Drivers of CO2 emissions from road transport in U.S. urban areas

Road transportation in U.S. urban areas accounts for roughly two-thirds of on-road CO2 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 to analyze street-level transportation emissions in 457 U.S. urban areas (hereinafter referred to as cities) in 2022, and decompose the key drivers of differences among them. Our study reveals that cities with greater population densities tend to have lower per capita road transportation emissions due to lower travel demand (R2 = 0.36) without significant increases in traffic congestion that represent only a fraction of the total (2-10%). Furthermore, we find that variations in vehicle fleets (e.g., electrification) are still a secondary driver of city-scale transportation emissions. These findings underscore the importance of tailored interventions to mitigate cities’ transportation emissions and may be used to support more sustainable urban transportation systems.