In addition to mass emissions, fuel economy is being calculated under the assumption that the distance travelled during the Federal test cycle is 7.5 miles. It has been proposed that the actual distance travelled on the dynamometer be measured and used in the mass emissions and fuel economy calculations. In order to be able to use the total distance travelled in the calculations, a means of accurately measuring the distance and a change in the Federal Register are required. The report investigates this distance. It is recommended that the total distance travelled on the dynamometer be measured and also that the distances travelled during each phase of the Urban Dynamometer Driving Schedule exhaust test be used to calculate the mass emissions. The total distance travelled during the Highway Fuel Economy Test should be measured and used in the calculation of fuel economy.