Examkin

Question

Difficulty: HardAdjusting Margins in Wet Weather

You are driving at 50 mph on a wet single carriageway with surface water and spray. In dry conditions, your total stopping distance is 53 metres, comprising a 15-metre thinking distance and a 38-metre braking distance. Which of the following correctly describes how these conditions alter your stopping distance components and the minimum separation gap you must maintain?

  1. A
    Both your thinking distance and braking distance double, resulting in an overall stopping distance of 106 metres, and your following time gap must increase to at least 4 seconds.
  2. Your braking distance doubles to 76 metres while thinking distance remains 15 metres, resulting in an overall stopping distance of 91 metres, and your following time gap must increase to at least 4 seconds.Answer
  3. C
    Your overall stopping distance increases tenfold to 530 metres due to surface water, and your following time gap must increase to at least 10 seconds.
  4. D
    Your braking distance doubles to 76 metres, but your following time gap can remain at 2 seconds provided your vehicle is fitted with tyres of legal tread depth.

Answer

Your braking distance doubles to 76 metres while thinking distance remains 15 metres (resulting in a total stopping distance of 91 metres), and your following time gap must increase to at least 4 seconds.
On wet asphalt, reduced friction between tyres and the road surface doubles braking distance (from 38 metres to 76 metres at 50 mph). Because thinking distance remains unchanged at 15 metres, the overall stopping distance becomes 91 metres. Under Highway Code Rule 126, drivers must double their following separation from 2 seconds to at least 4 seconds.

Step-by-Step Solution

1
Analyze how wet weather affects individual stopping distance components.
Wet road surfaces reduce tyre grip and friction, which doubles the braking distance from 38 metres to 76 metres. Thinking distance depends purely on driver reaction time and travel speed, so it remains 15 metres.
Road surface friction impacts vehicle deceleration during braking, not the physical reaction time of the driver.
2
Calculate total stopping distance under wet road conditions.
Total stopping distance = 15 metres (thinking) + 76 metres (braking) = 91 metres.
Total stopping distance is always the sum of thinking distance and braking distance.
3
Determine the required separation gap adjustment according to the Highway Code.
The standard dry weather 2-second time gap must be doubled to at least 4 seconds.
Rule 126 of the Highway Code mandates doubling separation distance on wet roads to provide a safe buffer for doubled braking distances.

Key Concept

Adjusting braking distance calculations and following margins in wet conditions
Estimated Time:1m 15s
Rate this question

Topics

Adjusting Margins in Wet Weather

More questions from this topic