\"A freeway exit ramp has a single lane and consists entirely of a horizontal cu

Question

"A freeway exit ramp has a single lane and consists entirely of a horizontal curve with a central angle of 90 degrees and a length of 628 ft. If the distance cleared from the centerline for sight distance is 19.4 ft., what design speed was used to design the curve?"

A freeway exit ramp has a single lane and consists entirely of a horizontal curve with a central angle of 90 degrees and a length of 628 ft. If the distance cleared from the centerline for sight distance is 19.4 ft., what design speed was used to design the curve?

Explanation / Answer

Ms = 19.4 - 6 = 13.4 ft
L = 2 pie R delta/ 360

R = 360L/2pie delta

= 360 * 628 /(2*3.14*90) = 400 ft

Rv = 400 - 6 = 394 ft..

SSD = pie Rv/90 * cos inverse {Rv - Ms}/Rv

       = 3.14 * 394/90 cos inverse {394-13.4}/394
       
       = 206 ft

hence Speed = 30 mph

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