As transportation and air quality officials confront the contribution of the transportation sector to climate change, there is a growing interest in understanding the role travel efficiency strategies can have on reducing the impacts of travel on greenhouse gas (GHG) levels in the atmosphere. The impact of travel activity on total GHG emissions in the United States cannot be overlooked. Based on GHG emissions reporting for 2008, the transportation sector accounted for around 27 percent of the total U.S. GHG emissions. This represents the second largest source of GHG emissions, exceeded only by electricity generation. Since 1990 transportation has been one of the fastest-growing sources of GHG in the country, representing 41 percent of the total increase in GHG (EPA 2010a). The Environmental Protection Agency (EPA), as well as state and local air quality and transportation agencies, has a strong interest in supporting efforts to reduce criteria pollutants as well as GHG emissions. Many criteria pollutants and their precursor emissions also impact climate, presenting win-win scenarios for climate and air quality when they are reduced (Shindell et al., 2008). The Transportation and Regional Programs Division (TRPD) of EPAs Office of Transportation and Air Quality (OTAQ) provides analysis, guidance and technical assistance on transportation policy and program effects on mobile source emissions and air quality to federal, state, and local agencies. These stakeholders are increasingly interested in understanding the effectiveness of the Transportation Control Measures (TCM) listed in the Clean Air Act (CAA) and other measures, such as road pricing and smart growth, to reduce emissions and vehicle miles traveled (VMT). The term TCM is used broadly in this report to include those travel efficiency measures listed in the CAA and other approaches for reducing VMT.