Estimating Traffic Changes and Pavement Impacts from Freight Truck Diversion following Changes in Interstate Truck Weight Limits

This paper reports on two methodologies that were developed and used in a study for the State of Maine. The study examined the pavement, crash, and bridge costs of higher truck weight limits being allowed on an Interstate route. These higher weight limits would attract to the Interstate route high-weight (between 80,000 and 100,000 lb gross vehicle weight) combination trucks that currently use alternative routes on Maine state roads (which already allow these higher weight limits). The first methodology estimated the changes in freight truck traffic volumes. The methodology estimates gains and losses in vehicle miles traveled by route and by vehicle configuration and the associated gains and losses in equivalent single-axle loads (ESALs) on these routes. The second methodology estimated road cost per ESAL by road type; this allows pavement costs to be derived from the ESAL effects estimated by the first methodology. The data used for the methodologies included TRANSEARCH data, weigh-in-motion station data, traffic classification count data, and the Maine Department of Transportation's TIDE road database system. The traffic estimation methodology used successive (iterative) rounds of expert opinion derived through interviews, data analysis, and route mapping. This paper also discusses the key role of an evolving picture of the system within the analysis team.