Abstract
The rapid expansion of high-speed rail (HSR) has reshaped China’s transport infrastructure system, yet its relationship with transport-sector carbon emission efficiency (TCEE) remains unclear. This study constructs a multidimensional High-Speed Rail Infrastructure Supply Index (HSRSI) based on operating mileage, station numbers, infrastructure density, and service coverage, and measures TCEE using a super-efficiency SBM model with CO2 emissions as an undesirable output. The analysis traces the spatiotemporal evolution of HSRSI and TCEE across 30 provincial-level units in China from 2003 to 2022 and estimates their conditional association with a two-way fixed-effects model. The results show that TCEE declined in the early years, recovered after 2008, and increased markedly toward the end of the study period, whereas HSRSI increased continuously. Both indicators exhibited pronounced regional disparities, although their spatial evolution was not fully synchronized. Nationally, HSRSI was significantly negatively associated with TCEE. In baseline regional regressions, the association was insignificant in eastern China, negative in central China, and positive in western and northeastern China. Economic development, transport structure, industrial structure, and innovation capacity were positively associated with TCEE at the national level, while urbanization showed a negative association. The regional estimates suggest that the association between HSR infrastructure supply and TCEE varies across regions. For sustainable transport planning, these differences highlight the importance of considering each region’s transport-sector carbon emission efficiency when assessing proposed HSR investments.