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19. O utsloping (i.e., sloping toward the downhill side of the 

 road) from 3-5 percent is preferable, to insloping because it 

 eliminates the need to develop facilities to dispose of the 

 water draining down the inside of the road. Outsloping can be 

 unsafe in some situations because of particular traffic requirements 

 or unusual site conditions such as clayey road surfaces that are 

 very slippery when wet. In addition, outsloping should only be 

 used where runoff will flow off the road onto stable surfaces, 

 normally, this precludes the use of outsloping on fill portions 



of the road unless fill slopes are small and low in erodibility 

 or are well protected by mulches, vegetation, or both. 



20. I nsloping (i.e.* sloping toward the uphill side) of the road surface 

 is preferred to outsloping in areas of unstable fills, except in 

 the case of a contour road where there is no chance for lateral 



flow along the road. Water draining from the road is carried 

 along the inside of the road either on the road surface itself 

 or more commonly in a ditch. Culverts are installed periodically 

 to carry the water under the road. Some points to consider when 

 designing an insloped road are: 



(a) Avoid using ditches or keep ditches to a minimum width and 

 increase the number of cross drains to reduce the total area 

 disturbed by construction. 



(b) Plan ditch gradients steep enough (generally greater than 2 

 percent) to prevent sediment deposition. 



(c) Install culverts frequently enough to avoid accumulations of 

 water that will cause excessive erosion of the road ditch and 

 the area below the culvert outlet. Surface the ditch in areas 

 of erodible material (e.g., weathered granitics). 



