Question

A horizontal circular curve with a centre line radius of 250 m is provided on a 2-way, 2-lane State Highway. The width of two-lane road is 7.5 m. Design speed = 90 kmph. The brake reaction time is 2.5 seconds and coefficient of friction in longitudinal and lateral direction are 0.35 and 0.15 respectively. The set back distance from the central line of the road considering $L_c$ > SSD is

• A. 11.90 m
• B. 13.71 m
• C. None of these
• D. 11.30 m

Answer 1

The correct option is B 13.71 m

SSD = $v{t}_r+\frac{v^2}{2gf}$
$=0.278\times 90\times 2.5+\frac{(0.278\times 90{)}^2}{2\times 9.81\times 0.35}=153.66m$

For $L_c>SSD$
Set back distance
$\left(m^{\prime }\right)=R-(R-d)cos\frac{\alpha }{2}$;
$\frac{\alpha }{2}=\frac{180\times SSD}{2\pi (R-d)}={17.74}^{\circ }$
$m^{\prime }=250-(250-1.875)cos17.74=13.68m$