Risk assessment of existing road tunnels - The case of the Grand Saint Bernard Tunnel

This thesis aims to provide a comprehensive and in-depth overview of road tunnel safety by analyzing major historical accidents, the regulatory responses that followed, and the technical solutions necessary to reduce risk levels and mitigate the consequences of potential critical events. Following a brief review of major historical accidents in recent years—such as the fires in the Mont Blanc Tunnel, the Tauern Tunnel, and the Gotthard Tunnel between 1999 and 2001—the focus shifts to the main European regulations enacted to enhance road tunnel safety. Particular attention is given to EU Directive 2004/54/EC, introduced by the European Commission in 2004 in response to these tragic events. The primary goal of this directive is to improve safety standards for all Trans-European Road Network (TERN) tunnels longer than 500 meters, by establishing a unified framework and context. Additionally, the directive defines the Risk Assessment Process as a fundamental tool for enhancing, optimizing, and verifying road tunnel safety. However, it does not prescribe a single risk analysis methodology at the European level, given the heterogeneity of infrastructure across member states. Instead, the European Commission is tasked with identifying best practices. As a result, over the years, each European country has developed the methodology best suited to its needs. Each of these approaches has its advantages in specific areas but differs significantly in terms of theoretical foundations, objectives, and levels of detail. Currently, Europe is still far from having a uniform methodology for assessing risks in road tunnels. This thesis focuses particularly on the regulatory framework in Italy and Switzerland, as well as the risk analysis methodologies developed in these two countries (IRAM for Italy and the ASTRA method for Switzerland), highlighting the main similarities and differences. The case study chosen for this work is the Grand Saint Bernard Tunnel, a 5,798-meter bidirectional tunnel that connects the municipality of Bourg-Saint-Pierre in Switzerland with the municipality of Saint-Rhémy-en-Bosses in Italy. The final part of the thesis provides an in-depth analysis of its technical and structural characteristics, emergency procedures adopted to address the risks of accidents and fires, and its compliance with the minimum safety requirements set by regulations. Special emphasis is placed on the risk analyses conducted before and after the commissioning of the Service and Safety Tunnel (SST) in July 2022. This thesis seeks to highlight the complexity of road tunnel safety, particularly in the process of risk assessment and estimating the safety level within these infrastructures. It was particularly interesting to explore the adaptation of existing regulations in two different countries for an international tunnel such as the Grand Saint Bernard Tunnel, as well as the application of risk analysis methodologies to a practical case, including the necessary simplifications to address the complexity of the process.