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Difficulty: MediumStopping and Following Distances

You are driving a car at a speed of 30 mph30\text{ mph} on a road with surface water following heavy rain. According to the UK Highway Code, what is the expected total stopping distance under these wet conditions?

  1. A
    23 metres23\text{ metres} (75 feet75\text{ feet})
  2. 46 metres46\text{ metres} (150 feet150\text{ feet})Answer
  3. C
    37 metres37\text{ metres} (120 feet120\text{ feet})
  4. D
    230 metres230\text{ metres} (750 feet750\text{ feet})

Answer

The expected total stopping distance on a wet road at 30 mph30\text{ mph} is 46 metres46\text{ metres} (150 feet150\text{ feet}).
Under the UK Highway Code, the typical stopping distance for a car travelling at 30 mph30\text{ mph} on a dry road is 23 metres23\text{ metres} (75 feet75\text{ feet}). When the road surface is wet, reduced tyre adhesion doubles the overall stopping distance, making it 46 metres46\text{ metres} (150 feet150\text{ feet}).

Step-by-Step Solution

1
Determine the baseline stopping distance for the given speed on a dry road surface.
At 30 mph30\text{ mph}, the standard total stopping distance on a dry, level road is 23 metres23\text{ metres} (75 feet75\text{ feet}), comprising 9 metres9\text{ metres} thinking distance and 14 metres14\text{ metres} braking distance.
The UK Highway Code specifies standard baseline stopping distances for cars with good tyres and brakes in dry conditions.
2
Apply the appropriate weather adjustment factor for wet road conditions.
The total stopping distance doubles: 23 metres×2=46 metres23\text{ metres} \times 2 = 46\text{ metres} (75 feet×2=150 feet75\text{ feet} \times 2 = 150\text{ feet}).
Water on the road reduces tyre adhesion, requiring drivers to double their separation margin and stopping distance.

Key Concept

Highway Code stopping distances at 30 mph and the wet weather doubling rule
Estimated Time:1m 0s
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Topics

Stopping and Following Distances

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