Book Description

This report describes two major studies that were conducted to determine the effect of truck size and weight on accident experience and traffic operations. The first study involved a field evaluation of the effect of truck size and weight on traffic operations. The second study addressed the effect of truck size and weight on accident experience. The field study examined traffic operational effects associated with truck size and weight. Selected highway geometric conditions were: upgrades (short, long; slight, steep), downgrades (long, steep), curves (freeway, non-freeway), grade/curve combinations, merge areas, ramps, and urban intersections. Matched weight and operational data were gathered on nearly 6,000 trucks ranging in gross weight from approximately 20,000 to 160,000 pounds. Extensive traffic operations measures obtained via electronic roadway sensors included: flow (e.g., speed, acceleration), perturbations (e.g., speed variance, deviation from traffic speed), accident potential (e.g., closure rate, projected collision time), delay (e.g., speed delays by following vehicles), and passing behavior (e.g., relative passing speed). The objective of the accident study was to determine the effect the size and weight of large trucks has on accidents and traffic operations. The effect on accidents was determined by comparing the accident rates for a variet of truck types defined in terms of configuration, size, and weight. The accident rate is obtained by dividing the number of accidents of a specific truck type, size, and weight by the exposure mileage (opportunity to have an accident) for that same truck type, size, and weight. Data were collected for all large truck accidents occurring on 78 roadway segments in six states. In total, 2,112 accident involvements were investigated in-depth over a 1-1/2-year period in 1976-1977.