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Abstract
The allocation of highway costs is constantly debated among legislatures, highway agencies, and
highway users as it directly relates to concerns about equity in terms of cost responsibility and
actual user charges. One of the major challenges in highway cost allocation stems from the need to
estimate pavement damage by different vehicle classes. Normally, the calculation of damage caused
by heavy vehicles to the highway infrastructure utilizes the concept of Equivalent Single Axle Load
(ESAL). This concept was empirically established after the American Association of State Highway
Officials America (AASHO) Road Test almost half a century ago. Although the ESAL concept is
widely used in pavement design, it has a number of shortcomings when applied for the estimation of
pavement damage by different vehicle classes. Some of these limitations include: failure to account
for specific infrastructure and environmental conditions, disregard of the differences in traffic
configurations and composition, and the inability to capture different distress types. This leads to a
fairly inaccurate and generic estimation of pavement damage by vehicle class.
This paper proposes an innovative and more rational highway cost allocation approach
based on the recently completed guide for the “Mechanistic-Empirical Design Guide of New and
Rehabilitated Pavement Structures” developed under the National Cooperative Highway Research
Program (NCHRP) Project 1-37A. The Guide accounts for all factors that contribute to pavement
deterioration, thereby addressing the shortcomings of an ESAL-based analysis listed earlier.
Estimates for pavement damage attributable to each vehicle class can thus be accurately simulated.
For the purposes of this study, traffic data collected at a weigh-in-motion station in Texas were used
to estimate the highway cost shares of different vehicle classes, given different pavement structural
capacities.