Real MPG - Putting the Truth in Your Tank
Thursday, July 13, 2006

Real MPG - Putting the Truth in Your Tank

The U.S. would have imported about 20 percent less foreign oil in 2005 if automakers met federal fuel efficiency or miles per gallon (MPG) standards based on real world driving conditions. That reduction is equivalent to more than 1.3 times the amount of oil imported from Saudi Arabia in 2005, or about two million barrels of oil per day. For consumers this translates into 33 billion gallons of gasoline saved that year.

Instead, over the past 20 years, car company lobbyists and their friends in Congress have dramatically increased US dependence on foreign oil by prohibiting the EPA from requiring MPG tests that reflect how people actually drive.

In the car company test for compliance with corporate MPG requirements, cars never exceed 60 miles per hour, never have the air conditioning on, never go up hills, never accelerate rapidly and always drive in perfect weather. According to several EPA analyses, these test results exaggerate real world MPG by about 25 percent for city driving and 30 percent on the highway.



Bogus mileage tests are the cornerstone of car company compliance with government MPG standards. Since 1985, car companies have generally been required to meet fleet MPG averages of 27.5 for cars, and between 19.5-22.2 for trucks [†1]. Real world MPG is far lower, at about 21.7 for cars and 16.3 for trucks.

Congress publicly identified this problem in 1980. If car company lobbyists, at that time, had not blocked congressional action to base federal fuel efficiency standards on real world driving conditions the U.S. would currently be saving 710 million barrels of oil per year, or about 20 percent of all the United States' imports in 2005.

That is the equivalent of more than 1.3 times the 525 million barrels that the United States imported from Saudi Arabia last year.

Significant oil savings do not require an increase in MPG standards. Congress could achieve vast savings simply by requiring automakers to stop deceiving the public and instead subject their vehicles to real fuel efficiency tests rather than the inaccurate, outdated tests currently prescribed by law.

[†1] According to the U.S. Department of Transportation, cars were first required to meet a standard of 27.5 miles per gallon in 1985. The standard dropped to 26.0 in 1986 through 1988, rose to 26.5 in 1989 and returned to 27.5 in 1990 where it has remained.


A Quarter Century of Deceit

Many drivers know that the mileage number on their car's window sticker is inaccurate, and that cars rarely get the mileage that is advertised. But few people know that the number on the window is not the one that car companies use to meet corporate gas mileage standards. Instead, car company lobbyists and Congress have created what the Center for Auto Safety calls two sets of books when it comes to gas mileage (CAS 2004).

This legally sanctioned deception dates back more than 25 years. In 1980, the U.S. House of Representatives Committee on Government Operations assessed the effectiveness of fuel efficiency standards that Congress had passed in 1975. The Committee found that:

...most new cars sold in this country do not achieve on road the fuel economy standards set by Congress. However, it should be noted that car manufacturers are deemed in compliance with the fuel economy standards mandated by Congress in 1975. American car owners and the entire U.S. economy will both be the losers if that situation is not remedied. Both will pay millions of dollars more, and both will remain more reliant on foreign oil sources, as a direct result of the needless waste of automobile fuel (HCOGO 1980).

The Committee found that model year 1978 cars with government rated fuel efficiency of 27.5 miles per gallon achieved only 19 miles per gallon on the road, a shortfall of 30 percent that is essentially the same shortfall that occurs today. In addition, the Committee found that the shortfall between the government mileage ratings and real world driving could cause the U.S. to burn an extra one million barrels of gasoline per day by 1985.

How the Automakers Drive/How You Drive

The problem, the Committee found, was the grossly inaccurate testing procedures for measuring fuel efficiency; procedures that remain in place today. The city portion of the test is based on a simulated drive to work in Los Angeles in 1965 when congestion was much lower than it is today. The highway portion of the test was developed by the Environmental Protection Agency (EPA) in 1974 and was designed to represent a mix of interstate and freeway driving at a time when the national speed limit was 55 miles per hour. Congress eliminated the national speed limit in 1995 and states have instituted speed limits of 65 or 70 miles per hour (EPA FR 2006).

Not surprisingly, neither the highway nor city test reflects real world driving behavior or gas mileage. One major difference is speed. On the highway test, cars average just 49 miles per hour and never exceed 60 miles per hour. Yet according to the EPA, recent reports show that 28 percent of all driving occurs at speeds greater than 60 miles per hour. Higher speed can dramatically reduce fuel efficiency (EPA FR 2006).

In addition, the acceleration rates in both the city and highway tests are 3.3 miles-per-hour per second despite recent studies of real world driving which show that acceleration rates can be as high as 12 miles-per-hour per second. Rapid acceleration can seriously cut gas mileage. Even when the tests were developed, acceleration rates were higher in the real world. Yet, at the time, the dynamometers (treadmills for cars) on which the tests were completed did not allow for faster acceleration. Today's dynamometers allow for rapid acceleration even though rapid acceleration is not incorporated in mileage testing (EPA FR 2006).

Other significant differences between the driving tests and real world driving are the use of accessories and ambient temperature. Neither the city test nor the highway test uses accessories such as air conditioning, heating or defrosting. Air conditioning in particular can reduce fuel efficiency. In addition, the tests are conducted at 75 degrees F even though only 20 percent of all driving occurs within five degrees of this temperature. Fuel efficiency is lower at temperatures that are above and below 75 degrees.

Finally, because the tests are conducted on a dynamometer rather than on the road, the automakers do not have to account for a variety of conditions that can reduce fuel efficiency including roadway roughness, hills, wind, tire pressure, heavier loads (trailers, cargo, multiple passengers), the effects of ethanol in gasoline and others (EPA Preamble 2006).

A Band-Aid Approach

Despite these discrepancies, Congress and the automakers have resisted real change. In 1980, confronted by inaccuracies in the testing program, automakers General Motors and Ford suggested that the car labels be adjusted so that consumers would have more accurate information. However, the automakers opposed changing the driving test so that they would comply with federal fuel efficiency standards. "That approach is anathema to the auto makers," the Committee on Government Operations reported. Ford argued to the Committee that the testing procedures were fixed by law despite evidence that EPA could have modified the test. The Committee recommended changing the test to accurately reflect mileage for the 1986 and later model years.

In 1984, the EPA adopted the approach favored by the automakers. Since that year, the Agency has adjusted the mileage figures produced by the driving test downward before placing the numbers on cars' window stickers (CAS 2004). The agency lowers the city test figure by 10 percent and the highway figure by 22 percent (EPA 2006). This adjustment provides consumers with somewhat more accurate information. But the test for determining compliance with fuel efficiency standards remains grossly inaccurate.

Congress Ensures that Automakers are Falling Short

The result of the inaccurate driving test is that automakers are failing to meet federal fuel economy standards established by Congress in 1975. Automakers' current fleet of cars must average 27.5 miles per gallon while SUVs and light trucks must average 22.2 miles per gallon. According to EWG's estimate, the true figures are closer to 21.7 miles per gallon for cars and 16.3 miles per gallon for SUVs and light trucks. A recent on-road study by Consumers Union of more than 300 cars and trucks found that 274 delivered lower fuel economy than promised by EPA (CU 2005). Consumers Union found that its estimated mileage for 2003 model year cars was 30 percent lower than that reported to the government for purposes of complying with federal fuel efficiency standards. This discrepancy is the same as that reported by the House Committee on Government Operations for 1978 model year cars.


Moving Toward RealMPG

For more than a quarter century, federal law has required automakers to save oil by meeting mileage standards for their cars. This law grew out of concern over the United States' economic vulnerability to unstable foreign sources of oil. Congress acknowledged that one of the best ways to reduce this vulnerability is simply to use less oil. But as long as the mileage standards have been on the books, the automakers have evaded the spirit of the law by using a bogus driving test. The test allows automakers to claim that they are meeting federal mileage standards when in fact they are not. The losers in this scheme are citizens who must now pay $3.00 a gallon for gasoline to operate vehicles that deliver significantly less gas mileage than advertised. In addition, the U.S. is more dependent on foreign oil than ever before — in no small part because of the automakers' deliberate gas mileage deception.

It does not have to be this way. EPA has designed emissions tests that incorporate many of the real-world driving standards and uses them to measure automakers' compliance with pollution emissions standards. For example, EPA tests auto emissions using a cold weather city driving test known as Cold FTP in which fuel efficiency is about 12 percent lower than in the normal city test. EPA also measures car pollution using a test with the air conditioning on known as SC03 that produces fuel efficiency numbers that are about 21 percent lower than in the normal city test. And EPA runs a third test known as the US06 that incorporates rapid acceleration and high speed. Results from this test are about 30 percent lower than mileage results from a composite of the normal city and highway tests.

Acting on a petition by Bluewater Network, EPA recently announced that it plans to use these three tests to produce more accurate mileage stickers for consumers. But EPA has said that it will not use the tests to improve automakers' compliance with vehicles' fuel efficiency.


It's time for Congress to mandate one test for pollution, MPG compliance, and the sticker on the window in the showroom. Test methods similar to those found in Senate Bill 3543 would be a good start. It is outrageous that car companies have been allowed to deceive the American public for decades about the real MPG of their cars. Requiring a real driving test is not a substitute for enacting higher mileage standards for cars, but it is an essential step to making cars more efficient and to reducing dependence on foreign oil.


About This Report

Authors: Dusty Horwitt, Richard Wiles

Special thanks to the Bluewater Network and the Center for Auto Safety.

This report was made possible by a grant from the Energy Foundation. The opinions expressed in this report are those of the authors and editors and do not necessarily reflect the views of our supporters. EWG is responsible for any errors of fact or interpretation contained in this report.




Environmental Working Group calculated the amount of gasoline and oil saved in 2005 if automakers had met federal fuel efficiency or miles per gallon (MPG) standards based on real world driving conditions beginning in 1978. In order to make this calculation it was necessary to know the composition of the U.S. car and truck fleet, how many of each model year were on the road in 2005. EWG used data from a commercial automobile information company to determine how many cars and light trucks from each model year were on the road as of January 2006. We estimated how many miles each model year is currently driving using data from the U.S. Department of Energy on miles driven by age of car (DoE 2001). The DoE reported, for example, that cars less than one year old traveled an average of 14,500 miles per year while cars ten years old and older traveled an average of 8,100 miles per year.

EWG then referred to Department of Transportation data which shows the automakers' reported miles per gallon for cars and light trucks using the government's inaccurate driving test (DoT Fuel Efficiency 2006). We used a recent Consumer Reports analysis of city and highway fuel efficiency for more than 300 cars and light trucks to estimate the ratio of city to highway miles per gallon (CU 2005). We then applied this city/highway fuel efficiency ratio to MPG data from the DOT -- data that are derived from the current, inaccurate driving test.

We then discounted the highway figure by 22 percent and the city figure by 10 percent — the same percentages by which the EPA discounts highway and city miles per gallon figures before placing them on cars' window stickers. We discounted the highway figure by an additional 10 percent and the city figure by an additional 15 percent because the EPA has estimated that a real world driving test would further reduce the window sticker figures by these percentages (EPA Sticker 2006). Finally, we combined the highway and city figures, using EPA's estimate that 45 percent of driving is city driving and 55 percent of driving is highway driving (FR 2006). We multiplied our final figure (.73) by the DoT figures for each model year to determine the real world miles per gallon figures for each model year.

Then we divided the total miles traveled per year by cars and light trucks in each model year by the real world miles per gallon figure for each model year. The result was the gallons of gasoline currently consumed. EWG's calculation is almost exactly the same as DoT's most recent published estimate of car and light truck gasoline consumption (DoT VMT 2004). We made the same calculation using the miles per gallon standards that automakers are required to meet under federal law. The result was the gallons of gasoline that cars and light trucks should be consuming. Then we subtracted the gallons cars should be consuming from the gallons that cars are currently consuming. The difference is more than 33 billion gallons, the total number of gallons of gas saved in 2005 if cars had to meet federal mileage standards based on real world driving tests. The result includes cars from the 1978 model year and later and light trucks from the 1982 model year and later. Cars were first required to meet federal mileage standards in 1978 while light trucks received their own standards beginning in 1982.

The U.S. Department of Energy reports that the heat content of each barrel of gasoline is 5.218 million British Thermal Units (BTUs). There are 42 gallons in each barrel, so 33 billion gallons of gasoline is equivalent to about 789 million barrels or about 4.1 quadrillion BTUs. The DoE reports that there are 5.8 million BTUs in each barrel of oil so we divided 4.1 quadrillion by 5.8 million to determine that the U.S. would be saving about 710 million barrels of oil per year if automakers met federal mileage standards based on a real world driving test.


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Consumers Union (CU). 2005. An In-Depth Comparison of Consumers Union's Passenger Vehicle Average MPG Estimates with Those Published by EPA and NHTSA.

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