Risk Comparison of Transporting Hazardous Materials in Unit Trains versus Mixed Trains

This research developed an integrated, generalized risk analysis methodology for comparing hazardous materials transportation risk in unit trains versus mixed trains for the same amount of traffic demand. The risk methodology accounted for FRA track class, method of operation, annual traffic density, train length, speed, point of derailment, the number and placement of tank cars in a train, tank car placement, tank car safety design, and population density along the rail line. With these inputs, the methodology estimates train derailment rate, the probability of tank car derailment and release, and release consequence by train configuration. The analysis showed that tank car positions could affect the risk comparison between unit trains and mixed trains in transporting hazardous materials. In particular, if all tank cars were in positions that were least prone to derailment, distributing tank cars to many unit trains could reduce the overall risk. Otherwise, consolidating tank cars into unit trains could lead to a lower risk. The methodology has been implemented in a computer-aided decision support tool that automatically calculates the risk values for various track, rolling stock, and operational characteristics.