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Difficulty: MediumFactors Affecting Braking Distance

On a dry road surface, a car travelling at 50 mph50\text{ mph} (80 km/h80\text{ km/h}) has a standard braking distance of 38 metres38\text{ metres}. According to The Highway Code, wet road conditions reduce tyre grip and cause the braking distance to double. What is the expected braking distance, in metres, for this car on a wet road surface?

Answer: 76 metres

Answer

The braking distance on a wet road surface is 76 metres.
Under wet road conditions, surface water creates a barrier between the tyre tread and the tarmac, significantly reducing friction. According to The Highway Code, this doubles the braking distance from the dry baseline of 38 metres38\text{ metres} at 50 mph50\text{ mph} to 76 metres76\text{ metres}.

Step-by-Step Solution

1
Identify the base braking distance on a dry road surface
Dry braking distance = 38 metres38\text{ metres}
The Highway Code establishes 38 metres38\text{ metres} (125 feet125\text{ feet}) as the standard braking distance at 50 mph50\text{ mph} under dry, optimal conditions.
2
Apply the wet road condition factor
Multiplier = 22
Water on the road reduces tyre adhesion and increases the distance required for the vehicle's brakes to bring it to a complete stop by at least double.
3
Calculate the final wet braking distance
38 m×2=76 metres38\text{ m} \times 2 = 76\text{ metres}
Multiplying the base dry braking distance by the wet weather factor yields the expected distance.

Key Concept

Braking distance is directly affected by road surface friction; wet road conditions double the braking distance compared to dry conditions.
Estimated Time:1m 0s
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Factors Affecting Braking Distance

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