Following Distance on a Wet Motorway
You are driving a 1,600 kg car on a motorway at 130 km/h in heavy rain. Visibility is about 150 m. Your tyres have 2.2 mm of tread in the centre grooves and are correctly inflated. The car ahead is a lorry travelling at 90 km/h. You are currently 40 m behind it. Your reaction time is about 1 second. On a dry road your car needs roughly 55 m to stop from 130 km/h; the wet surface roughly doubles that braking distance. The lorry's spray reduces your view of its brake lights. There is a hard shoulder to your right and a continuous line of traffic in the left lane.
1. Assess whether your current gap and speed are appropriate, using the numbers given.
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No. Your closing speed is 130 − 90 = 40 km/h, about 11 m/s. At a 40 m gap you would reach the lorry in under 4 seconds even if it kept constant speed - and it may brake. Your own stopping distance from 130 km/h on this wet road is roughly 2 × 55 = 110 m plus about 36 m of reaction distance (130 km/h ≈ 36 m/s, so 1 s ≈ 36 m), i.e. around 146 m in total. That already exceeds the 150 m visibility, so 130 km/h is too fast for the conditions.
You must reduce speed substantially and increase the gap. A practical rule in rain is at least a 3–4 second gap to the vehicle ahead; at 130 km/h that means 110–145 m, which visibility does not allow. So slow down until you can stop within the distance you can see to be clear, and until the gap to the lorry is several seconds.
2. What is the tyre issue and how does it interact with the wet road?
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2.2 mm of tread in the centre grooves is close to the legal minimum and well below what is needed to clear water at motorway speed. Shallow tread cannot expel water fast enough, so a film builds between tyre and road and grip falls sharply - aquaplaning risk rises with speed and with standing water in the wheel tracks.
Combined with the doubled wet braking distance, this means the car's real stopping performance is worse than the 110 m estimate, and steering response during braking will be vague. The correct response is to slow down, avoid sudden steering or braking inputs, and plan to replace the tyres. Increasing the gap is the only measure that buys time to react to the lorry's brake lights, which the spray partly hides.