Motorway sign

Fog warning (motorway signal) sign

Fog warning motorway signal: a black panel showing the word Fog in white lights, with amber lamps at the corners — Sign image: Department for Transport, © Crown copyright

What does the Fog signal sign mean?

Warns that there is a risk of fog ahead. Slow down and be ready for visibility to drop suddenly.

What it means

There is a risk of fog on the motorway ahead, even if it looks clear where you are.

The amber lamps flash to warn of a hazard, and the word tells you what it is.

Slow down, check your mirrors, and leave a bigger gap. Fog can come in banks, so it may suddenly get much thicker.

Where you'll see it

On motorway signals above the lanes or at the side of the motorway.

Rules to know

The signal warns of a risk of fog ahead.
Know Your Traffic Signs, p. 105
If 'Fog' is shown on a sign but the road is clear, be prepared for a bank of fog or drifting patchy fog ahead.
The Highway Code, Rule 234
When driving in fog, be able to pull up well within the distance you can see clearly, particularly on motorways.
The Highway Code, Rule 235

Common mistakes

Mistake: Ignoring it because the road ahead looks clear.
Instead: Fog can be patchy and appear suddenly. Slow down before you reach it.

Test yourself

Recalling the answer helps it stick. Pick an answer to see how you did.

Question 1 of 1

What does this sign mean?

Black panel with a short word made of white lights and an amber lamp in each corner

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© Crown copyright. Free to reuse under the Open Government Licence v3.0, as long as the sign is reproduced accurately and not in a misleading context.

See also
Advised speed (motorway signal)
Motorway sign
A motorway signal advising a lower speed.
See also
End of restrictions (motorway signal)
Motorway sign
Shows when the restriction or warning ends.

More motorway signs

All motorway signs

Sources

Know Your Traffic Signs (Department for Transport, Sixth edition, 2023), Motorway signs, signals and road markings, p. 105
The Highway Code, Rule 234

Sign image: Department for Transport, Traffic sign images (diagram 6011). © Crown copyright, reused under the Open Government Licence v3.0.

Last reviewed 6 October 2026. This page explains the sign in our own words; for the full rules, see The Highway Code. How we source and check content