For a roadway of 100 km/hr design speed, if the maximum allowable superelevation rate is 0·12 and the maximum friction coefficient is 0·12, the minimum radius of curvature will be
- A328 mCorrect
- B304 m
- C288 m
- D264 m
Solution
Concept
Minimum radius
Formula
R = V² / [127 (e + f)]
Step-by-step solution
1. R = 100² / [127 × (0.12 + 0.12)] = 10 000 / 30.48 = 328 m.
Explanation
The minimum radius follows from equilibrium of the vehicle on a banked curve with side friction fully developed.
Why the other options are wrong
304, 288 and 264 m do not equal 10000/30.48.
Shortcut
R = V²/127(e + f), V in km/h.
Common mistake
Using 0.12 only.
Correct answer: A) 328 m