An investigation of the effects of lorry suspension performance on road maintenance costs

A mathematical model of the interaction between a fleet of heavy vehicles and a spray-sealed road surface is developed and validated using field performance data. Key features of the model include: (a) modelling the dynamic performance of the vehicle fleet using an ensemble of,quarter car' vehicle models; (b) careful accounting for the 'spatial repeatability' of tyre forces; (c) use of accelerated pavement performance test data to model the evolution of the road surface profile; (d) surface maintenance intervention based on permanent deformation (rutting), potholing and excessive surface roughness. The model is used to predict long-term road maintenance intervention costs and to compare the predicted road maintenance costs for various suspension scenarios in the vehicle fleet. The simulation results indicate that conversion of the heavy vehicle fleet from conventional leaf spring suspensions to 'road-friendly' suspensions would results in a reduction in road maintenance costs per tonne-km of 14 per cent. Increasing the freight load by 3.0 tonnes per vehicle would reduce this benefit to approximately 1 per cent. If the fleet was to have 50 per cent poorly maintained shock absorbers, the simulations show an increase in road maintenance expenditures per tonne-km: about 5 per cent higher than conventional suspensions at the lower weights and 21 per cent higher at the higher weights.