Question

A road is designed for a ruling minimum radius of 300m, for a design speed of 80 kmph in plain terrain. If the road is upgraded to a design speed is 100 kmph, then the percentage change in a radius required is (Maximum available lateral friction coefficient = 0.15)

• A. 56.23%
• B. 49.92%
• C. 23.86%
• D. 19.3%

Answer 1

The correct option is D 19.3%

Case I :

Super elevation
e = $\frac{V^2}{225R}=\frac{{80}^2}{225\times 300}=0.094>0.07$

Hence 'e' is restricted to 0.07

e + f = $\frac{V^2}{127R}=\frac{{80}^2}{127\times 300}=0.168$

f = 0.168-0.07 = 0.098< 0.15. Hence OK

Case II:

Using e = 0.07 and f = 0.15

0.07 + 0.15 = $\frac{V^2}{127R}$

0.22 = $\frac{{100}^2}{127\times R}$

R = 357.91 m

Percentage change in radius

= (357.91-300) / 300$\times 100$ = 19.3%