Modeling risk in the dynamic environment of maritime transportation

The Washington State Ferries are one of the largest ferry systems in the world. Accidents involving Washington State Ferries are rare events. However, low probability, high consequence events lead to difficulties in the risk assessment process. Due to the infrequent occurrence of such accidents, large accident databases are not available for a standard statistical analysis of the contribution of perceived risk factors to accident risk. In the WSF Risk Assessment, a modeling approach that combined system simulation, expert judgement and available data was used to estimate the contribution of risk factors to accident risk. Simulation is necessary to capture the dynamic environment of changing risk factors, such as traffic interactions, visibility or wind conditions, and to evaluate future scenarios that are designed to alter this dynamic behavior for the purposes of risk reduction or improved passenger service. The paper describes the simulation component of the model used in the Washington State Ferries Risk Assessment.