Practical Approach for Determining Permit Fees for Overweight Trucks

Abstract

A practical approach is presented for determining permit fees for overweight (OW) trucks based on consumption of service life of highways. A mechanistic–empirical design philosophy is used to estimate deterioration of the pavement structure. The methodology uses permanent deformation, load-related fatigue damage, and roughness scores as descriptors to estimate service life consumption for flexible pavements and punchouts and roughness measures for rigid pavements. The experiment included flexible and rigid pavement sections with varying structural numbers and slab thicknesses from sections across Texas to account for climatic and geographical differences. Each pavement section was simulated under different loading conditions reflecting the full spectrum of axle weights characteristic of single, tandem, tridem, and quad axles. The exercise provided the basis for developing group equivalency factors and axle load factors for individual axle groups. Axle-specific parameters enabled a modular approach toward determining gross load equivalencies for any truck category without restriction on axle weights or configuration. Consumption of service life was calculated as the additional pavement structure required to accommodate OW traffic in excess of the design truck volume while ensuring the same terminal distress condition. The cost incurred in providing the additional structure to offset the accelerated consumption was assigned to the responsible truck fleet in proportion to the marginal load equivalency over the legal gross vehicle weight and axle weight tolerances. Permit fees of 3.7¢/mi per equivalent single-axle load for flexible pavements and 2.9¢/mi per equivalent single-axle load for rigid pavements were found to be practical.