When visibility is below 50 metres, the general speed ceiling is 50 km/h, including on motorways. A lower restriction still applies and conditions can require an even lower speed.
Reduce speed early enough
Dense fog can appear after a clear stretch. Slow progressively before you can no longer distinguish the road ahead. The previous vehicle must not become your only guide: following its lights too closely removes braking margin. Observe road markings and maintain a stable position in your lane.
Be visible without dazzling
Use suitable lights and check that automatic operation has not left the vehicle inadequately lit. High beams can reflect unhelpfully in fog. Rear fog lights are reserved for the permitted conditions of fog or snow; they must not be used for rain alone. Turn special lights off when the conditions no longer justify them.
Choose a safe stopping option
If fog makes driving too difficult, find a rest area or a place away from traffic. Do not deliberately stop in a lane or on the shoulder to wait for clearing if a safe location is accessible. In mountains, check road conditions too. Fog, cold and a wet surface together can make grip uncertain.
Use the rear fog light at the right time
The rear fog light is permitted in fog or snow, not in rain alone. Its intensity can bother nearby vehicles. Locate its dashboard indicator and switch it off when conditions no longer justify its use.
Do not rely on a moving guide
Following the vehicle ahead very closely reduces your ability to react to its braking. Maintain your own margin and use visible fixed references without staring at one point. If you need a break, find a rest area or safe exit; the road and emergency shoulder are not resting places.
Visibility changes abruptly between two parts of the journey.
Slow progressively, keep your distance and check appropriate lighting. Look for road markings without staring at the previous vehicle’s lights; drive according to your own visibility.
What to avoid. Following another car closely to guide yourself removes reaction margin.
Practical checks
- Match speed to what you can see
- Preserve a following gap
- Check which lights are actually on
- Switch off the rear fog light after the fog
Common questions
Are rear fog lights suitable for rain?
No. They can dazzle and are not permitted for rain alone. Check the rules for fog or snow.
Does poor visibility make high beams useful?
High beams can be counterproductive in fog and can dazzle. Choose lighting appropriate to conditions and other road users.
Official references
This English translation concerns rules and services in France. It does not make them applicable in another country. Local signs, official instructions, vehicle manuals and contracts may specify your situation. Linked references and service pages are in French.
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