Safety in tunnels has been an issue ever since the construction of the first tunnel in the Netherlands (Maastunnel, 1942). For a few decades the majority of tunnels that were constructed were immersed. While their designs showed much resemblance, their safety concept was much alike. During the ‘90’s this standard concept changed due to the introduction of bored tunnels and land tunnels. Besides, the length of tunnels gradually increased and the debate on transport of dangerous goods resulted in less restrictions on the national highway for this type of transport. Finally, multiple use of space is becoming more and more popular. This means that tunnels become a part of a multi-level system, which has a large impact on the safety concept. Therefore the safety concept had to be evaluated. The two major fires in tunnels in the Swiss Alps (Mont Blanc 1999 and St. Gotthardtunnel 2001) fuelled the public aversion of tunnel accidents and brought safety in tunnels even higher on the political agenda. This gave rise to the question whether our safety budget is spent in such a way that the highest possible safety level in our tunnels is reached. Hence the aim of this research was to investigate the cost effectiveness of safety measures in road tunnels in the Netherlands, comparing the investment costs related to safety measures on one hand and their effect on the risk on the other. For this purpose three different tunnel types were investigated: a bored, a land and an immersed tunnel. An effort was made to find an economic optimal safety level for these three tunnels. An inventory of the causes of accidents in tunnels showed that are three types of accidents: normal accidents (that also occur on the rest of the highway), jammed accidents (where people get stuck in the vehicle as a result of the accident and have to be freed by the fire department, which is a little more difficult in a tunnel environment) and calamities (accidents with a very low probability, but with a large consequence, e.g. an exploding tanker). The normal accidents account for more than 90 % of the expected fatalities, the jammed accidents for about 9% and the calamities for less than 1%. In the Netherlands the number of accidents per million kilometres travelled per vehicle appears to be slightly higher in tunnels than on the open road. Nevertheless, while the Dutch highway system has a relatively low accident frequency, Dutch tunnels are considered to be among the safest in Europe. The evaluation of the risks in tunnels was done using the probabilistic method. In this method, an inventory is made of all possible consequences of accidents in tunnels. All these scenarios are then assigned probabilities. For this investigation, the consequences of accidents were expressed in fatalities, injuries and material damage. In order to come to an economic evaluation of safety, a monetary value was assigned to all casualties. The risk of tunnel accidents can then be calculated by the sum of the damage costs of every scenario times its probability. Of the safety measures applicable to tunnels, a division was made into structural measures (related to the tunnel configuration, like emergency exits), installations (e.g. ventilation and detection systems) and regulatory measures (e.g. speed reductions and separating the transport of dangerous goods). Of the possible safety measures, the costs for implementation, maintenance and renovation were investigated, as well as their effect on the level of safety of the tunnel. This investigation showed that it is not possible to find an economic optimum safety level for tunnels using the same approach as is used in economic analysis on flood defence systems. The main reason is that the basic approach of the cost optimisation of the flood defence system depends on just one safety measure that can be applied at various levels (height of the dyke), while there are numerous ways to improve safety in tunnels. An economic optimum safety level for tunnels therefore can only be found by comparing all sorts of combinations of safety measures. While both the investment and the risk could be expressed solely in money, the cost efficiency of safety measures could be made visible. The the costs of safety measures were therefore plotted in relation to the risk for the tunnel as built (taken as a reference), and for all safety measures under consideration. It is concluded form this probabilistic investigation of safety measures, that increasing the number of emergency exits, construction of a shoulder and installing a sprinkler system are all not cost effective. Concerning the removal of safety equipment, removing the fire equipment turned out to be cost effective. This indicates that the safety levels of the tunnels as they are designed at the moment depend not only the probabilistic approach on safety. Finally it is concluded that in relation to the tunnels as they are built, safety measures like a fire resistant lining are very cost efficient. The most cost efficient safety measures in tunnels are the regulatory measures like the introduction of a minimum distance between vehicles and enforcing speed reductions. Besides the influence of human behaviour in case of a tunnel accident is very important. Therefore it is recommended to do more research on the human behaviour. For the cost effectiveness of safety measures in relation to the three different types investigated, it can be concluded that the differences in costs for safety measures for a Land and Immersed tunnel are very little. The choice between safety measures therefore mainly depends on the length of the tunnel, the daily traffic volume and the number of trucks transporting dangerous goods. Besides the main differences in costs for safety measures for the three tunnel types, are the costs related to structural safety measures. For a Bored tunnel the costs related to structural safety measures are high compared to the other two. This means that in a cost optimisation of safety measures for a Bored tunnels, the focus should definitely be on traffic management solutions. (Author/publisher)
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