Does high-speed rail improve urban carbon emission efficiency in China?

Based on various quasi-natural experimental high-speed rail scenarios in China, this paper both selects the panel data of 285 cities from 2003 to 2018 and adopts the Multi-time Difference-in-Differences method to analyze the impact of high-speed rail on urban carbon emission efficiency. Following this, the possible transmission mechanisms are explored. The results show that high-speed rail can significantly improve urban carbon emission efficiency with the conclusion still valid after conducting a series of robustness tests. The heterogeneity results indicate that the promoting effects of high-speed rail on urban carbon emission efficiency are more significant in non-resource-based cities and large cities. Further analyses of the transmission mechanisms show that high-speed rail may improve urban carbon emission efficiency through technological innovation, structural optimization, a strengthening of environmental regulations and a weakening of market segmentation.