Cities, traffic, and CO2

Cities, with their dense populations and public transit systems are often seen as hotbeds of green innovation--places where bicycles, subways, and light rail are transforming how we get around. But new research shows that fast-growing cities are some of the worst culprits when it comes to CO2 emissions from cars. In a study published in PNAS, researchers dug through 33 years of traffic data from across the country, and used it to estimate local carbon emissions. They found that cities with large amounts of suburban sprawl were among the worst offenders. As cities like Salt Lake City, Atlanta, Houston, and Phoenix have grown in population, they have spread out and CO2 emissions from vehicles have increased sharply. However, declines in per-capita emissions are observed in cities that are already very dense such as New York and Boston. “DARTE (the Database of Road Transportation Emissions) reveals that urban areas were responsible for 80 percent of the growth in vehicle CO2 emissions since 1980, and for 63 percent of total 2012 vehicle CO2 emissions,” said Conor Gately, the lead author of the paper. DARTE also has demonstrated that although planners and researchers often use population density figures to predict local levels of CO2 production by vehicles, such predictions may be wildly off. Providing a better baseline for studying vehicle emissions, DARTE will help to answer major policy questions in urban development. The DARTE data are available from the ORNL DAAC: