Warning sign
Tunnel sign
What does the Tunnel sign mean?
Warns that a tunnel is ahead. Keep a steady speed and leave a safe gap to the vehicle in front.
Also known as: Tunnel ahead
What it means
There is a tunnel ahead.
The symbol shows a tunnel mouth. It warns you that the road goes into a tunnel, where the light and conditions can change quickly.
Leave enough space between you and the vehicle in front, and keep a steady speed and lane inside the tunnel.
Where you'll see it
On the approach to road tunnels.
Rules to know
The sign warns of a tunnel.
Know Your Traffic Signs, p. 12
Allow at least a two-second gap between you and the vehicle in front in tunnels where visibility is reduced. If you have to stop in a tunnel, leave at least a 5-metre gap.
The Highway Code, Rule 126
Common mistakes
Mistake: Stopping or changing lanes suddenly inside the tunnel.
Instead: Keep a steady speed and lane, and leave a safe gap.
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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.
Related signs
See also
Hump bridge
Warning sign
Another warning about the road structure ahead.
See also
Traffic queues likely ahead
Warning sign
Queues can build up near tunnels.
More warning signs
All warning signs
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- Know Your Traffic Signs (Department for Transport, Sixth edition, 2023), Warning signs, p. 12
- The Highway Code, Rule 126
Sign image: Department for Transport, Traffic sign images (diagram 529.1). © Crown copyright, reused under the Open Government Licence v3.0.
Last reviewed 11 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