Low bridge signs
Updated 5 December 2023
Applies to England, Scotland and Wales
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Each year there are hundreds of incidents in which bridges are struck by vehicles too high to pass under them. Both rail and road users have been killed in these incidents. Look out for signs in this section and make sure that you are not a bridge basher.
All bridges with a clearance of less than 16 feet 6 inches (about 5 metres) are normally signed. Both regulatory roundels and warning triangles can be used, depending on the type of bridge.
Bridges particularly at risk from strikes may have a variable message sign that is activated by high vehicles passing through an infra-red beam. When the sign is activated, 4 amber lights flash, the top pair alternating with the bottom pair.
Regulatory signs
At non-arch bridges mandatory signs may be used; it is unlawful for an overheight vehicle to pass one of these. They are placed on the bridge and at the side of the road in front of the bridge.
Some height restrictions may still show imperial units of measurement only. These signs will be replaced when they reach the end of their life.
No vehicles over the height shown may pass the sign (height shown in metric and imperial units).
Advance warning of a mandatory height restriction ahead; the sign may include an arrow, if the restriction is on a side road.
Location of mandatory height restriction ahead, with indication of an alternative route.
Warning signs
A warning sign indicates the maximum headroom under a bridge or other overhead obstruction, in metric and imperial units. This sign may be sited well in advance of a bridge, with the distance (in either yards or miles) shown on a plate; this may have an arrow to indicate that the bridge is on a side road at a junction ahead.
Older signs not displaying metric and imperial units in one panel will be replaced when they reach the end of their life.
Chord markings used indicate the points between which different headrooms over different parts of an arch bridge are available.
The maximum safe headroom at an arch bridge is shown on the triangular warning signs. Road markings guide high vehicles through the highest part of the arch. Drivers of all vehicles should give way to oncoming high vehicles in the middle of the road when there is insufficient room to pass. Drivers of cars and other low vehicles may keep to the left-hand side of the road, crossing the road markings, where this would enable them to pass oncoming vehicles in safety.
To make a bridge more conspicuous, black and yellow bands may be added to the arches or beams and to the abutments.
Where reduced headroom over a road is due to an overhanging building or structure, a plate may be added below the warning triangle to indicate this (‘building’ may be varied to ‘buildings’ or ‘structure’).
Location of a low bridge ahead, with indication of an alternative route.
Signs incorporating height restriction roundels and warning triangles
Roundels or warning triangles will sometimes be incorporated into directional signs that may also indicate an alternative route to take to avoid the low bridge.
Roundels may also be incorporated into road works signs to indicate temporary height restrictions.
Sign indicating a reduction in headroom
Temporary or permanent reduction in bridge headroom ahead (temporary sign).