Impact mechanisms of high-speed railway accessibility on urban expansion in China: An analysis based on the mediating effect model

High-speed railway (HSR) has emerged as a transformative force in China, markedly reshaping urban development and spatial structures. Here, we examine the indirect mechanisms through which enhanced HSR connectivity influences urban land expansion. We construct national HSR networks for 2011, 2014, and 2017, and assess city-level accessibility based on network structure, direct connectivity, and service frequency. Urban expansion is measured using the average annual intensity of urban land growth during the periods 2011–2014, 2014–2017, and 2017–2020,taking data from 278 cities in China. Using a mediation and interaction effect models, we explore how HSR accessibility has influenced urban expansion through multiple pathways, including real estate investment, employment density, and industrial restructuring. The results reveal a fundamental paradigm shift: rather than simply stimulating sprawl, high HSR network centrality acts as a “structural brake valve” that significantly inhibits extensive and disorderly outward expansion, driving cities toward compact development. Mechanism analyses indicate that high internal employment density effectively reinforces this centripetal inhibitory effect. Conversely, increased HSR service frequency triggers a strong “masking effect” by stimulating real estate investment, which drives short-term spatial sprawl and obscures the network’s intrinsic compacting tendency. However, interaction models confirm that as the HSR network matures, frequent services combined with capital investment reverse this sprawl, guiding development toward high-density Transit-Oriented Development (TOD).Our findings underscore that HSR has transitioned from a catalyst for urban sprawl to a key driver of intensive, stock-based urban transformation, offering critical policy insights for coordinating transportation infrastructure with sustainable land-use planning and curbing local “land finance” impulses.