Effect of Train Speed on Railroad Hazardous Materials Transportation Route Risk Analysis

This paper considers the effect of train speed on railroad hazardous materials transportation risk. A statistical method was developed to estimate the speed-dependent conditional probability of release (CPR) of tank cars involved in accidents with the objective of assessing its effect on risk analysis results. A case study of a representative hazardous materials route was conducted in which risk estimates were developed using conventional, average-speed CPR and compared to the analysis of the same route using speed-dependent CPR. The calculated risk results differed indicating that use of speed-dependent CPR may be an important refinement for accurate calculation of route risk. The effect of track-class upgrades on risk was also considered. Higher FRA track classes have lower accident rates, but the higher permissible speeds increase CPR if a tank car is derailed in an accident. Consequently, evaluation of the effect of track upgrades must account for both factors to understand the net impact on risk. In the track-class upgrade analysis two scenarios were considered: upgrades without speed increase, and upgrades with speed increase. The increased tank car release rate at the higher speeds permissible on higher track classes was more than offset by the reduction in accident rate for all the track-class upgrade scenarios considered. For the particular route analyzed in the case study, using speed-dependent CPR resulted in a slight increase in the overall risk estimate, and upgrading class-3 track provided the greatest reduction in risk. Such results will be route-specific; however, use of speed-dependent CPR enables more accurate analysis of local risk and provides a better evaluation of risk reduction options that involve changes in operating and track characteristics.