In the estimation of minimum radius of horizontal circular curve on non-urban highways following IRC: 73-1980, using the equation R = v² / [g(e + f)], the notation 'f' represents:
- ACo-efficient of side friction between vehicle tyres and pavementCorrect
- BVehicle speed
- CSuperelevation ratio
- DWidth of roadway
Solution
Concept
On a horizontal curve, the centrifugal force is resisted by superelevation (e) and side friction (f).
Formula
R = v2 / [g(e + f)], or R = V2 / [127(e + f)] with V in km/h
Step-by-step solution
1. Write the equation: R = v2 / [g(e + f)]. 2. Here v is the vehicle speed and g is the acceleration due to gravity. 3. e is the superelevation ratio. 4. f is the coefficient of side friction between the tyres and the pavement (IRC takes f = 0.15). 5. So the answer is (A).
Explanation
When a vehicle moves on a curve, centrifugal force acts outward. Superelevation (e) and side friction (f) together balance this force. In this equation, f is the coefficient of side friction between the tyres and the road.
Why the other options are wrong
B: Vehicle speed is v, not f. C: Superelevation ratio is e, not f. D: Width of roadway does not appear in this equation.
Shortcut
e = superelevation, f = friction. IRC uses f = 0.15.
Common mistake
Using the longitudinal friction value (0.35 to 0.40) instead of the lateral friction value (0.15).
Correct answer: A) Co-efficient of side friction between vehicle tyres and pavement