Low-bridge signs should connect to an operator control
A driver must recognise and obey the sign, while the operator’s system should be designed to prevent an unsuitable vehicle from being routed towards the restriction. Evidence should connect the verified travelling height with the cab notice, route planning, driver briefing and subsequent supervision.
Official height-restriction artwork
Images are official Department for Transport reproduction artwork. © Crown copyright, reproduced under the Open Government Licence v3.0.
Mandatory roundels and warning triangles
A red-ring roundel gives an order. Department for Transport guidance states that it is unlawful for an overheight vehicle to pass a mandatory sign at a non-arch bridge. A warning triangle identifies the maximum headroom at a bridge or overhead obstruction.
At an arch bridge, the signed headroom is available through the marked part of the opening. The operator must therefore consider vehicle width and route position as well as height.
Evidence before dispatch
- verified height of the tractor, trailer, load and relevant equipment
- correct maximum height displayed in the cab where the driver can read it
- route checked against that travelling height
- driver briefed on restrictions, alternatives and the escalation contact
- changes after loading, reloading, trailer swaps or equipment adjustment recorded
Official bridge-strike guidance states that vehicles with an overall travelling height over 3 metres must display the correct maximum height in the cab. The operator should be able to show how the figure was obtained and when it was updated.
What a route-control record should show
Keep the height used for planning, the planned route, the source used to check restrictions and any alternative issued. A navigation system can support the process, but it does not remove the need to verify vehicle data or obey temporary and permanent signs.
Where a route changes, record who checked the alternative and how the driver was told. This is especially important where a diversion, collection point or customer instruction moves the vehicle away from the planned road.
Review after a warning, near miss or strike
Preserve vehicle and trailer details, load information, height measurements, cab notice, route plan, navigation data, messages and photographs. Establish whether the failure began with measurement, dispatch information, route selection, driver response or supervision.
Corrective action should address the cause and then be tested. A training note alone does not show whether cab-height records, route approval or trailer-change checks improved.
Official sources
- Department for Transport: Low bridge signs, updated 5 December 2023
- Department for Transport traffic sign reproduction artwork and terms
- Prevention of bridge strikes: good practice guide for Transport Managers
Return to the Commercial Vehicle Signs, Symbols and Codes centre.