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 improved to anv 

 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 



OPRREI2638 



a tile drain, Montgomery County, Md. 



