Do high-speed railways accelerate urban land expansion in China? A study based on the multi-stage difference-in-differences model

High-speed railway (HSR) have become the main transportation mode in China and a crucial contributing factor for the formation and development of urban and regional spatial structure. This study aims to investigate the effects and mechanisms of HSR on urban land expansion in China. The multi-stage difference-in-differences (DID) estimation method is used to explore the cases of 35 mega cities. The main results are presented as follows. 1) Opening HSR can positively influence urban land expansion, as evidenced by the 9.5% increase in the urban land expansion index after such opening. 2) The increase in the number of HSR station and route can accelerate urban land expansion. Each newly added station increases the urban land expansion index by 2.4%, and urban land expansion increases 4.8% when a new HSR route is added. 3) The positive effects of the opening of HSR on urban land expansion generally have a time lag of five years. 4) Compared with cities in the east, the midwestern ones are more vulnerable to the impact of HSR. The net effect of HSR on urban land expansion for midwestern cities is 10.9% higher than that for cities in the east. Furthermore, the mechanisms of the effect of HSR on urban land expansion are the industrial agglomeration