Probabilistic methods of risk optimization are applied to identify the most effective safety measures considered in design of road tunnels. The total consequences of alternative tunnel arrangements are assessed using Bayesian networks supplemented by decision and utility nodes. It is shown that the probabilistic optimization based on the comparison of societal and economic consequences may provide valuable information enabling a rational decision concerning effective safety measures. Thereby risk acceptability criteria are critically reviewed. A general procedure is illustrated by the optimization of a number of escape routes. It appears that the discount rate and specified life time of a tunnel affect the total consequences and the optimum arrangements of the tunnel more significantly than the number of escape routes. The optimum number of escape routes is also significantly dependent on the ratio of the cost of one escape route and acceptable expenses for averting a fatality based on the LQI. Further investigation of relevant input data including societal and economic consequences of various hazard scenarios as well as experience related to the effectiveness of safety systems are needed.
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