Low Bridge Signs

Every year within the UK, there are hundreds of accidents, some leading to death or serious injury due to high sided vehicles attempting to pass through a bridge that is too low.

Bridges that have a clearance of less than 16 feet and 6 inches, or around 5 metres will usually have signs, either regulatory order signs (those with a circular red ring) or the triangular warning sign, warning drivers of high sided vehicles.

The types of sign used depends on the type of bridge. This section details the various low bridge height signs along with their meanings. Questions regarding low bridge signs are often asked on the theory driving test.

Vehicles over height displayed must not pass sign. Height displayed in metric and imperial units.
Vehicles over height displayed must not pass sign. Height displayed in imperial units only.

Regulatory low bridge signs

Regulatory road signs are often used at non-arch bridges. Regulatory signs, or road signs that give orders provide mandatory instruction and it’s therefore illegal for vehicles that exceed the height displayed on the sign to proceed and pass one of these signs.

Regulatory low bridge height signs are placed on the bridge and at the roadside in front of the bridge. For more information on regulatory road signs, see order road signs.

Advanced warning of mandatory height restriction
Location of mandatory height restriction

Advanced warning and location of mandatory height restriction signs

Some low height bridges may have an advance warning of a mandatory height restriction up ahead. Directional arrows may be placed on the sign if the restriction is on a side road. Other signs may include the location of the mandatory height restriction with a suggestion of a safe alternative route.


Directional sign incorporating mandatory height restriction
Yellow road works sign with temporary mandatory height restriction

Road signs incorporating mandatory height restrictions

Green or white directional signs may also incorporate the mandatory height restriction roundel sign. See white road signs for further information.

Yellow road works signs can also incorporate mandatory height restriction signs indicating a temporary height restriction. See road works signs for further information.

Height restriction warning sign with imperial units
Height restriction warning sign with metric units

Height restriction warning signs

Warning signs are triangular with a red border (see warning signs for further examples) and can be used to indicate a low bridge or obstruction in imperial or metric units. Two signs detailing both units may also be used.

Height restriction warning signs may be situated well in advance of the low bridge and may include distance to the hazard on a separate plate.


Road signs incorporating a warning

Road signs incorporating a warning height restriction sign

Other road signs such as the directional white sign to the right may also incorporate warning signs. Triangular signs with a red border signify a warning ahead to motorists. See warning road signs for further examples and their meanings.

Variable message sign used at low bridges

Variable message signs used at low bridges

Low bridges that are particularly at risk of vehicle strikes can use electronic variable message signs / light signals. Infra-red beams are used that are activated by high-sided vehicles. When the sign becomes activated, alternating flashing amber lights illuminate. The top pair alternating with the bottom pair.

Road signs test quiz

The driving theory test involves many questions on the various road signs found throughout the UK. Once you have finished looking through this section on low bridge ahead and height restriction signs, take the road sign test knowledge quiz to test your ability for passing the theory test.


Other theory test road signs

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