Fuel Economy and Annual Travel for Passenger Cars and Light Trucks: National On-Road Survey

Glenn G. Parsons

Abstract

• From 1977 to 1981, on-road fuel economy of cars increased by 41 percent; for light trucks, from 1978 to 1981, the increase was 17-26 percent.

• Fuel efficiency improvements in the 1978-1981 vehicles will reduce fuel consumption by 45.6 billion gallons - a dollar equivalent reduction of $53.8 billion.

• On-road fuel economy is consistently below laboratory (EPA) ratings, ranging from 15-20 percent depending on vehicle type.

• Average annual travel per vehicle is about 6,000 miles; both per vehicle and total fleet travel, based on odometer data, are markedly less than estimated by prior surveys.

Executive Summary

Over a decade has passed since the 1973 Arab oil embargo which presaged a worldwide energy crisis. This initial shock was followed by several years of tight fuel supplies and steadily rising energy prices which had major impact on the U.S. economy as well as the economies of most other world countries.

One of the actions taken in response to this energy problem in the United States was the enactment of the Energy Policy and Conservation Act (EPCA) in 1975 by the Congress. Among other steps taken by this Act, one was aimed at energy conservation in the transportation sector through the establishment of Federal Corporate Average Fuel Economy Standards for new passenger cars and light trucks. Responsibility for administering this motor vehicle fuel economy program was assigned to the Secretary of Transportation who, in turn, delegated it to the Administrator of the National Highway Traffic Safety Administration (NHTSA). Thus motor vehicle fuel economy joined motor vehicle safety and other Federal regulatory programs administered by NHTSA.

Fuel Economy Standards for passenger cars for the first three years (1978-1980) and for 1985 and thereafter were originally set by the Congress in the 1975 Energy Policy and Conservation Act. More recently, NHTSA, by virtue of the statutory authority provided in the 1975 Act, amended the passenger car standard for Model Year 1986. Also a notice of proposed rulemaking (NPRM) has been issued concerning revision of the passenger car standards for Model Years 1987 and 1988. Standards for light trucks have been established for Model Year 1979 through Model Year 1988. All light truck standards have been set by NHTSA. Chapter 1, (Table 1-1) of this report lists the individual fuel economy levels, in terms of miles per gallon, as currently set by the standards.

This study is an assessment of the actual fuel economy levels, and reduction in energy consumption of the new, more fuel-efficient vehicles produced from Model Year 1978 through 1981. It should be noted that, in addition to the fuel economy standards (which took effect for passenger cars in Model Year 1978 and for light trucks in Model Year 1979), consumer demand and other market forces provided incentives for greater fuel economy during that time period. This study does not attempt to determine what portion of the improved fuel economy is attributable to the Federal standards.

A second major portion of this study develops estimates of annual vehicle miles traveled (VMT) by age and type of vehicle (passenger car and light truck) using vehicle odometer readings. It is believed that this is the first time that estimates of VMT have been developed using actual odometer readings from a large-scale national sample of the U.S. vehicle fleet.

The study was conducted to comply both with Executive Order 12291 concerning the review of Federal regulations, and with NHTSA's regulatory review plan published in March 1982 (Regulatory Reform - The Review Process).

As with most of NHTSA's evaluation studies, data reflecting "real-world" or "on-road" experience are used. The data come from a specially conducted survey, using probability sampling methods, of the Nation's fleet of privately owned and operated passenger cars and light trucks. Vehicle owner/drivers provided fuel-mileage logs or diaries for approximately 9,000 vehicles. Each log contained data on fuel purchases and odometer readings for approximately a one-month period. The sample was fielded in twelve monthly replicates throughout an entire one year period in order to account for seasonal effects on fuel economy and on vehicle travel.

This study is not an evaluation or assessment of official compliance with the Federal fuel economy standards. The process by which official compliance is determined was established via statute as part of the Energy Policy and Conservation Act of 1975 which authorized the standards. For each manufacturer, the Environmental Protection Agency (EPA) computes an overall average fuel economy for each model year. This overall average fuel economy (or miles per gallon) is based on laboratory measurements generated by the EPA during its testing of vehicles for emissions levels and for determining compliance with Federal emissions standards. Fuel economy measurements are made for each basic vehicle type for each manufacturer and a harmonically weighted average figure is calculated based on the number of vehicles of each basic type sold by each manufacturer within each model year. This overall fuel economy is thus a sales-weighted average and is commonly referred to as the corporate average fuel economy, or "CAFE." It is this CAFE which determines official compliance with the Federal fuel economy standards.

While the laboratory results generated by the EPA provide a standardized controllable, repeatable, convenient, and economical (i.e., the production of fuel economy data as a byproduct of emissions testing was already in place prior to enactment of the ECPA in 1975) method of assessing manufacturer progress vis-a-vis the Federal standards, it has nonetheless been well established by several prior studies¹ that laboratory tests do not necessarily reflect fuel economy under typical, everyday driving conditions; laboratory results are typically higher than actual on-road fuel economy.² Also as has been noted previously, it has been the policy of NHTSA to utilize data reflecting actual "on-road" experience, wherever feasible in its studies of the effects of its programs and motor vehicle regulations.

The general objectives of this study are to:

• (1) Estimate the on-road fuel economy improvements for passenger cars and light trucks produced from the beginning of fuel economy standards through Model Year 1981.
• (2) Compare the on-road fuel economy with the respective laboratory-based, or corporate average fuel economy (CAFE) levels as computed by the Environmental Protection Agency and as specified in the Energy Policy and Conservation Act of 1975.
• (3) Compare the on-road fuel economy with the levels set by the respective Federal Fuel Economy Standards.
• (4) Estimate the reduction in energy (fuel) consumption, and dollar equivalent value, for vehicles produced from Model Year 1978 through Model Year 1981.
• (5) Estimate annual vehicle miles traveled by the U.S. fleets of passenger cars and light trucks, by age of the vehicle and overall average per vehicle.

FINDINGS AND CONCLUSIONS

Following are the principal findings and conclusions reached in this study:

• (1) On-Road Fuel Economy of Passenger Cars
• a. From Model Year 1978 through 1981, the on-road fuel economy of the U.S. fleet of passenger cars increased by 41 percent, rising from 15.2 mpg in Model Year 1977 to 21.4 mpg in Model Year 1981.
• b. The greater portion of this gain in fuel economy is attributed to the domestic fleet (39 percent gain) compared to the import fleet (13 percent gain). This is to be expected considering the large differences in the original size and fuel economy of the two fleets prior to promulgation of the standards, and prior to the significant increase in fuel prices following the "second oil shock" of 1979.
• c. Among domestic manufacturers, overall fuel economy gains for the four model year period-ranged from a low of 25 percent for American motors to a high of 70 percent for Chrysler, which had a large jump of nearly 6 mpg from Model Year 1980 to Model Year 1981.
• d. Gains among foreign manufacturers were modest except for Volkswagen's 30 percent increase, from the 1977 to 1981 models, attributable to a large penetration of diesel vehicles.

• (2) On-Road Fuel Economy of Light Trucks
• a. From Model Year 1979 through 1981, on-road fuel economy increased by 26 percent (13.4 mpg to 16.9 mpg) for 2-wheel drive vehicles; for 4-wheel drive trucks, the increase was 17 percent (12.3 mpg to 14.4 mpg).
• b. As was true for passenger cars, fuel economy gains were greater for domestic vehicles. The relative gains from 1978 to 1981 model fleets were:

• (3) On-Road Fuel Economy Compared to Laboratory-based (EPA) CAFE⁴
• a. For the model years surveyed, on-road fuel economy is consistently below laboratory-based CAFE levels. For passenger cars the difference is 15 percent; for 2-wheel drive trucks, 16 percent; for 4-wheel drive trucks, almost 20 percent.
• b. Except for 4-wheel drive trucks, domestic vehicles exhibited a somewhat greater difference than import vehicles.
• c. The CAFE to on-road difference among domestic manufacturers was approximately the same with AMC and Chrysler showing slightly less difference than GM and Ford.
• d. Among import vehicles, the greatest CAFE to on-road difference was noted for the captive imports of Ford and Chrysler. Only one manufacturer, Volkswagen, had an on-road mpg consistently at or above its CAFE.
• e. This finding that on-road fuel economy is consistently below laboratory-based CAFE is not new. It has been shown in several prior studies although the data bases used and the magnitudes of the CAFE to on-road differences found have differed somewhat from those in this study. This study is believed to be the first which develops on-road fuel economy estimates from a nationwide, large-scale probability sample of the total national population of privately-owned vehicles.

• (4) On-Road Fuel Economy Compared to Federal Fuel Economy Standards
• a. For the three categories of vehicles, passenger cars, two-wheel drive trucks, and four-wheel drive trucks, the on-road fuel economy ranges from 8 to 9 percent below the Federal standard levels for Model Years 1978-1979; for 1980-1981, on-road mpg is much closer to the standard levels and in some instances, slightly above.
• b. Domestic vehicle on-road mpg is approximately 10 percent below the Federal standards; import vehicle on-road mpg ranges from 20 to 45 percent above the Federal standards. As stated earlier, this is primarily due to the smaller average size of import vehicles compared to the average size of domestic vehicles. Relative fuel economy gains were greater for domestics than for imports.
• (It should be noted, as previously stated, that compliance with the Federal standards is determined through laboratory testing by the Environmental Protection Agency. All vehicles, both import and domestic, complied with the Federal Standards during the study period).

• (5) Estimated Reduction in Energy Consumption and Dollar Equivalent Value
• a. Estimated, vehicle lifetime, reduction in energy consumption and dollar equivalent value (in 1984 dollars) for all vehicles (cars and trucks) manufactured under the Federal standards through Model Year 1981 are:

The baseline periods for these estimates are Model Year 1977, for passenger cars, and Model Year 1978, for light trucks.

Costs of implementing the Federal fuel economy standards were not estimated for reasons described in the report.

• 6. Vehicle miles Traveled

An analysis of odometer readings for the approximately 9,000 vehicles covered in the survey gave the following estimates concerning vehicle miles of travel by the Nation's population of privately owned vehicles:

• a. Average annual miles of travel for passenger cars and light trucks is essentially the same - approximately 6,000 miles per year for the average vehicle.
• b. Average annual miles of travel show little differences of a practical nature between classes of vehicle (e.g., small versus large car; 2-wheel drive versus 4-wheel drive truck, etc.).
• c. Average annual miles of travel per vehicle shows a sharp decline with vehicle age. First year travel is estimated at 14,000 miles, but by the fifth year of age, travel drops to less than half, or about 6,500 miles.
• d. Total miles traveled was found to be considerably higher for diesel vehicles than for conventionally powered gasoline vehicles. This difference was more pronounced for passenger cars than for light trucks. Also, in contrast to the finding for the overall fleet, vehicle size appeared to be an important factor here as well, with small diesel powered vehicles showing a greater increase in miles driven over their gasoline powered counterparts, than large diesel powered vehicles.
• e. Average annual travel estimates from the On-Road Survey are similar to estimates of other prior surveys for the initial few years of vehicle life.
• For later years, however, the On-Road results show a much greater rate of decline in average annual travel than prior surveys.
• f. Results from the On-Road Survey indicate that average annual travel per passenger car or light truck, and total travel for all vehicles may be substantially lower than heretofore estimated. Although fleet and business use vehicles were not included in the survey, travel by this class of vehicles does not appear to be of sufficient magnitude to account for the lower VMT (vehicle miles traveled) findings in this study.

This is believed to be the first study to develop VMT estimates from odometer readings of a large national probability sample of the Nation's population of privately owned passenger cars and light trucks.

Footnotes

¹ These studies have been done both by other Federal agencies and by companies within the motor vehicle industry. The results of these studies are discussed later in this report.

² Largely as a consequence of this situation, the EPA has recently begun discounting its laboratory data on fuel economy which are displayed on "window stickers" of new motor vehicles and which are published in the EPA annual consumer booklet, "Gas Mileage Guide."

³ 1980 to 1981 Increase

⁴ It should be noted that the EPA recently issued a final rule (50 FR 27172, July 1, 1985) adjusting its fuel economy measurements for Model Year 1980 and later, to account for test procedure changes. While this information was not available at the time this study was written, the effect of this EPA adjustment is to increase somewhat the differences between EPA CAFE values and on-road fuel economy, as estimated in this study, for Model Years 1980 and 1981.