Fuel Economy Testing and Labeling
1.
Why should I trust EPA's fuel economy values?
The MPG estimates on the EPA/DOT Fuel Economy and Environment Label (or
window sticker) are based on standardized laboratory test procedures to ensure they
are reliable, repeatable, and fair across different car models. That means consumers
can compare mpg for different vehicles on an 'apples-to-apples' basis to determine
which vehicle is more fuel efficient.
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a case-by-case basis. We also have the opportunity to review real-world driving data voluntarily
submitted by consumers through the "My MPG" tool on the joint EPA and Department of
Energy website fiieleconomy.gov. The average fuel economy reported through this tool is higher
than the corresponding label value.
3. Why are EPA's fuel economy tests conducted in an indoor laboratory? Wouldn't it be
better to test cars on roads or at least on an outdoor track?
Testing vehicles in controlled laboratory conditions establishes a level playing field for all cars
and ensures that the test results are consistent, accurate, repeatable, and equitable among differ-
ent vehicle models and manufacturers. Vehicles are driven on a dynamometer (a device similar
to a treadmill) using five standardized driving patterns or test cycles. These test cycles represent
a variety of driving conditions including speed, acceleration, braking, air conditioning use, and
ambient temperatures. The test results from the five driving cycles are combined to yield indi-
vidual "city" and "highway" values, and a "combined" fuel economy value that assumes a 55%
city/45% highway split.1
We also account for the impact of other conditions that may occur during ordinary driving, but
which are not directly reflected in our tests, in our fuel economy calculations. These include
wind, low tire pressure, rough roads, hills, snow or ice, carrying cargo, and certain differences
between the gasoline we use for our tests and that which is typically available at the pump (see
Q5). Collectively, we estimate that these conditions reduce fuel economy by about 10%. This is
reflected in the fuel economy values that you see on the label.
On average, combined label values with today's label methodology are about 20% lower than
the traditional city and highway tests used to calculate Corporate Average Fuel Economy, or
CAFE. This is because Congress requires manufactures to demonstrate that they meet CAFE on
a specific set of laboratory test procedures. The label, however, is meant to be more reflective of
the fuel economy under the range of conditions the average driver can expect. The additional
test cycles, plus the adjustments for other conditions, do just that.
Although testing a vehicle on the road may seem like it would result in a more representative
mpg value, road tests can only provide a snapshot of driving conditions at one point in time. On
the other hand, EPA's laboratory tests cover a broad set of conditions drivers may experience
throughout the year and are designed to represent national average, real world driving.
1 To cafcufate combined fuel economy, we harmonicaify average the city mpg and highway mpg assuming 55%
and 45% driving shares, respectivefy: FE = (0.55/mpgcity + 0.45/mpg^)1. Note that when averaging muftipie fuei
economy vaiues, it is important to use harmonic averaging because this method correctiy accounts for the fact that
more fuei is consumed at iower mpg. By contrast, a simpie arithmetic average is misieading because it equaiiy
weights iow and high mpg vaiues. For a detailed explanation of harmonic averaging, please see Light-Duty
Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 Through 2013 (p.109-111),
available at: epa.gov/otaq/fetrends-complete.htm.
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4.	I heard that the top speed in EPA's highway test is 60 mph. Since everyone knows
that people drive much faster, why should I believe EPA's highway (and combined) mpg
estimates?
Vehicles are tested at a top speed of 80 mph in order to calculate the highway mpg estimates.
EPA utilizes five test cycles to represent real-world driving conditions. While it's true that the
test cycle historically labeled as the "highway" test has a top speed of 60 mph, this test is currently
meant to represent driving on lower speed highways as well as rural and suburban driving. EPA's
highway mpg estimates are primarily derived from a separate "high speed" test cycle, which has a
top speed of 80 mph. The remaining three tests are designed to simulate stop-and-go city driving,
high air conditioning use, and driving in cold temperatures. For more information on the five
test cycles and how EPA calculates its mpg estimates, go to epa.gov/fiieleconomy.
5.	When I buy gas at the pump, it typically contains about 10% ethanol and other addi'
tives. Does EPA use a gasoline-ethanol blend for fuel economy testing?
No, EPA's test fuel does not currently contain any ethanol or other oxygenates. However, EPA
does account for the impact of low-level ethanol blends in our fuel economy estimates. Ethanol
has a lower energy density than gasoline—about 1 /3 less energy per gallon. That means a car
operating on 10% ethanol would require about 3% more fuel to travel one mile than a car
operating on gasoline and thus have about 3% lower fuel economy. EPA currently reduces all
fuel economy test values by about 10% to account for ethanol in gasoline and other factors
such as wind, hills, and road conditions.
Later this decade, EPA is phasing in a requirement to change our federal emissions test
fuel to include 10% ethanol by volume. Information about this change is available at:
epa.gov/otaq/tier3.htm.
6.	Driving behavior has changed significantly in the past 30+ years, but I read that EPA
has only made minor adjustments to the fuel economy testing and labeling methodology in
that time. Why?
Actually, EPA has made several significant updates to the methodology for determining fuel
economy estimates since we started providing these values to consumers in the 1970s.
In 1984, mpg results from the two tests then in use, the "city" and "highway" tests, were adjusted
downward by 10% and 22%, respectively, to better reflect real world driving and national aver-
age conditions. The methodology was updated again for model year 2008 and later vehicles.
Data from three additional tests designed to capture high-speed and aggressive driving, high air
conditioning and accessory loads, and operation during cold temperature are now incorporated
into the fuel economy values. Rather than applying an overall correction factor, this new meth-
odology accounts for the impact of these real-world driving conditions on each specific vehicle.
A correction factor is also applied to account for factors not directly reflected on our tests
(see Q3).
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Last year, EPA announced plans to re-examine how auto manufacturers group certain types of
car models for the purpose of fuel economy testing. This will likely have the greatest impact on
some hybrid cars and other very fuel efficient vehicles (see Q7).
7.	Are EPA's fuel economy tests accurate for hybrid vehicles? Why were the mpg estimates
revised for the Ford C-Max hybrid?
Yes, EPA's fuel economy tests are accurate for hybrid vehicles. However, that doesn't mean every
driver will get the exact mileage listed on the label.
Hybrid vehicles, as well as other very fuel efficient cars, use significantly less gasoline to travel
each mile than an average vehicle. As a result, even small increases in gasoline consumption—
such as that caused by aggressive driving, high AC use, cold temperatures, or driving over rug-
ged terrain—can have a relatively larger impact on mpg. That means hybrid drivers will likely
experience more variability in their mileage compared with EPA's (or any other published) fuel
economy estimates.
The Ford C-Max hybrid is a special case. EPA tested the C-Max after receiving consumer com-
plaints that the vehicle did not achieve the label values of 47 miles per gallon (mpg) for high-
way, city, and combined driving. Based on the results of these tests, EPA determined that the
fuel economy performance of the C-Max was lower than the original label values.
Label regulations allow vehicles with the same engine, transmission and weight class to use the
same fuel economy label value data, since, historically, such vehicle families achieve nearly
identical fuel economy performance. Ford based the model year 2013 Ford C-Max label on test-
ing of the related Ford Fusion hybrid, which has the same engine, transmission and test weight.
For the vast majority of vehicles this approach would have yielded an appropriate label value for
the car, but these new vehicles are more sensitive to small design differences than conventional
vehicles because highly efficient vehicles use so little fuel.
Ford has voluntarily re-labeled the Ford C-Max to match EPA's fuel economy estimates. Going
forward, EPA is planning to work with consumer advocates, environmental organizations, and
auto manufacturers to propose revised fuel economy labeling regulations that address the issue of
how vehicles are grouped for fuel economy testing purposes.
8.	What happened with Hyundai and Kia?
Each year, EPA tests a subset of the new vehicle models at our National Vehicle and Fuel Emis-
sions Laboratory (NVFEL) in Ann Arbor, Michigan to verify that the fuel economy estimates
provided by auto manufacturers are accurate.
In 2011 and 2012, EPA began performing an audit program of manufacturers' coastdown tests.
Coastdown testing is used to develop the dynamometer inputs for each vehicle model, so that
the laboratory tests accurately replicate its tire rolling resistance, friction due to bearings and
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brakes, and aerodynamics. EPA audit tested multiple vehicle models, including the model year
2012 Hyundai Elantra. Discrepancies between EPA coastdown test results and information pro-
vided to EPA by Hyundai resulted in an ongoing investigation into the data for other Hyundai
and Kia vehicles.
Hyundai Motor America and Kia Motors America lowered their fuel economy (mpg) estimates
for the majority of their model year 2012 and 2013 models to be consistent with EPA test results.
The mileage for most vehicles was reduced by one to two mpg. The largest adjustment was six
mpg highway for the Kia Soul.
9.	How many vehicles does EPA test each year?
Auto manufacturers are responsible for testing vehicles in their laboratories according to EPA
test specifications and reporting fuel economy values to EPA.
EPA re-tests a subset of these vehicles each year at its National Vehicle and Fuel Emissions
Laboratory in Ann Arbor, Michigan. Some vehicle models are selected for testing because of
consumer complaints; others are selected at random. Historically, we have audited between 10%
and 15% of new vehicle models (or about 150-200 vehicles), but this has grown to 15%-20% in
recent years.
10.	Why are CAFE values different than the mpg estimates given on a car's window sticker?
Will consumers achieve 54.5 mpg with new cars in 2025?
The Corporate Average Fuel Economy (CAFE) program has a different purpose than the EPA/
DOT Fuel Economy and Environment Label (or window sticker) and the mpg estimates used
for each program differ accordingly. CAFE is the required average fuel economy that individual
manufacturers must meet for their fleets of passenger cars and light trucks manufactured for sale
in the United States for each model year. The National Highway Traffic Safety Administration
(NHTSA), within the Department of Transportation, establishes and enforces the CAFE stan-
dards, while EPA performs vehicle testing and CAFE calculations.
CAFE values are calculated from the EPA vehicle fuel economy database (based on testing at
both EPA and automakers, including the test data used to determine the fuel economy estimates
for the labels.) However, the law requires that the methodology used to calculate fuel economy
for CAFE compliance be consistent with the 1975 test methods so, unlike the label values,
CAFE mpg estimates are not adjusted to reflect real-world driving conditions. As a general rule
of thumb, the combined mpg estimate on a vehicle's window sticker is about 20% lower than
its combined mpg estimate for CAFE, though the actual difference depends on the particular
vehicle. For consumers, the label value provides the best estimate of the fuel economy they are
likely to experience in real world driving.
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In the National Program, a joint rulemaking with DOT, EPA has established increasingly strin-
gent greenhouse gas (GHG) emissions standards that will require automakers to average about
54.5 mpg over EPA tests in model year (MY) 2025, assuming that all GHG improvements are
achieved with fuel economy technologies. EPA projects that compliance with these standards
will lead to an average label, or real world, value of about 40 mpg in 2025. This is compared to
an average real world value of 23.6 mpg in MY 2012.
11. Why does EPA measure fuel economy?
Congress directed EPA to establish test methods and procedures to measure the fuel economy
of passenger car and trucks, and to provide this information to the public. We designed our test
procedures to reflect national-average, "real world" driving conditions. The tests are standard-
ized for all vehicles and conducted in a controlled laboratory setting, ensuring they are repeat-
able, reliable, and fair.
If auto manufacturers each designed their own procedure for measuring and reporting mpg,
consumers would not be able to make 'apples-to-apples' comparisons of mileage among different
car models. By contrast, EPA's standardized test procedures create a level playing field for all
vehicles. Consumers can rely on these values when trying to determine which vehicles are more
fuel efficient.
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