POETLAND CEMENT CONCKETE ROADS. 



15 



of crown. The crown of a pavement may be either an arc of a 

 circle or a parabolic curve. In road construction it is generally cus- 

 tomary to make it an arc of a circle. 



SUPERELEVATION OF CURVES. 



For modern traffic it is becoming customary and desirable to 

 superelevate pavements on all curves. Superelevation of pavements 

 compensates centrifugal force, reduces the danger of skiddino- on 

 curves, and induces traffic to keep to the right side of the road. The 

 amount of superelevation necessar}^ will depend upon the radius of 

 the curve and the speed of the traffic, but under no circumstances 



I 









1 









AMO 



UNT 



CURVE ISHOWING 

 OF SUPERELEVATION 



PER FOOT 









a^4 



0.13 



I 



o 



5 



















OF WIDTH FOR VARIOUS RADII. 

 Based on a speed of 25 mi. per hr 









0.12 



& 

 ^ 



u. 



o 



1- 



















1 E = 0.067 1^ 1 

 E' Slope injfeet per ft. of width. 









O.ll 



li. 



o 













I 









S= Speed in miles per hour 

 R= Radius of curve in feet 











0.10 



1 



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u 

 n. 



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s 







Note: 



-For 'radii from 2000' to ZSOO'use ^-or .OZ'per ft. 

 2500' to 4000' use |'or .014' per ft 



OOfl 



t- 

















U" 













\ 







4000' to 6000' use ^'or .01' per ft 

 For radii qreater than 6000' no superelevation. 



Oj07 



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\, 





P 



















In choosing rate of superi 

 curve use nearest .01 ft 



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tion 



fror 



ri 





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N, 























0.05 





















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 u 









































0.03 



a 



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— 







.^ 



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ti. 

 o 



















Rad 



1 IN 



Feet 



















0.01 



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 o 



< 





s 





o 



1 



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3 



o 





8 



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o 

 o 



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o 



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o 



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i 



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•dl 



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jy 



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1 1 

 REES 



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V 







Fig. 2. — Curve showing superelevation per foot for curves of various radii. 



should it be so great as to be objectionable or dangerous to horse- 

 drawn traffic. The maximum superelevation for this latter class of 

 traffic should not exceed 1 inch per foot of width. The speed of 

 other vehicles on curves of short radius must therefore be reduced 

 to conform to this superelevation. If this maximum be adopted, the 

 amount of superelevation for the various radii of curvature may be 

 easily computed. The curve. Figure 2, shows the amount of superele- 

 vation per foot of width for curves of various radii and a superele- 

 vated curve is shown in Figure 2, Plate IX. 



Superelevation may be accomplished by rotating the pavement 

 about its central axis, i. e., lowering the" inner edge of the pavement 

 and raising the outer edge. If drainage conditions will not permit 



