PORTLAND CEMENT CONCRETE ROADS. 
15 
of crown. The crown of a pavement may be either an arc of a 
circle or a parabolic curve. In road construction it is generally cus- 
tomary to make it an arc of a circle. 
SUPERELEVATION OF CURVES. 
For modern traffic it is becoming customary and desirable to 
superelevate pavements on all curves. Superelevation of pavements 
compensates centrifugal force, reduces the clanger of skidding on 
curves, and induces traffic to keep to the right side of the road. The 
amount of superelevation necessary will depend upon the radius of 
the curve and the speed of the traffic, but under no circumstances 
I 
1 
1 
1 
AMOUNT 
CURVE iSHOWiNG 
OF SUPERELEVATION 
PER FOOT 
Otl4 
0.13 
I 
Q 
\ 
\ 
OF WIDTH FOR VARIOUS RADII. 
Based on a speed of 25 mi. per hr 
012 
a 
o 
\ 
\ 
\ 
| E - C.067 | 2 
E= Slope in feet per ft. of width. 
0.1 1 
o 
\ 
\ 
S= Speed in miles per hour 
R= Radius of curve in feet. 
0.10 
o 
a 
iS) 
\ 
\ 
\ 
0.09 
a: 
u 
a. 
u 
i 
\ 
\ 
Note: 
'-rorradii from 2000' to 2500" use £' or .02' per ft. 
| 2500' to 4000' use Cor .014' per ft. 
O.Ofl 
2f 
4000' to 6000' use \°or .01" per ft. 
For radii qreater than 6000' no superelevation. 
0.07 
Ll 
7 
i* 
In choosing rate of super* 
curve use nearest .01 ft. 
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Fig. 2. — Curve showing superelevation per foot for curves of various radii. 
should it be so great as to be objectionable or dangerous to horse- 
drawn traffic. The maximum superelevation for this latter class of 
traffic should not exceed 1 inch per foot of width. The speed of 
other vehicles on curves of short radius must therefore be reduced 
to conform to this superelevation. If this maximum be adopted, the 
amount of superelevation for the various radii of curvature may be 
easily computed. The curve, Figure 2, shows the amount of superele- 
vation per foot of width for curves of various radii and a superele- 
vated curve is shown in Figure 2, Plate IX. 
Superelevation may be accomplished by rotating the pavement 
about its central axis, i. e., lowering the inner edge of the pavement 
and raising the outer edge. If drainage conditions will not permit 
