Under standard UK Highway Code guidelines, a car travelling at 70\text{ mph} in dry condit… — UK Driving Theory Test

Under standard UK Highway Code guidelines, a car travelling at $70\text{ mph}$ in dry conditions requires an overall stopping distance of $96\text{ metres}$ , which consists of $21\text{ metres}$ of thinking distance and $75\text{ metres}$ of braking distance. If wet weather doubles the total stopping distance while the driver's thinking distance remains unchanged at $21\text{ metres}$ , what is the vehicle's new braking distance in metres?

Answer: 171 metres

Answer

171 metres

In good, dry conditions at

70\text{ mph}

, the standard overall stopping distance is

96\text{ metres}

(

21\text{ metres}

thinking distance plus

75\text{ metres}

braking distance). When road conditions are wet, the overall stopping distance doubles to

192\text{ metres}

(

96\text{ m} \times 2

). Since the driver's reaction time and thinking distance remain unchanged at

21\text{ metres}

, the new braking distance is

192\text{ m} - 21\text{ m} = 171\text{ metres}

Step-by-Step Solution

Calculate the total stopping distance on a wet road by applying the standard multiplier (doubling) to the dry total stopping distance of

96\text{ metres}

96\text{ m} \times 2 = 192\text{ metres}

The Highway Code establishes that wet road surfaces double the overall stopping distance due to reduced tyre grip.

Subtract the driver's constant thinking distance of

21\text{ metres}

from the total wet stopping distance.

192\text{ m} - 21\text{ m} = 171\text{ metres}

Total stopping distance equals thinking distance plus braking distance. Deducting thinking distance isolates the braking component.

Key Concept

Calculation of braking distance under wet road conditions from overall stopping distance

Estimated Time:1m 30s

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