The transportation of hazardous materials is a growing national problem. The percentage of highway and rail accidents that involve hazardous materials is increasing, the amount of damages per accident is escalating, and compliance with transportation regulations is eroding. A model for hazardous materials risk management is developed in this paper wherein vulnerability is a product of risk reduction (mitigation) and preparedness. Various risk assessment approaches to shipping hazardous materials along major routes were presented and applied to the state of Arizona so that transportation routes could be comparatively evaluated. Type and volume of flow were determined from a survey of commercial trucks that permitted an analysis of hazardous materials accident probabilities for individual routes. By using evacuation distances for chemical spills, a population risk factor was defined as the multiplicative product of hazardous materials accident probabilities and population-at-risk. The risk score for individual routes reflected the interaction of four variables:(a) the number of hazardous events that have occurred on the route,(bl hazardous materials accident probability,(c) population-at-risk and the potential hazard rating--a composite index incorporating potential incident severity, and (d) volume of hazardous materials by class.

The transportation of hazardous material or materials (HM) is a growing national problem. The number of highway accidents that involve HM has steadily increased since 1976, and HM rail accidents continue to increase as well as the costs per accident ll,~ l. Despite these trends, recent studies have found that management activities directed at reducing vulnerability to HM accidents are insufficient (l,.! l. Effective management to reduce risk and improve the level of preparedness to mitigate the adverse consequences of HM releases is contingent on understanding the magnitude and nature of the threat to local communities that reside near transport routes. Risk assessments of HM transport have recently emerged as a critical need and several models and approaches have appeared (2-. 2. l• Risk assessment of HM transport can be conceptualized as consisting of the following activities:(a) identification of the type and volume of HM transported;(bl the nature of the threat to the environment and populace of potential release;(c) the estimation of probabilities of HM accidents and chemical release, and (d) the consequences of release (10).