Light-Duty Automotive Technology,
Carbon Dioxide Emissions, and Fuel
Economy Trends:
1975 Through 2010
Appendix A
Database Details and Calculation Methods
Compliance and Innovative Strategies Division
and
Transportation and Climate Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
NOTICE
This technical report does not necessarily represent final EPA decisions or
positions. It is intended to present technical analysis of issues using data
that are currently available. The purpose in the release of such reports is to
facilitate the exchange of technical information and to inform the public of
technical developments.
SEPA
United States
Environmental Protection
Agency
EPA-420-R-10-023
November 2010
-------
Harmonically Averaging Fuel Economy Values
Dimensionally, fuel economy is miles divided by gallons. Then, presented with more than one
fuel economy value, an approach to averaging the values is to compute the result by determining the total
miles traveled and dividing that by the total gallons used.
Example: A motorist's fuel economy log for May shows that 704 miles were accumulated around
town in which the fuel economy was 16 mpg, and one 216 mile highway trip was taken on which the fuel
economy was 24 mpg. What is the average fuel economy for May?
The total miles are 704 + 216 = 920. The total gallons thus are 704 / 16 = 44 plus
216 / 24 = 9 or atotal of 53 gallons. The average mpg is 920 / 53 = 17.4 mpg. Notice that the arithmetic
average of the two fuel economy values (16 + 24) / 2 = 20 mpg gives an individual result that is higher
than the total miles/total gallons result.
Even if the around-town miles traveled and the highway trip miles traveled were the same (460
miles), the average fuel economy would not be 20; it would be 19.2 mpg. This is because in the total
miles/total gallons approach, fuel consumption is arithmetically averaged, but fuel economy is
harmonically averaged, so for the second example (equal trip distances), the calculation would be:
Average MPG =
which is the same as arithmetically averaging the two fuel consumption values.
A specific example of this type of averaging approach is shown in the calculation of the overall
average fuel economy using the EPA "city" (MPGC) and EPA "highway" (MPGH) fuel economy values.
Total Miles
Averaqe MPG =
a Total Gallons
Total Miles
City Gallons + Highway Gallons
Total Miles
I City Miles Highway Miles \
( City MPG + Highway MPG )
Now, if city miles are 55 percent of total miles and highway miles are the remaining 45 percent,
after dividing by total miles,
A-l
-------
Average MPG = Q^ Q
\MPGC ^ MPGf
and this average mpg would represent a composite mpg value based on the 55% city/45% highway
driving in this example. This 55% city/45% highway weighting is the metric in this report for laboratory
composite fuel economy values.
The same approach can be used when the average mpg of a group of vehicles with different mpg
values is to be calculated. Suppose a fleet of 100,000 vehicles is made up of two classes, one of 70,000
vehicles whose fuel economy is 10 mpg and the other of 30,000 vehicles whose fuel economy is 14 mpg.
Each vehicle in the fleet is assumed to travel the same number of miles (M),
Total Miles = 100,000 M
70,000 M 30,000 M
Total Gallons = — + •
10 14
and the average fuel economy is:
1
Average Fuel Economy = —^-=—ppr— = 10.9 mpg
_ + "
10 ^ 1
where .7 and .3 are the relative shares of each vehicle class in the fleet. Notice that, again, the arithmetic
average of the class fuel economy values (10 + 14)/2 = 12 mpg is higher.
In general, some form of a weighted harmonic mean must be used when averaging different fuel
economy values in order to maintain mathematical integrity.
While fuel economy values (in miles per gallon) must be harmonically averaged to maintain
mathematical integrity, fuel consumption values (in gallons per mile) and carbon dioxide emissions
values (in grams per mile) can be arithmetically averaged.
A-2
-------
Estimated and Final Production Data
Table A-l compares average laboratory 55/45 fuel economy for model years 1998 through 2009
at three points in time:
(1) an initial estimate determined early in the model year using projected production;
(2) for some years, a revised estimate determined by using trade publication sales data
that were obtained after the end of each model year, but before the final CAFE data were
submitted by automakers to the Federal Government; and
(3) final fuel economy values determined from CAFE compliance data provided by the
manufacturers to the Federal Government after the end of the model year.
Historically, the final car plus truck laboratory 55/45 fuel economy values have generally varied
from 0.4 mpg lower to 0.6 mpg higher compared to the original estimates based exclusively on projected
production. But, MY2009 was a very unusual year in this regard. The final car plus truck laboratory
55/45 value for MY2009 in this report is 1.8 mpg higher than the initial estimate for 2009 in last year's
report, due to the market turmoil in MY2009. The final adjusted car plus truck fuel economy value for
MY2009 is 1.3 mpg higher than the initial estimate in last year's report.
A-3
-------
Table A-l
Comparison of Laboratory 55/45 MPG
Cars
Trucks
Both
Model
Year
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Initial
Estimates
28.6
28.1
28.1
28.3
28.5
29.0
28.7
28.9
28.8
29.4
30.3
30.9
32.7
20.6
20.3
20.5
20.3
20.4
20.8
20.9
21.3
21.5
22.1
22.5
22.9
23.8
24.4
23.8
24.0
23.9
24.0
24.4
24.4
24.6
24.6
25.3
26.0
26.4
28.3
Revised
Estimates
28.6
28.2
28.3
28.3
28.5
28.9
28.9
29.2
29.2
30.3
20.6
20.4
20.5
20.4
20.3
20.9
20.9
21.2
21.9
22.1
24.4
24.0
23.9
24.0
23.9
24.2
24.4
24.6
25.3
25.7
Final
Value
28.5
28.1
28.2
28.4
28.6
28.9
28.9
29.5
29.2
30.3
30.5
32.1
20.9
20.5
20.8
20.6
20.6
20.9
20.8
21.4
21.8
22.1
22.7
23.8
24.5
24.1
24.3
24.2
24.1
24.3
24.0
24.8
25.2
25.8
26.3
28.2
A-4
-------
Use of 3-Year Moving Averages
Use of the three-year moving averages, which effectively smoothes the trends, results in an
improvement in discriminating real trends from what might be relatively small year-to-year variations in
the data. For this report, as shown in Table A-2, these three-year moving averages are tabulated at the
midpoint. For example, the midpoint for model years 2007, 2008, and 2009 is MY2008.
Table A-2
Light-Duty Vehicle Laboratory Fuel Economy and Truck Sales Fraction
Year
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Actual Data
55/45 Fuel Economy
Cars Trucks Both
15.8
17.5
18.3
19.9
20.3
23.5
25.1
26.0
25.9
26.3
27.0
27.9
28.1
28.6
28.1
27.8
28.0
27.6
28.2
28.0
28.3
28.3
28.4
28.5
28.2
28.2
28.4
28.6
28.9
28.9
29.5
29.2
30.3
30.6
32.1
32.7
13.7
14.4
15.6
15.2
14.7
18.6
20.1
20.5
20.9
20.5
20.6
21.4
21.6
21.2
20.9
20.7
21.3
20.8
21.0
20.8
20.5
20.8
20.6
20.9
20.5
20.8
20.6
20.6
20.9
20.8
21.4
21.8
22.1
22.7
23.8
23.8
15.3
16.7
17.7
18.6
18.7
22.5
24.1
24.7
24.6
24.6
25.0
25.7
25.9
25.9
25.4
25.2
25.4
24.9
25.1
24.6
24.7
24.8
24.5
24.5
24.1
24.3
24.2
24.1
24.3
24.0
24.8
25.2
25.8
26.3
28.2
28.3
Truck
Production
Fraction
0.194
0.212
0.200
0.227
0.222
0.165
0.173
0.197
0.223
0.239
0.254
0.283
0.278
0.298
0.307
0.302
0.322
0.334
0.360
0.404
0.380
0.400
0.424
0.449
0.449
0.449
0.461
0.485
0.496
0.520
0.495
0.471
0.471
0.473
0.398
0.411
Three-Year Moving Average
55/45 Fuel Economy Truck
Cars Trucks Both Production
Fraction
17.1
18.5
19.4
21.1
22.8
24.8
25.7
26.1
26.4
27.0
27.6
28.2
28.3
28.2
28.0
27.8
27.9
28.0
28.2
28.2
28.3
28.4
28.4
28.3
28.3
28.4
28.7
28.8
29.1
29.2
29.7
30.0
31.0
31.8
14.5
15.1
15.2
16.0
17.5
19.7
20.5
20.6
20.6
20.8
21.2
21.4
21.2
20.9
21.0
20.9
21.0
20.8
20.7
20.7
20.7
20.8
20.7
20.7
20.6
20.6
20.7
20.8
21.0
21.3
21.7
22.2
22.9
23.4
16.5
17.6
18.3
19.8
21.5
23.7
24.5
24.6
24.7
25.1
25.5
25.8
25.8
25.5
25.3
25.2
25.1
24.8
24.8
24.7
24.7
24.6
24.4
24.3
24.2
24.2
24.2
24.1
24.4
24.7
25.2
25.7
26.7
27.6
0.202
0.213
0.216
0.205
0.187
0.178
0.197
0.219
0.239
0.258
0.272
0.286
0.294
0.302
0.310
0.319
0.339
0.366
0.381
0.395
0.401
0.424
0.441
0.449
0.453
0.465
0.481
0.500
0.504
0.495
0.480
0.471
0.447
0.428
A-5
-------
Table A-2 (Continued)
Light-Duty Vehicle Adjusted Fuel Economy
Cars
Model
Year
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
Actual Data
CITY
12.3
13.7
14.4
15.5
15.9
18.3
19.6
20.1
19.9
20.2
20.7
21.2
21.2
21.4
20.9
20.5
20.5
20.0
20.3
20.0
20.0
19.8
19.8
19.7
19.4
19.3
19.4
19.4
19.5
19.3
19.6
19.4
20.1
20.3
21.3
HWY
15.2
16.6
17.4
19.1
19.2
22.6
24.2
25.5
25.5
26.0
26.8
27.6
27.7
28.2
27.9
27.5
27.6
27.5
27.9
27.7
28.1
28.0
28.0
28.0
27.5
27.3
27.3
27.2
27.5
27.4
27.6
27.5
28.3
28.5
29.7
COMP
13.5
14.9
15.6
16.9
17.2
20.0
21.4
22.2
22.1
22.4
23.0
23.7
23.8
24.1
23.7
23.3
23.4
23.1
23.5
23.3
23.4
23.3
23.4
23.4
23.0
22.9
23.0
23.1
23.2
23.1
23.5
23.3
24.1
24.3
25.4
Three-Year Moving Average
CITY
13.4
14.5
15.3
16.5
17.8
19.3
19.8
20.1
20.3
20.7
21.0
21.3
21.2
20.9
20.6
20.3
20.2
20.1
20.1
19.9
19.9
19.8
19.6
19.5
19.3
19.4
19.4
19.4
19.4
19.4
19.7
19.9
20.6
21.1
HWY
16.3
17.6
18.5
20.2
21.8
24.1
25.1
25.7
26.1
26.8
27.4
27.8
27.9
27.8
27.7
27.5
27.6
27.7
27.9
27.9
28.0
28.0
27.8
27.6
27.4
27.3
27.3
27.4
27.5
27.5
27.8
28.1
28.9
29.4
COMP
14.6
15.8
16.6
18.0
19.4
21.2
21.9
22.2
22.5
23.0
23.5
23.9
23.9
23.7
23.5
23.3
23.3
23.3
23.4
23.3
23.4
23.4
23.2
23.1
23.0
23.0
23.1
23.2
23.3
23.3
23.6
23.9
24.6
25.1
2010 21.7 30.1
A-6
-------
Table A-2 (Continued)
Light-Duty Vehicle Adjusted Fuel Economy
Trucks
Model
Year
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
Actual Data
CITY
12.6
12.4
12.1
14.8
16.0
16.3
16.5
16.1
16.2
16.8
16.8
16.2
15.9
15.6
15.9
15.5
15.5
15.3
15.0
15.1
14.8
14.9
14.6
14.7
14.6
14.4
14.6
14.3
14.6
14.9
15.1
15.5
16.2
HWY
14.1
13.7
13.1
17.1
18.6
19.0
19.6
19.3
19.4
20.2
20.5
20.2
19.8
19.8
20.3
19.9
20.1
19.7
19.5
19.9
19.5
19.8
19.2
19.4
19.1
19.1
19.3
19.2
19.8
20.1
20.4
21.0
21.9
COMP
13.3
12.9
12.5
15.8
17.1
17.4
17.8
17.4
17.5
18.2
18.3
17.9
17.6
17.4
17.8
17.4
17.5
17.2
17.0
17.2
17.0
17.1
16.7
16.9
16.7
16.7
16.9
16.7
17.2
17.5
17.7
18.2
19.0
Three-Year Moving Average
CITY
12.2
12.4
13.0
14.1
15.7
16.3
16.3
16.3
16.4
16.6
16.6
16.3
15.9
15.8
15.7
15.6
15.4
15.2
15.1
15.0
14.9
14.8
14.7
14.6
14.6
14.5
14.4
14.5
14.6
14.9
15.1
15.6
15.9
HWY
13.7
13.6
14.4
15.9
18.2
19.1
19.3
19.4
19.6
20.0
20.3
20.2
19.9
20.0
20.0
20.1
19.9
19.7
19.7
19.6
19.7
19.5
19.5
19.2
19.2
19.1
19.2
19.4
19.7
20.1
20.5
21.1
21.7
COMP
12.8
12.9
13.6
14.9
16.7
17.4
17.5
17.6
17.7
18.0
18.1
17.9
17.6
17.6
17.5
17.5
17.3
17.2
17.1
17.0
17.1
16.9
16.9
16.8
16.8
16.8
16.8
16.9
17.1
17.5
17.8
18.3
18.8
2010
16.2
22.0
19.1
A-7
-------
Table A-2 (Continued)
Light-Duty Vehicle Adjusted Fuel Economy
Cars and Trucks
Model
Year
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
Actual Data
CITY
14.0
14.7
14.9
17.6
18.8
19.2
19.0
19.1
19.3
19.8
19.8
19.6
19.1
18.7
18.8
18.2
18.2
17.8
17.7
17.6
17.4
17.2
16.9
16.9
16.8
16.6
16.7
16.3
16.8
17.0
17.3
17.7
18.9
HWY
16.6
17.5
17.4
21.5
23.0
23.9
23.9
24.0
24.4
25.0
25.3
25.2
24.8
24.6
24.7
24.4
24.4
23.8
24.1
24.0
23.6
23.6
23.0
23.0
22.8
22.5
22.7
22.4
23.1
23.4
23.9
24.4
26.0
COMP
15.1
15.8
15.9
19.2
20.5
21.1
21.0
21.0
21.3
21.8
22.0
21.9
21.4
21.2
21.2
20.8
20.9
20.4
20.5
20.4
20.1
20.1
19.7
19.8
19.6
19.4
19.6
19.3
19.9
20.1
20.6
21.0
22.4
Three-Year Moving Average
CITY
13.9
14.5
15.6
16.9
18.5
19.0
19.1
19.1
19.4
19.6
19.7
19.5
19.1
18.9
18.6
18.4
18.1
17.9
17.7
17.6
17.4
17.1
17.0
16.9
16.8
16.7
16.6
16.6
16.7
17.0
17.3
18.0
18.5
HWY
16.6
17.2
18.6
20.3
22.8
23.6
23.9
24.1
24.5
24.9
25.2
25.1
24.9
24.7
24.6
24.5
24.2
24.1
24.0
23.9
23.7
23.4
23.2
23.0
22.8
22.7
22.6
22.7
23.0
23.5
23.9
24.8
25.5
COMP
15.0
15.6
16.8
18.3
20.2
20.8
21.0
21.1
21.4
21.7
21.9
21.7
21.5
21.3
21.1
21.0
20.7
20.6
20.4
20.3
20.2
20.0
19.8
19.7
19.6
19.5
19.4
19.6
19.8
20.2
20.6
21.3
22.0
2010
19.0
26.1
22.5
A-8
-------
Vehicle Classification Exceptions
The truck size classification scheme used in this report is based primarily on published wheelbase
data. For cars, vehicle classification as to vehicle type, size class, and manufacturer generally follows
fuel economy label, Fuel Economy Guide, and fuel economy standards protocols; exceptions are listed in
Table A-3. The classification of a vehicle for this report is based on the authors' engineering judgment
and is not a replacement for definitions used in implementing automotive standards legislation.
Table A-3
Manufacturer
Chrysler:
Chrysler:
Chrysler:
Chrysler:
Chrysler:
Chrysler:
Chrysler:
Chrysler:
Chrysler:
Make/Vehicles
Colt 4WD Wagon*
Colt Vista*
Pacifica*
PT Cruiser
PT Cruiser Convertible*
Summit Wagon*
Dodge Ram Charger*
Dodge Magnum*
Eagle 4WD Wagon*
Classified As:
Small Wagon
Small Van
Large Wagon
Small Wagon
Subcompact
Small Van
Large Sedan
Midsize Wagon
Car
Ford:
Ford:
GM:
GM:
GM:
Nissan:
Toyota:
Toyota:
VW:
Other:
Other:
Other:
Other:
Other:
Other:
Other:
Ford Pinto Van*
Volvo V70 XC
HHR
Isuzu Oasis*
Pontiac Vibe
Infmiti EX35
Lexus RX300*
Matrix
Audi Allroad*
Subaru Outback AWD Wagon
Subaru Forester
Subaru Baja*
Suzuki X-90*
Mitsubishi Expo*
Mitsubishi Space Wagon*
Mercedes R-Series
Car
Midsize Wagon
Small Wagon
Midsize Van
Small Wagon
Midsize SUV
Midsize SUV
Small Wagon
Midsize Wagon
Midsize Wagon
Small SUV
Small Pickup
Small SUV
Small Van
Small Van
Large Wagon
* Not manufactured for MY 2010.
A-9
-------
Methodology for Adjusted Fuel Economy Values
for Model Years 1986-2010
On December 27, 2006, EPA published regulations that changed the methodology for calculating
the city and highway fuel economy label estimates for new passenger cars and light trucks (71 Federal
Register 77872). This revised methodology provides fuel economy estimates to consumers that better
reflect real world fuel economy. The methodology incorporates test data that directly account for several
important factors that affect fuel economy in the real world, such as high speeds, aggressive accelerations
and decelerations, the use of air conditioning, and operation in cold temperatures, and indirectly account
for a number of other factors that are not reflected in EPA laboratory test data such as changing fuel
composition, road conditions, etc.
These vehicle fuel economy label changes were implemented beginning with the 2008 model
year. For model years 2008-2010, manufacturers have two options for calculating city and highway fuel
economy labels: 1) use vehicle-specific "5-cycle" (Federal Test Procedure for urban stop-and-go driving,
Highway Fuel Economy Test for rural driving, US06 test for high speeds and aggressive driving, SCO3
test for air conditioning operation, and cold FTP test for cold temperature operation) fuel economy test
data in "composite" equations that calculate vehicle-specific city and highway fuel economy values using
weighting factors for data from each of the 5 EPA test cycles, or 2) use an industry-average "mpg-based"
method, which yields mpg-based adjustments based on a regression of recent 5-cycle fuel economy data
for the industry as a whole. Beginning in 2011, manufacturers must use the 5-cycle method. For more
details on the derivation of these options, the specific equations that allow an automaker to calculate new
label values using either the vehicle-specific 5-cycle test data or the industry-average mpg-based
approach, and the impact of these changes on average fuel economy label values, see the Preamble to the
new regulations (71 Federal Register 77881-77893).
Beginning with the 2007 Trends report, EPA has made significant changes in how adjusted (ADJ)
fuel economy values for model years 1986 through 2010 are calculated to reflect the revised EPA fuel
economy label methodology. These changes affect every table and figure in this report that involve
adjusted fuel economy data. Accordingly, adjusted fuel economy values for 1986 and later model years
should not be compared with the corresponding values from pre-2007 reports in this series. Specifically,
the adjusted fuel economy values for 1986-2010 in this report differ from those in pre-2007 reports as
explained below.
• For model years 2005-2010, EPA calculates adjusted fuel economy values for most of the
individual models in the fuel economy trends database using the following city and highway
"mpg-based" equations from the EPA fuel economy labeling rulemaking:
New ADJ CITY =
0.003259+ 1'1805
LAB CITY
New ADJ HWY = , - .,,
0.001376+ L3466
LAB HWY
A-10
-------
The above equations are not used if a manufacturer chooses the option of providing vehicle-
specific 5-cycle test data for an individual model. In that case, the adjusted fuel economy
values are calculated using equations with weighting factors for the data from the 5-cycle
tests. For MY2010, manufacturers chose this option for a small number of individual models.
Calculating fleetwide adjusted city and highway fuel economy values for a given model year
requires a harmonic, production-weighted average of all of the adjusted city and highway fuel
economy values for individual models.
The above equations yield a greater downward adjustment for higher fuel economy vehicles
than for lower fuel economy vehicles. For example, compared to the older fuel economy
label methodology, a 15 mpg city value will be reduced by an additional 10%, while a 50
mpg city value will be reduced by an additional 18%. Likewise, a 20 mpg highway value
will be reduced by an additional 7%, while a 50 mpg highway value will be reduced by an
additional 11%. EPA projected an overall average fleetwide adjustment of 11% lower for
city fuel economy and 8% lower for highway fuel economy, beyond that in the older label
adjustment methodology that has been used in pre-2007 reports in this series. These factors
can be used to convert older adjusted fuel economy values to the newer adjusted fuel
economy values for the current fleet as a whole, but would not be appropriate factors to use
for individual models or for a future fleet with different mpg characteristics.
This report seldom uses separate city and highway fuel economy values, but typically uses
the composite city/highway fuel economy value. Pre-2007 reports used a 55% city/45%
highway weighting for adjusted composite fuel economy values, the same weighting used for
laboratory composite values and for the CAFE compliance program. The analysis of real
world driving activity underlying the newer fuel economy label methodology assumed a
"speed cutpoint" of 45 miles per hour to differentiate between city and highway driving (71
Federal Register 77904). Based on this speed cutpoint, the correct weighting for correlating
the new city and highway fuel economy values with real world driving, on a miles driven
basis, is 43% city/57% highway. Accordingly, the 43% city/57% highway weighting is now
used for all adjusted composite city/highway fuel economy values in this report beginning
with the 2005 model year (note that the historic 55% city/45% highway weighting is still used
for both CAFE compliance and fuel economy labels).
The appropriate fleetwide factors to convert laboratory or older adjusted fuel economy values
to the newer adjusted fuel economy values are dependent on the city fuel economy-to-
highway fuel economy ratios in the fleet. On average, for the current fleet, combining the
11% lower adjustment for city fuel economy, the 8% lower adjustment for highway fuel
economy, and the shift to the 43% city/57% highway weighting, the newer adjustment for
city/highway composite fuel economy values is 6% lower than that used in the older label
adjustment methodology. This 6% lower value is the average impact for a fleet with the mpg
and city fuel economy-to-highway fuel economy characteristics of the current fleet, and
would not be the appropriate value for individual models, partial fleet segments, or for future
fleets with different mpg and city fuel economy-to-highway fuel economy distributions.
• For model years 1986 through 2004, EPA calculates adjusted fuel economy values based on
the assumption that the impacts of the factors that have led to lower real world fuel economy
have occurred in a gradual (i.e., linear) manner over the 20 years from 1986 through 2005.
A-ll
-------
On April 6, 1984, EPA published regulations that established the older fuel economy label
adjustment factors of 0.9 for city fuel economy and 0.78 for highway fuel economy that took
effect for model year 1985 vehicles (49 Federal Register 13832). EPA believes that these
adjustment factors were appropriate through the 1985 model year. EPA has not attempted to
perform a year-by-year analysis to determine the extent to which the many relevant factors
(including highway speed limits, more aggressive driving, vehicle horsepower-to-weight
ratio, suburbanization, congestion, use of air conditioning, gasoline composition, et al) that
have affected real world fuel economy since 1985 have changed over time. Rather, EPA has
made the simplifying, but we think reasonable, assumption that the collective impact of these
changes has been a linearly increasing impact over the 20 years from 1986 through 2005.
Using the equations shown above for individual models, EPA has assumed 1/20 of the fully
phased-in downward adjustment for city and highway values would be reflected in the 1986
data, 2/20 of this adjustment would be reflected in the 1987 data, etc., up to 19/20 of this
adjustment in 2004 and the full adjustment in 2005 and later years. Likewise, EPA has
assumed the 55/45 city/highway weighting changes to a 43/57 city/highway weighting in a
linear fashion over the 1986 to 2005 time period as well. As discussed above, the average
fleetwide composite city/highway fuel economy values for 2005-2010 are 6% lower than the
composite city/highway fuel economy value calculated with the older adjustment factors.
To generate precise adjusted city, highway, or composite fuel economy values for individual
models or for future fleetwide averages with different mpg or city fuel economy-to-highway fuel
economy ratios than the current fleet, it is essential to use the above equations to calculate adjusted city
and highway fuel economy values for individual models, then use the 43% city/57% highway weighting
to generate an adjusted composite fuel economy value for individual models, and then calculate the
harmonically production-weighted average of the individual models to yield the average composite fuel
economy for the fleet as a whole. Alternatively, for a first-order estimate of generic fleetwide factors that
one could use to convert values from the historic fuel economy trends database to the newer adjusted fuel
economy levels, see the factors in Table A-4, which are based on the mpg and city fuel economy-to-
highway fuel economy characteristics of the current fleet. For example, the industry-wide adjusted
composite city/highway fuel economy value for model year 1986 in this year's report, which will be
reported as ADJ COMP, is about .997 (1.0 minus 0.003, where 0.003 equals 0.3%, and the latter is equal
to 6% divided by 20) times the adjusted composite city/highway fuel economy value, or ADJ 55/45, from
pre-2007 reports in this series. Likewise, the same industry-wide ADJ COMP value for 1986 can be
approximated by multiplying the laboratory composite 55/45 value for 1986 by 0.851. The industry-wide
ADJ COMP fuel economy values for model years 2005-2010 in this year's report are all equal to 0.80
times the laboratory composite 55/45 values.
It is important to note that the above discussion, as well as all the data in this report, is focused on
new model year vehicle fleets, i.e., the data for a MY2000 vehicle is most directly relevant for that
vehicle operated on the road in calendar year 2000. Because most (though not all) of the real world
factors reflected in this methodology are relatively independent of vehicle design, the best approximation
of the adjusted fuel economy of a used MY2000 vehicle in calendar year 2010 would be to use the 2010
factors in Table A-4.
Table A-5 provides a comparison of adjusted composite fuel economy values, for cars and trucks
combined, using both the older fuel economy label methodology that has been used in pre-2007 reports in
this series as well as the newer fuel economy label methodology described above and used in 2007 and
later reports.
A-12
-------
No changes have been made in the way EPA calculates adjusted fuel economy values for 1975-
1985. For these model years, EPA still uses the 0.9 city/0.78 highway fuel economy adjustments
established in 1984, along with the 55% city/45% highway weighting factor. EPA believes that this
methodology was appropriate for the late 1970s and early 1980s and is not making any changes to
adjusted fuel economy values for 1975 through 1985.
No changes have been made in the laboratory (LAB) fuel economy values in this report. The
laboratory city value remains the fuel economy value over the EPA Federal Test Procedure, the laboratory
highway value remains the fuel economy value over the EPA Highway Fuel Economy Test, and the
laboratory 55/45 is a weighted value of these two tests, with a 55% weighting of the Federal Test
Procedure and a 45% weighting of the Highway Fuel Economy Test. The laboratory 55/45 values are
used for CAFE compliance, in conjunction with alternative fuel vehicle credits and test procedure
adjustments. Because the underlying methodology for generating and reporting the laboratory fuel
economy values have not changed since this series began in the mid-1970s, these values provide an
excellent basis with which to compare long-term fuel economy trends from the perspective of vehicle
design, apart from the factors that affect real world fuel economy that are reflected in the adjusted fuel
economy values.
Finally, this same methodology for including real world factors in the adjusted fuel economy
values is also reflected in the adjusted carbon dioxide (CO2) emissions data as well. As discussed in
Section IV, EPA back-calculated all CO2 emissions values in this report from corresponding fuel
economy values in the historical Trends database. Accordingly, the adjusted CO2 emissions values
explicitly account for the above methodology for 1986 and later model years.
A-13
-------
Table A-4
Approximate Factors for Converting Industry-Wide Fuel Economy Values from Previous
Reports to the New Fuel Economy Values in this 2010 Report
1975-1985
1986
1987
1998
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Factors to convert
older ADJ to new ADJ
CITY
1.000
0.995
0.989
0.984
0.978
0.973
0.967
0.962
0.956
0.951
0.945
0.940
0.934
0.929
0.923
0.918
0.912
0.907
0.901
0.896
0.890
0.890
0.890
0.890
0.890
0.890
HWY
1.000
0.996
0.992
0.988
0.984
0.980
0.976
0.972
0.968
0.964
0.960
0.956
0.952
0.948
0.944
0.940
0.936
0.932
0.928
0.924
0.920
0.920
0.920
0.920
0.920
0.920
55/45
1.000
0.997
0.994
0.991
0.988
0.985
0.982
0.979
0.976
0.973
0.970
0.967
0.964
0.961
0.958
0.955
0.952
0.949
0.946
0.943
0.940
0.940
0.940
0.940
0.940
0.940
Factors to convert
LAB to new ADJ
CITY
0.900
0.895
0.890
0.885
0.880
0.875
0.870
0.865
0.860
0.855
0.850
0.845
0.840
0.835
0.830
0.825
0.820
0.815
0.810
0.805
0.800
0.800
0.800
0.800
0.800
0.800
HWY
0.780
0.777
0.774
0.771
0.768
0.765
0.762
0.759
0.756
0.753
0.750
0.747
0.744
0.741
0.738
0.735
0.732
0.729
0.726
0.723
0.720
0.720
0.720
0.720
0.720
0.720
55/45
0.854
0.851
0.849
0.846
0.843
0.841
0.838
0.835
0.832
0.830
0.827
0.824
0.822
0.819
0.816
0.814
0.811
0.808
0.805
0.803
0.800
0.800
0.800
0.800
0.800
0.800
Important Notes for Table A-4:
1. Multiplying the factors above times the appropriate values from pre-2007 reports approximates the
newer adjusted (ADJ) fuel economy values in this 2010 report. Also, these factors can be used "in
reverse" to convert new adjusted fuel economy values in this report to corresponding old adjusted fuel
economy values or to corresponding laboratory fuel economy values, e.g., dividing an adjusted, combined
city/highway MY2010 fuel economy value in this report by .940 would yield a corresponding adjusted
fuel economy value based on the methodology used in pre-2007 reports.
2. These factors are first-order approximations relevant only for industry-wide fuel economy values for
the 1986 through 2010 timeframe.
3. Precise estimates for individual models require the use of the mpg-based equations for ADJ CITY and
ADJ HWY provided above as well as a linear phase-in, over the 1986 to 2005 time period, for both the
mpg-based equations and the change from a 55/45 city/highway weighting to a 43/57 city/highway
weighting.
4. These approximations would yield the largest error for individual models or fleets with high mpg
and/or high city fuel economy-to-highway fuel economy ratios.
A-14
-------
Table A-5
Comparison of "Old" and "New" Adjusted Composite Fuel Economy Values,
for Cars and Trucks Combined, for 2003-2010
Cars and Trucks Combined
Model
Year
2003
2004
2005
2006
2007
2008
2009
2010
"Old"
Adjusted
Composite
20.8
20.5
21.2
21.5
22.0
22.4
24.0
24.2
"New"
Adjusted
Composite
19.6
19.3
19.9
20.1
20.6
21.0
22.4
22.5
Important Notes for Table A-5:
1. "Old" adjusted composite fuel economy values are based on the EPA fuel economy label
methodology used in previous reports in this series, i.e., 10% downward city adjustment, 22% downward
highway adjustment, and a 55% city/45% highway weighting factor.
2. "New" adjusted composite fuel economy values are based on the new EPA fuel economy label
methodology, applicable to MY2010 vehicles and used for the first time in the 2007 report and described
in the previous section.
3. The "new" adjusted composite fuel economy values for cars and trucks combined are approximately
6% lower than the "old" adjusted composite fuel economy values for cars and trucks combined. For cars
only, the "new" adjusted composite fuel economy values would be more than 6% lower than the "old"
values, while for trucks only, the "new" adjusted composite fuel economy values would be less than 6%
lower than the "old" values.
A-15
-------
Comparison of EPA and NHTSA Data, 1975-2010
Table A-6 compares CAFE performance data reported by the National Highway Traffic Safety
Administration ("Summary of Fuel Economy Performance" report dated April 20, 2010 and available at
www.nhtsa.gov) with the adjusted and unadjusted (laboratory) composite fuel economy data in this
report. The NHTSA values in Table A-6 are generally higher than the EPA laboratory values due to
differences in alternative fuel credits, test procedure adjustment factors for cars, and vehicle classification.
In recent years for which both Agencies report final data, the NHTSA values are typically 0.6-0.8 mpg
higher than the EPA values. For MY2010, the preliminary NHTSA value is 0.9 mpg higher than the
preliminary EPA value. These preliminary projections are based on different data sets. The EPA value is
based on automaker submissions in the spring and summer of 2009 to support vehicle fuel economy
labels. The NHTSA value is based on automaker estimates provided in pre-model year CAFE reports
later in 2009. Final MY2010 results will be reported in next year's report.
Table A-6
EPA Adjusted, Laboratory, and NHTSA CAFE Fuel Economy Values by Model Year
Cars
Trucks
Both Cars and Trucks
Model
Year
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
EPA
Adj.
13.5
14.9
15.6
16.9
17.2
20.0
21.4
22.2
22.1
22.4
23.0
23.7
23.8
24.1
23.7
23.3
23.4
23.1
23.5
23.3
23.4
23.3
23.4
23.4
23.0
22.9
23.0
23.1
23.2
23.1
23.5
23.3
24.1
24.3
25.4
25.8
EPA
Unadj.
15.8
17.5
18.3
19.9
20.3
23.5
25.1
26.0
25.9
26.3
27.0
27.9
28.1
28.6
28.1
27.8
28.0
27.6
28.2
28.0
28.3
28.3
28.4
28.5
28.2
28.2
28.4
28.6
28.9
28.9
29.5
29.2
30.3
30.5
32.1
32.7
NHTSA
(CAFE)
n/a
n/a
n/a
19.9
20.3
24.3
25.9
26.6
26.4
26.9
27.6
28.2
28.5
28.8
28.4
28.0
28.4
27.9
28.4
28.3
28.6
28.5
28.7
28.8
28.3
28.5
28.8
29.0
29.5
29.5
30.3
30.1
31.2
31.6
32.6
33.8
Diff.
0.0
0.0
0.8
0.8
0.6
0.5
0.6
0.6
0.3
0.4
0.2
0.3
0.2
0.4
0.3
0.2
0.3
0.3
0.2
0.3
0.3
0.1
0.3
0.4
0.4
0.6
0.6
0.8
0.9
0.9
1.1
0.5
1.1
EPA
Adj.
11.6
12.2
13.3
12.9
12.5
15.8
17.1
17.4
17.8
17.4
17.5
18.2
18.3
17.9
17.6
17.4
17.8
17.4
17.5
17.2
17.0
17.2
17.0
17.1
16.7
16.9
16.7
16.7
16.9
16.7
17.2
17.5
17.7
18.2
19.0
19.1
EPA
Unadj.
13.7
14.4
15.6
15.2
14.7
18.6
20.1
20.5
20.9
20.5
20.6
21.4
21.6
21.2
20.9
20.7
21.3
20.8
21.0
20.8
20.5
20.8
20.6
20.9
20.5
20.8
20.6
20.6
20.9
20.8
21.4
21.8
22.1
22.7
23.8
23.8
NHTSA
(CAFE)
n/a
n/a
n/a
n/a
18.2
18.5
20.1
20.5
20.7
20.6
20.7
21.5
21.7
21.3
21.0
20.8
21.3
20.8
21.0
20.8
20.5
20.8
20.6
21.0
20.9
21.3
20.9
21.4
21.8
21.5
22.1
22.5
23.1
23.6
24.6
24.9
Diff.
3.5
-0.1
-0.2
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.4
0.5
0.3
0.8
0.9
0.7
0.7
0.7
1.0
0.9
0.8
1.1
EPA
Adj.
13.1
14.2
15.1
15.8
15.9
19.2
20.5
21.1
21.0
21.0
21.3
21.8
22.0
21.9
21.4
21.2
21.2
20.8
20.9
20.4
20.5
20.4
20.1
20.1
19.7
19.8
19.6
19.4
19.6
19.3
19.9
20.1
20.6
21.0
22.4
22.5
EPA
Unadj.
15.3
16.7
17.7
18.6
18.7
22.5
24.1
24.7
24.6
24.6
25.0
25.7
25.9
25.9
25.4
25.2
25.4
24.9
25.1
24.6
24.7
24.8
24.5
24.5
24.1
24.3
24.2
24.1
24.3
24.0
24.8
25.2
25.8
26.3
28.2
28.3
NHTSA
(CAFE)
n/a
n/a
n/a
19.9
20.1
23.1
24.6
25.1
24.8
25.0
25.4
25.9
26.2
26.0
25.6
25.4
25.6
25.1
25.2
24.7
24.9
24.9
24.6
24.7
24.5
24.8
24.5
24.7
25.1
24.6
25.4
25.8
26.6
27.1
28.8
29.2
Diff.
1.3
1.4
0.6
0.5
0.4
0.2
0.4
0.4
0.2
0.3
0.1
0.2
0.2
0.2
0.2
0.1
0.1
0.2
0.1
0.1
0.2
0.4
0.5
0.3
0.6
0.8
0.6
0.6
0.6
0.8
0.8
0.6
0.9
A-16
-------
Comparison of EPA and NHTSA Data for MY2008 by Manufacturer
The primary differences between EPA unadjusted laboratory fuel economy data and NHTSA
CAFE values are flexible fuel vehicle (FFV) credits that are available to manufacturers that produce
vehicles capable of operation on an alternative fuel (generally a blend of 85 percent ethanol and 15
percent gasoline), and test procedure adjustment (TPA) credits that apply to manufacturers of passenger
cars.
Table A-7 shows a detailed MY2008 comparison, for the thirteen highest-volume manufacturers,
of the EPA laboratory fuel economy values from this report and final NHTSA CAFE values based on the
year end fuel economy report data provided to EPA and NHTSA by automakers (MY2008 is the last year
for which NHTSA has published final CAFE values). This table shows how EPA laboratory values, FFV
credits, and TPA credits "add up" to CAFE values. It is important to emphasize that while the values in
Table A-7 approximately add up for most manufacturers, in some cases they do not add up precisely. The
primary explanation for this is that there are slight differences in car and truck classifications between
EPA and NHTSA, which can affect the individual car and truck comparisons, though not the combined
car and truck values. In the most notable example, NHTSA classifies the Subaru Forester as a car and the
Subaru Outback as a truck, while EPA takes the reverse position. Changing the classification of these
two vehicles actually does not affect Subaru's car values, however it does lead to nearly a 1 mpg
discrepancy between the truck EPA LAB and NHTSA CAFE values. In addition, rounding differences
can lead to slight discrepancies in Table A-7.
The manufacturer column in Table A-7 differs from the manufacturer columns elsewhere in this
report in two ways in order to be consistent with the way NHTSA reports CAFE data for MY2008. The
differences in Table A-7 are that GM includes Saab, and Ford includes Mazda (Table 28 gives different
EPA laboratory fuel economy values for Ford excluding Mazda, while the inclusion of Saab does not
change the GM values).
The FFV credit values in Table A-7 for the truck column were obtained directly from EPA's fuel
economy compliance program (trucks are not eligible for TPA credits). The FFV and TPA credits for the
car columns were generated by weighting the values for domestic cars and import cars by the NHTSA
sales for each car category (see cite below). The FFV and TPA credit values for the combined car and
truck columns were generated using the car and truck sales from the NHTSA report. For MY2008, four
manufacturers earned FFV credits for cars and four manufacturers did so for trucks. All thirteen
manufacturers were eligible for the TPA credits for cars.
All of the NHTSA CAFE values in Table A-7 were taken or generated from the April 20, 2010
NHTSA report "Summary of Fuel Economy Performance" available at www.nhtsa.gov. The car values
were generated from the NHTSA fuel economy and production data for the separate domestic car and
import car CAFE categories. The truck values were taken directly from the NHTSA report. The
combined car and truck values were generated from the NHTSA fuel economy and production data for
the separate domestic car, import car, and light truck CAFE categories. While there are no CAFE
standards for combined cars and trucks, this column is shown for illustrative purposes.
A-17
-------
Table A-7
Comparison of MY2008 EPA Laboratory and Final NHTSA CAFE Values
by Manufacturer
Passenger Car
Light Truck
Both Cars and Trucks
IV! snufscturcr
LAB
General
Motors /Saab 28.6
Toyota 36.0
Ford /Mazda 28.6
Honda 34.3
Chrysler 27.8
Nissan 32.2
Hyundai 33.8
Volkswagen 28.9
BMW 27.2
Kia 33.3
Daimler 25.3
Subaru 28.7
Mitsubishi 29.8
FFV
Credit
1.1
0.0
0.9
0.0
0.9
0.0
0.0
0.0
0.0
0.0
1.2
0.0
0.0
TPA
Credit
0.2
0.3
0.3
0.4
0.2
0.3
0.4
0.2
0.2
0.3
0.2
0.2
0.2
NHTSA
CAFE
29.7
36.4
30.3
34.6
29.3
32.2
34.2
29.1
27.4
33.6
26.9
28.9
30.0
EPA
LAB
21.6
23.9
22.4
25.5
22.4
22.0
25.6
20.2
22.9
24.2
20.8
26.4
24.2
FFV
Credit
1.2
0.0
1.2
0.0
1.2
1.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
TPA
Credit
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
NHTSA
CAFE
23.2
23.9
23.6
25.5
23.6
23.1
25.6
20.2
22.9
24.2
20.8
27.3
24.7
EPA
LAB
24.4
29.0
24.7
30.1
24.2
27.6
30.9
27.9
26.3
28.8
24.0
28.1
28.1
FFV
Credit
1.2
0.0
1.1
0.0
1.1
0.7
0.0
0.0
0.0
0.0
0.8
0.0
0.0
TPA
Credit
0.1
0.1
0.1
0.2
0.1
0.1
0.2
0.2
0.2
0.1
0.1
0.1
0.2
NHTSA
CAFE
25.7
29.0
26.0
30.3
25.1
28.3
31.1
28.1
26.5
28.9
24.9
28.2
28.5
* Final MY2008 CAFE values are based on manufacturer reports to EPA and NHTSA summarized in
"Summary of Fuel Economy Performance" dated April 20, 2010 and available at www.nhtsa.gov
A-18
------- |