24 BULLETIN 1077, U. S. DEPARTMENT OF AGRICULTURE. 
SHOULDERS AND DITCHES. 
The width and kind of shoulders necessary for concrete pavements 
will depend upon the width of pavement and the volume of traffic. 
On single-track pavements the shoulders must be sufficiently wide 
to provide for safety of passing vehicles and must be composed of 
material which will support them satisfactorily. On double-track 
pavements the shoulders should be of sufficient width to allow for 
irregular and unexpected actions by inexperienced drivers or fright- 
ened animals, and, where the volume of traffic is large, to permit auto- 
mobiles to turn out onto the shoulders for minor adjustments or 
tire repairs without blocking the traveled way. The width of each 
shoulder, then, should be not less than 5 feet ; a width of 6 or 7 feet 
is preferable. 
It has generally been customary to construct gravel or macadam 
shoulders to single-track roads on clay soils. This may be accom- 
plished by constructing gravel or macadam strips 3 feet wide on 
each side of the pavement, or in the case of a single-track pavement 
built on one side of the center line by placing the gravel or macadam 
strip all on one side and making the width 6 feet. These gravel or 
macadam strips are usually 4 to 6 inches thick. On soils of a 
gravelly nature which have rather good supporting power when wet. 
metaled shoulders are not used. A double-track road should be wide 
enough to permit the passing of vehicles without turning out on the 
shoulders, so no shoulder should be necessary for this pavement other 
than the natural soil. 
The slope of the shoulder should be such as will readily dispose of 
the water, and at the same time not be so steep that it will appear dan- 
gerous to drive on. Shoulders along a low-crowned pavement should 
have a slope as flat as possible so as not to accentuate the change in 
slope. A slope of ^ inch to 1 foot should prove satisfactory. Inas- 
much as the shoulders of a concrete road are seldom rolled, some slight 
settlement takes place, and it is usually found that if a very flat shoul- 
der is constructed it will have all the slope necessary after the road 
has been opened to traffic for a short time. 
Surface ditches are usually constructed of two general shapes — the 
V shape, and the trapezoidal shape. In rolling country, where the 
surface water can be turned aAvay from the road at frequent intervals, 
the V-shaped ditch has proved very satisfactory. Where it is neces- 
sary to carry water in the ditches for considerable distances the trape- 
zoidal ditch should be used. The bottom of the ditch should be at 
least IS inches lower than the center of the road; and when a large 
volume of water is to be carried the minimum depth should be 24 
inches. The slopes to the ditches from the shoulder should not be 
steeper than 2 to 1. 
