Question

A rising gradient of 1 in 20 meets another rising gradient of 1 in 40. If the stopping sight distance is 120m, then the length of the vertical curve is

Answer 1

Deviation angle

N = (1/20)-(1/40) = 1/40.

Hence a summit curve is required

Assuming L > S

Length of summit curve $=\frac{N{S}^2}{4.4}\times \left(\frac{1}{40}\right)\times \frac{{120}^2}{4.4}=81.82<120m$

Hence the assumption is incorrect.

Assuming L < S

Length of the summit curve

=2S - $\frac{4.4}{N}=(2\times 120)-(4.4\times 40)$

= 64m < 120 m

Hence the assumption is correct.