Maximum headroom sign: what it means
The maximum headroom sign warns of a low bridge or other overhead obstruction ahead. The figures show the clear height under it, in metres and in feet and inches.
What does the maximum headroom sign mean?
Know your traffic signs (low bridge signs) says the warning triangle shows the maximum headroom under a bridge or other overhead obstruction, in metric and imperial units. It may stand well before the bridge, with a plate giving the distance. All bridges with a clearance of less than 16 feet 6 inches (about 5 metres) are normally signed.
Quick quiz
What does the sign at the top of this page mean?
- No vehicles taller than shown.
- Overhead electric cables ahead.
- Low bridge ahead: the height shown is the clearance.
Show answer
C. Low bridge ahead: the height shown is the clearance. The maximum headroom under the bridge or obstruction ahead (Know your traffic signs). Source: Know your traffic signs: warning signs, GOV.UK; Know your traffic signs: low bridge signs, GOV.UK; Traffic sign images, Department for Transport, GOV.UK
Where will you see it?
Before railway bridges, arches and buildings that overhang the road.
What should you do?
Know the height of your vehicle, including any roof load, and of any trailer you are towing. If it is too high, take another route. At an arch bridge, high vehicles may use the middle of the road, so give way to an oncoming high vehicle.
What do people get wrong?
Forgetting about a hired van, a roof box or bikes on the roof. Each year hundreds of bridges are struck by vehicles that are too high (Know your traffic signs).
Common questions
What is the difference between the triangle and the round height sign?
The triangle warns of the headroom. The red circle is an order: no vehicles over the height shown may pass (Know your traffic signs).
Are all low bridges signed?
Bridges with a clearance of less than 16 feet 6 inches (about 5 metres) are normally signed (Know your traffic signs).
Compare with
Height limit signNo vehicles taller than shown.
Overhead electric cable signOverhead electric cables ahead.
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 (low bridge signs; warning signs).
- Know your traffic signs: warning signs, GOV.UK
- Know your traffic signs: low bridge signs, 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.