Question

On a single lane horizontal curve of radius 20m with a design speed of 60 kmph and length of curve as 200m, the Setback distance in 'm' is

Answer 1

Stoppiing sight distance,
$0.278Vt+\frac{V^2}{254f}$
$=\frac{0.278\times 60\times 2.+{60}^2}{(254\times 0.35)}$
$=82.19m$

Assume Length of curve > SSD

Set back distance

$=R-Rcos\left(\frac{\alpha }{2}\right)$
$\frac{\alpha }{2}=\frac{180S}{2\pi R}$
$=\frac{(180\times 82.19)}{(2\times 3.14\times 250)}=9.42degree$

Setback distance,
$=250-250cos\left(9.42\right)=3.37m$