A method has been developed for the prediction of gaseous pollutants emitted into the national environment from on-the-road gasoline powered vehicles. The method involves two quantities, the emissions emited per mile traveled, and the total mileage traveled. Vehicular emissions characterized by engine type and load under actual operating conditions. Five vehicle types and two classes were used to define characteristic vehicular emissions. Vehicle types were automobile (auto) light duty truck (LDT), and three weight classes of heavy duty trucks (HDT). The two classes were urban and rural. The method allows comparison between the possible degrees of control, methods of control, and implementation dates.