How Suburban Cars Are Clouding Up Cities

With cities in the midst of a revival, there's reason to believe they can help Americans be more frequent users of sustainable transportation. Dense urban centers with robust public transit—à la New York City—make cars seem almost unnecessary. Commuting to work with a greener alternative—the subway for instance, or the greenest alternative, walking—is often more convenient for those who live and work in a tight downtown. But new evidence shows that COemissions from cars in urban hubs are still on the rise, and curbing them is more complicated than simply planning dense, livable downtowns.

A trio of researchers from Boston University has developed a database that is useful for analyzing this very issue. The data set, called DARTE, shows that 80 percent of COemissions growth came from on-road vehicles in urban metros between 1980 and 2012. In 2012 alone, urban metros accounted for 63 percent of total vehicular carbon emissions in the United States. A full report on the new database and its findings were published Monday in the science journal PNAS.