Decoupling Urban Development and Transport Carbon Emissions: A Hierarchical Regression of the TOD 7D Framework in the Seoul Metropolitan Area

Given the huge contribution of the transportation sector to CO2 emissions in metropolitan areas, urgent countermeasures are needed to achieve carbon neutrality. In this study of 66 administrative units (cities, counties, and districts) in the Seoul metropolitan area, we applied cluster analysis and a hierarchical regression model to analyze the impact of the 7D factors of Transit-Oriented Development (TOD) on CO2 emissions from road transportation. The effects of TOD factors were found to vary in diverse contexts. A higher concentration of employment intensified regional travel demand, thereby increasing emissions—a phenomenon referred to as the Paradox of Concentration. In contrast, the expansion of urban rail and bicycle infrastructure facilitated modal shift toward sustainable transport but simultaneously stimulated commercial and logistics activities, leading to elevated overall emissions. Thus, a ‘two-faced infrastructure’ pattern is evident in the Seoul metropolitan area. Conversely, strengthened local self-containment by destination accessibility promoted short-distance travel, curbing emissions. These outcomes empirically exhibit that the low-carbon effect of TOD is contingent, implying that urban structure and policy context are key factors in determining emission pathways. The impacts of the TOD 7D factors are discussed in terms of emission effects, and differentiated policy directions reflecting inter-city heterogeneity are suggested. In particular, the results of our analysis emphasize the need for comprehensive TOD strategies that combine transportation infrastructure, demand management, local self-containment, and zero-emission logistics systems, beyond simple compact development strategies. The policy implications described here are applicable in other countries experiencing rapid urbanization.