Which one of the following is relevant for the determination of superelevation to be provided in horizontal curves of radius R in m in hill roads, given that the design traffic velocity is V kmph?

Which one of the following is relevant for the determination of superelevation to be provided in horizontal curves of radius R in m in hill roads, given that the design traffic velocity is V kmph?

A. V^2 /127R

B. V^2 /17.5R

C. V^2 /225R

D. (V+8)^2 /127R

Correct answer is option 'C'. Can you explain this answer?