Tunnel sign: what it means
The tunnel sign warns of a tunnel ahead. Expect darker light, less room and, sometimes, traffic queuing inside.
What does the tunnel sign mean?
It is a warning triangle; Know your traffic signs calls it “tunnel”.
Quick quiz
What does the sign at the top of this page mean?
- A tunnel ahead.
- Low bridge ahead: the height shown is the clearance.
- No vehicles taller than shown.
Show answer
A. A tunnel ahead. A tunnel ahead (Know your traffic signs). Source: Know your traffic signs: warning signs, GOV.UK; Know your traffic signs: regulatory signs, GOV.UK; The Highway Code, rule 126, GOV.UK; Traffic sign images, Department for Transport, GOV.UK
Where will you see it?
Before road tunnels in cities, under rivers and through hills.
What should you do?
Switch on dipped headlights if it is dark inside, take off sunglasses, and keep a safe gap. Rule 126 says to allow at least a two-second gap in tunnels where visibility is reduced, and to leave at least 5 metres to the vehicle in front if you have to stop.
What do people get wrong?
Following too closely. In a tunnel it is harder to see the car ahead braking, and harder to get out of the way.
Common questions
How big a gap should I leave in a tunnel?
At least two seconds when moving, and at least 5 metres if you stop (The Highway Code, rule 126).
Is the tunnel sign an order?
No. It is a warning triangle. Some tunnels also have their own restrictions, such as a ban on vehicles carrying dangerous goods, shown on separate regulatory signs (Know your traffic signs).
Compare with
Maximum headroom signLow bridge ahead: the height shown is the clearance.
Height limit signNo vehicles taller than shown.
Want to test someone else? Play a road-sign quiz with friends and family.
Sources
Checked on 3 November 2026 against Know your traffic signs (warning signs; regulatory signs) and The Highway Code rule 126.
- Know your traffic signs: warning signs, GOV.UK
- Know your traffic signs: regulatory signs, GOV.UK
- The Highway Code, rule 126, GOV.UK
- Traffic sign images, Department for Transport, GOV.UK
Contains public sector information licensed under the Open Government Licence v3.0. Traffic sign images are Crown copyright, from the Department for Transport. Sources and image credits.