Carbon Footprint and Energy Use of Road Tunnel Construction: A Systematic LCA Review and Case Study of Poland

Road tunnels are highly carbon-intensive due to material use, energy-intensive construction, and long service lives, yet major gaps remain regarding emission hotspots, construction method comparisons, and regional differences, particularly in Central and Eastern Europe. This article combines a PRISMA 2020-guided systematic literature synthesis with a Polish case-study life-cycle assessment (ISO 14040/14044, cradle to grave, functional unit of 1 m of tunnel, 100-year horizon) using Ecoinvent factors and the Polish energy mix, covering material production, construction, operation, maintenance, and end of life. The literature synthesis found substantial variability in tunnel carbon emissions, ranging from 1500 to 22,062 t CO2-eq per lane-kilometer depending on the construction method, tunnel type, and region. Material production was the largest contributor to construction-phase emissions (70–95%), with concrete and steel responsible for over 90% of material-phase impacts and 75–80% of construction-phase emissions, while operational energy use dominates over the full life cycle. Concrete and steel substitution (e.g., GFRP bars and calcium sulfoaluminate cement) offers the greatest construction-phase reduction potential, while operational measures, such as LED lighting, demand-controlled ventilation, and renewable energy, can cut long-term energy use by 30–50%. For Poland, low-carbon concrete, prefabrication, and renewable electricity could reduce tunnel emissions by 40–60%. These findings highlight pathways for decarbonizing tunnel infrastructure through material innovation, energy-efficient operation, and circular economy principles.