Rising carbon emissions from expanding highway tunnels and reduction pathways in China

Highway tunnels are expanding rapidly in China, driving rising operational carbon emissions, yet systematic assessment methods remain limited. Here, we develop a provincial-scale carbon intensity model using empirical data from Sichuan Province, integrating regional electricity emission factors and geological characteristics. The model estimated emission intensities across 30 provinces, yielding a national average of 16,805 tCO2-eq per km, and validation against 88 tunnel cases from five provinces shows prediction error of less than 5%. We further propose a low-carbon cross-section design strategy and evaluate three policy-technology interaction scenarios: baseline, high-reduction, and low-reduction. The high-reduction scenario could lower emissions by more than 18% relative to the baseline, whereas the low-reduction scenario leads to limited effectiveness. Establishing a nation-wide tunnel emission model is essential for infrastructure planning, policy design, and accelerating low-carbon transitions in China and other rapidly developing economies.