Cities, traffic, and CO2: A multidecadal assessment of trends, drivers, and scaling relationships
Conor K. Gately , Lucy R. Hutyra , and Ian Sue Wing Department of Earth and Environment, Boston University, Boston, MA 02215 Edited by Susan Hanson, Clark University, Worcester, MA, and approved March 13, 2015 (received for review November 12, 2014) Significance We use roadway-level traffic data to construct a 33-year, high-resolution inventory of annual on-road CO 2 emissions for the United States that differs markedly from other emissions estimates. We find a highly nonlinear relationship between population density and emissions, and identify large biases in regional estimates of CO 2 from inventories that rely on population as a linear predictor of vehicle activity. Geographic differences in the density–emissions relationship suggest that “smart growth” policies to increase urban residential densities will have significantly different effects on emissions depending on local conditions, and may be most effective at low densities. Our results highlight the importance