Question

A four lane divided carriageway has a curve 800 m long and a radius of 500 m. The safe stopping sight distance is 150 m. The pavement width is 3.5 m per lane. The minimum setback distance from the inner edge of the curve to ensure safe visibility will be:

• A. 5.71 m
• B. 9.17 m
• C. 7.47 m
• D. 10.92 m

Answer 1

The correct option is B 9.17 m

S=150m, L=800 m
$\because L>S$
$\therefore$ $m=R-(R-d)cos\frac{\alpha }{2}$
$\frac{\alpha }{2}=\frac{180\times 150}{2\pi [500-(3.5+\frac{3.5}{2}\left)\right]}={8.685}^0$
$\therefore$ set back distance from centre line,
$m=500-(500-3.5-\frac{3.5}{2})cos\left({8.685}^0\right)$
=10.923 m (from centre line of inner lane)

$\therefore$ Distance from inner edge to obstruction =
$(10.923-\frac{3.5}{2})=9.173m$