Question

Calculate the extra widening of pavement and the length of transition curve needed on a two-lane highway having a longitudinal circular curve of radius of 300 m. Design speed = 80 kmph, length of the wheelbase of largest vehicle = 6 m

• A. 0.606 and 141.78
• B. 0.606 and 70.89
• C. 0.12 and 57.6
• D. 0.486 and 90.98

Answer 1

The correct option is B 0.606 and 70.89

Extra widening is given by

$W_e$ = $\frac{n{l}^2}{2R}$ + $\frac{V}{9.5\sqrt{R}}$

n $\to$ no. of lanes

l $\to$ distance between the front and rear wheel

R $\to$ radius of curve

V $\to$ speed in kmph

$\Rightarrow$ $W_e$ = $\frac{2\times 6^2}{2\times 300}$ + $\frac{80}{9.5\sqrt{300}}$

= 0.12 + 0.486

= 0.606 m

Length of transition curve-

Criteria (1): Rate of change of centrifugal acceleration

$L_s$ = $\frac{v^3}{CR}$

Where C = $\frac{80}{75+V}$$m/s^3$
= $\frac{80}{75+80}$

= 0.516

$\Rightarrow$ $L_s$ = $\frac{{(80\times \frac{5}{18})}^3}{0.516\times 300}$
= 70.87 m

Criteria (ii): Rate of change of superelevation

Since the terrain is not given, we cannot compute this

Criteria (iii): IRC formula

Assuming plain terrain

L = 2.7 x $\frac{V^2}{R}$ = $\frac{2.7\times {80}^2}{300}$

= 57.6 m

L = max (70.89, 57.6)

Length of transition curve = 70.89 m.