Fog lights
Extra-bright lights for seriously reduced visibility — and a dazzle hazard the moment the fog lifts.
Rear fog lights are much brighter than ordinary tail lights, which is exactly what you want when someone is coming up behind you in fog and exactly what you do not want on a clear night. The rule follows from that: use them when visibility is seriously reduced, and switch them off as soon as it improves.
The figure the test uses for "seriously reduced" is around 100 metres. Below that, fog lights earn their place. Above it, they dazzle the driver behind and mask your brake lights, so the person most likely to be hurt by leaving them on is you.
Fog is also the condition where people drive to what they can see rather than what they can stop in. If you can see 50 metres, your whole stopping distance has to fit inside 50 metres — which at motorway speed it does not.
33 practice questions on this
Each one shows the answer, and our note on why every other option is not it.
Car
- You're following other vehicles in fog. You have your headlights on dipped beam. What else can you do to reduce the chances of being in a collision? Safety margins
- You're driving on a clear night. Which lights should you use if the national speed limit applies and there's a steady stream of oncoming traffic? Attitude
- You're driving in fog. Why should you keep well back from the vehicle in front? Vehicle handling
- What should you do if you park on the road when it's foggy? Vehicle handling
- When may front fog lights be used? Vehicle handling
- You're driving with your front fog lights switched on. What should you do if the fog has cleared? Vehicle handling
- Why should you switch off your rear fog lights when the fog has cleared? Vehicle handling
- What will happen if you use rear fog lights in good conditions? Vehicle handling
- Which lights must you use if you're driving on a well-lit motorway at night? Vehicle handling
- You're driving on a motorway at night. Which lights should you have on if there are other vehicles just ahead of you? Vehicle handling
- Which lights should you switch on when daytime visibility is poor but not seriously reduced? Vehicle handling
- Why are vehicles fitted with rear fog lights? Vehicle handling
- Which lights should you use when you're driving in a tunnel? Incidents, accidents and emergencies
- Other than direction indicators, how can you give signals to other road users? Rules of the road
- You're driving in heavy traffic on a wet road. Which lights should you use if there's a lot of surface spray? Other types of vehicle
- What lights should you use when you're driving on a wet motorway and vehicles are throwing up surface spray? Safety margins
- You've been driving in fog. What must you do when the visibility improves? Vehicle handling
- Why is it dangerous to leave rear fog lights switched on after the fog has cleared? Vehicle handling
- When must you use dipped headlights during the day? Vehicle handling
Motorcycle
Lorry & Bus (LGV/PCV)
- You're driving on a motorway in heavy rain. When are you allowed to use high-intensity rear fog lights? The road
- You're being followed by a marked police car. As well as flashing the headlights, what will the police officer do to signal you to stop? The driver
- What should you do when you drive into a tunnel? Incidents, accidents and emergencies
- You're driving in fog. When should high-intensity rear fog lights be used? The road
- You're driving in fog that's starting to clear. When should you switch off your high-intensity rear fog lights? The road
- What should you do if you see a vehicle too close behind when you're driving in traffic on the motorway? The road
- You're driving in fast-moving traffic along a motorway. What should you do if there's a stationary queue of traffic ahead? The driver
Driving Instructor (ADI Part 1)
- You're driving on a motorway in daylight. What lights should you use in light mist? Band 1 road procedure
- You're driving at night. What should you do if the headlights of a following vehicle are causing dazzle? Band 1 road procedure
- It's a foggy day. What should you do if you have to park your car on the road? Band 1 road procedure
- You must use your headlights when visibility is seriously reduced. What distance would be classed as seriously reduced? Band 3 driving test, disabilities, law
- You're driving in fog. What should you do if you use front fog lights? Band 1 road procedure