Question

Which of the following is equal to the stopping sight distance?

• A. (braking distance required to come to stop) + (distance travelled during the perception-reaction time)
• B. (braking distance required to come to stop) – (distance travelled during the perception-reaction time)
• C. (braking distance required to come to stop)
• D. (distance travelled during the perception-reaction time)

Hint:

Always remember: SSD = PRD + BD. The perception-reaction time is usually taken as 2.5 seconds in design, and both parts are additive.

Answer 1

The Correct Option is A

Step 1: Definition of stopping sight distance (SSD): Stopping sight distance is the minimum distance required for a vehicle to come to a complete stop after the driver perceives an obstacle. It consists of two components: \[ SSD = \text{Perception-Reaction Distance (PRD)} + \text{Braking Distance (BD)} \]

Step 2: Perception-reaction distance: During the perception-reaction time (\(t\)), the driver continues at the original speed \(V\). Thus, \[ PRD = V \times t \]

Step 3: Braking distance: This is the distance covered by the vehicle while brakes are applied until it comes to rest. For speed \(V\) and coefficient of friction \(f\), \[ BD = \frac{V^2}{2 g f} \]

Step 4: Combine both components: \[ SSD = PRD + BD \]

Step 5: Match with given options: Option (A) states exactly this combination — braking distance + distance travelled during perception-reaction time. \[ \boxed{\text{Stopping Sight Distance = (A)}} \]