EPA Report No.:
EPA-AA-CPSB-82-02
Technical Report
History and Description of the EPA
Motor Vehicle Fuel Economy Program
Clifford D. Tyree
September 1982
NOTICE
Technical Reports do not necessarily represent final EPA
decisions or positions. They are intended to present technical
analysia of issues using data which are currently available.
The purpose in the release of such reports is to facilitate the
exchange of technical information and to inform the puolic of
technical developments which may form the basis for a tinal SPA
decision, position, or regulatory action.
U. S. Environmental Protection Agency
Office of Air, Noise, and Radiation
Office of Mobile Sources
Certification Division
Certification policy and Support Branch
2565 Plymouth Road
Ann Arbor, Michigan 48105
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I. History of the Fuel Economy Program
For many years, the fuel economy data were only available
on a_limited basis from manufacturers and from trade and con-
sumer organizations. Even when available, these data were
often of questionable value because of differences in test
procedures. The* lack of reliable fuel economy aata, combined
with a growing national concern about our nation's fuel
consumption rate, led President Nixon to call for a voluntary
fuel economy labeling program for automobiles in his April 18,
1973 energy message to Congress.
At the time President Nixon called for this voluntary
labeling program, the EPA was already measuring exhaust
emission levels on representative vehicles from every
manufacturer which sold vehicles in the United States and
publishing these results in the Federal Register.
The fuel economy values for every vehicle tested in the
certification program (over 350) were derived from the exhaust
emission values measured during the certification program.
Thus, the only cost involved was in the calculation proce-
dures. Because of this capability, EPA published the first
comprehensive list of fuel economy results along with the
exhaust emission results for the 1973 model year in the May 2,
1973 Federal Register (38 FR 10868). The primary purpose of
these fuel economy data were to allow a consumer the oppor-
tunity to^make fuel economy comparisons.
Since the initial 1973 publication of tuei economy data,
the need, for fuel economy data has expanded to fulfill three
specific needs; (1) for vehicle labeling, (2) to determine the
corporate average fuel economy, and (3) to determine the
liability for a "Gas Guzzler Tax." In the August 27, 1973
Federal Register, EPA published the voluntary protocol for
calculating fuel economy values from exhaust emission results.
This voluntary protocol also contained a label format which was
to be used if the manufacturer chose to display the calculated
fuel economy on the vehicle. This program began in the 1974
model year.
The 1974 test procedure used to obtain the data used in
the exhaust emission certification program was a "city" type
driving cycle! and, therefore, the fuel economy result
reflected this type of driving pattern. However, the city
procedure represented only about 55 percent of the annual
1. Kruse and Huls, "Development of the Federal Urban Driving
Cycle." SAE paper 730553, May 1973.
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vehicle accumulation.2 EPA responded to this concern by
developing a second, nonurban driving cycle.3 AS a result,
the label program was modified to include the fuel economy
results from both the urban and nonurban driving cycles. These
fuel economy values were identified by the terms "city" and
"highway" and the results from the 1974 model year fuel economy
program were published in the November 5, 1973 Federal Register.
In 1975, Congress passed the Energy Policy and Conserva-
tion Act (EPCA) which replaced the voluntary fuel economy
program with a mandatory program beginning with the 1977 model
year. This action required that each vehicle have a label
depicting the EPA-determined fuel economy values. This act
also required DOE to make available to the public a compilation
of these values. This compilation is issued as the Gas Mileage
Guide. This Act specified that compliance with the fuel
economy standards would be determined on the basis of each
manufacturer's average fuel economy for ail vehicles produced
for sale in the United States. The fuel economy values used to
calculate the CAFE for each category (i.e., domestic light-
duty, import light-duty, etc.) was to be the average estimated
in-use fuel economy. This estimated in-use fuel economy was
determined by combining the average city and highway test
results, weighted according to the estimated in-use mileage (55
percent city and 45 percent highway—55/45).
In 1978, Congress passed, the Energy Tax Act and the
National Energy Conservation Policy Act (NECPA). The Energy
Tax Act .established a schedule of taxes to be levied on those
manufacturers which produce vehicles not achieving certain fuel
economy levels. This tax, which is commonly referred to as the
"Gas Guzzler Tax," is assessed by the Internal Revenue Service
(IRS) and is based on fuel economy^ata obtained from EgA's
emissions and fuel economy programst NECPA required tha.t.any
vehicle subject to a Gas Guzzler Tax bear a statement \Q£ 'that'
tax on the fuel economy label. r; "
£ n r
r- — i
From early in the voluntary program and into the" ,
mandatory program,,-data were emerging^hich suggested that
in-use passenger vehicles were not, ~$fi the average, achieving
the fuel economy levels listed on th£, :,Label and in :the. Gas
Mileage Guide values." The data indicated that, of^tijei three
T. U.S. Department of Transportation^,*Federal Highway
Administration News Release FHWA 08-74, January 1974.
3. Kruse and Paulsell, "Development of a Highway Driving Cycle
for Fuel Economy Measurements," U.S. Environmental Protection
Agency, March 1974. ,
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values listed on the labels and in the Gas Mileage Guide, the
city value was the closest to the average in-use fuel economy
for overall driving. EPA realized that to determine city ana
highway fuel economy values which are more representative of
in-use fuel economy would require substantial change to the
EPA's fuel economy program. EPA further realized that a
prerequisite to any change would be an in-depth study of data
which would take a considerable amount of time. An interim
solution was promulgated which specified that, until a better
data base could permit a more satisfactory solution, the label
and Gas Mileage Guide would use only fuel economy values
derived from the EPA city test (termed the EPA estimate). This
rule went into effect with the 1979 model year. Even though
the combined and highway values were dropped from the
information programs, these data were used for the purpose of
determining compliance with the CAFE standards. Manufacturers
continued using the highway values in their advertising.
Since the promulgation of the interim rule, EPA completed
a study of those facets of the current fuel economy program
which contribute to the shortfall between in-use and EPA-
determined fuel economy levels. The findings of this study
were reported to Congress in September of 1980.4
II. Current Program Description
The present fuel economy program performs three
functions: (1) generates fuel economy values and makes these
values available to the public on individual vehicle fuel
economy labels and in the Gas Mileage Guide, (2) establishes
manufacturers' Gas Guzzler Tax liability based on the general
fuel eco'nomy labe\l values, and (3) determines manufacturers'
compliance with CAFE requirements.
The EPA responsibilities for the above functions are to
(1) administer the testing^ program that generates the fuel
economy data used for cottipliance and public in-fbrmation and
(2) determine procedures fbr calculating fuel4 economy values
for labels;\the Gas Mileage Guide, and CAFE. r The following rs'
a description of the rules and procedures EPA currently uses -to
establish the various fuel economy values.
4. Murrell, "Passenger Car Fuel Economy: 'EPA and Road," U.S.
Environmental Protection Agency, August 1980.
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1. Definitions^; Before beginning the description of
the actual process, it is necessary to present the basic
terminology EPA uses in sorting vehicle models and designs.
EPA begins by sorting a manufacturer's product line as follows:
MANUFACTURER A
MODEL TYPE (INFORMATION) BASE LEVEL(CALCULATION)
- CAR LINE - INTERTIA WEIGHT CLASS
- BASIC ENGINE - BASIC ENGINE
- TRANSMISSION CLASS - TRANSMISSION CLASS
VEHICLE CONFIGURATION (TEST)
- ENGINE CALIBRATION (ENGINE
CODE)
- TRANSMISSION CONFIGURATION
- AXLE RATIO
A model type is defined as a unique combination of
car line, basic engine, and transmission class. EPCA estab-
lished the term "model type" as the classification of vehicles
for the purpose of averaging for CAFE values. EPA defined
model type* on the basis of vehicle characteristics readily
recognized by consumers and important from a fuel economy
perspective (e.g., the general name of the vehicle, engine, and
transmission).
A car line denotes a group of vehicles within a make
or car division which has a degree of commonality in construe-:,
tion. The level of decor or opuleqce is not considered ;*when f^
establishing a car line. Features suqh as roof line, number of
doors, seats or windows, generally do not distinguish
characteristics of a car line. Station wagons are considered
distinct car lines from sedans. For 'example, in the 1^80 Gas
Mileage Guide, Chevrolet, a division 9f General Motors,
Corporation, had listed ten car lines0(not including trucks):
Corvette, Camaro, Chevette, Monza, citation, Malibu, Monte
Carlo, Impala/Caprice, Malibu Wagon,'.and Impaia/Capri,ce Wagon.
Note that specific model nameplates such as Camaro~s'pprt Coupe
and Camaro Berlinetta are covered by ,one car line '(Camaro).
5~. The official listing of definitions used in the fuel
economy program can be found in 40 CFR 600.002-80.
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The basic engine classification includes the number
of engine cylinders, engine displacement, and the fuel system.
The transmission class is determined by whether it is a manual,
automatic, or semi-automatic, along with the number ot forward
gears (such as three speed or four speed). For example, in the
1980 Gas Mileage'Guide, the Chevrolet Citation car line lists
four basic engine and transmission combinations: 2.5-liter,
4-cylinder with a manual 4-speed (M-4) transmission; 2.5-liter,
4-cylinder with an automatic 3-speed (A-3) transmission; 2.8-
liter, 6-cylinder with a manual 4-speed (M-4) transmission; ana
2.8-liter, 6-cylinder with an automatic 3-speed (A-3) trans-
mission.
For testing and calculation purposes, each manufac-
turer's product line is subdivided into base levels with the
term base level defining a unique combination of inertia weight
class°, basic engine, and transmission class. The features
of a base level are nearly the same as model type except that
weight is substituted for car line. Those features distin-
guishing a model type are features which can be seen by a
consumer. However, in order to more accurately estimate the
fuel economy of a particular group of vehicles it is necessary
to divide a manufacturer's product line by features which
affect fuel economy. The first major division is "base level"
and separates the product line on the basis of vehicle weight.
Again using the Chevrolet example, a typical base level would
be 3,000-fJound inertia weight, 2.8-liter displacement,
6-cylinder engine with 2-barrel carburetor, catalyst, and
manual transmission.
i
The next level of division of a manufacturer's
product line is called a vehicle configuration. A vehicle
configuration is defined as a unique combination ot inertia
weight class, basic engine, and transmission class (all of
which determine a base level) plus engine code, transmission
configuration, and axle ratio*. Engine Code goes beyond the
definition of bas^ic engine by' isolating different variations ot
carburetor, distributor, and other key engine and emission
control system component calibrations. Transmission configura-
tion considers more than ju£t manual or automatic and the
number of forward gears. It also considers shift calibrations
and other design factors that determine the performance of the
3,000-pounds inertia weight with a 2.8-liter, 6-cyiinder
transmission. An example of a vehicle configuration is:
engine, 2-barrel carburetor, engine code A, 4-speed overdrive
manual transmission, and 3.23 axle ratio.
6. Inertia weight class is determined from the curb weight ot
the vehicle plus 300 pounds (called the loaded vehicle weight).
The inertia weight class contains a range of loaded vehicle
weights, as defined in 40 CFR 86.029-80.
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The most detailed designation of a vehicle is termed
a subconfiguration. A subconfiguration is a unique combination
of equivalent test weight, road-load horsepower, and other
characteristics determined to be significant by the
Administrator within a vehicle configuration.
2. Test Procedures; EPA first began obtaining tuel
economy values as a byproduct of the exhaust emission tests
that is required for emission control certification. Tne
emissions certification procedure includes the operation of
test vehicles on a laboratory chassis dynamometer to simulate a
7.5-mile urban trip. The vehicle's exhaust emissions are
measured during the procedure for comparison to applicable
emission standards. The emission results may also be used to
calculate the vehicle's fuel economy during the test cycle.
All of the data necessary for the fuel economy calculation for
city driving is measured as part of the emission test proce-
dure. The highway fuel economy is determined in a similar
manner by using a separate driving cycle that simulates driving
on urban highways or similar higher speed, major thoroughfares.
3. Fuel Economy Labeling: EPCA requires that
manufacturers have fuel economy labels installed on each car
and light truck it produces for sale in the United States.
Dealers are required to keep that label on the vehicle until it
is delivered to the consumer. Each label must include the
following information: (1) the EPA estimated fuel economy of
the automobile, (2) the estimated annual fuel cost associated
with the.operation of the automobile and (3) the range of fuel
economy of comparable automobiles. All the information is to
be determined according to rules prescribed by the Adminis-
trator. EPA is also responsible for specifying, by rule, the
form and content of the labels and1the manner in which they are
affixed.
> '.'•.
a. Types of Labels: There are currently two types
of fuel economy labels that manufacturers may attach to
vehicles. These are the specific label and the general label.
A specific label contains the fuel economy of a unique vehicle
configuration. EPA only allows the use of the specific labels
when there are not yet complete data to calculate a general
label value. This usually only occurs early in the model year,
before the manufacturer has completed testing of all of the
vehicles needed for the general label,. A manufacturer cannot
use both specific labels and general labels on vehicles within
the same model type.
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The general label displays a fuel economy
estimate for a model type. A model type can contain many
unique vehicle configurations. Thus, the model type fuel
economy value is calculated from fuel economy aata collected
from many vehicle configurations. This calculation, which is
described below,' is an average of the vehicle configuration
data, taking into account the anticipated sales of each vehicle
configuration. That is, it is a sales-weighted average. The
general label values are determined once for each model year,
and are not changed during that model year. This was done as a
cost and resources saving measure over updating label values
periodically or in case of new data from product changes.
b. Determination of the Label Value: The minimum
amount of data required for a general label value calculation
is that each base level must be represented by at least one
vehicle configuration test value. If there is more than one
configuration test value within a base level, the base level
fuel economy is determined by a sales-weighted average of the
fuel economies of all the tested configurations. The base
level fuel economy values within each model type are then
harmonically averaged to obtain the model type fuel economy
values. These are the fuel economy values printed on tne
vehicle labels. Figures 1 and 2 are illustrations of the
calculation process.
4.•* CAFE Compliance; In 1975, the newly enacted EPCA
mandated a 100 percent improvement in the average automobile
fleet fuel economy from the base year of 1974 to moael year
1985. EPA was charged with the responsibility for calculating
the fuel economy values and the Department of Transportation
(DOT) is authorized to assess penalties. Specifically, EPCA
requires that the sales-weighted average fuel economy of each
manufacturer's production of new car or light truck fleet (the
CAFE) meet minimum fuel economy values each year. These CAFE
standards increase in stringency with each new model year.
(The 1978 CAFE standard was.27.5 mpg.) CAFE standards tor
light trucks began with the'1979 model year and are different
than those1 for cars. •> i
If a manufacturer fails to meet the CAFE standard
for a given model year, DOT,is authorized to assess the
manufacturer a charge of $5 per vehicle manufactured for each
one-tenth mpg that the CAFE is over the standard.
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FIGURE 1. Example of Configurations Combining into a Base Level
Bate Level Values:
I40CID. IbW
4? Sum
M-4 Trifwniuton
27SOU»
City 19 31 MPG
Hwy 29 87
Comb 12 9«
Harmonic Sales—Weighted Average:
(City MPG)
But MPG
I
Sala(ayTot Saks Sak»(byTo< Salci
MPG(i)
MPG(b)
Etc
Configuration (a)
1 40 CIO. 2 bW
49 Sum
M 4 Transmission
308IA.I.
27SOLbl
Configuration (b)
I40OD 2bbi
4V Sam
En|jlwCodtE-4F
M-4 Tfwtsfniiiion
3 08 I Axle
I750Lta
Configuration (c)
140 CIO. 2 bW
4» Sons
EnflntCa
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EPCA requires that EPA calculate CAFE values based on
the weighted average of both the EPA urban driving cycle and
the EPA highway driving cycle. This average result of the two
tests (called the "combined11) is weighted at 55 percent urban
driving and 45 percent highway driving. The following is a
summary of how EPA determines CAFE values:
a. Data Requirements: The data base EPA uses to
calculate each manufacturer's CAFE value includes all of the
data used to calculate general label values. However, the CAFE
data base generally includes more data. The minimum data
requirement to calculate label values is data from one vehicle
configuration in each base level. The minimum requirements for
CAFE compliance is more extensive. A pictorial example of the
calculation process is shown in Figure 3_.
FIGURE 3. Fuel Economy Calculation Flow: from Test Data through Corporate Average
I Jonet Motor Co
MeMTypa
(Cricuhurf)
Configurations
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The final CAFE value for each manufacturer is
based upon actual fleet sales figures for that model year. (As
with general label values, the CAFE is a sales-weighted
average.) However, the manufacturers wanted EPA to establish a
protocol that would provide a mid-year preproduction rather
than establishing minimum data requirements to apply to an
actual sales at the end of the model year. As a result of the
manufacturers request, EPA established minimum requirements for
a preliminary CAFE calculation earlier in the model year. The
preliminary CAFE calculation uses projected fleet sales.
The preliminary CAFE currently serves several
functions. First, it establishes early in the model year CAFE
data requirements. Second, it estimates each manufacturer's
CAFE as a check against the CAFE standards. Third, it
establishes the data needs to cover changes manufacturers make
to their product lines during the model year.
As with the general label values, the CAFE
calculation uses base levels to group data from vehicle
configurations. For the preliminary CAFE calculation, the
manufacturer must supply fuel economy data from the highest
projected selling configurations in a significant base level
(those base levels with over 1 percent of the manufacturers'
total sales) until a minimum 90 percent of the sales for that
base level are represented. For nonsignificant base levels
(those with less than one percent of the manufacturer's total
sales), the manufacturer must supply fuel economy data from tne
vehicle configuration with the larger projected sales within
the base, level.
The manufacturer must submit the preliminary CAFE
calculation to EPA within 10 days of when EPA makes available
the range of fuel economy values for)fcomparable vehicles, or
within 30 days of the introduction of the manufacture? '-s first
model type. EPA makes no requiretmen^on when ,the manufacturer,
must calculate the preliminary CAFEBefore submitting it.
Thus, to a limited extent, the manufacturer has control over
what data to include in the preliminary CAFE. The.manufacturer
will have satisfied the preliminaryj .and the final CAFE data
requirements for the year provided the manufacturer does not
make any changes to the product line -during the model year.
This is discussed below. , - ;.
b. Production Design Changes (Running Changes):
Most manufacturers make changes to their product lines during -
the model year. These changes may include the addition o£ new
models, or design or specification changes to existing models.
EPA calls these changes running changes. Manufacturers make
their running changes for a variety of reasons. Among the
reasons are cost savings (e.g., use cheaper parts or eliminate
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unnecessary components), improvements to dnveability,
improvements to fuel economy, reductions in emissions, and
expansion of option availability. Obviously, not all of these
changes have the same effect on fuel economy. Under the
provisions of 40-CFR Part 86, manufacturers generally cannot
make changes or additions to their product line during the
model year unless EPA agress that the emissions certification
is still valid. Thus, EPA may require manufacturers to test
vehicles to prove that the running change does not cause the
affected vehicles to exceed emission standards. EPA usually
tries to select running change 'test vehicle designs that will
likely exhibit the worst emissions. Whenever possible, EPA
also tries to fulfill the fuel economy data needs at this time
in order to save additional testing for fuel economy under 40
CFR Part 600 (below).
40 CFR 600.507 sets minimum fuel economy data
requirements for running changes. These are commonly known as
supplemental requirements since the data are not required until
after the approval of the running change. For significant base
levels, EPA requires additional running change fuel economy
data for only those running changes which create new vehicle
configurations. Manufacturers must submit these tuel economy
data for only the projected highest selling new vehicle
configurations created by the running change. For nonsigni-
ficant ba§£ levels, EPA does not require additional data unless
the cumulative total projected sales of all base levels added
since the last calculation of the manufacturer's average fuel
economy \s 3 percent or more of the manufacturer's current
total applicable projected automobile or truck sales. The
manufacturer must recalculate1 its preliminary CAFE when the
total projected sales of added nonsignificant base levels
reaches 6r exceeds 3 percent; or when a running change adds a
new significant -base leve'l/' The new calculated preliminary
CAFE can b'e different because tne calculation is based upon all
available data including data from the top 90 percent of the
vehicle configurations of trie base level. The latest sales
projection may indicate tha€ additional data are required to
represent the present 90 percent.
i _ '
• Related to the7 running change, manufacturers
sometimes make another type of change during the model year.
This change, called a field fix, is intended to make changes to
vehicles already sold and in-use. Manufacturers usually make
these changes to fix driveability problems such as spark
knock. These changes can affect fuel economy, emissions, or
both. Manufacturers need 'hot submit emission data and gain EPA
approval for field fixes, but the manufacturers are still
responsible if the field f-ix causes vehicles to exceed emission
standards. For this reason, manufacturers often request EPA
approval of field fixes that may affect emissions. There are
currently no fuel economy data requirements for fiexd fixes.
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c. Test Vehicles: EPA is allowed to use fuel
economy data generated for emission certification testing in
the CAFE data base. This includes data from all emission-data
vehicles (vehicles, which run 4,000 miles with production
calibrations) used in the original preproduction certification
process, and data from emission-data vehicles required for
running change approvals. In addition, under 40 CFR 600.509, a
manufacturer is allowed to submit additional fuel economy data
at its option.
Because the Clean Air Act requires that vehicles
be certified as conforming to emission standards before they
are sold, manufacturers must build special preproouction test
vehicles for certification. These are called prototype
vehicles. EPA requires that these prototype vehicles be
representative of the production vehicles that manufacturers
will actually sell. Virtually all emission-data vehicles ar«ir
prototype vehicles, and these are often reused for emission''J
testing to gain running change approvals. The regulations
accept the use of any emission-data vehicle as a fuel economy
data vehicle.
/
The rules for test vehicles to be used for fuel
economy testing are very flexible. Manufacturers are allowed
to reconfigure vehicles for particular tests. This means that
the manufacturer can change components on a test vehicle to
make it represent a particular configuration from which they
need these data. They are also allowed to use development
vehicles, company fleet vehicles, or vehicles from many other
sources 'in addition to the emission program. Manufacturers may
continue to obtain fuel economy data from test vehicles that
have accumulated up to 10,000 miles. All of these flexibil-
ities were devised to save manufacturers significant test
vehicle costs in light of the number of tests EPA requires for
fuel economy. Thus, manufacturers can use vehicles from many
sources, use them repeatedly, and are allowed 10,000 miles to
extend the testing life of the vehicle.
d. CAFE Calculations: The method EPA uses to
calculate preliminary CAFE and final CAFE values begins the
same as the calculation of model type values. However, the
CAFE calculations go one step further. Once the model type
values are determined, the CAFE value is the sales-weighted,
harmonic average of all of the manufacturer's moael type
values. For the preliminary CAFE calculation, tne projected
sales are used, and for the final CAFE calculations, the actual
sales are used.
5. Gas Mileage Guide; As mentioned earlier, EPA is
responsible for generating the fuel economy values that appear
in the Gas Mileage Guide (Guide). The contents of the Guide,
aside from the fuel economy values, are established by both EPA
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and the Department of Energy (DOE). DOE is responsible for the
printing and distribution of the Guide. EPA regulations (40 "
CFR Part 600, Subpart E) require that vehicle dealers display
and make available the Guide. However, since the Guide is
prepared by the Federal government the contents are not
governed by regulation.
Vehicles are listed in the Guide according to car
line or truck line class. EPA determines these classes
according to interior volume for cars and carrying capacity for
trucks and vans. The general car.classes currently listed in
the Guide are: two-seater, minicompact, subcompact, compact,
mid-size, and large.
The fuel economy of vehicles listed in the Guide are
the same fuel economy values that are on the general labels.
These provide consumers with a convenient comparison shopping
guide for new vehicles. Since the Guide and the general model
type labels are the same, selecting vehicles from the Guide
gives as much fuel economy information as comparison shopping
in the dealer show rooms.
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