GEOMETRIC DESIGN FOR LARGE TRUCKS--AN OVERVIEW OF THE ISSUES FROM THE PERSPECTIVE OF THE AMERICAN TRUCKING ASSOCIATIONS, INC.

Size and weight regulations represent compromises between conflicting needs. There is a need to accommodate diverse kinds of highway transportation demands and a need to fit trucking into the capabilities of the highway system. A consistent pattern of size and weight regulation, characterized as the strategy, has evolved and does a good job of meeting most of these needs. Under this strategy, increased productivity in trucking has come about largely through changes in vehicle type and gross weight, not through increases in the maximum allowable axle loads. For instance, there have been only two general axle weight limit increases in the United States since weight regulation became of central concern. One came during World War II and the second in 1974. The spread-the-load weight regulation strategy strongly influences vehicle and thus also influences geometric highway design. The Federal-Aid Highway Amendments of 1974 formalized this weight regulation strategy, and the Surface Transportation Assistance Act (STAA) of 1982 accelerated the use of vehicles dictated by it. How the industry is adapting to the 1982 STAA criteria and why there is minimal overall impact on the highway network are described. Also presented are some specific examples of how size and weight regulations design the trucks used by the industry and a brief discussion of how future developments may be reasonably accommodated.