Driving in Fog in the UK: When to Use Fog Lights and How to Stay Safe

Fog reduces visibility, distorts your perception of speed and distance, and makes it much harder for other drivers to see you. It is one of the most common factors in multi-vehicle motorway pileups. Here is how to drive safely when visibility drops.

When to Use Fog Lights

The Highway Code states that you must use fog lights when visibility is “seriously reduced” — which it defines as below 100 metres. A practical way to judge this: if you cannot see the tail lights of the car in front at a normal following distance, visibility is below 100 metres.

Front vs Rear Fog Lights

Fog Driving Technique

• Slow down. Reduce your speed to match the visibility. If you can only see 50 metres ahead, you should be driving slowly enough to stop within that distance
• Use dipped headlights. Even during the day, dipped headlights help other drivers see you
• Increase following distance. The 2-second rule becomes a 4-second rule in fog as a minimum. If visibility is very poor, increase it further
• Do not hang on to the tail lights of the car ahead. It gives a false sense of security and means you are following too closely. If they brake suddenly, you will hit them
• Use the left-hand edge of the road. In very dense fog, use road markings and the left-hand kerb/verge as a guide rather than the centre line (which puts you close to oncoming traffic)
• Open your window slightly. You may hear traffic you cannot see
• Turn off your radio. Listen for other vehicles, especially at junctions

Motorway Fog

Fog on motorways is particularly dangerous because of higher speeds and the difficulty of judging distance. Many UK motorways have fog warning signs and recommended speed limits that activate automatically.

On a motorway in fog:

• Use the reflective road studs as a guide: white studs mark lane boundaries, red studs mark the left edge, amber studs mark the central reservation, green studs mark slip road entries/exits
• Do not overtake unless you can see far enough ahead to complete the manoeuvre safely
• If fog is very dense, consider leaving the motorway at the next junction and using a quieter route

When to Stop

If fog is so dense that you cannot see more than a few metres ahead, it may be safest to stop. Pull off the road completely into a car park, lay-by, or side road. Do not stop on the carriageway or hard shoulder unless it is a genuine emergency. Turn on your hazard lights if you are forced to stop in a dangerous position.

Final Thoughts

Fog demands respect. Slow down, use the correct lights, and increase your following distance. Never use main beam in fog, and always turn off your rear fog lights when visibility improves. If in doubt, slow down further — you can never drive too slowly in fog.