Energy tunnels for a sustainable future

Energy tunnels are an emerging class of sustainable infrastructure that combines structural, geotechnical and energy functions in a single system. By thermally activating tunnel linings, engineers can extract, store and exchange geothermal heat for applications such as urban heating, cooling and infrastructure de-icing. Beyond improving energy efficiency, this technology contributes directly to the decarbonisation targets outlined in the European Green Deal. This Brief Report summarises the principles, design framework, and strategic potential of energy tunnels, drawing on recent advances and case studies, including the Turin Metro Line 2, the Brenner Base Tunnel, and the Lyon–Turin connection, to illustrate how they can transform underground infrastructure into renewable energy assets. Energy tunnels transform transport infrastructure into renewable geothermal power sources for cities. Thermally activated tunnels can reduce CO₂ emissions by up to 60% in urban energy systems. Integrating energy tunnels with district heating and UTES unlocks year-round, low-carbon urban energy storage.