This project sought to better understand the greenhouse gas emissions (GHG) reduction potential of the U.S. transportation sector, with a focus on advanced vehicle technologies including zero emission vehicles and low-carbon, alternative fuels. The researchers analyzed a range of potential transition scenarios toward low-carbon transportation futures in the United States, exploring how policies and technology assumptions impact vehicle, fuel infrastructure, and resource requirements and costs. The analysis was carried out through development of a national level U.S. energy economic optimization model (US-TIMES), employing the widely-used MARKAL/TIMES framework. The model (1) provided detailed representation of all major transportation subsectors at a disaggregated level (light-duty, medium and heavy-duty, rail, marine, aviation and off-road); (2) focused model development on investments in both vehicles and fuel infrastructure; (3) assessed capital and operating costs of vehicle technologies and fuel infrastructure; and (4) used an integrated model to understand important linkages/synergies between the transport and other energy sectors. These models are useful for analyzing cross-sectoral policies like carbon caps and cross-sectoral energy issues like resource competition (e.g., biomass) and synergies (e.g., charging of electric vehicles). This initial analysis with the US-TIMES model shows how an energy system model can be used to analyze the role of vehicle technologies and fuels within a national energy system like that of the United States.