PARK AND CEMETERY. 
141 
ROAD and TRAIL BUILDING in the NATIONAL PARKS 
( Continued ) 
An address before the National Park Conference by 
E. A. Keyes, Inspector, Department of the Interior. 
It is my judgment that the width of 16 
feet of paved way is sufficient for most of 
the principal roads in our national parks. 
At the precipitous points, in order to give 
the tourists a feeling of more security, 
an earth shoulder might be added to the 
outer edge, but where such a point occurs 
on a maximum grade the grade should be 
decreased at the dangerous point, and; the 
road elevated at its outer edge upon the 
same theory that the outer rail of our 
railroads is elevated. 
Theoretically, the shortest radius' of 
curvature permissible on roads depends 
upon the width of road and upon the max- 
imum length of teams traveling on that 
particular road and upon the speed of the 
teams. The length of a Ahorse team and 
vehicle is ordinarily about SO feet. To 
permit such a team to keep upon a 16-foot 
roadway would require a radius of about 
75 feet for the inner edge. In laying out 
the alignment for the roads in our national 
parks consideration should be given the 
maximum length of teams used in that par- 
ticular park. It is also a good plan where 
these curves occur on steep grades to de- 
crease the grade on the curves. 
The principal requisites of a rock suit- 
able for broken-stone roads are hardness, 
toughness, cementing or binding power, 
and its resistance to the wear under the 
grinding action of wheels. The rock 
should also be homogeneous in order that 
the road surface should wear smoothly. 
The hard, dark-colored, igneous rock com- 
monly called trap rock is probably the best 
suited as road material, both as to its wear- 
ing and cementing qualities. The hard, 
uniform grained basalt, showing a steel- 
like fracture and free from gas blows, is 
probably the best road material to be 
found in this country. Next in order are 
the granites, but these vary so widely that 
many of them are practically worthless as 
road material. The fine-grained granites 
have been known to give good results, 
while the coarse, loose-grained ones are 
practically worthless as road material. 
According to some authorities' the gravel 
of the glacier drift furnishes excellent 
road-making material, and as a rule the 
gravel of bluish color will cement to- 
gether, while the reddish or brown gravel 
will not. However, so far as I am able 
to ascertain, this class of material has not 
been actually used in road construction to 
any great extent and little is therefore 
known of its action under traffic. 
In the construction of roads in our na- 
tiona parks the problem which will con- 
front the superintendent is not so much 
what is the best material for road con- 
struction, but what is the best available 
material on the ground, for this will re- 
quire a careful study of all available rock 
in that particular location, and in order to 
obtain the best material I would not hesi- 
tate to change the location of a road in 
order to make the material accessible to 
the particular job. It is thought that this 
is another case which would appear to 
warrant the necessity of a central office 
to which the superintendent could refer 
samples of rock to determine their suita- 
bility for road construction. 
Some authorities claim that the upper 
surface should be curved, while others 
claim that the upper surface should be 
two planes intersecting at the center of 
the road and having their angles of in- 
tersection slightly rounded off. Both forms 
are in common use throughout the coun- 
try, but the first or curved form is prob- 
ably the most commonly used ; both have 
their ardent advocates. The Massachu- 
setts State Highway Commission has 
adopted the form of two planes inter- 
secting at the center ; while the standard 
section for the New York state aid roads 
is curved. The curve usually adopted is 
not that of a circle,, as is' generally under- 
stood, but that of a parabola. My per- 
sonal objection to the form of two planes 
intersecting at the center is, first : After 
the road is built it gives the appearance 
of a poor attempt at making a curved sur- 
face; in the second place, when the flanks 
wear a little, to the eye they look sway- 
backed and at the same time allow water 
to- stand on the surface, which is detri- 
mental to the foundation of the road. 
The proper height of crown depends 
largely on the way of making repairs. 
If new material is added at long inter- 
vals, then the crown should be somewhat 
greater to compensate the wear, which 
would take place between repairs, but if 
the system of continuous repairs is used 
the crown may be somewhat lower. The 
transverse slope should be greater on nar- 
row roads than on wide ones to prevent 
the water from carrying the surface ma- 
terial into the side ditches. 
There should be more crown on steep 
grades than on flat ones, and indeed the 
crown should be in reality a function of 
the grade,— that is to say, there is no need 
of carrying the water to the gutter any 
faster than to prevent its flowing down the 
center of the road. In other words, the 
grade from crown to the gutter should be 
somewhat larger than the longitudinal 
grade of the road, and indeed a high ve- 
locity from crown to the gutter is unde- 
sirable, as it carries too much of the bind- 
ing material into the gutters, which must 
be shoveled out, and usually by hand, and 
at the same time produces ridges in the 
road. Another disadvantage of high 
crown is that in riding over the road, 
unless the wheels are centered over the 
crown, the vehicle will ride one-sided, and 
the occupants be forced against one an- 
other, thus making it somewhat uncom- 
fortable. In concluding this subject I 
would say that in the construction of roads 
in our national parks I believe a crown 
of 6 inchesl would be found to be suf- 
ficient. This might, however, be increased 
to a maximum of perhaps 12 inches upon 
our maximum grades. 
The object of placing a layer of broken 
stone under the roadway is to secure, 
first, a smooth, hard surface ; second, a 
water-tight roof, and, third, a rigid stra- 
tum which will uniformly distribute the 
pressure of the wheel over the area of the 
subgrade so that the bearing power of the 
soil will not be overtaxed. 
The smooth surface and tight roof will 
depend upon the quantity and quality of 
the binding material, and the rigidity of 
the layer depends upon the binder and 
largely upon the thickness of the stratum. 
The supporting power of the subgrade de- 
pends upon the nature of the soil and 
particularly upon the drainage. Therefore, 
for the above reasons the minimum thick- 
ness of the broken stone depends upon 
the nature of the soil, drainage, traffic, 
and binding material. The initial thickness 
of the roof depends upon the wear per- 
mitted before new material is added. If 
the repairs are continuous, the initial 
thickness may be a minimum, but if the 
repairs are made periodically, that is at 
intervals, the initial thickness must be equal 
to the minimum thickness, plus the amount 
allowed for wear between intervals at 
which repairs are made. After the road 
has been worn down three or four inches 
it is usually so uneven as to require re- 
surfacing, and for this reason it is un- 
economical if the road in this stage is 
much or any thicker than the minimum 
required to prevent its breaking through. 
There has been much discussion, and 
there is a great deal of difference of 
opinion, as to what shall be the proper 
depth of broken stone road. The depth 
considered necessary by the most extreme 
advocates’ of thick roads has decreased 
with more improved methods of construc- 
tion, particularly the use of good binder 
and the advent of the steam roller, and 
as the advantage of thorough underdrain- 
age has been better understood. 
In the early days a depth of from 18 to 
24 inches was frequently considered neces- 
sary for heavy traffic, while now 6 inches 
or less is usually considered sufficient. The 
