Subway network accessibility and carbon balance: evidence from China's dynamic centrality analysis

Amid the ongoing transition toward low-carbon urban development, subway networks, as a modern mode of transportation, have become a key focus of academic attention. However, existing research suffers from two critical gaps: first, a predominant focus on either carbon emissions or carbon absorption in isolation, rather than their equilibrium; second, a simplistic "point‑line" physical assessment of subways that overlooks network‑level accessibility and topology. This study addresses these gaps by adopting the carbon balance ratio (the ratio of terrestrial carbon absorption to anthropogenic emissions) as the outcome variable and employing Social Network Analysis to construct dynamic, station-level subway network centrality metrics in China. Empirical findings reveal that a one‑unit increase in county‑level subway network accessibility significantly improves the carbon balance ratio. This effect is strongest in economically underdeveloped regions, areas with compact spatial structures, and zones with lower residential electricity consumption. Mechanism analysis reveals a tri‑phase contribution: (1) during construction, subways preserve green space and carbon absorption capability by avoiding surface disruption; (2) during operation, they induce modal shifts that reduce transport emissions; and (3) through industrial transformation, their carbon benefits are amplified by supportive institutions, market mechanisms, and technological capabilities. By systematically integrating carbon balance measurement with network‑level subway accessibility, this study offers a comprehensive empirical framework and provides policy insights for integrating rail transit into low‑carbon spatial governance strategies.