PB82-126111
    PRELIMINARY CALCULATION OF FUEL ECONOMY ADJUSTMENT
    FACTORS.  (TECHNICAL REPORT. )
    Environmental Protection Agency
    Ann Arbor, MI
    Jul 81
                                                                      J
U.S. Department of Commerce
National Technical Information Service
NTT1S

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                                                     EPA/AA/CTAB/FE-81-17
           Technical Support Reporc for Regulatory Action
               Preliminary Calculation of Fuel Economy
                         Adjustment factors
                             July, 1981
                               Notice
Technical support reports for regulatory action do  not  necessarily
represent the  final  EPA decision on  regulatory  issues.  They  are
intended  to  present  a   technical  analysis  of  issues  and  recom-
mendations resulting  from  the assumptions  and constraints of  that
analysis.  Agency  policy constraints or  data received  subsequent
to  the  date   of  release  of this   report  may  alter  the  recom-
mendations  reached.   Readers  are  cautioned  to  seek  the  latest
analysis from EPA before using  the information contained herein.
    Control Technology Assessment and Characterization Branch
              Emission Control Technology Division
         Office  of  Mobile Source Air Pollution Control
               Office of Air,  Noise and Radiation
              U.S.  Environmental  Protection Agency
                       2565  Plymouth Road
                   Ann Arbor,  Michigan   48105

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                                    TECHNICAL REPORT DATA
                             (Please read Intinicrions on the reverse before completing)
 1. REPORT MO.
   EPA/AA/CTAB/FE-81-17
              3. RECIPIENT'S ACCESSION-NO.
                   PM1    12611  1
 •J. TITLE AND SUBTITLE
   Preliminary Calculation of  Fuel Economy Adjustment
   Factors.
              5. REPORT DATE
                July  1981
                                                                              -,A  n
                                                                              J  I  U
              6. PERFORMING ORGANIZATION CODE
 7. AUTHORISI
                                                             8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
    United  States Environmental Protection Agency
    Office  of  Mobile Source Air Pollution Control
    Control Technology  Assessment  & Characterization  Branch
    Ann Arbor, MI 48105
                                                              10. PROGRAM ELEMENT NO.
              11. CONTRACT/GRANT NO.
 12. SPONSORING AGENCY NAME AND ADDRESS
                                                              :3. TYPE OF REPORT AND PERIOD COVERED
                                                                 Technical	
                                                              14. SPONSORING AGENCY CODE
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT
         This report is a  dual  purpose report:   1)  it  is  a cover report for  EPA
    1'inal report 460/3-81-003,  "Development of Adjustment Factors for On-Road  Fuel
    Economy" and 2) it is  a  preliminary determination  of  fuel economy adjustment
    factors in support of  on-going fuel economy  rulemaking activity.
         In is role as a cover  for the EPA report,  it  extracts key findings, critiques
    the findings and offers  modifications to the findings where there is reason to
    adopt alternate assumptions.   In its rulemaking support role as an initial
    estimate of MPG adjustment  factors, it compares the EEA (Energy And Environmental
    Analysis) results with those  of other recent,  significant publications in  this area.
    The resulting preliminary adjustment factors herein are thus an amalgam  of the
    factors derived by these four data sources.
17.
                                 KEY WORDS AND DOCUMENT ANALYSIS
                   DESCRIPTORS
                                                b.IDENTIFIERS/OPEN ENDED TERMS
                           c.  COSATI Field/Group
    Fuel Consumption
    Computation
    Motor Vehicles
 Fuel Economy
 Calculation
13. DISTRIBUTION STATEMENT

   release unlimited
19. SECURITY CLASS (This Report/
    unclassified
21. NO. OF PAGES
   45
                                                20. SECURITY CLASS (This page/
                                                   unclassified
                                                                           22. PRICE
EPA Form 2220-1 (9-73)

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                                   ABSTRACT

This is a dual purpose report:

'a)    It  Is  a  cover  report  for  Contractor Final  Report  EPA-460/3-81-003,
       "Development  of  Adjustment  ?actors for  On-Road ?uel  Economy",   March
       1981, by Energy and Environmental Analysis,  Inc., (EEA);

(b)    It is a preliminary determination of fuel economy adjustment  factors  in
       support of on-going fuel economy rulemaking  activity.

In ita  role as  a cover for  the  EEA report,  it  extracts  key findings In  that
report and  che assumptions  associated  with them, critiques  those  findings and
assumptions, and offers modifications to the  findings where  there  is  reason  to
adopt alternate assumptions.   This is not  done "in a vacuum", however.   In its
rulemaking support  role as  an initial  estimate  of  MPG adjustment factors,  it
compares the EEA  results  with  those of other recent,  significant  publications
in this area.   The  resulting preliminary adjustment factors  herein are thus  an
amalgam of  the factors  derived by these four data  sources.  Data analysis  is
continuing.

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                                       -3-

I.     BACKGROUND and PURPOSE

There are currently four major "collection agents"  for  data  on the In-use fuel
economy of motor vehicles:

  a)   EPA's Emission Control Technology Division
  b)   DOE's Office of Policy Evaluation
  c)   General Motors Technical ("-enter
  d)   ford Motor Co. Fuel Economy Planning

EPA-ECTD,   primarily   through   its   Emission   factors   and   Inspection  and
Maintenance   Programs,   has  been   gathering   in-use  MPG   data  via   owner
questionnaires for  several  years,  and has accumulated over  10,000 data  points
on owner-perceived MPG of cars  and  light trucks from model  years  1975  through
1981.  Recently,  in-use  data on a subpopulation of  the  questionnaire-surveyed
Emission  factors  owners  has  been  collected using  postcard-type  fuel  economy
diaries,  which  give measurements  of miles  traveled  and gallons  of  fuel  for
several  successive  fuel purchases.   The  vehicles  surveyed  by EPA-ECTD  were
localized in the vicinities of the four  to  six commercial  test labs contracted
by EPA to administer the Emission factors and I/M Programs.

DOE  has  become  the  ad_ hoc  national  center  for  in-use   vehicle  MPG  data,
acquiring since 1977 a total  of  well over 50,000 data points  on  vehicles from
the  1975  through  1980  model years.   This data  base covers  a  large number  and
variety of  sources, including the aforementioned EPA  and auto company surveys,
along  with  those of  oil and chemical  companies,  non-auto/oil  light  industry
firms,  utilities,  commercial fleet  operators, commercial  collectors of  auto
maintenance  data,   and   a  host  of  state  agencies  who  operate  fleets.   In
addition  to collecting,  systematizing,  and analyzing  others'  data,  DOE  has
sponsored in-use MPG surveys of its own.

General  Motors  has surveyed  the in-use  MPG of  a  total  of  more than  6,000
General Motors cars  from the 1975,  1976,  and  1978 model  years,  and  recently
surveyed  approximately  5000  model  year   1980  in-use  cars  from   thirteen
manufacturers.  These GM surveys were nationwide and  generally multi-seasonal,
and employed postcard diaries for logging in-use mileage and  gallonage.

lord's in-use MPG surveys  are restricted to the more  recent model years,  but
are  respectably prolific nonetheless.  Since 1978,  rord has  collected  postcard
diary data  on 29,000 cord vehicles  from  model  years 1978 through  1980.   These
vehicles were leased and  operated by .7ord Motor Co.  employees  in many parts  of
the  country and  over  all  parts of  the  year.   Most  of  the  data,   however,
represents vehicle operation in  the  Detroit,. Michigan  area.

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                                       -4-
Some parts of  these  data bases were examined  by  EPA to  illustrate  approaches
to road  adjustment  factors in Technical  Support  Report for  Regulatory  Action
EPA/AA/CTAB/FE-81-6,"Light Duty Vehicle  ?uel  Economy Labeling", October 1980.
In  the   total  universe  of  analyses  that will  lead  to development  of  road
factors for the MPG labeling rulemaking,  that  report represented Round  One.

The EEA  report  is  considered  Round Two.   It  is  a  thorough,  detailed  analysis
of the  DOE  data base  (which  included  some of the  ECTD data,  some  of  the  GM
data,   and  some  of  the  ?ord  data  at  the  time);  it  perfected most  of  the
analytical approaches  that  will  be used  in the  final  rule  support analysis,
and — within  the  limits  of  its data  base and  assumptions — began to zero  in
on the quantitative ballpark for road adjustment  factors.

The final  rule support analysis,  Round  Three,  will use  all  of the data  from
all of  the  aforementioned sources,  plus any data supplied  to EPA in  the  rule
making  process,  and  will  of  course be  performed in-house.  The  data now  in
hand are being  cleaned and characterized.  The data  base has at  this writing
been  augmented with  climatic, demographic,  and  topographic data  to  permit
careful examination of the distributions  of fuel  economy  influences within and
among the  data sources.   The  data  are now  being assigned EPA MPG values  to
permit  calculation  of the  "in-use shortfall".   When  this  is  completed, the
full-scale analysis and determination of  road  factors will commence.

Pending completion of  these analyses, however, it is  necessary  to  identify the
approximate  range  of  values  within  which  some  forms  of  the  final  road
adjustment relationships  are expected  to  fall,  so that all  interested parties
can respond from an  informed standpoint  to the  Notice  of  Proposed  Rulemaking
for fuel  economy  labeling soon to  be  released.   This  report,   then,  provides
that estimate  of  the  probable  range of road adjustment factors.  It would  be
considered Round  Two  and  a_ Half.   It makes  that  estimate  by  examining  [not
data,  but]  reported  results of analyses  of data, from  the four major  in-use
data  sources.   In so  doing,  it  reviews  the  EEA  Report  results  along with
reports of analyses by the other  three  sources.

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                                       -5-

II.    DISCUSSION

A.     Data Sources

Table 1 lists  Che  four  reports  which are the subject of this  report.   All are
recent publicatons.

Details of  each  of the data bases  used  for the four reports'  analyses appear
in Table 2, and a  narrative  summary  of  the  distinguishing  features  of  the four
surveys is given in Table 3.

None  of  the  four data bases is  considered  "ideal"  in all respects.   The 1980
GM Survey  might  be evaluated as nearly  ideal based on tables 2 and  3,  but two
aspects of that  survey  not addressed  in  these  tables  are worth  mentioning:
(a)  The  overall  response  rate  was  quite  low  (11.62 of  mailed diar^^s were
returned;   after  screening,  79%  of these  survived,  leaving  a  net  usable
fraction of  9.2Z); this leaves  the possibility of  non-response  bias  in MPG,
which was  not  evaluated — although the distribution of  vehicle types  in the
returned  sample   was   quite  representative  of  the  model  year  1980  vehicle
population.  (b)  While the  GM  cars  in  the  survey  were  sampled from  GM sales
records, covering  all states,   the  other  manufacturers'  cars were  sampled via
R.L. Polk  registration data, which  excluded  15  states.  Most  notable among the
excluded states  are Massachusetts,  Connecticut, New  Jersey, and  Pennsylvania,
which together account for most of the VMT in the Northeast.

B.     Single Mode and Dual Mode Stratagies

At  present,  EPA  is  considering  two alternative  strategies  for fuel  economy
labeling:  a labeling system based on one MPG  number,  and a  system based on two
MPG  numbers.   The one-number  system would  use the  EPA  combined   (55M5)  MPG
value as the basis for road adjustment  ;  the two-number  system would  use the
EPA City and EPA Highway MPG values as the bases for adjustment.

The  general  case  of  the  adjustment relationship  for  both  strategies  is  an
equation of  the  form "Label MPG  equals a  function of  EPA  MPG".   Based  on
linear regression  analysis  in GPM  ratio  versus  EPA MPG  space,  as discussed  in
detail in  the  EEA  report,  the general equation form  is  "Label MPG  equals EPA
MPG/'a  +   b  EPA MPG)".   For  the  final  rule,   the  generalized case  will  be
analyzed in detail.

The  next  section,  Section  C,  addresses the  one-number  'single-mode)  system.
Almost  entirely,  it   addresses  the simple  case  of  no  dependence   of  the
shortfall on EPA MPG  level  (b=o).  This  results  in  a .simplified equation form:
"Label MPG  - K  EPA MPG" (K - I/a).

The section after  that, Section  D,  addreses  the two-number  (dual-mode)  system;
it discusses  some  results  in  terms of terms  of  the  "simple  multiplicative
factor"  form of the equation, and some results in terms  of the MPG-dependent
form.

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                                     -6-
                                 Table 1


                              Data Sources
"EEA":                         Energy   and  Environmental   Analysis,   Inc.,
                              "Development   of   Adjustment   Factors   for
                              On-Road   Fuel   Economy",   EPA-460/3-81-003,
                              March 1981.

'1980 Ford":                   N.  E.  South,  "1978 to 1980  ?ord  On-Road Fuel
                              Economy", SAE Paper 810383, February 1981.

'1980 GM":                     R.W. Schneider e£  al,  "In-Use Fuel Economy of
                              1980   Passenger   Cars",    SAE   Paper  810384,
                              February 1981.

'EPA Emiss.Fact":              B.  Bradley  e£ al,  "Fuel  Economy  of  In-Use
                              Passenger   Cars:  Laboratory  and  Road",  SAE
                              Paper 810780, June 1981.

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                                          -7-
                                        Table 2

                 In-Use F. E. Data Bases: EEA and Three Other Sources


Survey Characteristics
Model Years
Manufacturers
Geographic Spread
Seasonal Spread
Total No. Data Points
Average EPA Comb. MPG
Vehicle Characteristics
Car Size
Engine Size
Manual Transm.
Front Drive
Diesel
Air Conditioning
Avg. Odometer
Driving Characteristics
Consumer Use, Measured
Consumer Use, Perceived
Fleet Use, assumed meas
Avg. Miles per Day
Fraction City Driving
Overall Road MPG Factor
(vs. EPA Combined MPG)

EEA
1975-80
95% Domestic
Yes
Yes
25,239£/
19.6

60% mid-Lge
55% 8-Cyl
13%
5%
1%
7
8,000l/
. /
40%!'
40%d/
20%d/
7
7

0.90
1980
Ford
1980£/
All Ford
Mostly Detroit
Yes
8,689
21.0

7
?
20%
5%
None
?
3450

100%
—
—
52
54%

0.86
1980
Gen Mtrs
I980b/
76% Domestic
Yes
Mostly Fall
4,871
21.6

7
7
33%
23%
5%
7
3958

100%
—
—
45
53%

0.84
ay   Ford  also   ran   surveys   in  1978-79,   Ford
     vehicles only.

b/   GM also  ran  surveys  in 1975, 76, and  78,  GM
     vehicles only.

c_/   Includes  the  earlier  Ford  &  GM  data,  and
     also  EPA Emiss.  Fact,  and  I/M questioriaire
     (perceived; MPG data.

d/   Estimated.

e/   High  odometer  and  temp.   should   make  it
     higher;   extensive   A/C   use,   city   driving
     fraction, and  population  density should make
     it lower; effects apparently cancel.
                                                                         EPA
                                                                         Emis.Fact
                                                                         1975-80
                                                                         81% Domestic
                                                                         Mostly Houston
                                                                         Mostly Summer
                                                                         440
                                                                         20.0
                                                                         51% Mid-Lge
                                                                         46% 8-Cyl.
                                                                         24%
                                                                         16%
                                                                         None
                                                                         92%
                                                                         24,000
                                                                         100%
                                                                         33
                                                                         67%
                                                                         0.83£/

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                                     -8-
                                    Table  3
                           Comparison of Data Bases
EEA:              Multi-manufaccurer
                  Most: data points, good geographic & seasonal spreads
                  Smaller cars under-represented
                  Imports underrepresented
                  "Fuel Efficient" technologies underrepresented
                  60% of data does not represent measured, consumer use
                  Overall road factor 4Z-7Z higher than other surveys

1980 Ford:        Only Ford vehicles
                  Southeastern Michigan » locale for most driving
                  Front drives and Diesels underrepresented
                  All data measured, consumer use (Ford employees)
                  Highest miles per day
                  Lowest Avg. odometer

1980 GM:          Multi-manufacturer
                  Reasonably high import percentage
                  Most data represents October & November
                  All data measured, consumer use (private owners)
                  Fuel efficient technologies well represented
                  Avg. miles per day and city fraction are typical

EPA Emis. Fact:   Very small data base
                  Multi-manufacturer
                  Reasonable import percentage
                  All data measured (private owners)
                  Driving highly localized in geography & season
                  Manuals & front drives well-represented;  no Diesels
                  Highest odometer average
                  Low miles per day,  high city fraction
                  92% of vehicles were air-conditioned

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                                       -9-
C.     Single Mode Analysis

Table 4  summarizes  Che  four references'  findings on  single-mode  road factors.
Even wichin  a  given reference,  "the  answer"  is not  a  fixed road  factor,  but
depends upon how  it  is  calculated.  Using  EEA as an e::ample, if  one  takes  the
model year-specific  average on-road MPG  values (R)  and average EPA MPG values
^E)  from  EEA's  table 3-4,  the  model  year sample weightings from  their  table
3-3, calculates  a total  sample R of  16.5 and  a  total sample E of  19.6  and
takes the  ratio  of   these  values,  a  road factor of  0.84  is obtained.  But  if
one  enters  an  E  value  of  19.6  in  the  EEA MPG-dependent  algorithm,   this
produces  an  E/R  ratio  of 1.108,  yielding  a  road  factor  (R/E)  of  1/1.108  -
0.90.  Thirdly,  if  the  E/R ratio  is  taken for each  vehicle in  the  data  base
and  averaged, a  figure  of 1.109 results;  the  road  factor from this  method  is
then 1/1.109 - 0.90*.

Also shown in Table  4 is  the fact  that MPG dependence of  the shortfall, at  the
fleet  level  of  aggregation,   is not  the  same  for  the   three  sources  which
evaluated it.  for the EEA report, a 10 MPG increase  in EPA fuel  economy  gives
a 3.1% increase in road GPM ratio; for Ford, it is a  1.2%  increase, and for  GM
it is a 4.9% decrease.  This apparent  inconsistency  between sources can be  due
to  a number  of factors,  some  of which could  be or  could have  been adjusted
for, and some which cannot/could not.

One  of  these  factors  is  the  proportion  of  various unique-shortfall  vehicle
technologies in the  respective  survey  populations.  Given  the wide  variance  in
representation  of various  vehicle technology  types  among the  four  surveys
(Table 2), technology specific  shortfalls  and weightings should  be taken  into
account.  Even  if a road  adjustment  factor at  the  fully-aggregated  level  is
all  that  is  sought,  the  development   of  that  one factor  from  these  sources'
results still requires  disassembly of  their findings into  specific  technology
strata   and   reassembly   using  appropriate  weightings   of   those   strata.
Remember:  The  ultimate  use  of  road  factors will  be for post-1982  vehicle
fleets, not on fleets with the technology mixes of  these surveys.

Table 5  gives  the road  factors  for twelve  technology strata,  as developed  by
the  four analyses.
* The  EEA  report  does  not   include   this  calculation.    It   was
  furnished to EPA after publication.

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                                       -10-
Survey .\vcrage£'

MPG Dependence:
 - Method
                                      Table 4

                              Single-Mode Road factors
1980
,7ord
1980
Gen Mtrs
EPA
Emis.Fact
                          ERA
                           .84-. 90
 - Shortfall increases/decreases
   with higher EPA MPG
                                    .84-. 86
                          Increases:
                          f-  .915 
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                                      -11-
                                     Table 5
             Vehicle Technologies & Road factors: Four Data Sources

Vehicle Technology
RWD/Auto/Carb
RWD/Manu/Carb
RWD/Auto/FI
RWD/Manu/FI
RWD/Auto/Dsl
RWD/Manu/Dsl
FWD/Auto/Oarb
fWD/Manu/Carb
FWD/Auco/FI
rWD/Manu/FI
FWD/Auto/Dsl
rWD/Manu/Dsl
1980
EEA Ford
201277. 865£/ 6918/.8261/
2154/.888 1360/. 867
2637. 891
(2 cars)
2137. 898
(40 cars)
1687.975
6457.982 4H/.966
(19 cars)
12W.991
(2 cars)
727.983
1980 EPA
Gen Mtrs Emis.Fact
25397 800£/ 3C1/.798
7297.887 597.818
(4 cars)
(7 cars)
2017. 879
(23 cars)
7317.855 (15 cars)
5277. 975£/ (28 cars)
(13 cars)
— (13 cars)
667.849
557.949
aj  x/y denotes no. cars/road factor
b/  may include some rl;  does include 3159 overdrives
c/  may include some FI.

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                                       -12-


The "Acceptable Stratum Sample Size" Issue

Also  shown in  cable  5  are  the  sample  sizes  associated  with  the  technology
strata.  We have not shown road  factors  for  strata  with sample sizes less than
approximately 50*.

The "Which Vehicle Technology Weightings to Use" Issue

Table  6  shows  projected  sales  penetrations  for  the twelve  technology  strata
for  the  1981 model  year,  the  latest  model  year  for  which  we  have  reliable
predictions.  At  the  very least,  "new-fuel  efficient"   technologies  should  be
represented  at  these  sales   fractions in  re-aggregating   technology  specific
shortfall observations.

Other Issues .   Survey findings Weighted Equally, not by Sample Size

                Pooling of FI and Diesel Road Factors
                Retain or Discard Obsolescent Technologies
In  Table  7,   the  aforementioned  source/technology  road  factors  and  strata
weightings  are  brought  together.   ?or  each  stratum,   one   road  factor  was
determined  by   combining  the  sources'   individual  road  factors,   equally
weighted,  consumption-combined  (i.e.  harmonically  averaged).   This  approach
was  used rather than  sample  weighting.   The  rationale  is illustrated  by  the
following  analogy.   If  four inspectors  using  identical copies  of  an  NBS
standard   yardstick   measure   N]_,  N£,  N*3,   and  N4  widgets,   the   average
widget  length  vould,   by  all means,  properly  be  calculated as  a  weighted
average,  using  the  individual  inspectors'  average  measurements  and  their  N^
weights.   However, if  they  use  four  hand-crafted  but uncalibrated yardsticks,
sample-weighting does  not a_ priori lead to  the best estimate  of average widget
length.    The  measurements  made  by  inspector  //I  should  not  dominate  an
aggregate  calculation  just  because he had a good  day and  measured more widgets
than the  other  inspectors.  So  it is with in-use  fuel economy  surveys.   Until
there is a precise standard procedure (that is, a science)  for conducting such
surveys,   the   efforts    of    quite   competent   surveyors    will    feature
distinguishable, individualistic  traits (that  is,  art).   Sample  size,  then,  is
used  only  to  determine  a  threshold  of  acceptability   (50  cars  for  this
analysis), not as a weighting factor when aggregating across data sources.
    To estimate MPG  within a precision  of  +_ 1 MPG  in the neighborhood  of  20
    MPG  (+5%  precision),   with  a  coefficient  of  variation  of  20%,   at   a
    confidence  level  of   90%,  a  sample  size of  45  is  required;   for  95%
    confidence, a  sample  size  of 64  is  required  (from  P2  -  Z2  COV2  (1/N)
    and t-tables).

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                                          -13-
                                        Table  6

               Vehicle Technologies:  Sales  Fraction "1981)  and MPG Range


Drive
Rear
Rear
Rear
Rear
Rear
Rear
Front
Front
Front
Front
Front
Front


Transm.
Auto
Auto
Auto
Manu
Manu
Manu
Auto
Auto
Auto
Manu
Manu
Manu


Engine
Garb
FI
Diesel
Garb
Fl
Diesel
Garb
FI
Diesel
Garb
FI
Diesel


% Sales
43.6
3.2
3.4
9.5
2.4
0.1
18.8
2.0
0.6
13.4
1.8
1.2
EPA
Combined
MPG
12-32
10-28
25-29
12-45
13-32
30-31
18-34
17-29
23-25
24-42
23-33
41-47

Comments :
Transmission
>50Z Lockups
Mostly non-lock, non-OD
Mostly lockup
-50/50 OD/non-OD
Mostly OD
Mostly non-OD
Mostly non-OD
No OD
No OD
Mostly 'OD
Mostly OD
All OD
Note - Diesels:
Each of :h«; *. strata has narrow EPA MPG range,
and the 4 MP& ranges are mutually-exclusive
(non-overlapping)
Note - FWD Automatics:  There are no lockups in these strata in 1981.

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                                        -14-
                                        Table  7

                        Sales Significance  and Road Factors  for
                   Technology Strata and Upward  Aggregations of  Them


RWD-Auto (sales)
(road factor)£/
RWD-Manu (sales)
(road factor)
FWD-Auto (sales)
(road factor)
FWD-Manu (sales)
(road factor)
All RWD (sales)
(road factor)
All FWD (sales)
(road factor)
All Auto (sales)
(road factor)
All Manu (sales)
(road factor)
All (sales)
(road factor)

Carb
.436
.82
.095
.86
.188
.92
.134
.97
.531
.83
.322
.94
.624
.85
.229
.92
.853
.87

FI
.032
.89
.024
— —
.020
— —
.018
.99
.056
.89
.038
.99
.052
.89
.042
.99
.094
.93

Diesel
.034
.89
.001
— —
.006
•85-/
.012
.97
.035
.89
.018
.92
.040
.88
.013
.97
.053
.90

All
.502
.33
.120
.86
.214
.91
.164
.98
.622
.84
.378
.94
.716
.85
.284
.93
1.000
.87
All Gasoline
(Carb + FI)
.468
.83
.119
.86
.208
.91
.152
.98
.587
.83
.360
.94
.676
.85
.271
.93
.947
.87
All FI
(FI + Dsl)
.066
.89
.025
— —
.026
•85-/
.030
.98
.091
.89
.056
.97
.092
.88
.055
.98
.147
.92
a/  Road factor • simple average of the
    applicable surveys' road factors;
    all source/strata with  >50 cars
    are counted.

b/  Obsolescent version of FWD-Auto technology?

-------
                                       -15-


The combining of technology straca in Table  7  was  done via sales-weighted har-
monic averaging.

Noting more similarity between the road  factors  of  gasoline  FI  and Diesel cars
than between  those of  gasoline  fl and carbureted gasoline cars,  a pooled road
factor was calculated for both gasoline fuel injected and Diesel cars.

It  should be  noted  that  the  road  factor for  front  drive  automatic  Diesels
comes mainly  from cars whose design r'-.r«..
-------
                                         -16-
                                        Table 8
                       Summary - Constant Road factors,  One Mode
No. Straca
                                    Road MPG
                                    EPA Combined MPG
         Road Factor(s)
ONE:
  0.87
FOUR-
(a)  ?WD .94  RWD .84
(b)  Auto .85  Manu .93
(c)  Garb .87  FI-  .92

'a)  RWD-Auto .83  RWD-Manu .86  FWD-Auto .91  FWD-Manu .93
(b)  RWD-Carb .83  RWD-r"I .89  i?WD-Carb .94  fWD-FI  .97
^c)  Auco-Carb .85  Auto-fl .88  Manu-Carb .92   Manu-FI .98
EIGHT
RWD-Auto-Carb  .82
RWD-Manu-Carb  .86
FWD-Auto-Carb  .92
?WD-Manu-Carb  .97
RWD-Auto-FI .89
RWD-Manu-FI (?)
                                                             d/
                                              FWD-Manu-FI .98
a/  There are chree cwo-scraca opcions
b/  FI means gasoline FI and Diesel pooled
£/  There are chree four—scrata options
d/  Obsolescent version of i?WD-Auto technology?

-------
                                     -17-


                                   Table 9

     Apparent  Effect  of  Combustion/Carburetion Technology on Road Factor*

                               (Strata >50 cars)
Gas FI vs. Carb.

Diesel vs. Garb.


Diesel vs. Gas FI
D =• DOE/EEA

E =» EPA Emis. Fact

F = Ford

G =• GM
                      RWD-Auto
D +3Z
G +8%

D +1%
              RWD-Manu
FWD-Auto
G -IX
FWD-Manu

D -H2

D 0%
G -3%

D -1%
       For  example,  in  the  GM survey,  RWD-Auto Diesels had an 8 per cent higher
       Road Factor  than did RWD-Auto Carbureted vehicles.

-------
                                    -18-
                                   Table 10
           Apparent Effect of Drive Train Technology on Road Factor
                              (Strata  >50 cars)
Manu vs. Auto, RWD
Garb Cars
D +2%   F +4%
E +2%   G'+9%
                                           FI Cars
Diesel Cars
Manu vs. Auto, FWD    D +1%   G +12%
FWD vs. RWD, Auto     D +11%  G +6%
FWD vs. RWD, Manu     D +9%   F +10%
                              G +9%
                                       G +10%
                                       G -3%
D =  DOE/EEA
E =  EPA Emis. Fact,
F =  Ford
G =»  GM

-------
                                    -19-

                                   Table 11

    MPG Dependency of GPM Ratio, evaluated at the Technology Stracum Level
Range of MPG
coefficients
                      EEA               GM£/             EmFacJi/

                      .0033-.0159       .0023-.0082      .0030-.0156
Average of MPG
coefficients
                      .009
.006
.006
Trend?!/
                                        No
                 No
b/
   not counting one negative slope known to be
    influenced by spurious cars (Cadillacs) and
    mixing of Garb and ?I cars

   not counting one negative slope based on

    15 cars (R2 = 0.017) in an MPG range that is

    too narrow to really develop an MPG dependence

£'i.e. does the GPMR slope increase, or decrease,
    consistently with MPG level?

-------
                                       -20-
Histogram Tests of Single-Mode Road Adjustment Systems

Using  Che  adjustment  factors  derived  above,   the   effectiveness   of  road
adjustment  at  various  levels   of   technology  aggregation  was  tested.   The
Emission  Factors  Postcard  data  base   (the  only  one  fully  accessible  for
computer analysis at the time) was the test "subject".

The  test  consisted  of multiplying  each  car's EPA  combined MPG  (Eo)  by  the
appropriate  road  factor,  taking  the  difference  between  this  road-adjusted
value (£') and actual road MPG,  and histographing this difference.

Figure  1  is  the  histogram  for  road A MPG  using  unadjusted  EPA MPG as  the
reference.  Figure  2 is the road A MPG histogram  using the  single-factor  (no
strata) adjusted  EPA MPG as  the reference.   The effect  of the adjustment  in
moving the distribution toward zero average A MPG is obvious.

Table  12   summarizes  the  effects  of  the   various  road  adjustment  schemes.
Conclusions  that  can  be  drawn  from  this  test,   in  order  of  increasing
subtlety/complexity, are:

       Road  adjustment  unquestionably  produces  label  values  that  reflect
       in-use average MPG better than the unadjusted EPA 55/45 values.

       There  is  an  average  error  of -3.6 MPG  using  raw  EPA numbers,  while
       average error .Is reduced to less than 1 MPG  with road-adjusted  numbers.

       Unadjusted EPA  numbers,  even  with a  2 MPG  discount,  are  too  high  for
       two-thirds of the in-use  cars; however—adjusted numbers, with a +2  MPG
       window, accurately reflect the road MPG experience of  two-thirds of  the
       population.

       In  this   particular   test,   stratification  produces   no   significant
       improvement  in  the  adjusted  label values'  road representativeness,  on
       the average.

       The primary  reason  for  the  previous  conclusion is that  the  four-source
       road factors  are not  the  best  set  of  factors  to try  on only one  of  the
       sources'   data.   The  four-source  no-strata  adjustment  factor   is  0.87,
       while  the  appropriate factor for  the Emission  Factors data base  is
       0.83.   Obviously, the  0.87  factor is  not  stringent  enough, as verified
       by the consistently  negative residual MPG  errors  remaining after  road
       adjustment.

       The distribution inclusion/exclusion  results  of  this  test  also  show
       little or  no  improvement  for  stratification  compared  to  a  single
       fleetwide adjustment factor.

       The  primary  reason  for  this   is  that  this  one  influence,  vehicle
       technology,  is  responsible  for  only  a  fraction  of  the  total  in-use
       variation;  all  of  the  other  influences  (driving  habits,  etc.,  etc.)
       still  contribute to the dispersions in the in-use data.

-------
                                           -21-







                                         Figure 1




                         Difference:  EPA 55/45 MFC minus  Road MFC
:DPOINT   HIST*  COUNT
:o
9
8
•?
6
.000
.000
.000
.000
.000
5.000
4
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0000
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0000
0000
0000
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0000

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0000
0000
0000

0000
.000
0.
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2.
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7.
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OTAL
440

-------
                                            -22-


                                          Figure 2

                     Difference: Adjusted EPA 55/45  MPG minus Road  MPG
DPOINT   HISTZ  COUNT

5.000      0.      0 +
4.000      0.      0 +
3.000      0.      0 +
2.000      0.      0 +•
1 .000      0.      0 +
0.000       .2     1 + X
.0000       .7     3 + XXX
.0000       .5     2 + XX
.0000      1.1     5 +XXXXX
.0000      1 .6     7 +XXXXXXX
.0000      4.1    18 +XXXXXXXXXXXXXXXXXX
.0000      5.0    22 +xxxxxx*xxxxxxmxxxxxx
.0000     10.5    46 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.XX
.0000     14.4    72 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000     18.2    80 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
          12.0    53 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000     13.2    58 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000      6.6    29 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000      4.1    18 +XXXXXXXXXXXXXXXXXX
.0000      3.0    13 +XXXXXXXXXXXXX
.0000       .9     4 +XXXX
.0000       .7     3 +XXX
.0000       .7     3 +XXX
.0000       .7     3 +XXX
.0000      0.      0 +
D.OOO      0.      0 +
1.000      0.      0 +
2.000      0.      0 *
3.000      0.      0 +
4.000      0.      0 +
5.000      0.      0 +

]TAL             440

-------




Number of
Strata
1
1
2
2
2
4
4
4
8


Results of
Road Adjustment

Strata Adjusted
No adjustment
Fleet adjustment
FWD/RWD
Auto/Manual
Carb/FI
R-A/R-M/F-A/F-M
R-C/R-FI/F-C/F-FI
A-C/A-FI/M-C/M-FI
Each Technology


Histogram
Factors:
(One-Mode
Avg. Error
(MPG)
-3.6
-0.8
-0.6
-0.9
-0.9
-0.6
-0.5
-0.9
-0.5
-23-
Table 12
Tests of Four-Source
Test Subject - Emis.
Adjustment System)


Composite
Fac. Data Base

X of Population
Below Within 2 MPG of E1
67
24
20
25
25
22
20
25
19
31
66
68
65
66
68
68
66
69
Above




 2




10




11




10




 9




11




12




 9




12

-------
                                       -24-


D.  Dual-Mode Analysis

The dual-mode  analysis  chat can be mined  from  che chree non-EEA  sources is
narrower in scope Chan Che  foregoing single-mode analysis:

         The  ?ord  paper did  noc separate  "ciCy-driven"  cars and  "highway-
         driven" cars  and  develop mode-specific  road  factors;   it  did  com-
         pare  all  driving  modes'  aggregate  MPG  results with  the  EPA  City
         value  (R -  1.01 Ec,  a  1%  overage)  and  with the EPA Highway value
         (A  -  O.d8  Eg,  a  32%   shortfall);   it  also  showed  the percent  of
         all  of the  sample cars'  MPG experience  that  would be captured  by
         two-number  ranges  built from  several combinacions of  City  and High-
         way adjustment  factors.

         The  Emission  factors  paper  did show  road  factors  for  city-driven
         and  highway-driven cars for  the  sample  fleet,  but  not for vehicle
         technology  straca;   like  the ford  report,  it also  compared  all  of
         the data to the EPA city  value (R -  0.96  Ec,  a 4Z  shortfall)  and
         to the EPA  Highway value (R - 0.68 EH,  a 32% shortfall).

         The GM paper compared  overall fleet  MPG  to  the EPA City value  (R »
         0.95  Ec,  a 5%  shortfall),  but not  to the Highway  value.  The  GM
         paper  also  gave   technology-specific  equations  involving   city
         driving fraction  and  the  EPA City  value,  from which road  factors
         for city-driven cars of the specific technologies can be derived.

Table 13 lists  the two-mode road factor  results from  the  cord, GM,  and Emis-
sion Factors papers.

The EEA  report presented an  extensive two-mode analysis, including MPG  de-
pendence and  technology  stratification,  and  using two  versions  of  two-mode
analysis on  the more  highly-populated cechnology strata.   The  downside  of
EEA's cwo-mode  analysis  rescs  with its use of  only  perceived  MPG  data  from
the 1978-79 J.D. Power survey.

Table 14 gives  the  equations  for MPG-dependent City  and Highway GPM  ratios
from  the  EEA  report,  for  conventional  technology  (carburetted,   automatic
transmission)  vehicles.  The  A  and  B sets  of  equations come from the  two
alternate analysis techniques used by  EEA  to  develop dual-mode factors.   The
techniques are  described in the report,  and will not  be discussed further
here except to  point,out that one  technique calculates  road  factors  directly
by using only  city-driven cars  and  highway—driven cars,  and  the other  (more
complex) technique uses  all of  the data and  the  full  range  of city driving
fractions.

Dual-mode road  factors  for  alternative  technologies were  determined in  the
"constant"  form (MPG independent);  they appear  in  Table 15.   The factors
shown as estimated  (type  B)  do not exactly match those calculated by EEA  for
the two technologies  shown;   they are  EPA estimates based on EEA report data
but on different assumptions  than  those  used by EEA.   Two  points  should  be
noted about these  estimates:

-------
                                    -25-

                                   Table 13
             Two-Mode Road  Adjustment  ?accors  from Non-EEA Sources
A.  Ford Motor Co.
            City Adjustment
                factor
                          Highway Adjustment
                                factor
                Z Cars Included!/
                Between the Adjusted
                Numbers
0.79
0.77
0.74
0.69
0.81
0.82
0.84
0.88
80Z
85Z
90*
952
    a/ Excluded cars are equally distributed high and low.
B.  Emission Factors
Type of
Driving
All City
Mostly City
Both
All Highway
Mostly Highway
Both
% of
Sample
25%
32Z
57Z
2%
10%
12%
City Adj
factor
.88
.93
.91
—
—
                                                        Highway Adj,
                                                        cactor
                                                          .79
                                                          .73
                                                          .74
C.
General Motors
                                                         b/
                  City Adjustment factors,  by  Technology —
      rtWD-Auto-Gas,
      RWD-Manu-Gas,
      RWD-Auto-Dsl,
                     .89
                     .92
                     .95
FWD-Auto-Gas,
FWD-Manu-Gas,
fWD-Auto-Dsl,
FUD-Manu-Dsl,
 .95
 .97
 .93
1.03
    W   From the  paper1 s table  12;  all  technologies  evaluated at  100Z city
        friction,  44.6  miles/day,  3958  odometer  miles,  and  54.6°?.   These
        factors are  MPG-dependent.

-------
                                     -26-

                                    Table 14

             Two-Mode  Road  Adjustment Algorithms  from  Che EEA Report
                       (Conventional Technology vehicles)

      Using subsets of pure mode-driven cars (46% of the data)
      City GPM ratio*:
      Hwy GPM ratio:
B.     Using all of the data
      City GPM ratio:
      Hwy GPM ratio:
RWD-Auto-Carb (1978 + 1979), 0.782 + .0181E
                                           c
RWD-Manu-Carb (1978 + 1979), 0.717 + .0134E
RWD-Auto-Carb (1978 + 1979), 1.130 -I- .0097Et
RWD-Manu-Carb (1978 + 1979), 1.017 + .0097E,
                                                                            H
RWD-Auco-Carb (1978), .845 + .0136E
                                   c
              (1979), .963 -1- .0091E
                                 RWD-Manu-Carb (1978),  .591 + .0208E
                                               (1979),  .557 + .0166E
RWD-Auto-Carb (1978),  1.127 -I- .0096E
              (1979),  1.144 + .0088E
                                 RWD-Manu-Carb (1978),  1.312  (no  MPG dependence)
                                               (1979),  1.343  (no  MPG dependence)
     road  MPG adjustment  factor  is  the  inverse  of GPM  ratio.

-------
                                    -27-
                                   Table 15

             Two-mode Road Adjustment factors from the EEA Report
                       (Alternative Technology Vehicles)
A.   As presented in EEA report:
                       1-mode GPM ratios:
     Technology
     
-------
                                       -28-
          for good reason at  the time, EEA  excluded  certain 1978 models  from
          the 2-mode  road factor calculation for ?WD-Manu-Carb  vehicles;   EPA
          used all of the data.

          due to  sample  size considerations, EEA chose  not to  recommend  spe-
          cific two-mode factors for ^WD-Diesels;  although  somewhat  risky,  we
          did estimate them.

Before filling  the matrix of two-mode road  factors for  all of  the  technology
strata,  we  must  return  to  the  matter  of the MPG-dependent factors for  con-
ventional technologies (Table 14).  Since  the alternate  technology factors  are'
MPG  -  ^ndependent,  upward  aggregation of  all   technologies'  factors is  best
done in a constant-factor scenario,  as was done  in the one-mode analysis.

The  question for  the conventional  technologies  is:   what MPG values  should  be
selected  to  extract  constant  factors  from  the  equations?   The answer  chosen
for  this  report is  as follows.   (a)  given  a fleet  55/45 MPG level, estimate
the  fleet City  MPG  and Highway MPG using  reasonable  Highway to City, City  to
55/45,  and  Highway   to  55/45  MPG   ratios;    v'b)   assume   that  the   manual
transmission subfleet  will  have higher average  MPG  values  than the  automatic
transmission  subfleet,  as  has  been  the  case  historically;   (c)   select
reasonable MPG  ranges  for the  subfleets  consistent  with 'a) and  (b) and  use
them in the factor equations to determine  constant City and Highway factors.

Table 16 summarizes  this  process and its results.

To make  a conservative estimate* of che  range of  the two-mode GPM  ratios,  it
is assumed  that  a 20  MPG Automatic-RWD-Carb  subfleet has  with it  a  25  MPG
Manual-RWD-Carb subfleet, and a  25  MPG Automatic-RWD-Carb subfleet has with  it
a 30 MPG  Manual-RWD-Carb subfleet.   A consistent pairing  of GPM ratios would
be   RWD-Auto-Carb,   City,   1.100   and  RWD-Manu-Carb,   City,  0.996.   These
Lower-bound  values  are  the  ones that correspond to  the alternate  technology
GPM  ratios in  Table  15.   Thus,  for the  EEA data base,  an array of  constant,
technology-specific GPM ratios would be (next page):
*An assumption of  a  5 MPG difference  between  automatic and manual  subfleets'
EPA average is conservative compared to actuality:
                                             Auto MPG      Manual MPG

          EPA Emission "actors Survey          18.3           28.2

          1979 Models                          18.9           26.9

          1980 Models                          21.9           28.2

          1981 Models                          23.3           30.8

-------
                                       -29-


                                      City         Hwy

              RWD-Auto-Carb           1.10         1.36

              RWD-Manu-Carb           1.00         1.30

              FWD-Auto-Carb           0.92         1.15

              FWD-gas Fl              0.88         1.22

                  etc.

                  etc.

                  etc.
Projecting  the  conventional  technologies'  GPM ratio  growth  of 0.06 for  a  5
MPG  increase in  fleet  MPG  onto  the alternate  technologies  as  well,  GPM
ratios appropriate to cars in a higher MPG space might be:
                                      City         Hwy

              RWD-Auto-Carb           1.16         1.42

              RWD-Manu-Carb           1.06         1.36

              FWD-Auto-Carb           0.98         1.21

                  etc.

                  etc.

                  etc.
The  technology-specific  dual mode road MPG  adjustment  factors  ^the  inverse
of  che  above  GPM ratios)  can now  be specified,  and  also  collapsed  into
four-, two-, and one-strata  systems, sales-weighted, as was done  in Tables  7
and  8  for the single-mode  analysis.   The  resulting two-mode MPG  adjustment
factors are given in Table 17.

Histogram Tests of Dual-Mode Road Adjustment  Systems

As was done  in  the  Single-Mode analysis,  the effectiveness of  two-mode  road
adjustment was tested at  various  levels of technology aggregation, using  the
Emission /actors postcard  data base as the  test  subject.   These  tests  used
adjustment factors in the middle of the ranges given in  Table  17.

For  the   dual-mode  system,  there are  two  measures of  the  usefulness of
adjusted MPG values.  One  is  the  degree  to which the two numbers  accurately
represent their  respective types  of driving;   in  effect,  the  adjusted  City

-------
                                -30-
                              Table 16

       Estimation of Single Two-Mode Factors for Conventional Vehicles


A.  Reference MPG levels


         If EPA 55/45 MPG is:       20^        25^         30
    then EPA City MPG is (approx): 17.4        21.8         26.1
    and EPA Hwy MPG is  (approx):   24.4        30.5         36.6
                          c/
B.  Pooled road GPM ratios—  at the indicated MPG levels
RWD-Auto-Carb,

RWD-Manu-Carb,

City
Hwy
City
Hwy
1.100
1.364
—
—
1.165
1.421
0.996
1.305
__
—
1.065
1.365
—   Approximately equal to the Model Year 1979 U.S. fleet EPA average
    and approximately equal to the four data sources' EPA average.

—   Approximately equal to the Model Year 1981 U.S. fleet EPA average.
c/
—   Calculated from the equations in Table 14 and averaged.

-------
                                      -31-
                                    Table 17
                   Summary - Constant Road Factors,  Two Modes

                             /   B   Road MPG for driving type i.\
                             \• *•              EPA MPG<           i
No. Strata            Road c'aetors
ONE:          C .93-.98, H .73-.77

TWO         (a)  FWD C 1.01-1.08, H .78-.82      RWD C .88-.93,  H .71-.75
            (b)  Auto C .91-.96, H .73-.77       Manu C .98-1.04, H .73-.77
            ,'c)  Garb C .94-.98, H .73-.77       FI* C .97-1.03, H .73-.76

FOUR        (a)  RWD-Aut C .87-.92, H .70-.73    RWD-Man C .94-1.00,  H .73-.76
                 fWD-Aut C 1.02-1.09,  H .82-.86  FWD-Man C 1.00-1.07,  H  .74-.77

            (b)  RWD-Crb C .87-.92, H .71-.74    RWD-FI C .93-.98, H  .70-.73
                 FWD-Crb C 1.01-1.06,  H .78-.82  FWD-FI C 1.07-1.14,  H .78-.82

            v'c)  Aut-Crb C .90-.96, H .73-.77    Aut-FI C .96-1.02, H .72-.75
                 Man-Crb C .97-1.03,  H .73-.76   Man-Fl C 1.00-1.06,  H .75-.78

SEVEN       RWD-Aut-Crb C .86-.91, H  .70-.73      RWD-Man-Crb  C.94-1.00,H  .73-77
            RWD-FI  C .93-.98,  H .70-.73         FWD-gasFI C  1.07-1.14, H .78-.82
            FWD-Aut-Crb C 1.02-1.08,  H .82-.87   FWD-Man-Crb  C  .99-1.05,  H  .73-.76
            FWD-Dsl C 1.06-1.14, H .80-.84
*   FI means gasoline FI and Diesel pooled
    unless noted otherwise.

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                                       -32-
number La  tested as a  mode MPG  estimator  against the  in-use MPG of  city-
driven cars,  and  the   adjusted  Highway number  is  tested against  highway-
driving MPG.  The other measure  is  the fraction of the  total  MPG  population
captured between the two numbers  (also  of interest  is  the distribution  of
the MPG tails outside the inclusion range).

The results  of  the  first kind of test,  mode  MPG estimates, are typified  by
figures 3  through 6.   Figure  3  is  the City  histogram  for unadjusted  City
values, and  Figure  4 the corresponding  Highway  histogram.  figure 5 is  the
City histogram  for  che  first (unstratified) level of adjustment,  and  Figure
6 is the corresponding Highway histogram.

Table 18 summarizes  the mode estimate  histogram  test  for all levels  of  tech-
nology  stratification.    The need  to  adjust  the EPA  Highway  numbers  is
obvious.   There  is a slight  hint  that  increased  technology specificity  helps
the adjusted City number  to  become  increasingly  representative;  considering
that  the  adjustment factor  system comes  from  J.D.  Power data,  it is  en-
couraging  that  this test  on a  totally  different  data  base shows any  such
trend at all.

Figures 7 through 10 illustrate the range inclusion type of test.  Figures 7
and 8 compare all MPG experience  to the  unadjusted City  and Highway  numbers,
respectively, and Figures 9  and  10  give the same  type of  comparison against
fleet-adjusted  numbers.   The included range  is  easily  determined from  such
pairs of histograms:  those data which fall neither below  the  City value  nor
above  the  Highway value are, by definition,   included in  the  range between
the  two  numbers.   Table 19  summarizes  the   results  of  all  of  the   range
inclusion  tests.  When  viewed  in  the  range   inclusion  sense,  it is   again
clear  that  road adjustment  of  some kind  is  beneficial.   Again,  technology
specificity shows a weak tendency to improve representativeness.

-------
                                -33-


                              Figure  3

             Difference:  EPA City MPG  minus Road MPG
                          (City-driven  Cars)
MIDPOINT   HISTZ  COUNT

-13.000      0.       0 +
-12.000       .4     1 + X
-11.000      0.       0 +
-10.000      0.       0 +
-9.0000       .8     2 +XX
-8.0000      0.       0 +
-7.0000      1.6     4 + XXXX
-6.0000       .8     2 +XX
-5.0000      7.3    18 +XXXXXXXXXXXXXXXXXX
-4.0000      7.7    19 +XXXXXXXXXXXXXXXXXXX
-3.0000     14.2    35 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
-2.0000     19.1    47 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
-1.0000     17.9    44 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 0.          13.4    33 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 1.0000      6.9    17 +XXXXXXXXXXXXXXXXX
 2.0000      4.5    11 +XXXXXXXXXXX
 3.0000      2.8     7 +XXXXXXX
 4.0000       .8     2 +XX
 5.0000       .8     2 +XX
 6.0000       .4     1 +X
 7.0000       .4     1 +X
 8.0000      0.       0 +
 9.0000      0.       0 +
 10.000      0.       0 +

 TOTAL             246

-------
                   -34-

                  Figure  4
Difference: EPA Highway  MPG  minus Road MPG
            (Highway-driven  Cars)
  MIDPOINT   HISTZ  COUNT
-22.000
-21.000
-20.000
-19.000
-18.000
-17.000
-16.000
-15.000
-14.000
-13.000
-12.000
-11.000
-10.000
-9.0000
-8.0000
-7.0000
-6.0000
-5.0000
-4.0000
-3.0000
-2.0000
-1.0000
0.
1.0000
2.0000
0.
0.
1.7
1.7
0.
1.7
1.7
1.7
3.4
1.7
1.7
6.8
3.4
10.2
11.9
10.2
15.3
6.8
11.9
5.1
1.7
0.
0.
1.7
0.
0 +
0 +
1 + X
1 + X
0 +
1 + X
1 +X
1 -fX
2 + XX
1 +X
1 +X
4 + XXXX
2 +XX
6 +XXXXXX
7 +XXXXXXX
6 +XXXXXX
9 +XXXXXXXXX
4 +XXXX
7 +XXXXXXX
3 +XXX
1 +X
0 +
0 +
1 +X
0 *
 TOTAL

-------
                                  -35-

                                 Figure 5

           Difference: Adjusted EPA City MPG minus Road MPG
                        (City-driven Cars)
MIDPOINT   HI5T2  COUNT

-12.000      0.       0 +
-11.000      0.       0 *
-10.000       .4     1 +X
-9.0000      0.       0 +
-8.0000       .8     2 + XX
-7.0000      0.       0 +
-6.0000      1.2     3 + XXX
-5.0000      1.2     3 +XXX
-4.0000      8.1    20 +XXXXXXXXXXXXXXXXXXXX
-3.0000      7.3    18 +XXXXXXXXXXXXXXXXXX
-2.0000     16.3    40 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
-1.0000     20.7    51 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 0.          17.1    42 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 1.0000     12.2    30 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 2.0000      4.9    12 +XXXXXXXXXXXX
 3.0000      5.3    13 +XXXXXXXXXXXXX
 4.0000      2.0     5 +XXXXX
 5.0000       '.8     2 +XX
 6.0000      1.2     3 +XXX
 7.0000      0.       0 *
 8.0000       .4     1 +X
 9.0000      0.       0 +
 10.000      0.       0 *
 11.000      0.       0 +
 12.000      0.       0 +

 TOTAL             246

-------
                        -36-
                      Figure  6
Difference: Adjusted EPA Highway  MFC minus Road MPG
            (Highway-driven Cars)
       HIDPOINT   HISTZ  COUNT
-12.000
-11.000
-10.000
-9.0000
-8.0000
-7.0000
-4.0000
-5.0000
-4.0000
-3.0000
-2.0000
-1.0000
0.
1.0000
2.0000
3.0000
4.0000
5.0000
6.0000
7.0000
8.0000
9.0000
10.000
1 1 .000
12.000
0.
0.
0.
1.7
3.4
1.7
1.7
3.4
1.7
3.4
16.9
22.0
15.3
11.9
6.8
5.1
1.7
3.4
' 0.
0.
0.
0.
0.
0.
0.
0 +
0 +
0 +
1 + X
2 + XX
1 + X
1 +X
2 +XX
1 +X
2 + XX
10 +XXXXXXXXXX
13 mxxxxxxxxxxx
9 +XXXXXXXXX
7 +XXXXXXX
4 +XXXX
3 +XXX
1 +X
2 +XX
0 *
0 +
0 «•
0 *
0 +
0 +
0 +
        TOTfll              59

-------
                         -37-





                        Table IS




Results of Histogram Tests  of Two-Mode Adjustment Factors
Test Subject = Ends. Fac. Data Base
** Mode MPG Estimate **
Number of ~ Average
Strata Strata Adjusted MPG Error
1

1

2

2

2

4

4

4

7

No adjustment City
Hwy
Fleet adjustment City
Hwy
FWD/RWD City
Hwy
Auto/Manual City
Hwy
Carb/FI City
Hwy
R-A/R-M/F-A/F-M City
Hwy
R-C/R-FI/F-C/F-FI City
Hwy
A-C/A-FI/M-C/M-FI City
Hwy
Each technology City
Hwy
-1
-7
-0
-0
-0
^ ^
-0
-0
-0
-0
-0
-0
-0
-1
-0
-1
-0
-0
.6
.9
.7
.9
.2
.1
.6
.9
.8
.9
.1
.8
.1
.1
.1
.0
.1
.9
% of mode-specific experience
Below Within 2 MPG Above
33
97
19
17
14
24
18
17
19
17
13
24
13
27
18
17
14
20
62
3
71
73
75
63
74
73
71
73
79
64
76
61
74
73
77
68
5
0
10
10
11
14
8
10
9
10
8
12
11
12
8
10
9
12

-------
                                            -38-


                                          Figure  7

                         Difference:  EPA City MPG  minus Road MPG
                                      (All Cars)
DPOINT   HISTZ  COUNT

3.000      0.      0 +
2.000       .2     1 + X
1 .000      0.      0 +
0.000       .2     1 + X
.0000       .5     2 + XX
.0000       .7     3 +XXX
.0000      1.4     6 +XXXXXX
.0000       .7     3 +XXX
.0000      5.2    23 +XXXXXXXXXXXXXXXXXXXXXXX
.0000      5.7    25 +XXXXX-XXXXXXXXXXXXXXXXXXXX
.0000      9.3    41 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000     u.i    7i +xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxmxxxxxxxxxxxxxxxxxmxxxxxxxxxxxm
.0000     17.7    73 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXJUXXXXXXXXXX
          14.1    62 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000     10.0    44 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000      6.8    30 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000      4.5    20 +XXXXXXXXXXXXXXXXXXXX
.0000      2.5    11 +XXXXXXXXXXX
.0000      2.0     9 fXXXXXXXXX
.0000       .7     3 *XXX
.0000       .9     4 +XXXX
,0000      0.      0
.OCOO       .7     3 +XXX
).000      0.      0

iTAL             440

-------
                                       -39-
                                      Fignre 8

                    Difference: EPA  Highway MPG minus  Road MFC
                                (All Cars)
MIDPOINT   HISTZ  COUNT
-23.000
-22.000
-21 .000
-20.000
-19.000
-18.000
-17,000
-le.OOO
-15.000
-14.000
-13.000
-12.000
-11 .000
-10.000
-9.0000
-8.0000
-7.0000
-6.COOO
-5.0000
-4.0000
-3.0000
-2.0000
-1 .0000
0.
1 .0000
2.0000
0.
.2
.2
.5
.9
.9
.5
1 .1
1 .4
3.0
3.2
4.8
8.2
7.5
12.0
13.4
T3.0
10.7
8.9
5.2
2.3
1 .4
.?
0.
1
• *.
0.
0
1
1
o
i.
4
4
A.
5
6
13
14
21
36
33
53
59
57
47
39
23
10
6
3
0
1
0
                       + XX
                       + XXXX
                       + XXXX
                       + XX
                       +XXXXX
                       +XXXXXX
                       mxxxxxxxxxxx
                       +XXXXXXXXXXXXXX
                       +XXXXXXXXXXXXXXXXXXXXX
                       +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
                       'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
                       +xxxxxxxxxxxxxxxmxxxxxxxx'xxxxxxxxxxxmxxxxxmxxxxx
                       +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
                       uxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
                       +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
                       +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
                       *uxxxxmxxxxxxxxxxxxxx
                       +XXXXXXXXXX
                       +XXXXXX
                       + XXX
 TOTAL
440

-------
                                            -40-


                                          Figure  9

                     Difference:  Adjusted EPA City MPG minus  Road MPG
                                  (All Cars)
DPOINT   HISTZ  COUNT

2.000      0.      0 +
1 .000      0.      0 +
0.000       .2     1 + X
.0000      0.      0 +
.0000       .7     3 + XXX
.0000       .2     1 *X
.0000      1.4     6 +XXXXXX
.0000      1.1     5 +XXXXX
.0000      5.2    23 +XXXXXXXXXXXXXXXXXXXXXXX
.0000      5.9    26 +XXXXXXXXXXXXXXXXXXXXXXXXXX
.0000     10.7    47 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000     17.3    76 +XXXXXXXXXXXXXXXXXXXXX.XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
          17.0    75 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000     13.4    59 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000      9.3    41 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
.0000      7.0    31 +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX  •
.0000      3.2    M +XXXXXXXXXXXXXX
.0000      3.2    14 fXXXXXXXXXXXXXX
.0000      2.0     9 +XXXXXXXXX
.0000       .5     2 +XX
.0000       .5     2 +XX
.00,00       .5     2 +XX
;.ooo       .7     3 +xxx
;.000      o.       o +
2.000      0.       0 +

JTAL              440

-------
                                             -41-
                                           Figure 10

                     Difference: Adjusted EPA Highway MPG minus  Road MPG
                                 (All  Cars)
:HPOIN7    HISTZ   COUNT

 2.000       0.       0  +
 1.000        .5      2  tXX
 0.000        J      3  + XXX
'.0000        .7      3  +XXX
1.0000       1.1      5  +XXXXX
'.0000       2.3     10  +XXXXXXXXXX
,.0000       3.6     16  +XXXXXXXXXXXXXXXX
i.OOOO       8.4     37  tXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 .0000       8.2     36  +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.XXXX
 .0000      12.7     56  +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.XXXXXXXXXXXXXXXXXXXXXXXXX
 .0000      17.3     76  +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 .0000      17.3     76  fXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.XXXXXXXXXXXXXXXXXXXX
           10.7     47  +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 .0000       7.7     34  +XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 .0000       3.6     16  +XXXXXXXXXXXXXXXX
 .0000       2.0      9  +XXXXXXXXX
 .0000       1.4      6  +XXXXXX
 .0000       1 .4      6  +XXXXXX
 .0000        .5      2  +XX
 .0000       0.       0  +
 .0000       0.       0  +
 .0000       0.       0  +
 0.000       0.       0  *
 I.000       0.       0  *
 2.000       0.       0  +

 OTAL              440

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                         -42-






                       Table 19




Results of Histogram Tests of Two-Mode Adjustment Factors

Number of
Strata
1
1
2
2
2
4
4
4
7
** Range
Strata Adjusted
No adjustment
Fleet adjustment
FWD/RWD
Auto/Manual
Carb/FI
R-A/R-M/F-A/F-M
R-C/R-FI/F-C/F-FI
A-C/A-FI/M-C/M-FI
Each technology
Inclusion **
Z of all
Below Between
40
25
20
26
27
19 ••"• •-
*
19
25
19

MPG experience
C'-l and H'+l
60
66
70
65
65
69
71
66
69

Above
0
9
10
9
9
11
10
q
12

-------
III.       CONCLUSIONS

A.  The preferred general equation  for  analyzing  and expressing the relation
    between  Road MPG  (R)  and  EPA  MPG (E)  is an  MPG-dependent  fuel  con-
    sumption ratio;  (1/R) T (1/E) - a + b E;

    this is equivalent to:  E/R - a + b E;

    the general  expression  for road  adjustment factors to  multiply EPA MPG
    numbers by is:  £ - l/(a + b E);

    a  special  case of the  road  adjustment  factor,  wherein  there  is  no MPG
    dependence and therefore b - zero,  is:   f • I/a;

    a  road adjusted EPA MPG number (E') is:  E' • f x E.

B.  All  four data  sources  evaluated  herein agree  that  the  ETA- 55/45 MPG
    value overestimates average in-use  fuel  economy  in  the range -from 102 to
    20%.   A  road  adjustment  factor  between  0.8  and  0.9  is  therefore
    indicated.   (Road  factors  will be calculated to two  decimal places  in
    susbsequent  analyses.)

C.  In  single-mode  analyses,  there  is  a  consensus among  those  data sources
    which investigated vehicle technology stratification that:

           Front  wheel  drive (FWD)  cars  have  less  MPG shortfall  than  rear
           wheel  drive  (RFD)  cars,  for   carburetted,   automatic   or  manual
           transmission power trains;

           Diesel  powered  cars  have  less  MPG shortfall   than  carburetted
           gasoline cars, for RWD-automatic  transmission configurations;

    -      Manual transmission cars  have less MPG  shortfall  than automatics,
           for carburetted FWD and RWD power trains;

           Generally,  specific  vehicle technology strata  show a  worsening
           MPG shortfall as MPG level increases.

D.  Depending on the mix of technology  strata in a data base,  MPG dependence
    of  shortfall for  the  strata  may  be  obscured  when  the data base  is
    analyzed at  high levels of  aggregation;   however,  such obscuration  of
    MPG  dependence  via  high  aggregation  analysis  does  only  that:    it
    obscures it.  It does not make it cease to exist.

E.  Using emission factors data,  histograms  show  that 672 of in-use MPG ex-
    perience falls  more than  2  MPG below  the  EPA 55/45  MPG value;   how-
    ever—when  single-mode  road  adjustment  factors are  applied  to  these
    data,  more than  652  of  the population is accurately represented (within
    a window of + 2 MPG) by the adjusted 55/45 value.

F.  In  dual-mode analysis,  332  of  city  driving  MPG  experience falls  more
    than 2 MPG below the EPA City  value (702 of city-driven MPG  falls below

-------
                                  -44-
    the  City   value);    however,   road-adjusted   City  values   accurately
    represent more than 702 of the city driving population, within  a  ^ 2 MPG
    window;

    For highway driving, 97% of  in-use  MPG experience falls more than  2 MPG
    below  the  EPA Highway  value  (99.8Z  of it  falls  below  the  Highway
    value);   with road adjustment, more  than 60% of  the highway  driving MPG
    experience (+ 2 MPG) is accurately represented.

G.  At  the  fleet  level,  city  adjustment  factors   of   0.9   to   1.0  are
    indicated;  highway  factors  of 0.7  to O.S are indicated.   (Road  factors
    will be calculated to two decimal places in subsequent  analyses).

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                                   -45-
IV.       ISSUES  FOR FUTURE ANALYSES

Some  of  Che  issues which  surfaced  in  this  analysis  are  listed  below.
Section II described how  this  analysis dealt with  them,  but  future analysis
will reconsider  them carefully;   they  may  be  dealt  with differently in these
future analyses.

A.  Is  minimum acceptable sample  size for a  given stratum  to  be  fixed  by
    preordained  precision   and   confidence  level  specifications   and   an
    estimated  measure of  variance,  or are precision and  confidence  level  to
    be  outputs  of  a stratum  analysis, given  its  sample size  and  actual
    measure of variance?

B.  When aggregating  across  data  sources,  should  they  be equally  weighted  or
    sample-weighted,  i.e.,   is   the   analogy   of   the   widget   inspectors
    accurate?

C.  When  aggregating   technology-specific  road  factors  or  road  factor
    algorithms, what sales-weighting values should be used?

D.  Should data  from obsolescent vehicle technologies be discarded?

E.  What vehicle technologies can/should be pooled,  and what  criteria should
    determine  whether to pool  or not to  pool:   sample  size?   engineering
    argument?  similarity of shortfall behavior?

F.  Should pre-1979  models  of manual  transmission  vehicles whose  shortfall
    changed  significantly  in 1979 be  excluded from future  road  factor de-
    velopment  (che  premise  being that  shift  schedule  optimization  has been
    stopped),  or should they be  included CChe premise   being that the  return
    of shift schedule optimization cannot/will not be prevented)?

G.  What method  ("driving-mode  extremes" versus  "all  data")  should be used
    Co develop cwo-mode adjustment faccors?

H.  Will perceived MPG  daca  be  accepced as  chough  it  were measured,  thrown
    out because  it isn't, or can  it  be "corrected"  to  make it comparable  to
    measured MPG data?

I.  Is an analysis at the  model-cype  level  an appropriace one  Co employ?

-------