The article presents results of inventorying pollutant emission from road transport in Poland in the years 2000–2015, prepared at the National Centre for Emissions Management (KOBiZE) of the Institute of Environmental Protection – National Research Institute. The pollutant emission was determined by modelling, which was carried out with using the EU-recommended COPERT 4 program. The fleet sizes and annual mileage (in kilometres) of vehicles classified in each cumulated category have been given. The motor vehicle traffic was characterized by the shares of vehicle mileages covered in the urban, extra-urban (rural), and high-speed (highway) driving modes in the total vehicle mileage and by the average vehicle velocity values determined for the said different driving modes. Data on annual national emission of carbon monoxide – CO, volatile organic compounds – VOC, nitrogen oxides – NOx, particulate matter – PM, and carbon dioxide – CO2 have been specified for the years 2000–2015, for which the emission balance was inventoried. A marked downward trend was revealed in the annual national emission, especially for carbon monoxide and volatile organic compounds. This is an effect of technological progress in the field of automotive engineering. The average specific distance emission and average emission factor values were also experimentally determined. Based on results of these tests, conclusions have been formulated as regards clearly visible improvement in the environmental properties of motor vehicles in the years 2000–2015; an effect of this improvement is a considerable reduction in the environmental loading caused by road transport.