Quantifying Rural Highway Safety Performance: Application of the Highway Safety Manual and Development of Mixed Distribution Statistical Models for Predicting Crash Frequency

This thesis work investigated two crash modelling techniques for calibrating highway safety performance for roadway segments in South Dakota: application of Highway Safety Manual (HSM) recommended predictive methods, and developing userdefined predictive models. HSM predictive methods were applied on three different state highway facility types in South Dakota. This study first directly applied the HSM predictive methods to calculate the predicted crash count on highway segments. The analysis of the prediction results revealed large deviation between observations and predictions for segments of different facility types, which prompted the necessity of modifying the HSM predictive methods to fit the South Dakota data. Next, modifications were conducted on the HSM predictive methods for rural state highway segments using the safety data requested from the South Dakota Department of Transportation (SDDOT). The calibration factors yielded by the modified methods are closer than one than the original methods. The goodness-of-fit of the two methods were compared and the result presents similar overall prediction performance