EPA-AA-SDSB  79-09
          An Analysis of Test Procedure Changes Made During
       1975-1979 With Respect to Measured Fuel Economy Effects
                             December 1978
Technical Reports do not  necessarily  represent  final  EPA  decisions
or positions.   They  are intended to present technical  analysis  of
issues using  data  which are currently  available.   The purpose  in
the release of  such reports  is  to  facilitate the  exchange of tech-
nical  information  and  to  inform  the  public of technical  develop-
ments which may form  the  basis for a final EPA decision,  position
or regulatory action.
              Standards Development and Support  Branch
                Emission Control Technology Division
            Office of Mobile Source Air Pollution Control
                 Office of Air, Noise and Radiation
                U.S. Environmental Protection Agency

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Introduction

     This paper presents an analysis of each of the changes in EPA
test procedure  since  1975  which  have  been identified  as potential
areas where it  may  be argued  that  changes in EPA regulations  have
resulted in  a decrease in measured  vehicle fuel economy.   These
areas are:

     A.    Changes  in the EPA  prediction  of the dynamometer power
absorption.

     B.    Changes  in allowable practices for  determining  and
requesting alternate dynamometer  power  absorptions.

     C.   Changes in the dynamometer  inertia simulation increments.

     D.   Changes  in allowed  alternate  shift  point schedules.

     E.   Changes in dynamometer  calibrations.

     F.   Changes in vehicle selection.

     G.   Changes in laboratory humidity levels.

     H.    Use  of   the  actual  simulated  distance traveled  by  the
vehicle versus the  nominal  test distance.

     I.    Changes  of  the  value used for  the density of CC^ in the
EPA calculations.

     In many  cases  these changes  were technical improvements which
increased  the  accuracy of the  test  procedure  or provided  for
improved fuel  economy recognition  of  technical  improvements.   In
other instances  these changes  were considered necessary to prevent
or restrict abuses  of various  aspects  of the EPA  fuel  economy
measurement procedures.   In  the  first  category,  these  changes
either  increased measured  fuel economy or had  no net directional
effect.  The  second type of change generally reduced measured  fuel
economy; however,  these  changes  were  introduced only  as  the  need
arose.   Consequently,  they  generally corrected abuses  which did not
exist  in  1975,  since there was  little pressure  for  fuel economy
improvements  in that model  year.  The  changes would not have
affected the  1975  results,  but were necessary  to  insure  that  the
results of  future  model years were  comparable  to those  of 1975.

     In general,  it  is  easy   to demonstrate  that under  specific
circumstances  a given vehicle might  show  a  degradation  in  fuel
economy between  the  1975  and  the 1979 model year test procedure.
Therefore,  if the true net  fuel economy difference between the test
procedures of  these  years  is  to  be  evaluated  the following ques-
tions must be asked:

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     Did the change have an effect  on all vehicles or what percent-
age of the total population of vehicles were  affected?

     Was  the  change systematic for  all vehicles  affected  or what
was the net effects of this change?

     Would the change have had an  effect on  the 1975 test results?

     What was the net effect of all changes?

     It is intended that this paper provide the background informa-
tion  and  the direction  for indepth  questioning  of  premises that
changes  in  EPA  regulations  since  1975 have  reduced  measured fuel
economies.

Analysis of the  Changes in EPA Procedures

     The  following  sections  address  each of  the previously identi-
fied changes  in  EPA test  procedures or  test  conditions.   In those
instances where  EPA Technical Support Reports, Analyses of Comments
in  response  to  NPRMs, or  other  supporting material  is available,
this material is provided as attachments or referenced.

     A.   Changes  in  the  EPA  Prediction of  the Dynamometer Power
          Absorption.

     For  the  1979  model  year, EPA  revised  the  equation  used  to
predict the  dynamometer  adjustment for LDV  testing.   The revision
replaced  the  existing table  based on the vehicle  inertia weight
with an equation primarily based  on the vehicle reference area, but
also  including  the effect  of vehicle protuberances  and tire type.

     This change was developed, at  least partially,  in response to
requests  by  the  automotive  industry for  a  change  in EPA practices
to  better represent the  fuel economy advantages of  radial tires
which  were  not  directly  reflected  in  the  twin  roll  dynamometer
tests.

     The potential effect of the change to the area based equation
can be seen  from the attached  plot.   This graph indicates that the
dynamometer  adjustments  obtained  by EPA were, on the  average,  in
good  agreement  with the existing  weight-based  table  for vehicles
with  bias or bias  belted  tires.   For vehicles  with radial ply
tires, the data  indicated that the  current table was approximately
8%  higher than  appropriate for a  median vehicle.   This  result  is
reflected in the  frontal  area  equation which  was subsequently
developed by regressing  these data against  frontal area data
supplied by the  vehicle manufacturers.

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     Approximately 80% of  the  1979  OEM tires were radials; there-
fore,  the majority  of all  light-duty vehicles  currently tested
would  be  expected  to have  slightly  lower  predicted  dynamometer
power  absorption  than  would  have occurred if  this  change  had not
been  made.   This effect  is estimated  to be  about 1.5  percent
increase  in  measured fuel economy  or  about  0.3 mpg for a 20 mpg
vehicle.

     The  previous analysis  assumes  that  the  vehicle  weight-area
relationships remain the same  as  observed  in 1975,  the model year
most  predominant  in the  EPA vehicle  sample  used to  develop the
reference area based prediction equation.  To some extent this has
changed,  since  some vehicle weight reductions may  have occurred
without reduction  in vehicle reference area.   To  the  extent that
this has  occurred,  a vehicle tested with a dynamometer adjustment
based on the reference area formula  might show  reduced fuel economy
compared with test  results using  the previous  weight based table.
However, since the area based  formula more accurately predicts the
aerodynamic   drag  of the  vehicle,  which  is  the predominant  force
simulated by the dynamometer, the use of this equation should more
accurately simulate  the road experience  of the vehicle.   That is,
the  previous weight-based  table  would have  provided a  larger
predicted fuel  economy  reward for changes  in  vehicle  weight,
without changes  in  vehicle reference area,  than would  have occur-
red in consumer  use of the vehicle.

     EPA  technical  support  reports  have  discussed the development
of the area-based equation in detail.(1,2)  This material was also
presented to the technical community in the form of an SAE paper.(3)
The  analysis of  comments received in response  to the proposed
change  from  the  weight-based  equation  is  also available  in the
public  docket.(4)    When   reviewing  these  comments,  it  should  be
noted that they  were received in response to  an  originally proposed
equation which was considerably more complex  and which, in general,
predicted higher  dynamometer power  absorptions.   As  a  result  of
these  comments  the  equation was revised  to  its  present  simpler
form.

     B.   Changes in  Allowable  Practices  for  Determining  and
          Requesting Alternate Dynamometer  Power Absorptions.

     EPA  has  always provided  the  option that  a  manufacturer may
request,  for specific  vehicles,  dynamometer  adjustments  which are
different from  the  values predicted by  EPA.   A  request  for such
alternate dynamometer  power  absorptions  must be supported  by road
test  data demonstrating  the appropriateness  of the request.   In
1975,  the regulations  implied  that  manifold  pressure measurements
were the required method of generating  acceptable road data.  Later
the manifold  pressure  approach was  deleted,  and  subsequently the

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coastdown technique has  become the prevalent method of  generating
supporting  data  for  alternate  dynamometer  power  absorption  re-
quests.  An acceptable coastdown procedure has  been  provided  to  the
industry as an  EPA Recommended  Practice which has been distributed
as an attachment to Advisory Circular 55.

     Advisory Circular 55 has been revised several times  to clarify
the requirements of similarity  between the road  test vehicles,  the
production vehicles represented and  the  exhaust emission certifi-
cation  vehicles.   Technical  changes have  also  been made  to  the
Recommended Practice to  improve precision and to make the standard
test conditions more representative of typical vehicle use.   While
many of the revisions  to AC-55 may appear  to  increase the resulting
dynamometer power  absorption slightly, these  changes  were  intro-
duced  to eliminate abuses which  became prevalent after  1975.

     In  general,  compared with the  practices  of 1975,   the  entire
area of alternate dynamometer  power absorption should  result  in
reduced  loadings of the  test vehicles.   This has occurred because
very few alternate dynamometer  adjustments were  requested in 1975,
while the use of  alternate  dynamometer power absorptions is  preva-
lent today.   Since  an  alternate dynamometer  power absorption  is
generally only requested when it is  beneficial  to the manufacturer,
much of  the current testing  is  conducted  at vehicle loadings  lower
than those which would have been used if the  same vehicles had been
tested  in 1975.   EPA is currently investigating in detail  the
average  dynamometer adjustments used in the 1979 model year  versus
the  inertia weight table values  of the  Federal Register  Code  of
Regulation prior to the 1979 model year.(5)

     Even for those vehicles  for  which  alternate dynamometer  power
absorptions were  requested  in 1975,  the  current test procedure  is
likely  to  yield slightly  lower values.    This  occurs  because  the
added  experience   and  precision  of  the  current  procedure   allows
correction to more ideal  standard conditions.  While these correc-
tions were not  prohibited in 1975,  the procedures  actually  in  use
were generally not this sophisticated.

     C.   Changes  in   Dynamometer  Inertia  Simulation  Increments.

     Beginning with the 1979 model year, EPA  reduced the  increments
of simulated inertia by approximately a factor  of two.  This  change
was made because  it was becoming apparent that manufacturers were
increasingly  tending  to  design vehicles  which  were  at  the  upper
bound of the older, larger inertia weight  increments.

     This decrease  in  the  inertia  weight increments  improves  the
precision of  the  emissions  and fuel economy measurements from  any
given test vehicle.  It will decrease the  fuel  economy results only

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if  the  vehicle  would otherwise have been tested at  a lower,  less
appropriate inertia weight  class.(6)

     When  the reduction of  the inertia  weight  increments  was
proposed, none of  the  manufacturers  argued  that  this change  would
have  reduced the  fuel economy  results of the  1975 model year.
Comments were received  that  this change would reduce  some of  the
fuel economy benefits that  had been anticipated from vehicle weight
reduction programs.   These comments supported EPA's  concern  that
vehicle down-sizing  programs  were directed  toward  the EPA inertia
weight  classes.    To the extent  that this  was  occurring,  EPA  mea-
surements would  have over-estimated  the fuel  economy benefits of
vehicle down-sizing  if  the intervals of simulated  inertia weights
were not reduced.

     The full record of the comments received in  response to  the
rulemaking which decreased  the inertia  weight  increments,  and  the
analysis  of  these comments  by  EPA can be found  in the public
docket.(7)

     D.   Changes  in Allowed Alternate  Shift  Point Schedules.

     In  1975, the  regulations provided  that  test vehicles  would
normally be shifted at 15,  25 and 40 mph.  In order to provide for
unusual vehicles  the regulations also  provided  for  the  option of
shifting the  vehicle at  the  shift points recommended  by  the  manu-
facturer.   During 1975 model year  testing, most vehicles were
shifted at the default,  15-25-40  shift points.

     On July  16, 1976,  the  default  shift points  were deleted  from
the regulations   and  the vehicles were  to be  shifted  according to
the manufacturer's  recommendation to the ultimate  purchaser.   EPA
soon  began  to receive  shift  point  requests  which  appeared to be
selected  primarily to  minimize emissions or  to maximize  fuel
economy.   For example,  different  requested  shift  speeds  for  hot
versus cold vehicle operation and generally very early shift points
for the EPA  Highway Cycle.   The shift  point  recommendations  pro-
vided by  the  manufacturers  to the  vehicle  consumer were  generally
not nearly as specific  as the shift point requests recieved by EPA,
but rather were  sufficiently  vague  to  encompass  the  requests  made
to EPA.

     EPA investigated this problem and  concluded that  many of  the
shift schedules  requested by  vehicle manufacturers were unrepresen-
tative  of typical vehicle  use.  This  investigation was docu-
mented in an EPA technical  report. (8)

     In order to insure more reasonable future shift  schedules  EPA
restricted acceptable  shift  schedules  with Advisory  Circular  No.
72.  This Advisory Circular provides that allowable

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may  be the  15-25-40 mph  schedule  originally  presented  in the
regulations,  a  shift  schedule  based  on  a  percentage  of maximum
recommended engine RPM which was developed in the attached report,
or  any other recommended shift  schedule  based  on typical vehicle
use data.

     At the present time virtually all manufacturers are using the
15-25-40 shift  points  schedule,  as was the  case in 1975.  Conse-
quently, the changes in allowed  shift  schedules eliminated an abuse
which  occurred primarily after 1975.   Consequently,  change in
allowable  shift  schedules can  account  for little or  no  syste-
matic  fuel  economy  degradation  between the 1975  and present model
years.

     E.   Changes in Dynamometer  Calibrations.

     In 1975, EPA used a manual method of  adjusting the dynamometer
power  absorption  prior  to  each   test.   In this  case a dynamometer
warm-up vehicle was used to  drive  the dynamometer at 50 mph while
the vehicle  operator  adjusted the  water level in the hydrokinetic
power  absorber,  by  means of  a  solenoid  valve,   until  the desired
torque reading was obtained.

     In May 1977, EPA changed to  an electronic feedback dynamometer
control system  which  eliminated  the  need  for manual adjustment of
the  dynamometer  prior to  each test.   This change reduced the
laboratory effort required  for each test and  reduced  test variabil-
ity .

     This change, if  independently made,  could have  resulted in a
change in the loading  experience  of the test  vehicles.  However, at
the same time  EPA altered  the dynamometer calibration procedures,
both  because  this was  required  to support  the  automatic control
features and to ensure that  the  change to  the automatic dynamometer
adjustment  would  not  result  in  a  net change in  the dynamometer
experience  of the test vehicle.   The most  significant change in the
calibration procedure  was  an allowance  for the  angular velocity
differences between the front  and  rear  dynamometer  rollers which
were  previously observed with  the dynamometer adjustment vehicle.

     The changes  in the operation  modes and the  dynamometer cali-
bration procedures have  been described in detail in the EPA com-
munications. (9)

     F.   Changes in Vehicle  Selections.

     It has been  suggested  that  changes  in  the  selection of test
vehicles may have  resulted  in a decrease  in the measured vehicle
fuel economy.  However, when attempting to research  this question,
few changes  could be  identified  in the vehicle  selection process.

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     The emission test vehicles are selected on a structured basis
which provides for several EPA selections of  "worst case" vehicles.
It  is possible  that  EPA  is currently  more  astute in the selection
of  "worst case"  vehicles; however,  this would not reflect  any
change in the procedure or the intent  of the  procedure.

     In addition  to  the  emission  test vehicles which are selected
by  EPA,  the manufacturer can  elect  to test  supplementary fuel
economy vehicles.   In  1975 the  fuel economy  program was voluntary,
and  the manufacturers  were consequently  given greater latitude in
the  selection  of these  optional  vehicles  and  in the use  of  the
resulting data  than  is presently  allowed.   Currently the optional
fuel economy vehicle  selections are constrained so that hopefully
the data from these vehicles  increases the accuracy with which the
EPA  sample  represents the  total  vehicle  population.   These con-
straints probably reduce  the  fuel economy  advantage  obtained by a
manufacturer for each optional test vehicle.   However, in 1975 few
optional  vehicles  were tested  compared with those  tested  in  the
1979 model year.  The  net  effect  these optional vehicle selections
have had on  the corporate average fuel economies between the 1975
and  1979 model years is difficult to accurately assess.  Certainly
the  two major  factors,  the  increase in the  number of optional
vehicles test data  in  the 1979  data base,  and the EPA constraints
on  the  selection of  these  vehicles tend  to  be compensatory.

     A vehicle selection process also  occurs  in the review of fuel
economy data  and  selection of  vehicles  for  confirmatory testing.
EPA  is currently conducting a greater number of confirmatory tests
than were  conducted  in 1975.   If  these results  are consistently
lower than those reported  by manufacturers, inclusion of these data
into  the  fuel  economy calculations  could reduce  the computed
corporate average fuel economy.   If this is  affecting fuel economy
results,  it is a more vigilant maintenance of unbiased results,  not
a change in the EPA procedure.
     G.   Changes in Laboratory Humidity Levels.

     In April 1976 EPA changed the  average  laboratory humidity from
approximately 55  grains  of water  per  pound of air  to  75 grains.
This change was made to reduce the magnitude of the effects of the
humidity correction factor in  the calculation of the NOx emissions.
Reducing the correction factor effect was desirable to improve the
accuracy of the determination  of vehicle NOx emissions.

     This  change  would,   in general,  be expected  to  decrease the
measured fuel economy of  a vehicle  since the combustible portion of
the incoming fuel-air charge would  be reduced and the vehicle would
tend toward enriched operation.  This is,  however, entirely depen-
dent on  the calibration  of  the vehicle.   For 1975  through  1978

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model  vehicles,  the  theoretically  anticipated  enrichment effect
would probably result  in  some  loss of fuel economy.  However,  for
1979  and later model year vehicles using  fuel system feedback
technology, this enrichment condition would be  sensed  and  compensa-
tion  would be made  in the fuel  delivery.   Therefore,  no  fuel
economy  degradation  would  be  anticipated  for current  or future
vehicles using sensor-feedback  technologies.   In fact, under some
conditions  the  increased  humidity might  benefit  fuel economy  and
exhaust  emissions  in  the  same  manner as exhaust gas  recirculation
can be  beneficial.  That  is,  a non-combustible diluent can reduce
engine  pumping  losses and  allow  optimization  of  the spark timing
without knock or excessive NOx  production.

     It  should also be  noted  that the higher test humidity condi-
tions were chosen as standard  conditions  well before 1975.  This  is
evident  since  the  NOx correction  factor  in  the  EPA exhaust emis-
sions calculations has used 75 grains of water per pound  of air  as
the standard  condition from very  early  in the  regulations.    The
only  change which  was made was  to make  the actual test  conditions
correspond  to  the  theoretical  standard conditions of the  calcula-
tions.   This change  was  made as  soon as the Ann Arbor  facility
could  consistently and accurately maintain the  higher  humidity.

     H.   Use  of   the  Actual  Simulated  Distance  Traveled  by   the
          Vehicle Versus the Nominal  Test Distance.

     In 1975 EPA calculated fuel  economy  based  on  the  nominal, that
is theoretical, distance of the  test  cycles.  This was done primar-
ily  for convenience  in  the  calculations  even though  the actual
simulated distance  traveled  by  the vehicle might be  slightly
different from this value.

     Deviation from the nominal value can occur  for two  reasons,
normal  allowable  driver fluctuations about  the  test speed versus
time  schedule  and  the  inability  of  the vehicle  to  maintain  the
speed called for by the test schedule. EPA investigated variations
in the  simulated distance  traveled in 1975 and concluded  that most
of the distance variations occurred because of  driver  fluctuations.
This  investigation  was presented  in  an  EPA technical report.(10)
The largest data base,  which  considered  the results of 170 repeat
tests on a  single  vehicle,  was  contributed by Ford Motor  Company.
These data indicated that  the  coefficient of variability  of repeat-
ed  fuel economy  measurements  would  diminish  by  about  30% (a  de-
crease  from approximately 3.6% to 2.4%)  when  the actual  distance
was used  in the  fuel  economy  calculations.  These same data indi-
cated this  change would result in  an  increase  in  the harmonic mean
fuel economy of 0.16%.

     It was concluded that  for most vehicles no significant effect

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on measured  fuel economy occurred when  the actual simulated dis-
tance was used in the fuel economy calculation.  Consequently, the
change  was  made  in  the fuel  economy calculation  to  reduce test
variability.   For some  underpowered vehicles which might  not  be
able to follow the EPA driving  schedules, some systematic decrease
in vehicle  fuel  economy  would result  from this change.   Few  of
these vehicles, however, were  present  in the 1975 test fleet.  If
such vehicles are becoming more prevalent it would be  illogical to
credit  these  vehicles with  greater  fuel economies  than actually
achieved because  of  an erroneous assumption  that  they traveled a
greater distance  than was actually  simulated  in the fuel economy
test.

     I.   Change of  the  Value  Used   for  the  Density  of CC^  in the
          EPA Calculations.

     On November 14,  1978 EPA changed the value  for the density of
C02  used  in  the  fuel economy  calculations  from 51.85  gm/ft3  to
51.81  gm/ft3.  This change was  made so that the value for the
density of  CO^ would be  the  same  in all EPA  calculations.   The
current value is considered  to  be  more accurate,  and it is believed
that the slight  discrepancy  from  the previous value may have been
the  result  of round-off error in  calculations of the original
density.

     This change  will have  a direct  systematic  effect  on  all EPA
light-duty vehicle fuel  economy calculations.   It will  increase the
measured fuel economy by slightly less than 0.08% or 0.015 mpg for
a 20 mpg  vehicle.   This effect  is  quite  small,  however,  it  is
significant  because  it   systematically  improves all  fuel  economy
measurements.

Conclusions

     It is concluded  that none  of  the identified  changes in the EPA
test procedures should result  in  a  net systematic decrease  in the
measured corporate fuel  economies.  The  one  possible exception, the
change  in  laboratory humidity, might  reduce the  fuel  economy  of
some vehicles  not using  the advanced  technologies  introduced  by
some manufacturers in 1979  and widely  anticipated  in  the 1980's.

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                             References
 1.   G.  D.  Thompson,  "Light-Duty Vehicle Road Load Determination" ,
     EPA Technical  Report LDTP-76-3, December 1976.

 2.   G.  D.  Thompson,  "Prediction of Dynamometer Power Absorption to
     Simulate  Light-Duty Vehicle Road Load" , EPA Technical Report,
     April  1977.

 3.   G.  D.  Thompson,  "Prediction of Dynamometer Power Absorption to
     Simulate  Light-Duty  Vehicle  Road Load",  Society of Automotive
     Engineers,  780617.

 4.   Analysis  of  Comments received in response to the September 10,
     1976 EPA NPRM regarding  fuel economy  and  emissions  testing.

 5.   J.  D.  Murrel,  Discussion.

 6.   T.  R. Norman,  T.  Rarick,  "The Effect  of  Dynamometer  Weight
     Simulation  on  Fuel Economy Measurements" , EPA Technical Report,
     February  1976.

 7.   Analysis  of  Comments op cit.

 8.   R.  A. Rykowski,  "Shift  Schedules  for Emissions and  Fuel
     Economy  Testing"  ,  EPA Technical  Report,  November  1977.

 9.   D.  Paulsell,   "Analysis  of  Ford Presentation  Regarding  Road
     Load Problems",  Memorandum  to Michael Walsh, August 28, 1978.

10.   T.  Rarick,  "Dynamometer Distance"*, EPA Technical Report, July
     1975.

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