Question

The following data are related to a horizontal curved portion of a two lane highway: length of curve 200 m, radius of curve = 300 m and width of pavement = 7.5 m. In order to provide a Stopping Sight Distance (SSD) of 80 m, the set back distance (in m) required from the centre line of the inner lane of the pavement is

• A. 7.96
• B. 7.10
• C. 4.55
• D. 2.54

Answer 1

The correct option is D 2.54

Length of curve,
$L_c=200m$
Radius,
$R=300m$
Width,
$W=7.5m$
SSD,
$S=80m$
$\therefore L_c>S,$

Set back distance,

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

$\frac{\alpha }{2}=\frac{180S}{2\pi (R-d)}=\frac{180\times 80}{2\pi \times (300-\frac{7.5}{4})}$
$={7.687}^{\circ }$

$m=\left(300\right)-(300-\frac{7.5}{4})\times \cos \left(7.687\right)$

$=4.554m$

Set back distance required from the centre line of the road,
$=4.554-\frac{7.5}{4}=2.679m$

Option (a) is the closest.