Inventory approaches for truck and bus emissions rely heavily on certification data, and no comprehensive results have been published to date. Two transportable chassis dynamometer laboratories developed and operated by West Virginia University (WVU) have been used extensively to gather realistic emission data from heavy-duty vehicles tested in the field, in controlled, simulated driving conditions. By default, a comprehensive database has been assembled, that comprises a wide variety of vehicles, engines, fuels, and driving scenarios. A subset of these data is analyzed in this paper for an illustration of practical utilization of such information, either for inventory assessments, or for comparative and correlation studies. General guidelines for data screening and analysis approaches are provided, along with examples of specific results and discussions for a selected cross-section of samples. The paper is focused on the exhaust emissions of nitrogen oxides (NOx) and Particulate Matter (PM), since these are considered to be critical for meeting current regulations and standard requirements. Emission results generated through testing of transit buses on the Central Business District (CBD) cycle provide a broad and reliable baseline of typical data, that can be used with confidence for inventory, or correlation studies of diesel emissions from heavy-duty vehicles. Certain examples are described in the paper for this and other samples of data included in the West Virginia University's database.