A roadside FOG warning still matters when the stretch immediately ahead looks clear. Highway Code Rule 234 warns that a bank of fog or drifting patches may lie farther along the road. You can move from a clear view into thick fog unexpectedly.
Look beyond the clear foreground
The warning does not promise that every metre of road will be foggy. A gap between patches can make conditions appear better than they are farther ahead. Treat the message as a reason to anticipate a change in visibility.
The original educational image accompanying this article illustrates this distinction: the foreground is relatively clear, while a fog bank obscures the road in the distance. It is an AI-created illustration, not a photograph of a documented incident.
Check mirrors before slowing
Before entering fog, check your mirrors and then slow down. Knowing what is behind you helps you prepare for the reduction in speed. Do not wait until the road disappears into the fog before recognising that conditions have changed.
Once in fog, Rule 235 says to keep a safe distance from the vehicle ahead and be able to stop well within the distance you can see clearly. Following another vehicle's rear lights too closely can give a false sense of security.
Use lights for the actual conditions
Rule 226 requires headlights when visibility is seriously reduced, generally when you cannot see for more than 100 metres. Fog lights may also be used in seriously reduced visibility, but must be switched off when visibility improves. A warning sign alone is not a reason to leave fog lights on in clear conditions.
Quick revision check
A FOG signal is showing, but your current stretch is clear. Can you assume the warning is irrelevant?
No. A fog bank or drifting patches may be ahead. Prepare for reduced visibility, and check mirrors then slow down before entering fog.
The matching Short uses recorded channel narration and explains the warning in Highway Code Rule 234. Watch the matching Short below.
Independent revision, checked against Rules 226 and 234–236 on 17 October 2026.
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