394 ROADS AND PAVEMENTS 



points of division erect perpendiculars, the lengths of which 

 measured from the line joining the edges of the gutters 

 are determined by multiplying the rise at the center by the 

 number given on each perpendicular in the figure. The 

 rise at the center should be as follows: For earth roads, A of 

 the width; for gravel roads, & of the width; and for broken- 

 stone roads, sfe of the width. 



EXAMPLE. Find the ordinates for an earth road 30 ft. wide. 



SOLUTION. The center height must be 28 = .75 ft. The 



distance between the center of the road and the edge of the 



gutter is 15 ft.; the points of division are, therefore, 1.5 ft. 



apart. The ordinates are as follows (see the illustration) : 



At the center 75 ft. 



At H ft. from the center 75X .99 = .74 ft. 



At 3 ft. from the center 75 X. 96 = .72 ft. 



At 4i ft. from the center 75X .91 - .68 ft. 



At 6 ft. from the center 75X.84 = .63 ft. 



At 7i ft. from the center 75 X .75 = .56 ft. 



At 9 ft. from the center 75X .64 = .48 ft. 



At 10 J ft. from the center 75 X. 51 = .38 ft. 



At 12 ft. from the center 75 X .36 = .27 ft. 



At 13 Jft. from the center 75X.19 = .14 ft. 



At 15 ft. from the center 00 ft. 



Width of Roadway. The width of the wheelway required 

 to accommodate two lines of travel is 18 ft.; for a single line of 

 travel, 8 ft. is sufficient, but suitable turnouts must be provided 

 at frequent intervals. 



Curves. The straight parts of the roads must be joined by 

 curves, the least permissible radius of which depends on the 

 length of the teams using the road. As a rule, the greatest 

 possible radius should be used, and no curve should have a 

 radius of less than 50 ft. The curves may be either circular 

 or parabolic. A parabolic curve is often preferred, on account 

 of the ease with which it can be laid out. 



DRAINAGE 



Water is the greatest enemy of roads. Through its solvent 

 action, it softens and dissolves the materials of which the road 

 is constructed, and by its expansion while freezing disrupts 



