From Phenomena to Accountability: A Mechanism-Driven Framework for Urban Road Traffic Emissions Management

Against the backdrop of the global carbon neutrality agenda, precisely deconstructing and governing carbon emissions from megacity transport systems has become a central challenge for sustainability science. However, a fundamental disconnect persists in current research paradigms: while emission maps are increasingly detailed, the understanding of critical mechanisms—such as congestion-induced contributions and functional responsibility—remains highly fragmented. To bridge this gap, this study develops a road-level dynamic carbon emission model based on over 2.5 million citywide origin–destination trajectories, enabling a systematic analysis of the spatiotemporal patterns and underlying mechanisms of transport-related emissions at the urban scale. The results show that total road traffic emissions during the morning and evening peaks reached approximately 6,251 tons and 5,198 tons of CO₂, respectively, with a distinctive “ring-and-radial” spatial pattern and pronounced inequality—where 20% of road segments account for 80% of emissions. Furthermore, by introducing a comprehensive framework to evaluate congestion-induced emissions, we reveal that excess emissions attributable to peak-hour congestion amount to 1,302 tons (20.8%) in the morning and 1,002 tons (19.3%) in the evening, highlighting cross-district commuting corridors and peri-urban junctions as critical control points for emission reduction. Building on this, a multi-scale tracing analysis linking road segments, urban regions, and land-use functions clarifies the differentiated roles of functional zones within the urban emission network, identifying typical categories such as pure liability exporter, emission channels, and composite emission sources. This methodological framework offers a replicable technical pathway for low-carbon traffic governance in megacities and provides scientific support for developing carbon neutrality strategies in cities worldwide.