Subway opening enables urban green development: Evidence from difference-in-differences and double dual machine...

Urban rail transport is an important part of transport infrastructure, which is significant in empowering green-oriented urban development. However, few studies in the existing literature explore the effect of subway opening on urban green development. This paper uses Chinese data of 281 prefecture-level cities from 2008 to 2021 to explore the influence and mechanism of subway opening on urban green total factor productivity (GTFP) through the difference-in-differences (DID) and double dual machine learning (DDML) methods. The results show that subway opening can improve urban GTFP, and realize urban green and innovative development. This conclusion is supported by several robustness tests. With regard to pathways, subway opening can broaden the frontiers of production possibilities and promote technological progress by upgrading industrial structure and improving innovation capacity, thus increasing urban GTFP. Moreover, the effect of subway opening on urban GTFP is heterogeneous in city size, city location and regional resource endowment. Considering the heterogeneity difference of GTFP, it is found that subway opening has a stronger "green" effect in cities with high level of green development. Digital infrastructure and regional competition play a positive role in regulating the effect of subway opening on urban GTFP. Economic growth target has a strong constraint on the impact of urban GTFP by subway opening, while the constraint effect of the environmental target is not significant. These findings help to provide valuable empirical evidence for urban green development from a transport-related perspective.