Evaluation of ship collision risk assessments using environmental stress and collision risk models

In Korea, ship collisions represent the majority of marine accidents and are substantially more likely in port areas where ship traffic is dense. To improve the safe navigation of vessels, the Korea Maritime Safety Audit (KMSA) has been conducting maritime traffic flow evaluations based on the Environmental Stress (ES) model since 2009. The ES model quantifies the subjective stress felt by the navigator; however, it does not reflect the relative bearing between ships. Risk assessment models using the ship domain are designed to consider the conditions of a potential encounter with a target ship and the possibility of avoidance action. However, even if the target ship does not invade the domain of the own ship, collision may occur at the closest point of approach (CPA). Therefore, in this study, the Collision Risk (CoRI) model which moves the existing ship domain to the CPA is applied to compare the collision risk according to the navigator's awareness of the vessel encounter conditions. The results demonstrate that the CoRI model is a better risk assessment method than the ES model because it sensitively reflects the risks due to collision avoidance action, such as course alteration and speed changes.