Low-Carbon Transition Pathways for Sustainable Rail Transit Through Green Electricity Substitution and Carbon Trading Synergy: Difference-In-Differences Evidence and Scenario Simulation Based on Operating Data of Listed Companies

The sustainable transition of rail transit is central to sustainable mobility under China's dual-carbon goals, yet energy use and carbon emissions from operations keep rising as networks expand, and most of the evidence is city- or line-level, with little known about what operators' own green practices deliver. Using a 2017–2025 panel of eight A-share listed rail transit operators, this study applies a two-way fixed-effects difference-in-differences specification to compare changes in estimated carbon intensity and financial performance around firms' green practices — an exploratory descriptive comparison, since identification rests on a single treated firm — and then simulates four pathways for 2026–2030 — business as usual, green electricity and technology, inclusion in carbon trading, and their combination — calibrated on Shentong Metro's 2025 operating data, and extrapolates the results to industry level. Existing green practices remain marginal: green electricity purchased by Beijing–Shanghai High-Speed Railway in 2025 covered about 1% of its estimated electricity use, and the comparison detects no statistically significant change in carbon intensity (β = 0.225, p = 0.421) or on financial performance. The green-technology pathway cuts carbon intensity by 41.6% below the baseline by 2030, with cumulative abatement of about 39.8 kt CO2 and a cumulative net profit gain of 9.15 million CNY over five years; the combined pathway delivers the same abatement with stronger cost resilience under tightening quotas. Raising the green-electricity share of China's urban rail transit to 40% would abate about 6.46 Mt CO2 per year. By quantifying and monitoring the sustainability performance of rail operators at the firm level, this study provides reproducible measurement tools and evidence-based references for sustainability policy and corporate sustainable strategy in the transport sector.