Question

A valley curve of a state highway is formed by a descending gradient of 1 in 30 meeting an ascending gradient of 1 in 40. Assume allowable rate of change of centrifugal acceleration as $0.6m/se{c}^3$ and design speed of 75 kmph . The length of a valley curve to fulfill comfort condition is equal to

Answer 1

Length of valley curve for comfort condition is , given by
$L=\sqrt{\frac{N{v}^3}{C}}$
$N=n_1-n_2=\left|\begin{array}{c}\frac{-1}{30}-\frac{1}{40}\end{array}\right|=\frac{7}{120}$
$L=2\sqrt{\frac{\frac{7}{120}(\frac{5}{18}\times 75{)}^3}{0.6}}=593m\simeq 60m$