Rule 307 - The Highway Code

Overhead electric lines. Tramway overhead wires are normally 5.8 metres above any carriageway, but can be lower. You should ensure that you have sufficient clearance between the wire and your vehicle (including any load you are carrying) before driving under an overhead wire. Drivers of vehicles with extending cranes, booms, tipping apparatus or other types of variable height equipment should ensure that the equipment is fully lowered. Where overhead wires are set lower than 5.8 metres, these will be indicated by height clearance markings - similar to ‘low bridge’ signs. The height clearances on these plates should be carefully noted and observed. If you are in any doubt as to whether your vehicle will pass safely under the wires, you should always contact the local police or the tramway operator. Never take a chance as this can be extremely hazardous.