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Shelters in single‐tube road tunnels : a study of the strength of knowledge

This study investigates shelters as a risk reducing measure for road-users enforced to self-rescue in existing single-tube road tunnels, in which smoke engulfment is a plausible emergency scenario. Once people are engulfed in smoke the uncertainties regarding toxicity and immediate danger is imminent, and there must be solutions available for the road-users within a short time span. One such solution is shelters. To avoid any value-laden terminology we have established the acronym SWETO, which stands for Shelter Without an exit leading to Escape routes To the Open. The term is stating that the rooms are connected to the outside only through the tunnel space. The Norwegian Public Roads Administration (NPRA) needs to scrutinize the possibilities to integrate SWETOs in tunnels, because the current conditions of the evacuation systems are critical. There are no absolute requirements for emergency exits in existing road tunnels. The regulations address traffic volume as an important indicator of tunnel classification and the need of emergency exits. Previous events show that serious accidents can occur in tunnels where the traffic volume is low. The self-rescue strategy in a specific tunnel is ultimately to be based on a risk analysis and associated choice of dimensioning scenarios for the evacuation system. Integrating emergency exits in existing Norwegian road tunnels’ evacuation systems is a major task in terms of costs and constructability. SWETOs are an alternative that accommodate these issues, but road owners are currently prohibited from establishing SWETOs in tunnels covered by the Directive 2004/54/EC. However, despite the current tunnel safety regulations, the NPRA takes a clear stand to incorporate SWETOs as part of the evacuation system in some single-tube, bi-directional road tunnels. The hypothesis is that shelters, given appropriate design and management, can provide a positive contribution to safety. A general prohibition, as in the EU-directive, is not reasonable. The assumption that safe shelters are merely a design issue and a sociotechnical challenge to ensure intended performance needs to be discussed. The NPRA has initiated two pilot studies in addition to the already operational SWETOs in the Oslofjord tunnel, that include exceptions to the prohibition of "shelters without an exit leading to escape routes to the open". These projects are the Flekkerøy tunnel in Agder county municipality and the Frøya tunnel in Trøndelag county municipality. Agder county municipality and Trøndelag county municipality are obliged to participate in a follow-up R&D project after the tunnels have been built. Experiences from the pilot projects could influence any initiative to change the regulations on this matter. The study reported in this document had the intention to update and supplement the basis already established by the R&D project "Safety management in road tunnels" (NPRA, 2020a) and concretizing the content of the R&D program for the pilot projects. Four research questions have been raised as important issues for justifying or rejecting SWETOs for long single tube bi-directional tunnels: - RQ1: What characterizes the official European approach towards SWETOs in the work preceding Directive 2004/54/EC and the following implementation and supervision of the directive? - RQ2: What do we currently know about Norwegian tunnel systems, major events, and previous and ongoing research that reflects the benefits and challenges of SWETOs to improve the safety of tunnel users in single-tube road tunnels? - RQ3: What does recent scientific studies contribute with in terms of supporting, contradicting and/or expanding our knowledge about benefits and challenges of SWETOs to improve the safety of tunnel users in single-tube road tunnels? - RQ4: To what extent does current knowledge support our understanding of benefits and challenges associated with SWETOs to improve the safety of tunnel users in single-tube road tunnels, and what are reasonable next steps to strengthen our knowledge? While RQ1 is associated with understanding historical processes, RQ2-4 is about exploring what knowledge is needed to assess whether SWETOs are an appropriate safety measure in the Norwegian context or not, and subsequently what is the strength of available knowledge. The following functional requirements (FR) and connected topics were identified as a framework for collecting and analyzing the strength of knowledge: - FR1: The tunnel and associated technical systems must be designed and constructed considering tunnel users’ behavior in road tunnels in general and in accident situations specifically. o Driving behavior in road tunnels. o Human behavior in accident situations in road tunnels and situations associated with major uncertainties and stress. - FR2: The tunnel users must be aware of and have sufficient knowledge about the safety measures in the road tunnel in case of an accident. o Tunnel users’ general level of knowledge about tunnel safety. o TCC operators’ ability to gain situation awareness and communicate relevant information to tunnel users. o Tunnel users’ ability to understand and follow instructions during an evolving accident situation. - FR3: The SWETO’s construction must, over time, withstand relevant accident loads for a sufficient time to make rescue operations possible. o Relevant accident loads now and in the future? o Fire resistance of individual construction elements and combined systems’ effect, e.g., fixed firefighting systems’ cooling effect on wall elements. o Fire and rescue services’ knowledge and capacity to combat relevant accident loads in road tunnels, and their ability to adjust response tactics to an emerging situation. o Operation, maintenance, and degradation of safety measures in road tunnels. To investigate the status of knowledge, we initiated seven research activities (RA). RA1 was a study of public documents and literature associated with the development and implementation of Directive 2004/54/EC and RA2 included discussions with professionals involved with the same process. RA3 included the involvement of experts through a - workshop. RA4 was the development and presentation of a paper at the International Symposium on Tunnel Safety and Security 2023 in Stavanger. The conference normally attracts more than 200 delegates and was seen as a possible arena to present the Norwegian opinions on modern SWETOs and exploring the international response. RA5 was a study of recently published (limited to 2015-2023) literature in scientific peer-reviewed journals on the issues FR1 – FR3. RA6 was a system theoretic process analysis (STPA) of SWETOs in single-tube road tunnels, which served as a foundation for identifying functional requirements and safety constraints to SWETOs. RA7 was an analysis of available knowledge associated with FR1 – FR3 organized as a discussion.