Background & Objective
After the severe tunnel accidents in 1999 and 2001 many authorities and research institutes in Europe spent ever more time discussing and clarifying standards for road tunnels. One of the results of this discussion process was the development and publication of the EC Directive 2004/54/EC on Road Tunnel Safety in April 2004, defining minimum standards for road tunnels. Besides safety measures and organisation standards, Article 13 of the Directive obliges all Member States to develop a methodology for risk analyses at national level. In case of tunnels with special characteristics and/or deviations from the requirements of the Directive, these analyses are applied in the form of a risk evaluation tool in order to confirm that the tunnel is sufficiently safe.
Therefore, the Austrian Ministry of Transport, Innovation and Technology (BMVIT) started a design process to develop a methodology which meets the specific requirements of Austrian road tunnels. The work process was coordinated with a group of tunnel safety and ventilation experts. The group started its work in 2003 by collecting data on accidents, tunnel design and equipment and traffic characteristics. After evaluating, comparing and completing the data with foreign data sources, a methodical approach was defined. The tunnel risk model “TuRisMo” was first published in the RVS 09.03.11 guideline (Austrian Road Construction Regulations) on 1 August 2008. A simplified risk assessment method was published in the RVS 09.02.31 guideline (tunnel ventilation) for assessing standard tunnels as part of the calculation of the risk equivalent.
In May 2006 the Austrian tunnel safety law was passed and the results of the tunnel risk analyses had to be taken into account for all tunnel projects in Austria. Due to the large number of risk analyses conducted in Austria and other European countries, extensive experience with this risk evaluation tool and knowledge about achieved and exceeded limit values was gained.
After 5 years of practical experience with the Austrian Tunnel Risk Model the focus has changed. In the first phase of its application the focus was on standard cases e. g. defining the risk class of a tunnel, later emphasis shifted towards applying it as a decision making tool, thus addressing new and more complex problems.
As costs are becoming an ever more critical factor for investments in tunnel safety, risk assessments are increasingly applied to evaluate the effects of different design alternatives and / or additional risk mitigation measures on tunnel safety in a quantitative manner, to be able to optimise the cost / benefit ratio.
In 2011, the expert group started to adapt and extend the tunnel risk model TuRisMo, and finally published an updated RVS 09.03.11 guideline on 1 April 2015. The updated TuRisMo version is available in the standard and the extended version. The latter includes detailed analyses of fire risk, based on the specific smoke propagation characteristics of a tunnel.
Risk analyses are often used as a decision support tool during the design phase or during refurbishment of existing tunnels. In early phases of design or preparation of refurbishment, a risk analysis can easily show the effects of individual safety measures or their combinations without costly tunnel modifications. Risk analyses are also often combined with cost-benefit considerations.
The aim of the tunnel risk analysis model is to present a quantitative analysis and evaluation of both the potential risks related to road tunnels and their impacts on tunnel users. Along with both legal regulations and requirements defined in guidelines, the tunnel risk analysis model represents an additional tool for guaranteeing tunnel users a level of safety that meets the respective requirements. In addition, risk analyses should also help to optimise tunnel safety investments in terms of cost-effectiveness. As far as the required recorded data are available, the tunnel risk analysis model provides the opportunity to both produce a quantitative record of almost all factors that influence tunnel safety and to evaluate them.
The present method is a system-based tunnel risk analysis model that has been developed for carrying out evaluations of road tunnels in terms of overall safety. It is especially applicable for making risk comparisons on a quantitative basis.