EFFECTS OF TRUCK SIZE AND WEIGHTS ON HIGHWAY INFRASTRUCTURE AND OPERATIONS: A SYNTHESIS REPORT

The North American Free Trade Agreement (NAFTA) calls for harmonization of truck standards among the trade partners. Combined with the desire of U.S. industry to reduce freight costs, this aspect of NAFTA has stimulated interest in how liberalization of truck size and weight limits in the U.S. would affect highway infrastructure and safety. This report distills the findings from the extensive literature on this topic, to which a major recent addition was the Comprehensive Truck Size and Weight Study prepared by the U.S. Department of Transportation. Allowing extra weight for a given type of truck can cause substantial pavement damage because of the increase in the weights of the axles. However, the truck size and weight liberalizations that have received most attention in the literature would encourage a switch from the dominant type of heavy truck, the 5-axle tractor semitrailer, to trucks that have higher payloads and additional axles. Such reforms do not necessarily create substantial pavement costs: estimates of their effect on pavement costs are generally modest and sometimes negative. More likely, they will create substantial costs for upgrading bridges to accommodate the increases in gross vehicle weights. The effects on safety are especially hard to predict. Improvements in driver performance and vehicle design can offset the safety drawbacks of larger, heavier trucks. In addition, since higher payloads reduce the number of trips required to transport a given volume of freight, allowing heavier trucks could even reduce the number of accidents. Estimation of the overall effect on safety is not possible with available data on crash rates for heavy trucks.