Light-Duty Automotive Technology and 


Fuel Economy Trends: 


1975 through 2007


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. 

EPA420-R-07-008


September 2007

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 a total 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 = 2 / (1/16 + 1/24) = 19.2 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” (MPG C) and EPA “highway” (MPG H) fuel 

economy values. 

 Average MPG = Total Miles

 Total Gallons 

 = _____Total Miles____________ 

 City Gallons + Highway Gallons 

 = _____Total Miles______________________________

 City Miles/City MPG + Highway Miles/Highway MPG 

EPA420-R-07-008 A-1 Appendix A 
Now, if city miles are 55 percent of total miles and highway miles are the remaining 45 

percent, after dividing by total miles, 

Average MPG = 1__________ 

 (.55/MPG C) + (.45/MPG H) 

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

 Total Gallons = 70,000 M / 10 + 30,000 M / 14 

and the average fuel economy is: 

Average Fuel Economy = 1 

 .7/10 + .3/14 

 = 10.9 mpg 

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. 

EPA420-R-07-008 A-2 Appendix A 
Estimated and Final Sales Data

Table A-1 compares average laboratory 55/45 fuel economy for model years 1998 

through 2005 at three points in time, and for MY2006 at two points in time: 

(1) an initial estimate determined early in each model year using just projected sales;

(2) 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. 

The final car plus truck fuel economy values have varied from .4 mpg lower to .3 mpg 

higher compared to the original estimates based exclusively on estimated sales. The revised car 

plus truck value for MY2006 in this report is 0.7 mpg higher than the initial estimate for 2006 in 

last year’s report, which suggests that sustained, higher gasoline prices have led to some changes 

in consumer demand relative to what manufacturers expected prior to the start of 2006. 

 Table A-1 

 Comparison of Laboratory 55/45 MPG 

 Model Initial Revised Final 

 Year Estimate Estimate Value 

Cars 1998 28.6 28.6 28.5 

 1999 28.1 28.2 28.1 

 2000 28.1 28.3 28.2 

 2001 28.3 28.3 28.4 

 2002 28.5 28.5 28.6 

 2003 29.0 28.9 28.9 

 2004 28.7 28.9 28.9 

 2005 28.9 29.2 29.5 

 2006 28.8 29.2 *** 

Trucks 1998 20.6 20.6 20.9 

 1999 20.3 20.4 20.5 

 2000 20.5 20.5 20.8 

 2001 20.3 20.4 20.6 

 2002 20.4 20.3 20.6 

 2003 20.8 20.9 20.9 

 2004 20.9 20.9 20.8 

 2005 21.3 21.2 21.4 

 2006 21.5 21.9 *** 

Both 1998 24.4 24.4 24.5 

 1999 23.8 24.0 24.1 

 2000 24.0 23.9 24.3 

 2001 23.9 24.0 24.2 

 2002 24.0 23.9 24.1 

 2003 24.4 24.2 24.3 

 2004 24.4 24.4 24.0 

 2005 24.6 24.6 24.8 

 2006 24.6 25.3 ***

EPA420-R-07-008 A-3 Appendix A 
Use of 3-Year Moving Averages

Use of the three-year moving averages, which effectively smooth 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 2002, 2003, and 2004 

is MY2003. 

 Table A-2 

Light-Duty Vehicle Laboratory Fuel Economy and Truck Sales Fraction 

 Actual Data Three-Year Moving Average 

 55/45 Fuel Economy Truck 55/45 Fuel Economy Truck 

Year Cars Trucks Both Sales Cars Trucks Both Sales 

 Fraction Fraction 

1975 15.8 13.7 15.3 0.194   ** **   ** *** 

1976 17.5 14.4 16.7 0.212 17.1 14.5 16.5 0.202 

1977 18.3 15.6 17.7 0.200 18.5 15.1 17.6 0.213 

1978 19.9 15.2 18.6 0.227 19.4 15.2 18.3 0.216 

1979 20.3 14.7 18.7 0.222 21.1 16.0 19.8 0.205 

1980 23.5 18.6 22.5 0.165 22.8 17.5 21.5 0.187 

1981 25.1 20.1 24.1 0.173 24.8 19.7 23.7 0.178 

1982 26.0 20.5 24.7 0.197 25.7 20.5 24.5 0.197 

1983 25.9 20.9 24.6 0.223 26.1 20.6 24.6 0.219 

1984 26.3 20.5 24.6 0.239 26.4 20.6 24.7 0.239 

1985 27.0 20.6 25.0 0.254 27.0 20.8 25.1 0.258 

1986 27.9 21.4 25.7 0.283 27.6 21.2 25.5 0.272 

1987 28.1 21.6 25.9 0.278 28.2 21.4 25.8 0.286 

1988 28.6 21.2 25.9 0.298 28.3 21.2 25.8 0.294 

1989 28.1 20.9 25.4 0.307 28.2 20.9 25.5 0.302 

1990 27.8 20.7 25.2 0.302 28.0 21.0 25.3 0.310 

1991 28.0 21.3 25.4 0.322 27.8 20.9 25.2 0.319 

1992 27.6 20.8 24.9 0.334 27.9 21.0 25.1 0.339 

1993 28.2 21.0 25.1 0.360 28.0 20.8 24.8 0.366 

1994 28.0 20.8 24.6 0.404 28.2 20.7 24.8 0.381 

1995 28.3 20.5 24.7 0.380 28.2 20.7 24.7 0.395 

1996 28.3 20.8 24.8 0.400 28.3 20.7 24.7 0.401 

1997 28.4 20.6 24.5 0.424 28.4 20.8 24.6 0.424 

1998 28.5 20.9 24.5 0.449 28.4 20.7 24.4 0.441 

1999 28.2 20.5 24.1 0.449 28.3 20.7 24.3 0.449 

2000 28.2 20.8 24.3 0.449 28.3 20.6 24.2 0.453 

2001 28.4 20.6 24.2 0.461 28.4 20.6 24.2 0.465 

2002 28.6 20.6 24.1 0.485 28.7 20.7 24.2 0.481 

2003 28.9 20.9 24.3 0.496 28.8 20.8 24.1 0.500 

2004 28.9 20.8 24.0 0.520 29.1 21.0 24.4 0.504 

2005 29.5 21.4 24.8 0.495 29.2 21.3 24.7 0.492 

2006 29.2 21.9 25.3 0.461 29.4 21.8 25.2 0.482 

2007 29.4 22.1 25.3 0.490   ** **   ** *** 

EPA420-R-07-008 A-4 Appendix A 
 Table A-2 (Continued) 

 Light-Duty Vehicle Adjusted Fuel Economy 

 Cars 

Model Each Year’s Data 3 Year Moving Avg. 

Year CITY HWY COMP CITY HWY COMP 

 1975 12.3 15.2 13.5   ** **   

 1976 13.7 16.6 14.9 13.4 16.3 14.6 

 1977 14.4 17.4 15.6 14.5 17.6 15.8 

 1978 15.5 19.1 16.9 15.3 18.5 16.6 

 1979 15.9 19.2 17.2 16.5 20.2 18.0 

 1980 18.3 22.6 20.0 17.8 21.8 19.4 

 1981 19.6 24.2 21.4 19.3 24.1 21.2 

 1982 20.1 25.5 22.2 19.8 25.1 21.9 

 1983 19.9 25.5 22.1 20.1 25.7 22.2 

 1984 20.2 26.0 22.4 20.3 26.1 22.5 

 1985 20.7 26.8 23.0 20.7 26.8 23.0 

 1986 21.2 27.6 23.7 21.0 27.4 23.5 

 1987 21.2 27.7 23.8 21.3 27.8 23.9 

 1988 21.4 28.2 24.1 21.2 27.9 23.9 

 1989 20.9 27.9 23.7 20.9 27.8 23.7 

 1990 20.5 27.5 23.3 20.6 27.7 23.5 

 1991 20.5 27.6 23.4 20.3 27.5 23.3 

 1992 20.0 27.5 23.1 20.2 27.6 23.3 

 1993 20.3 27.9 23.5 20.1 27.7 23.3 

 1994 20.0 27.7 23.3 20.1 27.9 23.4 

 1995 20.0 28.1 23.4 19.9 27.9 23.3 

 1996 19.8 28.0 23.3 19.9 28.0 23.4 

 1997 19.8 28.0 23.4 19.8 28.0 23.4 

 1998 19.7 28.0 23.4 19.6 27.8 23.2 

 1999 19.4 27.5 23.0 19.5 27.6 23.1 

 2000 19.3 27.3 22.9 19.3 27.4 23.0 

 2001 19.4 27.3 23.0 19.4 27.3 23.0 

 2002 19.4 27.2 23.1 19.4 27.3 23.1 

 2003 19.5 27.5 23.2 19.4 27.4 23.2 

 2004 19.3 27.4 23.1 19.4 27.5 23.3 

 2005 19.6 27.6 23.5 19.4 27.5 23.3 

 2006 19.4 27.5 23.3 19.5 27.6 23.4 

 2007 19.5 27.6 23.4 ** **   ** ** 

EPA420-R-07-008 A-5 Appendix A 
Table A-2 (Continued) 

 Light-Duty Vehicle Adjusted Fuel Economy 

 Trucks 

Model Each Year’s Data 3 Year Moving Avg. 

Year CITY HWY COMP CITY HWY COMP 

 1975 10.9 12.7 11.6   ** **   

 1976 11.5 13.2 12.2 11.7 13.3 12.3 

 1977 12.6 14.1 13.3 12.2 13.7 12.8 

 1978 12.4 13.7 12.9 12.4 13.6 12.9 

 1979 12.1 13.1 12.5 13.0 14.4 13.6 

 1980 14.8 17.1 15.8 14.1 15.9 14.9 

 1981 16.0 18.6 17.1 15.7 18.2 16.7 

 1982 16.3 19.0 17.4 16.3 19.1 17.4 

 1983 16.5 19.6 17.8 16.3 19.3 17.5 

 1984 16.1 19.3 17.4 16.3 19.4 17.6 

 1985 16.2 19.4 17.5 16.4 19.6 17.7 

 1986 16.8 20.2 18.2 16.6 20.0 18.0 

 1987 16.8 20.5 18.3 16.6 20.3 18.1 

 1988 16.2 20.2 17.9 16.3 20.2 17.9 

 1989 15.9 19.8 17.6 15.9 19.9 17.6 

 1990 15.6 19.8 17.4 15.8 20.0 17.6 

 1991 15.9 20.3 17.8 15.7 20.0 17.5 

 1992 15.5 19.9 17.4 15.6 20.1 17.5 

 1993 15.5 20.1 17.5 15.4 19.9 17.3 

 1994 15.3 19.7 17.2 15.2 19.7 17.2 

 1995 15.0 19.5 17.0 15.1 19.7 17.1 

 1996 15.1 19.9 17.2 15.0 19.6 17.0 

 1997 14.8 19.5 17.0 14.9 19.7 17.1 

 1998 14.9 19.8 17.1 14.8 19.5 16.9 

 1999 14.6 19.2 16.7 14.7 19.5 16.9 

 2000 14.7 19.4 16.9 14.6 19.2 16.8 

 2001 14.6 19.1 16.7 14.6 19.2 16.8 

 2002 14.4 19.1 16.7 14.5 19.1 16.8 

 2003 14.6 19.3 16.9 14.4 19.2 16.8 

 2004 14.3 19.2 16.7 14.5 19.4 16.9 

 2005 14.6 19.8 17.2 14.6 19.7 17.2 

 2006 15.0 20.2 17.6 14.9 20.1 17.5 

 2007 15.1 20.4 17.7 ** **   ** ** 

EPA420-R-07-008 A-6 Appendix A 
Table A-2 (Continued) 

 Light-Duty Vehicle Adjusted Fuel Economy 

 Cars and Trucks 

 Model Each Year’s Data 3 Year Moving Avg. 

 Year CITY HWY COMP CITY HWY COMP 

 1975 12.0 14.6 13.1   ** **   

 1976 13.2 15.7 14.2 13.0 15.6 14.1 

 1977 14.0 16.6 15.1 13.9 16.6 15.0 

 1978 14.7 17.5 15.8 14.5 17.2 15.6 

 1979 14.9 17.4 15.9 15.6 18.6 16.8 

 1980 17.6 21.5 19.2 16.9 20.3 18.3 

 1981 18.8 23.0 20.5 18.5 22.8 20.2 

 1982 19.2 23.9 21.1 19.0 23.6 20.8 

 1983 19.0 23.9 21.0 19.1 23.9 21.0 

 1984 19.1 24.0 21.0 19.1 24.1 21.1 

 1985 19.3 24.4 21.3 19.4 24.5 21.4 

 1986 19.8 25.0 21.8 19.6 24.9 21.7 

 1987 19.8 25.3 22.0 19.7 25.2 21.9 

 1988 19.6 25.2 21.9 19.5 25.1 21.7 

 1989 19.1 24.8 21.4 19.1 24.9 21.5 

 1990 18.7 24.6 21.2 18.9 24.7 21.3 

 1991 18.8 24.7 21.2 18.6 24.6 21.1 

 1992 18.2 24.4 20.8 18.4 24.5 21.0 

 1993 18.2 24.4 20.9 18.1 24.2 20.7 

 1994 17.8 23.8 20.4 17.9 24.1 20.6 

 1995 17.7 24.1 20.5 17.7 24.0 20.4 

 1996 17.6 24.0 20.4 17.6 23.9 20.3 

 1997 17.4 23.6 20.1 17.4 23.7 20.2 

 1998 17.2 23.6 20.1 17.1 23.4 20.0 

 1999 16.9 23.0 19.7 17.0 23.2 19.8 

 2000 16.9 23.0 19.8 16.9 23.0 19.7 

 2001 16.8 22.8 19.6 16.8 22.8 19.6 

 2002 16.6 22.5 19.4 16.7 22.7 19.5 

 2003 16.7 22.7 19.6 16.6 22.6 19.4 

 2004 16.3 22.4 19.3 16.6 22.7 19.6 

 2005 16.8 23.1 19.9 16.7 23.0 19.8 

 2006 17.1 23.5 20.2 17.0 23.4 20.1 

 2007 17.1 23.6 20.2 ** **   ** ** 

EPA420-R-07-008 A-7 Appendix A 
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/ 

origin 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 

Group/Manufacturer/Vehicles Years Are Classified As: 

DC: Chrysler Colt 4WD Wagon All Small Wagon 

DC: Chrysler Colt Vista All Small Van 

DC: Chrysler Pacifica All Large Wagon 

DC: Chrysler PT Cruiser All Small Wagon 

DC: Chrysler PT Cruiser Convertible All Subcompact 

DC: R-Series All Large Wagon 

DC: Chrysler Summit Wagon All Small Van 

DC: Dodge Ramcharger All Car 

DC: Dodge Magnum All Midsize Wagon 

DC: Eagle 4WD Wagon All Car 

Ford: Ford Pinto Van All Car 

Ford: Volvo V70 XC All Midsize Wagon 

GM: HHR All Small Wagon 

GM: Isuzu Oasis All Midsize Van 

GM: Pontiac Vibe All Small Wagon 

Toyota: Lexus RX300 All Midsize SUV 

Toyota: Matrix All Small Wagon 

VW: Audi Allroad All Midsize Wagon 

Other: Subaru 4WD Sedans/Wagons All Cars 

Other: Subaru Forester All Small SUV 

Other: Subaru Baja All Small Pickup 

Other: Suzuki X-90 All Small SUV 

Other: Mitsubishi Expo All Small Van 

Other: Mitsubishi Space Wagon All Small Van 

EPA420-R-07-008 A-8 Appendix A 
New Methodology for Adjusted Fuel Economy Values

for Model Years 1986-2007 

On December 27, 2006, EPA published new 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). The new methodology will provide fuel economy 

estimates to consumers that better reflect real world fuel economy. The new 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 accounts for a number of other 

factors that are not reflected in EPA test data. 

These new vehicle fuel economy label changes take effect beginning with the 2008 

model year. For model years 2008-2010, manufacturers will have two options for calculating 

city and highway fuel economy labels: 1) using 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) using 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 industryaverage 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). 

EPA is making significant changes in this 2007 report in how adjusted (ADJ) fuel 

economy values for model years 1986 through 2007 are calculated to reflect the new EPA fuel 

economy label methodology. These changes affect every table and figure in the 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 previous reports in 

this series. Specifically, the new adjusted fuel economy values for 1986-2007 in this report 

differ from those in previous reports as explained below. 

• For model years 2005-2007, EPA now calculates adjusted fuel economy values for 

individual models in the fuel economy trends database using the following city and 

highway “mpg-based” equations from the EPA fuel economy labeling rulemaking: 

 1 

New ADJ CITY = -------------------------------------------- 

0.003259 + 1.1805

 LAB CITY 

EPA420-R-07-008 A-9 Appendix A 
 1 

New ADJ HWY = ------------------------------------------ 

0.001376 + 1.3466

 LAB HWY 

Calculating fleetwide adjusted city and highway fuel economy values for a given 

model year requires a harmonic, sales-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 previous reports in this series. These factors can be used to convert 

older adjusted fuel economy values to the new 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. In the past, this report has used 

a 55% city/45% highway weighting, the weighting used in the CAFE compliance 

program. The analysis of real world driving activity underlying the new 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, this weighting is now used for all adjusted 

composite city/highway fuel economy values beginning with the 2005 model year. 

The appropriate fleetwide factors to convert laboratory or older adjusted fuel 

economy values to new 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 new 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-tohighway 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. 

EPA420-R-07-008 A-10 Appendix A 
• For model years 1986 through 2004, EPA now 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. 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-toweight 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, 2006, and 2007. 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-

2007 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-tohighway 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 sales-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 new 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 previous 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 2005-2007 

in this year’s report are all equal to 0.80 times the laboratory composite 55/45 values. 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 past reports in this 

series as well as the new fuel economy label methodology described above and used for the first 

EPA420-R-07-008 A-11 Appendix A 
time in this report. For data from MY2003-2007, the adjusted fuel economy values using the 

new EPA fuel economy methodology are 1.1-1.3 mpg lower than they would be using the older 

EPA fuel economy label methodology. 

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. 

Finally, 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. 

EPA420-R-07-008 A-12 Appendix A 
Table A-4 

Approximate Factors for Converting Industry-Wide Fuel Economy Values from Previous 

Reports to the New Adjusted Fuel Economy Values in this 2007 Report 

Factors to convert older ADJ to new ADJ Factors to convert LAB to new ADJ

CITY HWY 55/45 CITY HWY 55/45

1975-1985 1.00 1.00 1.00 .900 .780 .854 

1986 .995 .996 .997 .895 .777 .851 

1987 .989 .992 .994 .890 .774 .849 

1998 .984 .988 .991 .885 .771 .846 

1989 .978 .984 .988 .880 .768 .843 

1990 .973 .980 .985 .875 .765 .841 

1991 .967 .976 .982 .870 .762 .838 

1992 .962 .972 .979 .865 .759 .835 

1993 .956 .968 .976 .860 .756 .832 

1994 .951 .964 .973 .855 .753 .830 

1995 .945 .960 .970 .850 .750 .827 

1996 .940 .956 .967 .845 .747 .824 

1997 .934 .952 .964 .840 .744 .822 

1998 .929 .948 .961 .835 .741 .819 

1999 .923 .944 .958 .830 .738 .816 

2000 .918 .940 .955 .825 .735 .814 

2001 .912 .936 .952 .820 .732 .811 

2002 .907 .932 .949 .815 .729 .808 

2003 .901 .928 .946 .810 .726 .805 

2004 .896 .924 .943 .805 .723 .803 

2005 .890 .920 .940 .800 .720 .800 

2006 .890 .920 .940 .800 .720 .800 

2007 .890 .920 .940 .800 .720 .800 

Important Notes for Table A-4: 

1. Multiplying the factors above times the appropriate values from previous reports 

approximates the new adjusted (ADJ) fuel economy values in this 2007 report. 

2. These factors are first-order approximations relevant only for industry-wide fuel economy 

values for the 1986 through 2007 timeframe. 

EPA420-R-07-008 A-13 Appendix A 
3. Precise estimates for individual models require the use of the mpg-based equations for ADJ 

CITY and ADJ HWY in the text 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. 

Table A-5 

Comparison of “Old” and “New” Adjusted Composite Fuel Economy Values, 

for Cars and Trucks Combined, for 2003-2007 

Cars and Trucks Combined 

Model 

Year 

“Old” 

Adjusted 

Composite 

“New” 

Adjusted 

Composite 

2003 20.7 19.6 

2004 20.5 19.3 

2005 21.2 19.9 

2006 21.5 20.2 

2007 21.5 20.2 

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 MY2008 vehicles and used for the first time in this 

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.

EPA420-R-07-008 A-14 Appendix A 
 Comparison of EPA and NHTSA Data

Table A-6 compares CAFE data reported by the National Highway Traffic Safety 

Administration (NHTSA) 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 unadjusted or 

laboratory mpg values due to differences in vehicle classification, test procedure adjustment 

factors for cars and alternative fuel credits. The NHTSA data for MY1979 trucks in this table is 

just for vehicles up to 6000 pound GVW; but for all other years the NHTSA data includes 

vehicles up to 8500 GVW. The NHTSA data for MY2006 is based on mid-model year data. 

The EPA data for all years in the table includes vehicles up to 8500 GVW. In addition, the EPA 

data in the table is final through MY2005, but preliminary for MY2006 and MY2007. 

Table A-6 

 EPA Adjusted, Laboratory, and NHTSA CAFE Fuel Economy Values 

 by Model Year 

 Cars Trucks Both Cars and Trucks 

Model EPA EPA NHTSA EPA EPA NHTSA EPA EPA NHTSA 

Year Adj. Unadj. (CAFE) Diff. Adj. Unadj. (CAFE) Diff. Adj. Unadj. (CAFÉ) Diff. 

1975 13.5 15.8 n/a 11.6 13.7 n/a 13.1 15.3 n/a 

1976 14.9 17.5 n/a 12.2 14.4 n/a 14.2 16.7 n/a 

1977 15.6 18.3 n/a 13.3 15.6 n/a 15.1 17.7 n/a 

1978 16.9 19.9 19.9 .0 12.9 15.2 n/a 15.8 18.6 19.9 1.3 

1979 17.2 20.3 20.3 .0 12.5 14.7 18.2 3.5 15.9 18.7 20.1 1.4 

1980 20.0 23.5 24.3 .8 15.8 18.6 18.5 -.1 19.2 22.5 23.1 .6 

1981 21.4 25.1 25.9 .8 17.1 20.1 20.1 .0 20.5 24.1 24.6 .5 

1982 22.2 26.0 26.6 .6 17.4 20.5 20.5 .0 21.1 24.7 25.1 .4 

1983 22.1 25.9 26.4 .5 17.8 20.9 20.7 -.2 21.0 24.6 24.8 .2 

1984 22.4 26.3 26.9 .6 17.4 20.5 20.6 .1 21.0 24.6 25.0 .4 

1985 23.0 27.0 27.6 .6 17.5 20.6 20.7 .1 21.3 25.0 25.4 .4 

1986 23.7 27.9 28.2 .3 18.2 21.4 21.5 .1 21.8 25.7 25.9 .2 

1987 23.8 28.1 28.5 .4 18.3 21.6 21.7 .1 22.0 25.9 26.2 .3 

1988 24.1 28.6 28.8 .2 17.9 21.2 21.3 .1 21.9 25.9 26.0 .1 

1989 23.7 28.1 28.4 .3 17.6 20.9 21.0 .1 21.4 25.4 25.6 .2 

1990 23.3 27.8 28.0 .2 17.4 20.7 20.8 .1 21.2 25.2 25.4 .2 

1991 23.4 28.0 28.4 .4 17.8 21.3 21.3 .0 21.2 25.4 25.6 .2 

1992 23.1 27.6 27.9 .3 17.4 20.8 20.8 .0 20.8 24.9 25.1 .2 

1993 23.5 28.2 28.4 .2 17.5 21.0 21.0 .0 20.9 25.1 25.2 .1 

1994 23.3 28.0 28.3 .3 17.2 20.8 20.8 .0 20.4 24.6 24.7 .1 

1995 23.4 28.3 28.6 .3 17.0 20.5 20.5 .0 20.5 24.7 24.9 .2 

1996 23.3 28.3 28.5 .2 17.2 20.8 20.8 .0 20.4 24.8 24.9 .1 

1997 23.4 28.4 28.7 .3 17.0 20.6 20.6 .0 20.1 24.5 24.6 .1 

1998 23.4 28.5 28.8 .3 17.1 20.9 21.0 .1 20.1 24.5 24.7 .2 

1999 23.0 28.2 28.3 .1 16.7 20.5 20.9 .4 19.7 24.1 24.5 .4 

2000 22.9 28.2 28.5 .3 16.9 20.8 21.3 .5 19.8 24.3 24.8 .5 

2001 23.0 28.4 28.8 .4 16.7 20.6 20.9 .3 19.6 24.2 24.5 .3 

2002 23.1 28.6 29.0 .4 16.7 20.6 21.4 .8 19.4 24.1 24.7 .6 

2003 23.2 28.9 29.5 .6 16.9 20.9 21.8 .9 19.6 24.3 25.1 .8 

2004 23.1 28.9 29.5 .6 16.7 20.8 21.5 .7 19.3 24.0 24.6 .6 

2005 23.5 29.5 30.3 .8 17.2 21.4 22.1 .7 19.9 24.8 25.4 .6 

2006 23.3 29.2 29.8 .6 17.6 21.9 22.2 .3 20.2 25.3 25.4 .1 

2007 23.4 29.4 n/a 17.7 22.1 n/a 20.2 25.3 n/a 

EPA420-R-07-008 A-15 Appendix A