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5 CHAPTER TWO HISTORY AND EVOLUTION OF HIGHWAY COST ALLOCATION STUDIES In 1937, Oregon conducted the nation's first HCAS. Oregon, heavier vehicles the undeserved benefit of economies of more than any other state, was an early pioneer in terms of scale inherent in the provision of pavement strength. That is, both the development and implementation of state HCASs, each additional inch of pavement depth up to a certain point conducting five studies before the groundbreaking Federal can support an increasing number of equivalent single-axle HCAS completed in 1982 and implementing a three-tier sys- loads (ESALs) during the design life of the pavement. What tem of highway taxation (registration fees, fuel taxes, and made the shift possible was the revolution in computer weight-mile taxes on heavy trucks) with the flexibility to technology combined with major achievements in relevant fully implement the findings of the HCAS. Ten other states highway research. performed HCASs before the 1982 federal study--Arkansas, Colorado, Florida, Georgia, Kansas, Maine, Mississippi, The Federal Method, or variations on the Federal Method, New Mexico, Washington, and Wyoming. Federal HCASs gradually became accepted practice during the 1980s. The were conducted in 1965, 1982, and 1997. 1996 to 1997 Federal HCAS used this basic approach with several important refinements, the most significant of which was the development and application of the National HIGHWAY COST ALLOCATION STUDY METHODS Pavement Cost Model or NAPCOM. The FHWA continued to develop and refine NAPCOM over a 10-year period dur- Before the 1982 Federal HCAS, the methodology used in ing the 1990s. Refinements made as part of the 1997 Federal most state HCASs was some form of what is called the "In- HCAS made the model practical for use by states. cremental Method," which was the set of methods developed in Oregon and refined in the major benchmark Federal NAPCOM applies a set of pavement deterioration analy- HCAS conducted between 1957 and 1965 and published in ses to a large sample of pavement sections to determine what 1965. The Incremental Method assigns responsibility for types of deterioration will occur and which vehicles are highway costs by first determining the costs of constructing responsible for each type of deterioration. Heavy axles cause and maintaining facilities for the lightest vehicle class and more damage per passage than light axles. For some types of then building the facility up to account for the costs attributed pavement deterioration, doubling the axle load causes 15 to to each increment of larger and heavier vehicles. All vehicles 20 times as much damage; for other types of deterioration, are allocated the costs of the base highway system in propor- doubling the load only doubles the damage. NAPCOM was tion to their usage of the highway system, as if they all had developed because traditional approaches using simplistic the same size and weight. The additional costs of accommo- ESALs did not mesh well with empirical data on pavement dating heavier and larger vehicles are defined as their occa- wear (Federal Highway Cost Allocation Study Final Report sioned incremental costs, which could be avoided if those 1997). The 1999 Oregon HCAS was the first state study to additional classes were excluded from the highway system. use NAPCOM to allocate pavement costs (Stowers et al. 1999). Following the 1982 Federal HCAS, states across the nation adopted the "Federal Method." The Federal Recom- Several state HCASs developed and applied both the In- mended Method, or simply the Federal Method, was devel- cremental Method and the Federal Method, including the oped during the 1979 to 1982 Federal HCAS by adapting the first California study (1985 to 1987), the 1989 to 1990 older Incremental Method procedures for some expenditure Vermont study, and the 1989 to 1991 Minnesota study. elements and by developing new procedures for other ele- These have been the two most commonly used methods in ments. The Federal Method is a mixed approach. It applies a the United States. Almost all of the more recent state HCASs consumption approach to pavement rehabilitation and some have used the Federal Method and variations or refinements related work, while applying the traditional Incremental of that approach [Arizona (1991 to 1995), Nevada (1992), Approach or other methods for expenditure elements that California (1995 to 1997), Idaho (1994 and 2000), and could not be viewed as consumed by highway use. several others]. One reason for the shift from the Incremental to the Oregon has explored performing a full cost-based alloca- Federal Method was that the former approach gave larger and tion study that moves away from allocation of highway