Review on low-carbon tunnel technologies: Integrating lifecycle strategies and scenario-adaptive solutions

Amidst the accelerating pace of global urbanization and increasing climate urgency, the decarbonization of energy systems requires strategic utilization of underground space in general and underground networks (UNs), in particular, where tunnels represent critical nodes of pollutants and greenhouse gas emissions, as well as consumption of energy, raw materials, and final resources. Their high impact is due to their resource intensive construction, operational energy, and resource demands. Although lifecycle assessment (LCA) is commonly used to quantify carbon footprints, existing research on low-carbon tunnels (LCTs) still faces three persistent challenges: fragmentation across isolated lifecycle stages, lack of synergy between different phases, and insufficient consideration of scenario-specific adaptation such as geography and traffic load. To address these gaps, this study conducts a bibliometric analysis to map the current research landscape and identify technological hotspots, systematically integrates innovative low-carbon technologies across the entire lifecycle of both the tunnel itself and its installations, from design to decommissioning, and evaluates their effectiveness through case studies in different scenarios. Finally, based on the integrated analysis of low-carbon technologies across the tunnel lifecycle, this study discusses their potential for scaling up to support the decarbonization of broader underground networks, offering scenario-adaptive strategies and decision-support tools to promote sustainable and resilient underground network development under carbon neutrality goals.