Question

Assuming the safe stopping sight distance to be 80 m on a flat highway section and with a setback distance of 10 m, what would be the radius of the negotiable horizontal curve?

• A. 160 m
• B. 70 m
• C. 80 m
• D. 800 m

Answer 1

The correct option is C 80 m

When $L_c>S,$ the formula for set back distance is

$m=R-(R-d)cos\left(\frac{\alpha }{2}\right)$

$where\alpha =\frac{180S}{\pi (R-d)}$

S is stopping sight distance (SSD)
d is the distance between the centre line of the road and the center line of the inside lane
$L_c$ is the length of the curve
However, this formula is difficult to calculate so an approximate equation can be formulated by assuming that the length of the chord is equal to the SSD.

Given, M = 10 m S = 80 m

$\therefore R=\frac{M}{2}+\frac{S^2}{8M}$

$=\frac{10}{2}+\frac{(80{)}^2}{8\times 10}=85m$

The closest option is (c) i.e., 80 m