Eoad Drainage. 449 



down through the road-hed are the most important points to 

 be secured in the matter of maintenance. The surface of 

 every road, therefore, should be so shaped as to act like 

 a roof in throwing all rains quickly and completely off, 

 permitting only a little moisture to be drawn downward by 

 capillary attraction to moisten the material and lessen 

 the formation of dust. If the compacted material of the 

 road and the road-bed beneath it can be kept with only a, 

 small per cent, of capillary water in them the danger of 

 injury from frost is greatly lessened and the liability to 

 soften during wet periods is also largely removed. 



Water should under no conditions be permitted to stand 

 either upon the surface nor along the side of the road, the 

 shape being sufficiently rounded to throw the rains quickly 

 to either side, and the surface ditches deep enough, clean 

 enough and possessing sufficient capacity to carry all water 

 rapidly away. 



555. Slope of the Eoad Surface Fn order to have quick, 

 complete surface drainage it is necessary to so arch the 

 face as to make a road twelve feet wide three inches higher 

 in the center than at either margin, a slope of "about lum- 

 per cent, or four inches in 100 inches. But if the road 

 has itself a considerable grade, then the slope must be 

 made enough greater than four per cent, to force the water 

 to the side ditches rather than to permit it to flow down 

 the center of the road. But evenness or smoothness of 

 surface is the most important condition to be secured and 

 maintained in order to afford perfect drainage. If the 

 road surface is left uneven, or is permitted to become so, 

 no amount of slope which can be tolerated will secure the 

 drainage. 



The road must not be made too rounding or sloping for 

 the reason that then teams all drive in one place on the 

 surface and wear it into ruts and this prevents drainage. 



556. Water-Breaks. On steep grades where the hill is 

 long it is a common practice to throw a ridge obliquely 



