The New York Times maps and discusses vehicle emissions across American metropolitan areas:

Even as the United States has reduced carbon dioxide emissions from its electric grid, largely by switching from coal power to less-polluting natural gas, emissions from transportation have remained stubbornly high.

The bulk of those emissions, nearly 60 percent, come from the country’s 250 million passenger cars, S.U.V.s and pickup trucks, according to the Environmental Protection Agency. Freight trucks contribute an additional 23 percent…

Suburban driving, including commuting, has been a major contributor to the expanding carbon footprint of urban areas, Dr. Gately said.

But, he added, “Even in the densest cities, the vast majority of trips still happen in a motor vehicle.” These trips include work commutes, school drop-offs and millions of other daily errands as well as freight deliveries and other business traffic, each of which contribute to planetary warming.

The United States has organized much of its society around driving. Plus, many Americans like driving or the benefits they believe driving offers. It will be hard to enact quick large-scale changes to this though smaller efforts (such as fleets of electric vehicles or denser suburban areas) could add up to change over time.

The data from the Chicago area is interesting. Like most metro areas, the emissions are centered on major highways with some of the areas with most emissions being the Kennedy Expressway, the Dan Ryan Expressway, I-88 at I-294, and I-88 at I-355 (these are likely areas with high levels of congestion and gridlock). From the maps, it is hard to know how much of the emissions come from freight trucks but I would imagine the proportion could be high in the Chicago area given its central location, highways, and intermodal facilities. Chicago ranks 5th in total emissions – behind New York, Los Angeles, Dallas-Fort Worth, and Houston – and the per-person emissions ranks on the low end of metropolitan areas. Although the region is the third largest metropolitan region in the United States, it does have more mass transit than a number of other regions.