The 'fog' sign alerts drivers to locations known for sudden, localized reductions in visibility due to fog or mist.
It is common near low-lying valleys, river crossings, and coastal areas where fog banks form quickly without warning.
What this sign means
This sign features a car partially obscured by horizontal lines representing fog inside a red triangle.
It warns that visibility ahead may drop severely and suddenly, requiring immediate adjustments to speed and lighting.
- Red warning triangle showing vehicle enveloped in fog lines
- Warns of low-visibility sections ahead
- Found in fog-prone valleys, coasts, and motorways
What to do when you see it
Slow down, increase your separation distance, and switch on dipped headlights. Use rear fog lights if visibility drops below 100 metres.
- Use dipped headlights, not main beam
- Turn on fog lights if visibility falls under 100m
- Switch off fog lights as soon as visibility improves
How this sign is tested
Questions focus on the legal requirement for using fog lights and safe gap distances in limited visibility.
- Understanding when to turn fog lights on and off (100m threshold)
- Avoiding tailgating in reduced visibility
- Choosing correct headlight beam settings in fog
Common mistakes
Leaving high-beam headlights on (which reflect off fog and dazzle the driver) or leaving fog lights turned on after clear weather returns.
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Practise road sign questionsFrequently asked questions
When must I use fog lights legally?
You should use fog lights when visibility is seriously reduced, generally defined as below 100 metres (328 feet).
Why shouldn't I use main beam headlights in fog?
Main beams bounce off water droplets in the fog back into your eyes, creating glare and reducing vision further.
Is it illegal to leave fog lights on when visibility improves?
Yes. Leaving fog lights on in clear conditions dazzles other drivers and masks your brake lights.