Q.15 Consider the following distances: d₁ = distance travelled by the vehicle after applying the breaks. d₂ = distance travelled by overtaking vehicle, during reaction time for overtaking. d₃ = distance travelled by overtaking vehicle, during total overtaking time. d₄ = distance travelled by overtaken vehicle, during total overtaking time. The Overtaking Sight Distance, on a road with one-way traffic will be equal to:
- Ad₃ + d₄
- Bd₁ + d₂ + d₃
- Cd₁ + d₂ + d₃ + d₄
- Dd₂ + d₃Correct
Solution
Concept
On a one-way road there is no vehicle coming from the front, so OSD is the reaction distance plus the overtaking distance of the overtaking vehicle.
Formula
OSD (two-way) = d1 + d2 + d3 (IRC notation); OSD (one-way) = d1 + d2
Step-by-step solution
1. IRC OSD on a two-way road has three parts: reaction distance, overtaking distance and distance travelled by the opposing vehicle. 2. On a one-way road there is no opposing vehicle, so the third part is dropped. 3. In this question, d₂ is the distance travelled by the overtaking vehicle during reaction time. 4. d₃ is the distance travelled by the overtaking vehicle during the overtaking time. 5. So OSD (one-way) = d₂ + d₃.
Explanation
OSD on a one-way road needs only the distance covered by the overtaking vehicle during reaction time and during the overtaking act. There is no opposing vehicle, so no extra distance is added. Braking distance is part of stopping sight distance, not OSD.
Why the other options are wrong
A: misses the reaction time distance d₂, and d₄ is already included inside d₃. B: d₁ (braking distance) is not part of OSD. C: adds braking distance and counts the overtaken vehicle's distance twice.
Shortcut
One-way OSD = reaction distance + overtaking distance only.
Common mistake
Adding braking distance (from SSD) or the overtaken vehicle's distance separately into OSD.
Correct answer: D) d₂ + d₃