Growth trends in vehicle transportation for the year 1989 showed that truck travel has increased from 400 billion vehicle miles of travel to 600 billion vehicle miles from 1980 to 1989, a staggering 50% increase. If this trend continues, then truck travel will reach 800 billion vehicle miles by the end of the year 2000. This increase in truck travel poses operational and safety problems for both passenger vehicles and trucks. To improve the existing highway facilities for trucks as well as to determine the design standards for new truck facilities, an understanding of the relationship between truck accidents and highway geometry is required. A number of models have been developed in the past but none of them consider all of the geometric features of the highway which are crucial for truck travel and the causation of truck accidents.

The objectives of this study were to identify the roadway variables that affect truck accidents and to develop mathematical models which would determine truck involvement rates, per mile, per year.

Data from the Highway Safety Information System (HSIS) was used in this analysis. The HSIS is a new data base developed by FHWA which contains accident, roadway and traffic data from five States. Models for truck accidents on Interstates, 2 lane rural roads, and for over turning accidents on Interstates were developed. The models indicate that truck accidents are primarily affected by horizontal curvature and vertical gradient albeit their values are different for Interstates and 2 lane rural roads. The number of truck accidents decreases on 2 lane rural roads as the shoulder width increases, and the model indicates that gradient has no effect on truck accidents on these roads and this, may be due to the inadequacy of the data. The Interstate model indicates that the higher the degree of curvature and the percentage of gradient, the greater the number of truck accident, as well as overturning truck accident involvement rates.