Transportation is the leading source of carbon pollution in the United States, and transportation demand is a key determinant of emissions levels. Although the DDPP reports provide valuable analysis of a number of alternatives to slash GHG emissions, they do not investigate transportation demand in any depth. Opportunities to transform transportation are plentiful and could dramatically reduce GHG pollution and check the spread of roads, parking lots, and other aspects of our transportation system that can destroy carbon sinks. Steps should be taken at the federal, state, regional, and local levels to remove subsidies for driving; send better price signals to help internalize the costs of driving; remove barriers to low and zero-carbon transportation alternatives and provide meaningful rail, transit, bicycling, and walking options; and promote more compact, mixed-use development patterns that can shorten or eliminate trips. These steps often complement each other and are most effective if implemented together. The pressing question is whether the enormous potential to decarbonize transportation will be realized in time to help avoid the worst impacts of climate change. Rapid technological innovation, demographic changes, public support for cleaner transportation choices, and the multiple co-benefits these changes can bring—including health, economic, fiscal, national security, and equity co-benefits—can all help overcome barriers to decarbonizing transportation.