COMPARISON OF RISK MEASURES FOR THE TRANSPORT OF DANGEROUS COMMODITIES BY TRUCK AND RAIL

Current empirical evidence concerning the relative risks of transporting dangerous commodities by truck and by rail has been plagued by highly variable and inconsistent results. Much of the problem can be attributed to the nature of the risk assessment and its failure to consider two important aspects: (a) different ways of measuring risks and (b) a strong dependence between risk and the nature of the transport environment in which dangerous commodities are shipped. In this paper, the risks of transporting dangerous commodities by truck and rail are expressed by four constituent elements: accident rates, spill probabilities in an accident situation, hazard areas for different classes of damage, and expected impacts on population and environment along a specified road or rail corridor. Changes in the level of risk for individual shipments are considered for different material properties, spill characteristics, and transportation environments. Under most conditions, trucks exhibited significantly higher accident rates than trains. These results were consistent for two measures of shipment exposure: on a per-vehicle-kilometer and a per-tonne-kilometer basis. On the consequence side, the relative merits of one mode over another were not as clearly defined. Both trucks and trains reflect certain safety advantages over one another depending on the nature of the material being shipped and the assumed transport environment.