TRAFFIC LOADING AND ITS INFLUENCE ON THE DESIGN OF FLEXIBLE PAVEMENTS AND OVERLAYS

Proposals to alter the statutory axle loading limits in conformity with the intentions of the eec and the increasing number of heavy commercial vehicles coming into this country from abroad have focused attention on the relationship between traffic loading and the structural performance of pavements. On the basis of certain assumptions about the effects of increasing statutory axle limits on the actual loading of the vehicles, increases in structural damaging power corresponding to different statutory axle limits are evaluated. It is shown that a statutory limit of 13 tonnes would be likely to produce a smaller increase in damaging power than that currently existing between traffic flows in opposite directions at the same points in some of the major roads. The influence of these different levels of axle loading on the structural performance of pavements is investigated in several ways; the reduction in life that would result if the loading was increased above the original design level may be evaluated; and the increase in pavement thickness necessary to ensure that roads designed for different statutory axle limits would all have the same life can be estimated together with their relative costs. An alternative solution to the problems is to determine the thickness of asphalt overlay which would have to be applied to roads originally designed for a lower level of statutory axle limit to ensure that under increased axle loadings the same ultimate life would be obtained. The cost of these solutions is also estimated. (A) /TRRL/