The Impact of New Energy Carriers in Road Tunnels, Part I: Focus on Battery Electric Vehicles

Transport safety is a critical consideration in the design and operation of infrastructure, particularly in road tunnels, where specific measures are necessary to protect both users and first responders. Traditional safety concepts have been developed primarily for conventional vehicles, addressing scenarios such as tunnel fires, in which toxic gas emissions, reduced visibility, and thermal loads pose significant hazards. In response to the global climate crisis, there is a growing transition towards alternative fuels and vehicle technologies, including hydrogen, natural gas, and battery electric vehicles (BEVs). These technologies introduce new storage systems and operational characteristics, which differ from those of diesel and petrol vehicles and may affect established safety standards. A substantial body of analytical, numerical, and experimental research has investigated the behaviour of alternative fuel vehicles in fire and accident scenarios. However, the diversity of studies and data makes it challenging to synthesise the findings into a comprehensive assessment. This paper provides a structured review of the literature, focusing on BEVs, their battery technologies, thermal runaway mechanisms, toxic releases, and incident scenarios, as well as associated fire suppression strategies. Hybrid vehicles are also considered for comparative purposes. The consequences of these hazards for life safety are examined, including evacuation procedures, preventive measures, and qualitative risk assessment. By integrating current knowledge, the study aims to evaluate the adequacy of tunnel safety measures and identify areas requiring further research, providing a coherent framework for understanding the risks associated with new energy carriers in road transport.