Effect of Train Speed on Risk Analysis of Transporting Hazardous Materials by Rail

Abstract

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 hazardous material from tank cars involved in accidents. The objective was to assess how accounting for speed affects the results of risk analysis. A case study of a representative hazardous materials route was conducted. In that case study, risk estimates were developed by using conventional, average-speed CPR, and the estimates were compared with those obtained by analyzing the same route using speed-dependent CPR. The differences in calculated risk indicate that the use of the speed-dependent CPR may be an important refinement for the accurate calculation of the risk of a route. The effects of track-class upgrades on risk were also considered. Track with higher Federal Railroad Administration classes has lower accident rates, but the higher permissible speeds increase the 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. Two scenarios were considered in the track-class upgrade analysis: upgrades without an increase in speed and upgrades with an increase in speed. The increased tank car hazardous material release rate at the higher speeds permissible on higher track classes was more than offset by the reduction in the accident rate for all the track-class upgrade scenarios considered. For the particular route analyzed in the case study, use of the speed-dependent CPR resulted in a slight increase in the overall risk estimate, and upgrading of Class 3 track provided the greatest reduction in risk. Such results will be route specific; however, the use of a speed-dependent CPR enables the more accurate analysis of local risk and provides a better evaluation of risk reduction options that involve changes in operating and track characteristics.

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