Bridge height limits UK explained
Bridge height restriction signs are among the most misread in the UK. The red triangle warning sign tells you a low bridge is ahead. The blue circle with a measurement is the legal prohibition. And the plate fixed to the bridge structure shows the actual clearance your vehicle must fit under. Knowing which sign does what could save your roof - and a significant insurance claim.
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The low bridge warning sign
The low bridge warning sign is a red triangle containing a small bridge arch with an upward arrow and a height measurement. This is a hazard warning, not a legal prohibition. It tells you a low bridge is ahead and gives its maximum clearance height. If your vehicle exceeds that measurement, you need to find an alternative route before reaching the bridge.
These warning signs appear well before the bridge - sometimes several hundred metres ahead - to give drivers enough distance to turn around. The measurement shown is the maximum clearance at the centre of the arch; clearance at the sides may be lower.
Height restriction signs
A blue circle containing a white measurement in metres (and sometimes feet) is the maximum height prohibition. Vehicles exceeding the stated height must not pass. This sign has legal force - ignoring it risks a Penalty Notice and, more significantly, structural damage to the bridge that can close the route for hours and cost tens of thousands of pounds to repair.
Height restriction plates are also fitted directly to the bridge structure. These show the clearance of the lowest point. When reading a bridge, take the lower of any two figures - the plate on the bridge face gives the actual clearance your vehicle must fit under.
Weak bridge signs
A yellow plate on or near a bridge marked "WEAK BRIDGE" with a weight figure in tonnes means the bridge cannot support vehicles above that gross weight. The restriction applies to the total weight of the vehicle including fuel, passengers, and any load being carried - not just the vehicle's unladen weight.
For most private cars, weak bridge restrictions are not relevant. For vans and anything carrying a significant load, the laden gross weight must be checked carefully. Our guide to what vans can be driven on a car licence covers van weight categories and their implications.
What to do if you realise your vehicle is too tall
If you approach a bridge and realise your vehicle exceeds the restriction, turn around before reaching it. On a narrow road where turning is difficult, reverse to a safe turning point. Do not attempt to drive through on the basis that it looks fine - the clearance measurement is precise and a fraction of a metre of error can cause serious damage.
If you have already committed and become lodged, stop immediately. Do not attempt to drive forward or back if the vehicle is genuinely stuck - this causes further structural damage. Call 999 if there is immediate danger, or 101 for the police. Network Rail operates a dedicated hotline for railway bridge strikes: 03457 11 41 41.
Roof racks and roof boxes
The unladen height published by a vehicle manufacturer does not include roof racks, roof boxes, or any other roof-mounted equipment. If you have a roof box fitted, measure the total height yourself before travelling a route with low bridges. Sat-nav systems designed for motorhomes and taller vans can be configured to alert to low bridges based on your vehicle's height.
Frequently asked questions
What does the low bridge warning sign look like?
The low bridge warning sign is a red triangle containing a small bridge arch with an upward arrow and a height measurement. It is a hazard warning giving the maximum clearance of the bridge ahead, allowing drivers time to find an alternative route before reaching it.
What is the legal height restriction sign?
A blue circle containing a white measurement in metres is the maximum height prohibition sign. It is an offence for a vehicle exceeding the stated height to pass through. These signs have legal force - bridge strikes can result in a Penalty Notice and liability for the cost of repair.
What should I do if my vehicle is too tall for a bridge?
Turn around before reaching the bridge. If you are close and cannot pass safely, reverse to a turning point. Never attempt to drive through a bridge that your vehicle exceeds - a lodged vehicle can cause serious structural damage and close the road entirely.
What is a weak bridge sign?
A yellow plate marked 'WEAK BRIDGE' with a weight figure in tonnes means the bridge cannot support vehicles above that gross weight. The limit applies to the total laden weight of the vehicle including passengers and load. Most private cars are unaffected, but vans and lorries carrying loads need to check their weight carefully.
Does insurance cover a bridge strike?
Comprehensive cover will pay for damage to your own vehicle. However, you may also be held liable for the cost of repairing the bridge - particularly for a railway bridge strike, where repair bills can run into tens of thousands of pounds. The incident will be reported to your insurer and is likely to affect your renewal.
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