Implications of uncertainty on regional CO2 mitigation policies for the U.S. onroad sector based on a high-resolution emissions estimate

► State-level biases of road groupings are twice as large as biases of vehicle groupings. ► State-level fleet composition is a large driver of the biases. ► Emissions uncertainty is driven by uncertainties in VMT and fuel efficiency and less by fleet composition variation. ► Errors of ±60% corresponding to ±0.2 MtC at the state level for 10% emissions mitigation when using national averages. ► Recommendations are made on reducing uncertainty in onroad CO2 emissions.