Driving in Fog and Heavy Rain: The Law on Lights and Stopping Distances

Autumn is the season that catches drivers out. One morning it's clear, the next you're crawling through fog on the school run or pushing through spray on the motorway. Bad weather doesn't just make driving harder — it changes what the law expects of you, and how far your car needs to stop. Here's what the Highway Code actually says, and how to stay safe when the visibility drops.

Headlights: switch them on before you think you need to

The rule is simple. You must use dipped headlights when visibility is seriously reduced — generally taken as when you cannot see for more than 100 metres ahead. That covers fog, heavy rain, spray and the general gloom of a wet autumn afternoon.

The catch is daytime running lights. Many drivers assume that if the front of the car is lit, they're covered — but DRLs often don't switch on the rear lights at all. So in murk you can be driving a car that's invisible from behind. The fix costs nothing: turn the headlight switch to on (not auto) when the weather closes in, so the full set of lights comes on.

Fog lights: only when it's genuinely foggy — and off again after

Front and rear fog lights are much brighter and more focused than normal lights, which is why the law restricts them. You may only use them when visibility is seriously reduced — again, generally below 100 metres.

The part people get wrong is switching them off. Highway Code Rule 226 says you must turn fog lights off when visibility improves. There are good reasons:

• Rear fog lights dazzle the driver behind, especially in the wet when the glare reflects off the road.
• They can mask your brake lights — if the rear fog light is a similar brightness, the driver behind may not notice you braking.
• It can cost you. Driving with fog lights on in clear conditions can draw a police fine.

A useful habit: fog lights go on when you genuinely can't see, and the moment the road clears — even if the fog might come back in a mile — they go off.

Stopping distances: at least double in the wet

This is the number that matters most. In the wet, stopping distances are at least double those on a dry road (Highway Code Rule 227). On ice or packed snow, they can stretch to ten times longer.

That has a direct effect on how you follow other traffic. The familiar two-second rule — leaving a two-second gap to the car in front — becomes at least four seconds in the wet. Pick a fixed point like a sign or bridge, and make sure you don't reach it until four seconds after the car ahead has passed it.

And it's worth remembering what actually does the stopping: your tyres. All the braking force in the world is useless if the tread can't clear water fast enough to keep contact with the road. Worn tyres and heavy rain are a dangerous pair — if you're not sure yours are up to it, our guide to tyre tread depth and the law walks through the quick checks.

Standing water and aquaplaning

Heavy rain leaves standing water, and at speed your tyres can ride up on top of it — aquaplaning. The warning sign is the steering suddenly going light, as if the wheel has lost its weight. That means the tyres have lost contact with the road surface.

The instinct to brake hard is exactly the wrong one. Instead:

• Ease off the accelerator gently and let the car slow itself.
• Keep the steering light — no sudden inputs or corrections.
• Wait for grip to return as the tyres cut back through to the road, then carry on at a lower speed.

Slow down before deep water, never in the middle of it.

Driving in fog: the craft of it

Fog plays tricks, so a few habits help.

• Slow down and drive to what you can actually see, not what you expect to be there.
• Use your wipers and demisters — fog fogs the inside of the glass too, and a misted screen makes it far worse.
• Don't hang on the tail-lights ahead. Following someone's rear lights gives a false sense of security — you're driving off their judgement, not your own, and you'll have no time to react if they stop.
• Expect it to thin and thicken. A clear patch is not the all-clear; the next dip or field edge can be far denser.

The bottom line

Bad-weather driving comes down to two things: being seen, and leaving room to stop. Working lights are both a legal requirement and one of the most common reasons cars fail their MOT — a blown bulb you never notice by day becomes a real hazard in autumn fog. It's the same story with the warning lights on your dashboard: a fault flagged in summer is one you don't want to meet on a wet motorway.

Before the clocks change and the mornings turn dark, it's worth knowing your car is road-ready. Run a free MOT check to see your car's test history, any advisories, and when the next MOT is due — so the only thing you're fighting on a foggy morning is the weather.