The Dual Dimensions of Economic Structure and Energy Efficiency: A Study on the Compound Moderation Mechanism of Transportation Carbon Emissions in China

Reducing carbon emissions from transportation is critical for climate goals, while the mechanisms through which underlying economic dimensions, specifically structural intensity and energy efficiency, interact with transport systems to drive emissions remain unclear. This study investigates the compound moderating effects of road transport share and economic growth on the relationship between two key economic dimensions, including economic structure and energy efficiency, and transportation carbon emissions in China. Based on quarterly national data (2008–2024), this research employs principal component analysis to extract these synergistic economic dimensions from correlated indicators. It uses moderation models, with diagnostic checks for multicollinearity, to test how road transport share and economic growth condition the impact of these dimensions on sectoral emissions. The analysis identifies two key dimensions, both exerting significant negative direct effects on emissions. Road transport share significantly moderates these relationships, with its environmental impact contingent on the underlying economic context. In contrast, economic growth shows no significant direct or moderating effect. The findings demonstrate that transportation decarbonization depends not on isolated economic factors but on how the transport structure filters their influence. This underscores the need for context-sensitive, regionally differentiated infrastructure policies and a sustained focus on improving structural energy efficiency over short-term growth targets.