§ Lord Bradshawasked Her Majesty's Government:
What is the damage impact on road infrastructure of lorry axles weighing 10.5 tonnes, 11.5 tonnes and 12.5 tonnes respectively compared with the average motor car. [HL3764]
§ Lord WhittyFor both roads and bridges the structural damage caused by the average motor car is negligible. The wear on road pavements from lorries is generally considered proportional to the 4th power of the axle load. Thus, lorry axle loads of 11.5 tonnes and 12.5 tonnes cause about 40 per cent and 200 per cent more wear than a 10.5 tonne axle. A simple relationship for bridges does not exist.
Current design standards for main roads reflect all normally permitted lorries with axle weights up to 11.5 tonnes. The presence of abnormal vehicles with heavier axles including 12.5 tonnes is also allowed for in design and permitted on certain routes but represents only a minor percentage of lorries. Vehicle construction and use regulations aim to minimise wear by defining how the total vehicle weight is transferred to the road avoiding unduly heavy individual axles.