Height limitUnited States
Traffic rules
United States
35. Height limit
A height limit prohibits vehicles whose total height exceeds the value shown from entering or passing a road section, bridge, tunnel, gateway or other structure. The vehicle’s height includes its load and any equipment attached above it.
Drivers of high vehicles must know their exact height, observe advance warnings and use an alternative route when necessary. They should never rely only on visual judgement or attempt to pass beneath a structure when safe clearance is uncertain.
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What does a height-limit sign mean?
It prohibits vehicles whose total height exceeds the displayed value from continuing beyond the sign.
How can you recognise a height-limit sign?
It is commonly a circular regulatory sign showing a height in metres, feet or another local unit between vertical arrows.
What is included in the vehicle’s total height?
The height includes the vehicle, its load and any attached equipment, such as roof boxes, bicycles, machinery, antennas or raised loading equipment.
Does the limit apply to trailers?
Yes. Every part of a vehicle combination must fit beneath the restriction, including the towing vehicle, trailer and load.
Does the sign show the exact physical clearance?
Not necessarily. Road authorities may display a lower value than the measured clearance to provide a safety margin.
May a vehicle exactly as high as the displayed value pass?
The legal wording commonly prohibits vehicles higher than the displayed value, but drivers should not attempt to pass without a practical safety margin. Measurement errors, movement and road conditions can reduce the available clearance.
How can a vehicle’s height change?
Loading, tyre pressure, suspension settings, raised equipment, replacement tyres and road movement can alter the vehicle’s total height.
Can air suspension affect the height?
Yes. The vehicle may rise or lower depending on its suspension mode, speed and load. Use the maximum travelling height when planning the route.
Can the clearance vary between lanes?
Yes. An arched bridge, tunnel roof or overhead structure may provide different clearance in each lane. Follow lane-specific signs and markings.
Can the clearance vary across the width of one lane?
Yes. Clearance may be lower near the edge of an arch or where the road slopes sideways. Remain within the authorised marked path.
Can resurfacing reduce the available clearance?
Yes. A new road surface can raise the road level and reduce the space beneath a bridge or structure.
Can snow, water or road debris affect clearance?
Yes. Material on the road can raise the vehicle or restrict the usable route. Flooding may also conceal the road surface or another hazard.
Where are height restrictions commonly found?
They are common at bridges, tunnels, car parks, loading areas, gateways, railway structures and roads with overhead equipment.
Is a height-limit sign a warning or a prohibition?
It is normally a prohibition. A vehicle that exceeds the displayed height may not pass.
Does a height-limit sign impose a speed limit?
No. The applicable road or posted speed limit remains in force, although drivers should approach cautiously.
Does the sign change priority?
No. Traffic lights, priority signs and ordinary priority rules remain applicable.
Can a height restriction be announced in advance?
Yes. An advance sign may show the restriction and the distance to it so that high vehicles can choose another route.
What should you do when your vehicle is too high?
Do not continue. Stop where safe and follow the signed diversion or another suitable route. Do not reverse into traffic without assistance.
Should you rely on a navigation system?
No. Navigation may contain outdated or incomplete vehicle restrictions. Traffic signs and the actual road conditions always take precedence.
Should professional drivers know their vehicle’s height?
Yes. Drivers of trucks, buses, motorhomes and vehicles carrying roof loads should know and, where useful, display the vehicle’s maximum travelling height inside the cab.
What should you do when uncertain about your height?
Stop before the restriction in a safe place and verify the vehicle’s height. Choose another route when safe clearance cannot be confirmed.
May you move into another lane with greater clearance?
Only when signs and markings permit it and the manoeuvre can be completed safely. Do not cross a closed lane, continuous line or opposing traffic merely to gain clearance.
May you lower or remove equipment to pass?
Only in a safe place and when the equipment can be secured correctly afterwards. Never stop beneath the structure or in a live lane to alter the vehicle.
What should you do if your vehicle strikes a bridge?
Stop immediately where safe, activate the hazard warning lights and contact the emergency services or police. Do not continue because the vehicle, load or structure may be unstable.
Should traffic continue beneath a struck bridge?
No, when damage may have occurred. Keep away from the structure and follow instructions from the police, road authority or railway operator.
