The Utah Department of Transportation developed life-cycle benefit-cost analysis spreadsheets that allow engineers and analysts to evaluate multiple safety countermeasures. The spreadsheets have included the functionality to evaluate a roadway based on the 11 facility types from the Highway Safety Manual (HSM) with the use of crash severity distributions. The HSM suggests that local agencies develop crash severity distributions based on their local crash data. The Department of Civil and Environmental Engineering at Brigham Young University worked with the Statistics Department to develop crash severity distributions for the facility types from the HSM.The primary objective of this research was to utilize available roadway characteristic and crash data to develop crash severity distributions for the 11 facility types in the HSM. These objectives were accomplished by segmenting the roadway data based on homogeneity and developing statistical models to determine the distributions. Due to insufficient data, the facility types of freeway speed change lanes and freeway ramps were excluded from the scope of this research. In order to accommodate more roadways within the research, the facility type definitions were expanded to include more through lanes.The statistical models that were developed for this research include multivariate regression, frequentist binomial regression, frequentist multinomial, and Bayesian multinomial regression models. A cross-validation study was conducted to determine the models that best described the data. Bayesian Information Criterion, Deviance Information Criterion, and Root-Mean-Square Error values were compared to conduct the comparison. Based on the cross-validation study, it was determined that the Bayesian multinomial regression model is the most effective model to describe the crash severity distributions for the nine facility types evaluated.



College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering



Date Submitted


Document Type





crash severity, crash severity distribution, life-cycle benefit-cost analysis, Utah