Drivers of CO ₂ emissions from road transport in U.S. urban areas

Road transportation in U.S. urban areas accounts for roughly two-thirds of on-road CO 2 emissions. Yet the drivers of those transportation emissions and differences among cities are not well-understood owing to limited availability of detailed data until recently. Here, we use high-resolution Floating Car Data based on GPS records of position and speed onboard individual vehicles to analyze street-level transportation emissions in 454 U.S. urban areas (hereinafter referred to as cities) in 2022. Per capita emissions were decomposed into three key drivers: the traffic demand per capita, the vehicle fleet and the congestion effect. Our study confirms the primary importance of travel demand and the well-known trend of its decrease with higher density but finds no significant increase in emissions related to traffic congestion, which account for only 1%–13% of total emissions in urban areas. Among the secondary drivers, variations in vehicle fleet composition (e.g., electrification levels) contribute slightly more to emission factor differences than congestion effects. These findings underscore the importance of tailored interventions to mitigate cities’ transportation emissions and may be used to support more sustainable urban transportation systems.