Illustrated in this paper are ways in which the Poisson regression model can be used to evaluate the effect of highway geometric design on truck accident involvement rates and estimate and quantify the uncertainties of the expected reductions in truck accident involvements from various improvements in highway geometric design. The data source used in this study was the Highway Safety Information System, a highway safety database administrated by the Federal Highway Administration. Among the five Highway Safety Information states currently available for analysis, Utah was considered to be the state that had the most complete information on highway geometric design and was selected for illustration. Five years of highway geometric, traffic, and truck accident data for rural Interstate highways from 1985 to 1989 were used.