10 
BULLETIN 463, U. S. DEPARTMENT OF AGRICULTURE. 
water from the traveled way into the side ditches. Such devices 
usually are much more objectionable, especially to automobile traffic, 
than a rather heavily crowned road, provided the surface is not con- 
structed of material which becomes very slippery when wet, and they 
should be dispensed with except in extreme cases. 
An exception to the general -rules for crowning a road surface 
perhaps should be noted as applying to cases where the roadbed and 
surface are of sand. In such cases it is preferable that the cross 
section be flat so as to retain as much moisture as practicable, though 
in cold climates a slight crown may be desirable in order to afford 
drainage when the surface is frozen. But sand roads must be sur- 
faced with some other material if they are to be imT j^ed to any 
extent, and in that case the surface of the traveled way would have 
to be crowned as 
usual. Also, where 
curves occur in the 
alignment it is desir- 
able to "bank" or 
elevate the outer 
edge of the roadway 
and thus make the 
crown one way. 
Bearing in mind 
the foregoing discus- 
sion, the crown limits 
indicated for the 
typical cross sections 
(shown in figs. 15, 20, 
and 22, respectively) , 
should prove a* fairly 
reliable guide in de- 
termining the proper crown for earth, sand-clay, and gravel road 
surfaces under any set of conditions ordinarily encountered. 
Figure 9 shows a cross section sometimes used for roads cut into 
side hills. The advantages claimed for this section are that whatever 
skidding occurs will be toward the hill rather than over the bank, 
and that the drainage water collected in the side ditch can be turned 
across the road at suitable points instead of being allowed to wash 
away the face of the embankment and perhaps damage abutting 
property. Except where short curves occur in the road, these ad- 
vantages hardly seem sufficient to overcome the objection that all 
water falling on the upper portion of the surface must flow across 
the lower portion in order to reach the side ditch. Traffic naturally 
will seek the part of the road next to the hill, and this concentration 
of traffic, together with the additional water, will tend to produce mud. 
Fig. 8. — Constructing 
OPRREI2538 
a tile drain, Montgomery County, Md. 
