Impact and mechanisms of high-speed rail construction on carbon emissions: A quasi-natural experiment in China

Carbon emissions present a significant climate challenge for China. As a major source of these emissions, reducing transportation-related carbon output is essential to achieving the country's dual carbon goals. In this context, high-speed rail (HSR) emerges as a green, low-carbon alternative with an increasingly significant role in reducing carbon emissions. This paper explores the impact of HSR station construction on carbon emissions using data from 248 prefecture-level cities from 2003 to 2019, treating the construction as a quasi-natural experiment. Employing a spatial DID model, the research investigates how HSR construction affects carbon emission intensity within the region and in neighboring areas. It also considers socioeconomic factors to understand their mediating roles. The findings reveal that HSR construction significantly reduces regional carbon emissions over time, with long-term and gradually increasing effects. Spatially, HSR also has substantial spillover effects in reducing carbon emissions in adjacent regions. Numerically, HSR reduces carbon emissions by an average of 1.7% in the local region and 2.3% in the surrounding areas. The mechanism analysis indicates that the carbon reduction benefits of HSR stem from a complex interplay of multiple factors, with each selected factor playing a partial mediating role. Notably, the concentration of human capital and the flow of innovation are crucial pathways for regional carbon reduction. However, despite HSR's promotion of industrial structure upgrades and substitution of traditional transportation, these factors have not yet significantly contributed to carbon reduction under current conditions. These results underscore the critical position of HSR in carbon reduction and provide a theoretical foundation for future HSR planning and sustainable development policy formulation.