team should be driven so that the point of the blade will follow the
furrow made by the first round, plowing a full furrow with the
advance end of the blade and dropping the rear end somewhat lower
than before.
When the third round is made the machine should be guided
toward the middle of the road, thus shoving the earth previously
plowed toward the center. This is done by slightly elevating the
rear end of the blade to allow the earth to distribute under it and
to give the necessary crown to the sides of the road. Three times
FIG. 3. Exact model of road grader.
this operation should be repeated until three layers of earth have
been moved to the road center, but care should be taken not to leave
a ridge in the center.
It is advisable to use the machine when the ground is soft, the
grading being done in the early summer when possible in order to
give the loose earth time to settle and pack before the fall rains. If
the work be done in the fall no more than 3 or 4 inches of loose
earth should be put on at one working.
If the side of the road is covered with sod, this should be cut as
thin as possible with the road machine and moved toward the center
of the road, and the earth from the side ditches will then cover it
to such a depth that it can not be objectionable.
From 4 to 6 inches of loose earth is sufficient for one working.
EXHIBIT OF OFFICE OF PUBLIC ROADS. 23
ELEVATING GRADERS.
Figure 4 shows a miniature of the elevating grader, which con-
sists of a frame carried upon four wheels, the grading machinery
consisting of a plow and a wide traveling belt, this latter being in
sections and so adjusted that it may be raised or lowered.
The type of grader used in ordinary highway work will deliver
earth T feet vertically and from 14 to 17 feet horizontally, the plow
loosening the soil and passing it directly to the belt, which delivers
it either to an embankment or to wagons.
By changing the length of the belt and properly distributing the
earth the machine will build either a broad low embankment from
a deep narrow cutting or a narrow high embankment from a broad
shallow cutting.
FIG. 4. Exact model of elevating road grader.
This machine is especially adapted to building earth roads in
prairie country or on flat lands where it is desirable to raise the road
above the surrounding ground or the water table.
Like nearly all other machinery, the elevating grader comes in
various sizes, the largest usually being propelled by 12 horses, 8
pulling and 4 pushing. The smaller one, which is generally used,
is operated by 8 horses. A traction engine may be used instead of
horses, and it will be found to be cheaper.
In building roads or embankments this machine has a capacity of
about 1.000 cubic yards each ten hours and about 600 yards when
loading into wagons. It will grade about a quarter of a mile of
ordinary prairie road per day to a width of 25 to 30 feet with a depth
of 1 foot in the center.
o
(iaylord Mro-;.
Makers
Syracuse,**. V.
" PAT. JAN. 21. 1908
T'E
UNIVERSITY OF CALIFORNIA LIBRARY