HEAVY TRUCK SIZE AND WEIGHT AND SAFETY

Considerable debate has focused on the safety of US commercial heavy trucks, and particularly on the question of whether allowing truck sizes and weights to increase would degrade safety. Efforts to answer that question have centered on two approaches, crash data analyses and comparative analyses of the safety-related engineering performance capabilities of various truck configurations. This paper summarizes that work, and provides a new analysis. Medium/heavy trucks are a small part of the motor vehicle fleet, but account for a disproportionate number of fatal accidents. The number of medium/heavy truck fatal accidents is explained in part because their annual travel, or exposure, is much greater than automobiles and light trucks. Among the large trucks, multi-trailer combination trucks appear to have a better safety record on the basis of fatal accidents per mile of travel. However, when the data are disaggregated on the basis of highway classification, multi-trailer combinations are shown to be generally less safe per mile of travel, particularly on rural highways. Engineering analysis also indicates that multi-trailer configurations are less stable than standard single combination trucks and, therefore, more prone to accidents. This propensity is evident when multi-trailer combination fatal crash rates are analyzed under conditions of generally unrestricted use similar to that of single trailer combinations. Under these conditions multi-trailer combinations - as they are currently designed and configured - could be expected to experience an eleven percent higher overall fatal crash rate than single trailer combinations. (a) For the covering entry of this conference, please see IRRD 895232.