The Coordinating Research Council (CRC) sponsored a project focused on developing improved inputs for EPAs Motor Vehicle Emissions Simulator (MOVES), for use in the 2011 U.S. National Emissions Inventory (NEI). Under contract with CRC, ERG identified the most promising MOVES inputs for improvement, and performed a detailed review of candidate data sources for each. From this detailed evaluation, ERG centered on passenger car and light truck age distributions and populations and long-haul truck VMT allocations, and developed improved defaults to be applied at the local level. Age distributions and vehicle populations were developed for every county in the U.S. based on vehicle registration database purchased from IHS, Inc. The age distributions showed an average age range of 4 to 16 years for cars and trucks vs. MOVES national default of 9 years. Long-haul truck VMT allocations were derived from the 2007 Freight Analysis Framework (FAF), producing unique allocations by region of the country, urban/rural and interstate/non-interstate, and are intended to replace the uniform long-haul allocations currently used in MOVES. The updated long-haul fractions for combination trucks varied by region of the country, road type and urban/rural area, ranging from around 30 percent on urban unrestricted roads, to up to 90 percent for some rural restricted roads, in comparison to a static MOVES default of 59 percent. These updates will be used in the 2011 NEI, and provide a resource for emissions modelers at the federal, regional, state and municipal levels to improve local inventory and air quality modeling. While not ultimately implemented in A-88, other important findings were made for MOVES inputs related to heavy-duty truck idling and vehicle start activity that could be considered for future model and emission inventory improvements.