General Model of the Effect of Hazardous Materials Car Placement in Trains and their Probability of Derailment

Abstract

Recent changes in freight train operating practices call for improved understanding of the effect of hazmat car placement on hazmat release risk. In existing models, placement of hazmat cars in a train is either assumed to be random or in blocks of grouped cars. There has been little investigation of how different train configurations affect the number of hazmat cars that could potentially derail in an accident. This paper presents a probabilistic model that calculates the probability and number of hazmat cars derailed based on accident characteristics and train configuration. The model distinguishes between hazmat and non-hazmat cars in manifest trains and provides probability distributions and the expected number of hazmat cars derailed under a set of train placement scenarios. The results indicated that the number and distribution of hazmat cars derailed were affected by speed, percentage of hazmat cars in the train (given the same train length), train configuration, and number of hazmat cars in the train (given the same percentage of hazmat cars in the train). The model presented here could be used as a stand-alone tool to evaluate train-configuration-based hazmat car derailment risk, as well as an integral component of an enhanced, comprehensive rail hazmat transportation risk analysis framework. The model results could be used to answer questions in hazmat transportation risk assessment, rail shipment planning and optimization, and tradeoffs related to unit train versus manifest train operation. The results could also inform potential policies about hazmat car placement in trains and operating speed.