78 HIGHWAY CONSTRUCTION 



the case of streets in which the opposite sides are at different levels. 

 Transverse Contour or Crown. The reason for crowning a pave- 

 ment i. e., making the center higher than the sides is to provide 

 for the rapid drainage of the surface. The most suitable form for the 

 crown is the parabolic curve, which may be started at the curb line, 

 or at the edge of the gutter adjoining the carriage-way about one foot 



Fig. 53. 



from the curb. Fig. 53 shows this form, which is obtained by dividing 

 the ordinate or width from the gutter to tne center of the street into ten 

 equal parts, and raising perpendiculars the length of which will be 

 determined by multiplying the rise at the center by the respective 

 number of each perpendicular in the diagram. The amounts thus 

 obtained can be added to the rod readings; and the stakes, set at the 

 proper distance across the street, with their tops at this level, will give 

 the required curve. 



The amount of transverse rise, or the height of the center above 

 the gutters, varies with the different paving materials, smooth pave- 

 ments requiring the least, and rough ones and earth the greatest. The 

 rise is generally stated in a proportion of the width of the carriage-way. 

 The most suitable proportions are: 



Stone blocks, rise at center, V width of carriage-way. 

 Wood " " " " T ^ " " 



Brick " " " " V " 

 Asphalt" sV " 



Sub-Foundation Drainage of Streets. The sub-foundation 

 drainage of streets cannot be effected by transverse drains, because of 

 their liability to disturbance by the introduction of gas, water, and 

 other pipes. 



Longitudinal drains must be depended upon entirely; they may 

 be constructed of the same materials and in the same manner as road 

 drains. The number of these longitudinal drains must depend upon 



