Subway Openings and Urban Air Pollution Mitigation: Pathways to Sustainable Development in China

Air pollution not only affects urban production and residents’ lives but also threatens human health, and the construction of the subway is considered an important measure to improve urban traffic congestion and air quality. To test whether the construction and opening of subways with high operating costs can effectively improve urban air quality, this paper takes the opening of subways as a quasi-natural experiment. Based on panel data from 282 cities in China from 2014 to 2021, the difference-in-differences method is used to estimate the impact of subway openings on urban air pollution. It is found that (1) the subway opening significantly reduces urban air pollution, and this conclusion remains valid after a series of robustness tests. (2) Mechanism analysis indicates that subway openings mostly mitigate urban air pollution through the traffic substitution effect, which is generated through the substitution of private car travel. (3) Heterogeneity analyses show that the abatement effect of subway openings on air pollution is more significant when the city is a non-Yangtze River Economic Belt city, or when the city’s economic level is lower, or when the city is a non-resource-based city. Therefore, this paper puts forward targeted policy recommendations, such as optimising the subway layout, promoting the transit-oriented development mode based on the subway system, and implementing differentiated development strategies, with a view to providing certain references for promoting sustainable urban development.