Question

What will be ruling minimum radius for horizontal curve of NH (National Highway) in plain terrain? (Assume ruling design speed = 127 km/h, minimum design speed = 80 km/h, rate of super elevation e = 0.05 and coefficient of friction = 0.05)
1. 400 m
2. 800 m
3. 1270 m
4. 1300 m

Answer 1

Correct Answer - Option 3 : 1270 m

Concept:

The ruling minimum radius for the horizontal curve:

The ruling minimum radius is a limiting value of curvature for a given design speed.

A ruling minimum radius (R_ruling) is calculated on the basis of maximum superelevation and coefficient of friction.  

The radius of the curve should be higher than R_ruling.

\(e +f ={ V^2 \over 127R_{ruling}}\)

where, 

V = velocity (km/h)

R_ruling = radius of the circular curve (m)

e = superelevation

f = lateral coefficient of friction

Calculation:

Given Data

V = 127 km/h

e = 0.05

f = 0.05

So, The ruling minimum radius for the horizontal curve

\(e +f ={ V^2 \over 127R_{ruling}}\)

\(0.05 +0.05 ={ (127)^2 \over 127R_{ruling}}\)

Rruling = 1270 m