When to use fog lights and how to drive safely in fog (UK rules)
You should use fog lights only when visibility is seriously reduced, generally when you cannot see for more than 100 metres, or about the length of a football pitch. You must switch them off as soon as visibility improves, because they can dazzle other drivers and hide your brake lights. In fog, always use dipped headlights, slow down, and leave a bigger gap than usual.
This guide explains the Highway Code rules, how to judge 100 metres, how to drive safely in fog step by step, and the most common mistakes.
Last updated 29 September 2026. The rules come directly from the Highway Code on GOV.UK (rules 226 to 236).
Key takeaways
- Use headlights when visibility is seriously reduced, generally when you cannot see more than 100 metres (Rule 226).
- Use front or rear fog lights only in seriously reduced visibility, and switch them off when it improves (Rule 236).
- Use dipped headlights in fog, not main beam or sidelights alone.
- Slow down before you enter fog, leave a bigger gap, and be able to stop within the distance you can see.
- Stopping distances are at least double on wet roads and up to ten times greater on ice and snow.
- Check your lights, wipers and screenwash before poor weather arrives.
In this guide
- What are the rules on fog lights?
- When should you use fog lights?
- How to drive safely in fog
- How does bad weather affect stopping distances?
- Common mistakes when driving in fog
- How to prepare your car for foggy weather
- Frequently asked questions
- Sources and further reading
What are the rules on fog lights?
Two Highway Code rules cover this. Rule 226 says you must use headlights when visibility is seriously reduced, generally when you cannot see for more than 100 metres (328 feet). You may also use front or rear fog lights, but you must switch them off when visibility improves. Rule 236 says you must not use front or rear fog lights unless visibility is seriously reduced, because they dazzle other road users and can hide your brake lights.
| Light | When to use it | When to switch it off |
| Dipped headlights | Whenever visibility is seriously reduced, generally when you cannot see more than 100 metres | When visibility improves |
| Front fog lights | Only in seriously reduced visibility, such as thick fog | As soon as visibility improves |
| Rear fog lights | Only in seriously reduced visibility, and when it will not dazzle someone close behind you | As soon as visibility improves, or when a driver is close behind you |
| Main beam | Not in fog. It reflects back off the water droplets and makes it harder to see | Not applicable |
The words MUST and MUST NOT in the Highway Code describe legal requirements, so leaving fog lights on in clear or lightly misty conditions is not just annoying, it can lead to a penalty.
When should you use fog lights?
The Highway Code’s benchmark is 100 metres, which is roughly the length of a football pitch. That is a useful mental picture, but here are some practical ways to judge it:
- On a motorway, the roadside marker posts are 100 metres apart. If you cannot clearly see the next post ahead, visibility is likely to be below 100 metres.
- On other roads, pick a fixed object such as a lamp post or junction and work out roughly how far it is.
- If you can only see a few car lengths ahead, visibility is definitely seriously reduced.
Light mist, drizzle or a patch of spray do not usually justify fog lights. Heavy rain, snow and thick fog can, if they reduce visibility to below about 100 metres. Remember to switch them off as soon as it clears, because rear fog lights in particular can obscure your brake lights.
Front fog lights usually have a green indicator on the dashboard, and rear fog lights usually have an amber one, but check your handbook, because controls vary between cars.
How to drive safely in fog
The Highway Code (rules 234 and 235) gives clear guidance on driving in fog:
- Slow down before you enter the fog. Check your mirrors first, then reduce your speed. If a roadside sign says Fog but the road looks clear, be ready for a bank of fog or drifting patches ahead, because it can suddenly get thicker.
- Use your lights properly. Use dipped headlights, and fog lights only if visibility is seriously reduced. Do not rely on daytime running lights, which may not switch your rear lights on.
- Keep a safe distance. The Code warns that the rear lights of the car in front can give a false sense of security, so leave more space than you would normally.
- Pull up well within the distance you can see. This is especially important on motorways and dual carriageways, where speeds are higher.
- Use your wipers and demisters to keep the glass clear. See our guide on how to demist and defrost your windscreen.
- Beware of drivers who have not switched on their headlights. Some drivers do not use lights in fog, so they are harder to see.
- Do not speed up to get away from a car that is too close behind. Check your mirrors, then use your brakes so your brake lights warn drivers behind you that you are slowing.
- Take care at junctions. Stop in the correct position, listen for traffic, and when you are sure it is safe, move out positively rather than creeping into the path of traffic.
How does bad weather affect stopping distances?
Poor visibility is not the only factor. The Highway Code notes that weather also changes how far you need to stop.
| Conditions | What the Highway Code says about stopping |
| Wet roads | Stopping distances will be at least double those on dry roads, because tyres have less grip |
| Icy or snowy roads | Stopping distances can be up to ten times greater than on dry roads |
| Fog | Be able to pull up well within the distance you can see clearly |
Tyres matter as much as lights in poor weather. Read our guides on tyre tread depth and tyre pressure to check yours, and hydroplaning if the roads are wet as well.
Common mistakes when driving in fog
- Leaving fog lights on when the fog has cleared, which dazzles others and hides your brake lights
- Using main beam in fog, which reflects back and reduces your own visibility
- Following the rear lights of the car in front too closely
- Overtaking when you cannot see far enough ahead
- Driving too fast for the conditions, particularly on motorways
- Switching on only the sidelights, which are not enough for fog
- Relying on automatic lights or daytime running lights that may not illuminate the rear of the car
How to prepare your car for foggy weather
- Check that all your lights work, including brake lights and fog lights. Bulbs that do not work are a common MOT failure. See how to avoid failing your MOT
- Clean the windscreen, lights and number plates, and top up the screenwash
- Check your wiper blades are not smearing, and demist the screen before you set off
- Leave extra time for the journey, and check the weather forecast and traffic reports first
- Keep a fully charged phone, a torch and warm clothes in the car in case you break down. See why breakdown cover is a must-have for every driver
Frequently asked questions
Can I use fog lights in heavy rain?
Only if the rain reduces visibility seriously, which the Highway Code generally defines as being unable to see more than 100 metres. In ordinary rain, use dipped headlights, and switch fog lights off when visibility improves.
Is it illegal to drive with fog lights on when there is no fog?
Yes. Rule 236 says you must not use front or rear fog lights unless visibility is seriously reduced, and misusing them can lead to a penalty.
Should I use main beam in fog?
No. Main beam reflects off the water droplets and glares back at you, making it harder to see. Use dipped headlights, and fog lights if visibility is seriously reduced.
Do I need to use headlights in daytime fog?
Yes. If visibility is seriously reduced, you must use headlights, even in the daytime. Daytime running lights do not always switch on your rear lights.
What is a safe speed in fog?
There is no set limit, but you should be able to stop within the distance you can see clearly. If you can only see a short distance ahead, you need to be going slowly.
Why should I not follow the rear lights of the car in front?
The Highway Code warns that they give a false sense of security. You may be too close to stop if the car in front brakes suddenly.
How far is 100 metres?
Roughly the length of a football pitch. On a motorway, the roadside marker posts are 100 metres apart, which is a useful guide.
What should I do if I break down in fog?
If you can, move the car to a safe place, switch on your hazard lights, and call for help. On a motorway, get everyone out of the left-hand doors and behind the barrier if it is safe to do so.
Sources and further reading
- GOV.UK: The Highway Code, driving in adverse weather conditions (rules 226 to 237)
- Rated Driving: Driving in fog, everything you need to know
About this guide: Rooster is a UK car insurance provider. This guide is general information for UK drivers and is not legal advice. Always read the current Highway Code and follow the instructions of the police or traffic officers.
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