Quantifying the Influence of Tank Car Position and Train Configuration on the Risk of Rail Transport of Class 3 Flammable Liquids

As the amount of high-hazardous materials (hazmat) being shipped in high-hazard flammable unit trains (HHFUT) increases, mitigating the risks associated with railway transportation of hazmat remains an industry priority. Compared with HHFUT configurations, the placement of hazmat railcars in high-hazard flammable trains (HHFT) and the number of classification yards they traverse can affect the risk of derailment and subsequent hazmat release for HHFTs. This paper evaluates hazmat release risks associated with the transportation of U.S. Department of Transportation (U.S. DOT) Class 3 flammable liquids by tank cars. Specifically, it compares the risks of HHFUTs and HHFTs for shipping a designated amount of hazmat and considers both mainline and yard operations in alignment with existing regulations and practical guidance. The methodology quantifies the transportation risk in total expected release consequence (i.e., casualties) given the total amount of Class 3 flammable liquids transported in HHFUT and HHFT configurations with different tank car placement strategies. Based on the case study, we find that using five 100-railcar HHFTs, each with 20 tank cars in positions 66 through 85, is both practical and generates the lowest transportation risk. Some hazmat railcar placement strategies in HHFTs lead to a higher release risk than HHFUT operations, while others result in a lower release risk. The proposed methodology could be extended to diverse operating scenarios to better understand the impacts of train configuration and tank car placement on the risk of rail transport for flammable liquids.