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Current SAE practices for evaluating potential improvements in fuel economy on heavy-duty vehicles rely on gravimetric measurements of fuel tanks. However, the recent evolution of portable emissions measurement systems (PEMS) offers an alternative means of evaluating real-world fuel economy that may be faster and more cost effective. This paper provides a direct comparison of these two methods based on a recent EPA study conducted at Southwest Research Institute. More than 228 on-road tests were performed on two pairs of class 8 tractor-trailers according to SAE test procedure J1321 in an assessment of various chassis components designed to reduce drag losses on the vehicle. During these tests, SEMTECH-D™ portable emissions measurement systems from Sensor's, Incorporated were operating in each of the vehicles to evaluate emissions and to provide a redundant measure of fuel economy.

EPA new-model fuel economy figures are presented for passenger vehicles and light duty trucks (those with GVW ratings up to 8500 lbs). The 1981 models are emphasized, with some comparisons to prior years included. Reader familiarity with the EPA tests, data bases, and analytical methods is assumed. Principal two-way analyses include comparisons of domestic vs. import, gasoline vs. Diesel, and Federal (49-state) vs. California vehicles. Sales fractions for a number of vehicle and engine emission control design features are included. The principal finding is that increased use of newer vehicle and emission control technologies in 1981 has accompanied significant fuel economy gains in spite of the tougher 1981 emission standards.

EPA Fuel economy figures are presented for model year 1982 cars and light duty trucks. Comparisons with the MPG figures of prior years are included. Sales penetrations of various vehicle, engine, and emission control design features are given, and domestic cars' MPG characteristics are compared to that of imports', gasoline vehicle MPG is compared to Diesel MPG, and 49-states MPG is compared to California MPG. Usage of newer vehicle technologies is continuing to increase, leading to continued growth in fuel economy capability in spite of stringent emission standards.

This paper discusses the several reasons why vehicles do not achieve the EPA MPG values in service, and makes a numerical estimate of the magnitude of the individual effects. In addition, methods for adjusting EPA MPG values to estimate road fuel economy performance are presented and discussed.

This paper describes the development of adjustment factors applicable to the EPA City and Highway MPG values. The paper discusses the data bases used, and the analytical methods employed to arrive at adjustment factors of 0.90 for the EPA City MPG value and 0.78 for the EPA Highway MPG value.

This the twelfth in a series of Papers on trends in EPA fuel economy, concentrates as usual on the current Model Year (1984). Final Corporate Average Fuel Economy (CAFE) production volumes and MPG figures have been used to update the data bases through the 1982 Model Year. This paper is different from earlier papers in four ways: 1) manufacturer-supplied production forecasts have been adjusted for both model years 1983 and 1984. 2) sales weighted MPG values at the nameplate level of aggregation are presented. 3) much of the analysis is stratified at the Domestic/European/Japanese manufacturer level, and 4) fuel economy analysis for Light Duty Trucks is not included. Conclusions are presented on the trends in fuel economy of the fleet as a whole and for various classes of vehicles.

This, the thirteenth in a series of papers on trends in EPA fuel economy, covers both passenger cars and light trucks and concentrates on the current model year, 1985. It differs from previous papers in two ways: 1) Model years 1975, 1980 and 1985 are highlighted, with the model years in between these rarely discussed; 2) The progress of the industry, as a whole, in improving fuel economy since 1975 is emphasized, and individual manufacturer data are de-emphasized. Conclusions are presented on the trends in fuel economy of the car and light truck fleets; the Domestic, European and Japanese market sectors; and various vehicle classes.