26 



IOWA DEPARTMENT OF AGRICULTURE. 



SHAPE OF CROSS SECTION ON HILLS.— Where a road is con- 

 structed on a hill, the slope from the center to the sides should be slight- 

 ly steeper than on the level. The reason for this is that every wheel 

 track on an inclined roadway becomes a channel for carrying down the 

 water, and unless the curvature is sufficient these tracks are quickly 

 deepened into water courses which cut into and sometimes destroy the 

 best surface. (Fig. 4.) The slope must be sufficient to lead the water 







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Fig. 4.— Poorly crowned earth road on steep hillside. 



quickly into the side ditches instead of allowing it to flow down the mid- 

 dle of the road, but should not be so steep that water will rush off the 

 surface so quickly as to wash away berms or shoulders. The cross sec- 

 tion, consisting of two plane surfaces sloping uniformly from the center 

 to the sides, is perhaps a little better for a steep grade than the circu- 

 lar form because of the danger of overturning, which would necessarily 

 be increased if the circular or elliptical cross section were used. Water 

 should never be permitted to flow long distances or to collect in puddles 

 by the roadside, for it soon sinks into the adjacent soil and softens the 

 foundation of the road. Open drains should not be allowed to become 



