Rail plays an important role in hazmat transportation, transporting over two million carloads of hazardous materials (hazmat) in the United States annually. Compared with a truck trailer carrying a single hazmat car, a train has much more severe consequence of hazmat release due to carrying multiple connected hazmat cars (e.g., 50 to 120 flammable liquid cars). It is of high priority for the government and railroad companies to enhance the railroad hazmat transportation safety since the train accidents can cause severe railroad hazmat release incidents. Based on the data provided by Federal Railroad Administration (FRA) of the U.S. Department of Transportation (U.S.DOT), there are over 300 accident causes, including infrastructure failure defects, rolling stock failures, human errors, weather conditions, etc. It is significant to understand the relationship between hazmat transportation risk and accident cause to provide guidance for developing, evaluating, and prioritizing accident prevention strategies, thereby mitigating hazmat transportation risk. Therefore, this paper reviews the literature on rail transport of hazmat release risk analysis in order to capture the event chain leading to hazmat release, possible risk factors, and the state of the art on existing risk analysis methodologies.
We reviewed the related references based on a five-step process: (1) train accident occurrence, (2) number of cars derailed, (3) number of hazardous material cars derailed, (4) number of hazmat cars releasing, and (5) release consequences. First, many severe hazmat release incidents are caused by train accidents, particularly train derailments. Prior research found that over 70% of freight train mainline derailments were caused by either infrastructure defects or rolling stock failures. Possible strategies for reducing the probability of train accidents include the prevention of track defects, equipment condition monitoring to reduce in-service failures, and the use of more advanced train control technologies to reduce human error. Second, number of cars derailed is an important factor causing hazmat releasing. Based on the reviewed literature, the total number of cars derailed depends on accident cause, speed, train length, and point of derailment. Third, the literature implied that the total number of hazmat cars derailed is related to train length, number of hazmat cars and non-hazmat cars in a train, and their placement. Fourth, the number of hazmat cars releasing contents is influenced by hazardous materials car safety design, accident speed, etc. Finally, the consequences of a release can be measured by different metrics, such as property damage, environmental impact, traffic delay, or the affected population. Geographical information systems (GIS) can be used for consequence analysis integrated with other databases such as census and rail network data.