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GATE 2023 CE (CE2) – Question 23

Transportation Infrastructure · Geometric design of roadways: cross-section, sight distance, alignments · 1 mark · Multiple choice

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

  1. (braking distance required to come to stop) + (distance travelled during the perception-reaction time)
  2. (braking distance required to come to stop) − (distance travelled during the perception-reaction time)
  3. (braking distance required to come to stop)
  4. (distance travelled during the perception-reaction time)

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Correct answer: (A) (braking distance required to come to stop) + (distance travelled during the perception-reaction time)

Explanation

**Stopping sight distance (SSD)** is the minimum distance a driver needs to see ahead so that the vehicle can come to a stop before reaching an obstruction. It has two parts:

1. **Lag distance:** during the perception-reaction time $t$ (about 2.5 s in IRC practice) the vehicle keeps moving at speed $v$, covering $vt$.
2. **Braking distance:** after the brakes are applied, the vehicle travels $\dfrac{v^2}{2g(f\pm G)}$ before stopping.

$$SSD=vt+\frac{v^2}{2g(f\pm G)} .$$

So SSD is the **sum** of the braking distance and the distance travelled during the perception-reaction time (option A).