THE EFFECT OF PAYLOAD DISTRIBUTION AND VEHICLE MIX ON PAVEMENT LOADING

The road freight industry is responsible for the haulage of over 80% of all freight in Great Britain, amounting to approximately 1400 million tonnes per annum. The needs of freight in transit are wide-ranging and to meet these needs a range of vehicle types has evolved. Vehicle manufacturers, whilst designing to the needs of the freight industry, must ensure that their vehicles satisfy the motor vehicle (construction and use) regulations. In particular gross weight and axle loads must not exceed their plated values. In vehicle design it is assumed that the centre of gravity of the payload will be carried at the centre of the loadbed. Results of a recent survey have shown this to be the exception rather than the rule. In these circumstances the distribution of load on the axles is not as predicted, either by the manufacturer during design or by the Department of Transport in their allocation of pavement damage costs by vehicle class. This paper investigates the relationships that exist between the distribution of payload on heavy goods vehicles, vehicle mix and road type. Data have been collected at three separate sites and the relationships developed have been compared to the current design criteria adopted: (i) when designing heavy goods vehicles; (II) in pavement design (road note 29); (III) when allocating road track costs. Recommendations are made to revise these criteria and thus enable design to lead to more economic and reliable solutions. For the covering abstract of the proceedings see TRIS 450538. (Author/TRRL)