Question

At a horizontal curve portion of a 4 lane undivided carriageway a transition curve is to be introduced to attain required superelevation. The design speed is 60 kmph and radius of the curve is 245 m. Assume length of wheelbase of a longest vehicle as 6 m, superelevation rate as 5% and rate of introduction of this superelevation as 1 in 150. The length of transition curve (m) required, if the pavement is rotated about inner edge is

• A. 81.4
• B. 91.5
• C. 110.2
• D. 85.0

Answer 1

The correct option is C 110.2

1. According to rate of change of centrifugal acceleration
$L_s=\frac{v^3}{CR}...$

$L_s=\frac{(0.278\times 60{)}^3}{0.59\times 245}=31.56m$

C = $\frac{80}{V+75}=0.59$ (V is in kmph)

2. According to superelevation

Extra widening,
$w_e=\frac{n{l}^2}{2R}+\frac{V}{9.5\sqrt{R}}$

$w_e=\frac{4\times 6^2}{2\times 245}+\frac{60}{9.5\sqrt{245}}$

$w_e=.697m$

When pavement is rotated about inner edge-
$L_s=eN(w+w_e)$

$L_s=0.05\times 150(4\times 3.5+0.697)$

$L_s=110.23m$

3. According to empirical formula

Assuming plain and rolling terrain.
$L_s=\frac{2.7V^2}{R}$

$L_s=\frac{2.7\times {60}^2}{245}$

$L_s=39.7m$

Maximum of above three will be length of transition curve

$L_s=110.23m$