Much truck research undertaken during the 1980s has been directed toward measuring the impact of longer and heavier vehicles on the highway infrastructure. However, bridge costs have been neglected, principally because of the technical difficulties involved in measuring realistic impacts from the available data bases. Recent transportation research board (trb) studies on truck weight limits and turnervehicles attempt to resolve the issue of bridge costs by including estimates of bridge damage attendant on the operation of various large-truck configurations. At present, these trb studies constitute the most important sources of information currently available to researchers and policymakers. Yet the assumptions concerning mechanisms for determining bridge deficiencies seem worthy of further investigation, particularly because the trb findings suggest that productivity benefits substantially overwhelm infrastructure costs. Impact on the rural interstate bridge system of two long-combination vehicle (lcv) configurations that, although attractive to truckers, were not included in the terms of reference for the trb studies, is examined. These are double 48-ft trailers (turnpike doubles) and triple 28-ft trailers, both of which use the considerable investment made by the trucking industry in these trailer types. It is estimated that lcv operations on the rural interstate system result in greater bridge damage than predicted when using the trb methodology, and that user costs --not reported by the trb authors-- are likely to be extremely highon key rural structures, resulting in cost predictions that could exceed direct agency costs. This paper appears in transportation research record no. 1319, Bridge and hydrology research 1991.
Abstract