The impact of high-speed rail on urban carbon emissions: Evidence from the Yangtze River Delta

Clarifying the relationship between high-speed rail (HSR) and a city's carbon emissions is the critical premise behind transportation decarbonization and China's carbon target. Based on HSR's operational data, total carbon emissions data, and socio-economic statistics, this study examines how HSR affects a city's carbon emissions and the varying effects among different categories of cities using the Spatial Difference-In-Difference model from both static and dynamic perspectives. HSR would decrease a city's carbon emissions through the scale effect under the influence of the complex external and internal environment and the resulting uncertainty, with both substitution and stimulation. We find that, at the static level, the operation of HSR in cities with HSR stations, can statistically reduce carbon emissions by 0.58% at the 1% level. It also reduces the carbon emissions of neighboring cities' to a greater extent through the spillover effect, which is characterized by being multi-directional and multi-processed. The dynamic effect of HSR is related to its three-stage phase development, including the start-up phase, the expansion phase, and the intensification phase, which is characterized by a significant time lag. The intensity of HSR's carbon reduction effect on cities tends to increase initially and then decrease, as the HSR network improves and gradually reaches saturation. The impact of HSR on a city's carbon emissions varies with city characteristics, including economic growth, industrial structure, and city population. These findings can theoretically and empirically support the carbon reduction effect of HSR, and provide important decision-making reference for HSR construction driven by China's carbon target.