Correct Answer - Option 4 : 270.8 m
Concept:
Stopping Sight Distance:-
Stopping sight distance (SSD) is the minimum sight distance available on a highway at any spot having sufficient length to enable the driver to stop a vehicle travelling at design safely without collision with any other obstruction.
The stopping sight distance is the sum of the lag distance and the braking distance.
Lag distance is the distance the vehicle travelled during the reaction time ‘t’ and is given by vt, where v is the velocity in m/sec2.
Braking distance is the distance travelled by the vehicle during braking operation.
SSD = Lag distance + Braking distance
\(SSD = vt + \frac{{{v^2}}}{{2gf}}\)
Where 'v' is the design speed in m/sec,
't' is the reaction time in sec, 'g' is the acceleration due to gravity
'f' is the coefficient of friction.
Calculation:
Given,
→ -3.5% grade (i.e Downgrade), v = 110 kmph = 30.55 m/s
→ f = 0.28, t = 2.5 sec and G = 0.035
For Downward Gradient
\(SSD = vt + \frac{{{v^2}}}{{2g\times (f-\eta )}}\)
\(SSD = 30.55 \times 2.5 + \frac{{{30.55^2}}}{{2\times9.81\times (0.28-0.035 )}}\)
= 270.8 m
