Risk analysis study of maritime traffic in the strait of Istanbul

Abstract

The Strait of Istanbul, the narrow waterway separating Europe from Asia, holds a strategic importance in maritime transportation as it links the Black Sea to the Mediterranean. It is considered as one of the world’s most congested and difficult-to-navigate waterways. Over 55,000 transit vessels pass through the Strait annually, roughly 20% of which carry dangerous cargo. The aim of this study is to prove and implement a sound methodology and a quantitative basis to investigate and analyze safety risks pertaining to the transit vessel traffic in the Strait of Istanbul. For this purpose, first actual vessel traffic operations and data are studied and a simulation model (which considers the pertaining maritime traffic regulations, transit vessel profiles, scheduling practices, pilotage and tugboat services, local maritime activities, meteorological and geographical conditions) is developed to mimic the operation with its geographical and weather dynamics. Next, safety risk analysis is performed by incorporating a probabilistic accident risk model into the simulation model. Regarding risk assessment, two sets of factors are sought for during the execution of each transit: the probability of an accident and the potential consequences of this accident, at various points along the Strait during that particular transit. A mathematical risk model is developed based on probabilistic arguments regarding instigators, situations, accidents, consequences and historical data, as well as subject-matter expert opinions. Then, as a simulation run proceeds, the risks generated by each transit vessel (and/or at different regions of the Strait) are assessed. Scenario analysis is carried out to study the behavior of the accident risks, with respect to changes in the surrounding geographical, meteorological and traffic conditions. This analysis provides a platform to investigate the impact of various factors on the risk profile of the Strait. These factors included vessel arrival rates, scheduling and pursuit distance of vessel passages, one-way regime start time, pilot requirements of vessels, pilot service availability, and local traffic conditions. Our numerical investigations suggested some significant policy indications. Increasing local traffic density and more vessel scheduling (by decreasing the pursuit distances) to handle pileups at the entrances as a result of increase in arrivals are the two main factors increasing the risks at the Strait of Istanbul. On the other hand, the model indicates that pilots are of utmost importance for safe transit. Negative effects of increased local traffic and more vessels scheduling may be eliminated by mandatory pilot practice and significant risk mitigation may be achieved. Similarly, affecting the interaction of local traffic with one-way transit traffic (i.e. shifting the start time of one-way regime) helps to reduce accident risks. Additionally, results of the scenario analysis indicate that having a pilot on board during passage has much higher positive effect on accident probabilities rather than consequence. On the other hand, having many local vessels navigating close by increases the probability of involving in an accident for a transit vessel but its negative effect on accident consequences is higher. Also the general behavior of risk profile over the Strait and the resulting observations remains unchanged when numerical values of consequence impact levels are changed. Finally, the expert responses are examined through statistical inference tools in order to better understand the similarities and differences in the risk perception and response behavior of different expert groups. Analysis of expert responses to individual questions shows that there is no significant difference among the means of the different expert groups’ answers. On the other hand, answers to multiple questions inquiring the levels of a specific attribute in a questionnaire indicate that experts have different perceptions about the effects of situational attributes on risk values, except four situational attributes which are the nearest transit vessel proximity, current, zone and vessel reliability.