Estimation of the marginal cost of road wear as a basis for charging freight vehicles

Abstract

In Australia one option for improved freight vehicle productivity, as part of major road reform, is increasing the allowable freight vehicle axle loads above current load limits and reduce the transport cost per tonne-km. This can also potentially reduce greenhouse gas (GHG) emissions by reducing the number of freight vehicle movements for a given freight task. Decisions regarding increased axle loads on the existing road infrastructure can be founded on the marginal cost of road wear as the basis of a price for increasing axle loads. These prices can provide a clear signal for targeting maintenance and rehabilitation funding and works provided the revenue raised by the price is directly linked to the funding.The Freight Axle Limits Investigation Tool (FAMLIT) is a pavement life-cycle costing model that can be used to estimate load-wear-cost (LWC) relationships for a range of typical roads and pavement types for six heavy vehicle axle groups. Loads were incrementally increased above current load limits to estimate the LWC relationships. Life-cycle road wear costs were based on the present value (PV) of the routine and periodic maintenance and rehabilitation costs associated with managing each road type within agreed functional and structural conditions. The PVs of these costs were subsequently converted into equivalent annual uniform costs (EAUC) which were used to form LWC relationships with axle load (tonne-km) and standard axle repetitions (SAR-km), providing alternative independent variables. The marginal cost of road wear was determined by the first derivative of the LWC relationships.The estimated marginal road wear costs, in both short-run marginal cost (SRMC) form and long-run marginal cost (LRMC) form were found to vary across a range of road types and were highly dependent on the pavement/subgrade strength and traffic load. The marginal costs based on the LWC relationship using SAR-km as the independent variable were a constant value until axle group loads were increased significantly above current limits.