Current testing methods are often unrepresentative of real world use, causing mobile source emissions inventories to be inaccurate. Emissions inventories account for emissions produced by vehicles and stationary sources for a given area. Heavy-duty vehicle data for emissions inventories are usually taken from the federal certification test. This test often does not correspond with in-use emissions. To accurately account for inuse emissions, data must be gathered from in-use testing. West Virginia University has developed a Mobile Emissions Measurement System that recorded vehicle behavior, engine behavior, and exhaust emissions behavior during in-use testing. This system was used to obtain data from numerous vehicles over specified on-road routes. A study was conducted on on-road route repeatability. A methodology for finding repeatability had to be established, and factors influencing repeatability were identified. It was found that routes and drivers significantly influenced repeatability, and that further study of a larger sample group needs to be conducted before specific conclusions could be drawn about the influences of the vehicle on repeatability. A further study was conducted on how well the on-road routes compare to the federal emissions test. Engine behavior for on road testing was binned and compared to the federal certification test. It was found that routes that contained substantial portions of urban traffic were more representative of the federal test procedure than routes with mostly freeway driving.