Question

On a two-lane highway, a horizontal curve of radius 300 m is provided. The design speed is 80 km/h.
If the longest wheelbase of vehicle expected on this highway is 7 m, then the extra widening required (in m) is .......... (round off to two decimal places).

Hint:

When calculating extra widening on a horizontal curve, consider both mechanical widening due to vehicle width and phasing effects due to the design speed. Ensure to use the correct formula as per the IRC standards.

Answer 1

Given: - Number of lanes, \( n = 2 \)
- Radius of curve, \( R = 300 \, {m} \)
- Design speed, \( v = 80 \, {km/h} \)
- Longest wheelbase of vehicle, \( l = 7 \, {m} \) As per IRC (Indian Roads Congress) standards, the formula for extra widening \( W_e \) is: \[ W_e = W_m + W_{ph} \] Where:
- \( W_m = \frac{n l^2}{2 R} \) (widening due to mechanical reasons)
- \( W_{ph} = \frac{v}{9.5 \sqrt{R}} \) (widening due to phasing effect)
Substitute the values: \[ W_e = \frac{2 \times 7^2}{2 \times 300} + \frac{80}{9.5 \times \sqrt{300}} = \frac{2 \times 49}{600} + \frac{80}{9.5 \times 17.32} \] \[ W_e = 0.1633 + 0.4867 = 0.65 \, {m} \] Thus, the extra widening required is \( 0.65 \, {m} \).