EPA's Survey of In-Use Driving Patterns:        420R93901
PB94-118 502            Implications for Mobile Source Emission Inventories

                                 Phil Enns, John German, and Jim Markey
                                   U.S. Environmental Protection Agency
                              Office of Mobile Sources, Certification Division
                                2565 Plymouth Road, Ann Arbor, MI  48104

      ABSTRACT
         Preliminary data on in-use driving behavior and vehicle emissions are presented in this review of
      the Federal Test Procedure (FTP) Review Project. The driving  surveys suggest that certain in-use
      driving modes, such as high speeds and high accelerations, are not represented by the FTP. Also, in-
      use start driving behavior, trip length, and the distribution of  soak times all differ from their FTP
      representation. Through a limited vehicle emission test program,  EPA evaluated the emission
      impact of the above factors, as well as the emission impact of road grade and air conditioning.  In
      looking at the emission inventory implications of the test results, several pieces stand out.  Emissions
      for HC, CO, and NOx were all higher  for in-use driving relative to the  FTP; the  largest increase was
      in CO emissions.  Start driving and soak effects impacted NOx  and HC emissions.  Th?  use of air-
      conditioning had a large impact on NOx emissions, while road grade significantly elevated CO
      emissions.

      INTRODUCTION
         This paper presents EPA's preliminary findings on in-use  driving behav.'or and vehicle emissions.
      The data \veic collected as part of EPA's  Federal Test Procedure (FTP) Review Project.  EPA
      contracted for several large-scale studies of in-use driving patterns in ord"f to assess the  adequacy of
      the driving cycle ued in the current FTP.  While the principal focus of the CongressionalJy
      mandated pi eject was to evaluate the need for regulatory revisions, the  data and analyses are equally
      relevant to the understanding of mocor vehicle emission  inventories.  The- driving behavior
      characteristics co^red here  are: soak time, start driving, and  speed and acceleration net represented
      the current FTP.  Two additional factors, air conditioning  and road grade, are examined for their
      potential emission impact.
         Following this introduction, the paper  is divided into five  sections.  A brief review of the in-use
      driving surveys ajong with the key findings are presented  first. This is followed by a discussion of
      EPA's cycle development efforts.  The third section discusses the vehicle emission testing  program
      and the forth section presents an emission assessment based on  the results of  this test program. The
      last section summarizes the preliminary implications for current emission inventories.

      DRIVING SURVEYS
         With support from the American Automobile Manufacturers Association (AAM A)  and  the
      Association of International  Automobile Manufacturers (AIAM), EPA conducted surveys of driving
      behavior in Baltimore, MD, and Spokane, WA.  Two methods of data collection wf e employed.  In
      an instrumented vehicle study,  113 Baltimore and 102 Spokane vehicles were equipped with  "3
      parameter"  dataioggei packages that recorded second-by-secomi speed and iwo other variables daring
      7-10  dpyp  of vehicle operation.  As part of the same surveys,  the niarm.teclu'vrs rsrrultf-d 79  vehicles
      f ir study using "6-parameter" insTumciiis designed to me^/iure additional vgri^h'es.  A sc-ysrait chase
      car study collected similar speed data in the two cities u,ir':;g a laser device Lioiirted o/; u putiol ca:
      that tracked in-use target vehicles.  Compared to the instrumented vehicle approach, the chass car
      srjproach produced relatively short sequences of data, but  on  a much larger sample of vehicles.
         The Baltimore and Spokane surveys were supplemented by data collected in two other cities.
      FPYs Office of Research and Development sponsored an instrumented vehicle study in  Atlanta, GA.

                                            U.S. Environmental  Protection Agency
                                            Region  5, Library (PL-12J)
                                            77 West Jackson Boulevard, 12th Floor
                                            Chicago, IL  60604-3590

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Also, the California Air Resources Board (CARB) sponsored a chase car study in Los Angeles
similar to the chase car studies in Spokane and Baltimore.
    In May of this year,  EPA published the "Federal Test Procedure Review Project: Preliminary
Technical Report1."  This report presented a detailed discussion of the development of the driving
survey methods, data collection, and preliminary analyses of the driving survey data. For reasons
relating to representativeness, availability, and precision of the survey data, most of the  discussion in
the report and all discussion  in this paper are confined to driving observed in the Baltimore 3-
parameter instrumented vehicle study.  The key findings are discussed below.

Speed and Acceleration
    Speeds were much higher in Baltimore than are represented on the FTP.  The average speed in
Baltimore was 24.5 mph (median speed  was 23.7). The speeds observed ranged to almost 95 mph;
6.4% were above 60 mph and 2.6% above 65 mph.  By comparison, the FTP has an average speed
of 19.6 mph with a maximum of 56.7  mph.  About 8.5% of all speeds in Baltimore exceeded the
FTP maximum.
     Acceleration rates in Baltimore were also significantly higher than those on the FTP.  The
acceleration rates observed ranged up  to 15 mph/sec, with a standard deviation of  1.5.   The FTP has
a maximum acceleration rate of 3.3 mph/sec and a standard deviation of 1.4.  About 2.5% of all
driving in Baltimore exceeded 3.3 mph/sec.
    Power-related measures also indicate that the observed driving behavior  was more aggressive than
the FTP.  Specific power1 for the Baltimore sample ranged up to 558 mph2/sec and averaged 46.0,
with a median of 34.7. The FTP has  a maximum power  of 192, average of 38.6, and median of
21.6. An analysis was also done of the  scatter of speed-acceleration points  occurring in the
Baltimore sample outside the FTP envelope of speed and accelerations.   These points represent about
18% of total Baltimore driving time.
    Vehicle Age.  Newer vehicles (1983 and later) had higher average speeds than  older vehicles
(25.1 mph v. 21.2 mph), were driven  somewhat longer and farther per day,  and averaged fewer trips
and slightly fewer stops per  mile.  The data indicate that newer vehicles spend more time at high
speeds and are used for longer trips than older vehicles.  However, analyses of the aggressiveness of
the driving behavior, as measured by  acceleration and power distributions, indicate very little
difference between older and newer vehicles.
    Vehicle Type.  Speed distributions were fairly similar for each  of the three categories analyzed;
trucks, sedans, and high performance  vehicles.  However, high performance vehicles demonstrated
more aggressive driving behavior than the other classes, with over twice as  much operation at  power
levels above 200 mph2/sec.

Trip Patterns
    Average in-use trip lengths are much shorter than the FTP, which represents a 7.5 mile trip.  The
average observed tripb covered 4.9 miles.  The median value of trip distance indicates that "typical"
trips are even shorter, only 2.5 miles.  One of the in-use impacts of shorter trips is that a much
    aThe power needed from an engine to accelerate a vehicle is proportional to both the vehicle speed and the acceleration
 rate. Thus, neither variable, by itself, is a good measure of the load placed on the engine during acceleration. The joint
 distribution of speed and acceleration is the best measure, but it must be examined in three dimensions, which is difficult to
 visualize and  comprehend.  While not as good as the joint distribution of speed and acceleration, the best two-dimensional
 measure is "specific power," which is roughly equivalent to (2 * speed * acceleration). This measure has the units mph2/sec.

    ''For this analysis, a trip has been defined as beginning when the engine is turned on and ending when the engine is shut
 off (although engine off times of less than 18 seconds are ignored).

              'i

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higher proportion of overall driving is done within 0.67 mile of vehicle starts (12.0% v. 8.9% on the
FTP), prior to engines and catalysts reaching  normal operating temperatures.  The frequency of stops
on the FTP is also uncharacteristic of in-use trips; the average distance between stops on the FTP is
only 0.41  miles compared to 0.87 in Baltimore.  Despite these differences, the FTP and Baltimore
trips disagree only slightly  in the proportion of time spent in the four operating modes: idle, cruise,
acceleration, and deceleration.

Vehicle Soaks
   The in-use data contains a large proportion of intermediate soak periods (that is, the time between
the end  of a previous trip and the beginning of the next one) that are not reflected on the FTP.  The
FTP contains soak periods of 10 minutes and 12-36 hours; almost 40% of all soak periods in
Baltimore were between  10  minutes and 2 hours. As catalysts cool off much faster than engines and
most are almost completely cold in about 45-60  minutes, this is a potential emission concern.
Analyses indicate that only about 30% of all  in-use starts  occur with catalysts hot enough to be
immediately effective; the FTP implicitly assumes that 57% of all starts occur with hot catalysts.  On
the other hand, the FTP implicitly  assumes that 43% of all starts occur with cold engines, while less
than 25% of in-use starts occur with cold engines.

Trip Start Driving Activity
   While the  FTP has lower speeds and is less aggressive than in-use driving behavior, overall, the
reverse  occurs for the first few minutes after  a vehicle start.  The average observed speed during the
first  80  seconds of all trips (the initial idle period was not included in this period) was only 14.4
mph, compared to 23.1 mph for the first micro-trip  on the FTP.  The average in-use speed  81-240
seconds into the trip was 22.8 mph, compared to 29.8 for a comparable period on the FTP.  The
aggressiveness of the FTP was also off substantially, with the  first micro-trip on the FTP
substantially less  aggressive than in-use driving and the second FTP micro-trip much more
aggressive.

CYCLE DEVELOPMENT
   The next  step after the analysis of the driving patterns data was to assess the exhaust emissions
during such driving. This required reduction and synthesis of the driving data into "representative"
driving  cycles for use in vehicle testing.  EPA's approach to cycle development involved the
selection of actual segments of in-use driving which best matched the joint in-use distribution of
speed and acceleration.  The data set used in developing the in-use  cycles was the driving survey
data from Baltimore (discussed above) and the Los Angeles chase car data.   EPA felt cycles
targeted at different types of driving were necessary to capture the full range of in-use driving, given
the nonlinearity of emissions associated with certain driving behavior. In particular, a separate non-
FTP cycle was needed to properly characterize infrequent, high load events which occur in-use.

Cycle Methodology
   Under contract with EPA, Sierra Research developed a number  of driving cycles intended to
represent the range of in-use vehicle operation.  In generating a cycle, entire micro-trips (idle-to-idle)
were the basic building blocks used to match the "target surface" of the joint distribution of speed
and  acceleration.
   The cycle generation software  developed  for this task uses an iterative technique to find the
combination of microtrips which best match the target surface. The first step involves the  random
selection of a specified number of microtrips. Their speed-acceleration surface is computed and
compared to  the target surface.  The software then searches for the microtrip which provides the best
incremental fit to the target surface.  This micro-trip is then added to the cycle and the process is

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repeated until the desired cycle length is reached.  In this manner, a large number of cycles can be
generated  (several thousand) for the selection of the "best" cycle.  Final selection of the "best" cycle
is made by examining the differences between the speed-acceleration surface of each of the candidate
cycles and the target surface.
    Start cycle.  The start cycle (see figure 1, seconds  1-257) represents driving which occurs during
the  first four minutes after the start of the vehicle (excluding the initial idle). The driving
characteristics of start portion are important because of their potential impact on engine and catalyst
warm-up,  and  thus, emissions.  The cycle was developed by matching the in-use data set's joint
speed and acceleration distribution for 3 successive 80-second  segments of driving  after vehicle start.
    Non-FTP cycle. This cycle is intended to represent the distribution of speeds and accelerations
which are outside the boundary of the FTP.  However, using entire micro-trips as  the building
blocks makes it  impossible to create  a cycle which is exclusively non-FTP driving.  About 30% of
the  non-FTP cycle (figure 1) is actually FTP-like driving. In analyzing the emissions from this cycle,
the  cycle was  divided into a high speed portion (seconds 1-1182) and a high acceleration portion
(seconds 1183-1386)
    Remnant cycle. The remnant cycle was developed in order to have a set of cycles which
represent the full-range of in-use driving  (see figure 1, seconds 258-1494).   As the name suggests,
this cycle represents that portion of  in-use driving which is not represented by the non-FTP cycle or
the  start cycle.  As a result, much  of the  cycle is FTP-like driving, although there are segments of
non-FTP driving (low speed, high  acceleration) which were not represented by the non-FTP cycle.

VEHICLE  EMISSION TEST PROGRAM
    The objective of EPA's FTP Test Program was to assess the emissions from well-maintained,
current technology  vehicles over the in-use cycles.  Nine vehicles representing a range of vehicle and
engine types were selected for a limited test program.  Table 1 describes the eight  vehicles which
completed the program (one vehicle  was  lost due to malfunctions).  EPA's testing  was done in
coordination with test programs sponsored by AAMA/AIAM and the California Air Resources Board.
Both  test programs are in progress; the results from these programs will greatly enhance EPA's
limited testing.

Driving Behavior Testing
    Baseline FTP tests were run on each  vehicle to make sure  it complied with current emission
standards.  All of the in-use testing was designed to test the vehicle  in a hot,  stabilized condition; the
effect of cold  start  emissions was explicitly excluded for this portion of the test program. In addition
to the in-use cycles, bag 1 (505) and  bag  2 of the FTP driving  cycle  were tested in a hot, stabilized
condition for comparison purposes.  Bag emission data were collected, as well as one-second engine
parameters and catalyst temperatures.  A replicate test was run for each cycle.

Vehicle Soak and  Trip Start Driving Behavior Testing
    Unlike the other components of the testing program, this part specifically examined the impact of
soak  periods and start driving behavior on vehicle emissions.  A subset of 4 vehicles (the Crown
Victoria, Chevy Sonoma pickup, Dodge  Intrepid, and Saturn)  were tested using the new start cycle
after  a series of different soak times: 10 minutes, 20 minutes, 30 minutes, 45 minutes, 60 minutes,
90  minutes, 2 hours, and overnight.  For comparison, complete FTPs were conducted to establish 10
minute and  overnight soak emissions using the FTP driving cycle.  Also, to assess the potential
emission reductions from an intermediate soak emission standard, the above soak tests were repeated
on  each vehicle after insulating its catalyst. Bag emission data were collected, as  well as once-per-
second engine and catalyst temperatures.  A replicate test was run for each cycle.

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Air Conditioning and Road Grade Testing
   The objective of  both the air conditioning and road grade testing was to get a rough estimate of
the magnitude of their emission impact.  EPA lacked activity data on both factors, so we were
compelled to use "reasonable" simulations.  In the case of road grade,  the dynamometer load was
adjusted to simulate a constant 2% road grade throughout the entire test cycle.   The air conditioning
approach was simple and direct; the air conditioning was turned on  to maximum with maximum fan
setting.  The testing was done on the in-use cycles for a subset of vehicles:  the  Crown Victoria,
Saturn SL, and Honda Accord.

EMISSION ASSESSMENT

Driving Behavior
   Figure 2 presents a summary of the emission results for the 8 vehicles in the FTP test program.
The data are expressed in both grams per mile and grams per minute for comparison purposes. As
previously mentioned, all tests were run with the vehicle in a hot stabilized condition including  the
FTP driving cycles (505 and bag 2) . The highest grams per mile emissions  were found on  the high
acceleration portion of the non-FTP cycle. The  high speed portion  of the non-FTP cycle produced
high emissions on a grams per minute basis; however, due to the high average speed, the grams per
mile numbers were much lower.  This is an excellent example of the sensitivity of grams per mile
estimates to average speed.
   In order to assess the significance of the non-FTP emissions, proper weighting factors need  to be
applied.  The in-use and FTP cycles have explicit weights associated with their representation of in-
use vehicle operation. The weights are shown in table 2.
   As shown in figure 3, the weighted "in-use"  emissions are significantly higher than the  weighted
FTP emissions.  HC increased by 0.05 grams/mile, CO jumped by 2.6 grams/mile, and NOx rose by
0.06 grams/mile. The comparable grams per minute results showed  slightly larger percentage
increases for all 3 pollutants, a reflection of the  relatively high grams per minute emissions on the
high speed portion of the non-FTP cycle. (Note, the remainder of this paper will be limited to
reporting gram/mile results, as is conventional; the reader is encouraged to consider the alternative
grams per minute approach.)
    Figure 4 presents the in-use/ FTP comparison for each of the 8 vehicles tested.   While  one
shouldn't draw conclusions from a single vehicle's behavior, two points can be inferred from the  bar
charts.  First, the overall in-use increase in HC and CO emissions are fairly  consistent for   all the
vehicles tested.  However, the average NOx increase of .06 grams per mile can be attributed almost
exclusively to two vehicles:  the Ford Crown Victoria and Dodge Intrepid.  This high and variable
NOx emission response is not fully understood and requires further investigation.
   The increase in in-use emissions relative to the FTP cannot be credited to a single driving mode
or condition. In evaluating the relative significance  of the in-use components, their contribution to
the increase was calculated as:
                            (In-use component - FTP) * in-use component weighing factor

The total difference between in-use and FTP emissions is the sum of the weighted differences.
   Figure 5 shows each in-use component's contribution as a percent of the total increase.  The
results suggest that while "non-FTP" driving accounts for a large fraction of the increase (28% to
61%), the other in-use driving modes also make significant contributions, especially for HC and
NOx. Some of the observed emission increases were unexpected.  For example, substantial emission
increases for all three pollutants were observed on the Remnant cycle;  such  increases were  not
predicted given the Remnant cycle's similarity to the FTP in speed  and acceleration. One possible
explanation is that the emission increases are associated with the greater degree of speed variation

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found on the in-use cycles compared to the relatively "smooth" FTP cycle.  An analysis of jerk, the
second derivative of speed, should help to quantify this concept of speed variation.  EPA also plans
to examine the second-by-second emission data which are being collected in the auto manufacturers'
test program.

Vehicle Soaks and Trip Start Driving Behavior
    In order to calculate the in-use impact of soak periods, the frequency distribution of soak times
was used from the Baltimore data set.  In addition, the first  1.4 miles of driving on the new start
cycle was weighted by the  in-use proportion of start  driving, which is about 25% higher than the
implicit weighting of the first 1.4 miles on the FTP.  Figure 6 compares the in-use weighted
emissions over the first 3.6 miles of driving to the weighted bag I/bag 3 results from the FTP.  (The
test results are for only three of the four  vehicles tested, as the Sonoma pickup behaved erratically
during the test program).
    This comparison of in-use start emissions to  FTP start emissions is impacted by four different
factors:
    1)  Proportion of start driving.  As used here, this is the proportion of overall driving  that occurs
       within 1.4 miles of  the vehicle start,  which is 25% higher in-use than on the FTP.
    2)  Soak distributions.  There is a high proportion of "intermediate" soak periods (i.e.  between 10
       minutes and 2 hours) in-use that are not represented  on the FTP, with the result that  the FTP
       overestimates "cold" engine  starts and underestimates "cold" catalyst starts.  While these tend
       to be  offsetting factors, they could become significant under specific in-use conditions.
    3)  Start driving impact.  Compared to the FTP, the start driving cycle has lower speeds, is
       slightly more aggressive, and has substantially more  minor  speed variations. This  results in
       higher emissions, overall,  but the effect appears to be small and is hard to separate from the
       larger impacts due to vehicle soaks.
    4)  Effect of start driving behavior on engine and catalyst warm up.  The data indicates  slightly
       larger increases in emissions on the new  start cycle compared to the FTP after an overnight
       soak than  after a 10 minute  soak.  This means that the new start cycle may impact how the
       engine and catalyst  warm up, causing slightly increased emissions during the warm up period.
       However,  the effect appears to be small and is hard to separate from the large impact of
       overnight  soaks on vehicle emissions.
Of these four factors, the proportion of start driving  was clearly the most important on the three
vehicles tested.  EPA plans to conduct further soak/start testing to  better quantify the different factors
involved.
    Intermediate Soak Emission Reduction.  The current FTP incorporates only a 10 minute and an
overnight soak period.  Thus, manufacturers have had no incentive to reduce emissions  during starts
after intermediate soak periods (i.e. 10 minutes to 2  hours).  As engines  stay reasonably hot for
several hours after they are shut off but catalysts cool off relatively quickly, regulating vehicle
emissions after an intermediate soak period  may prove to  be feasible and cost-effective.  One
possible method to improve emissions would be to slow the rate of catalyst cooldown.  To
investigate the potential emission benefits from  such a strategy, EPA repeated the series of tests over
different soak periods  after insulating the catalyst. The results on  the three cars are presented in
Figure 7.  The average emission  reductions  on these three vehicles (two  of which included close-
coupled catalysts), weighted over all in-use  driving,  were 0.040 grams per mile HC, 0.2 CO, and
0.028 NOx.  While these reductions have no application to  existing emission inventories,  they may
apply to future emission inventories should  EPA establish intermediate soak  standards.

Air Conditioning and Road Grade
    The emission assessment for  road grade and air conditioning(A/C) was based on the emissions

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from the start, non-FTP, and remnant cycles weighted together. As for driving behavior analyses, all
emissions are for a fully warmed up vehicle.   For the three vehicles tested, figure 8 compares
baseline emissions (no A/C or road grade) to the results from the A/C and road grade simulations.
The effect of road grade was greatest for CO, with an average increase of 3.2 grams/mile. Nox
emissions also increased by 0.11 grams/mile; however, most of the increase can be attributed  to the
sharp increase for the Crown Victoria.  The  increase in HC was quite small for all vehicles..
   The results for air conditioning tests were less clear.  The impact on HC and  CO was very small
for the Crown Victoria and the Accord; on the other hand, the Saturn's CO emissions increased by
5.7 grams/mile.  Of greater concern is the large increase in NOx emissions exhibited by all three
vehicles with the A/C turned on.  The average NOx emissions increased by 0.21 grams/mile.  Like
road grade, the impact of A/C should be directly related to the increased load placed on the engine.
The A/C results suggest that additional factors are  involved which result in NOx emissions being
particularity sensitive to the  use of air conditioning.  EPA plans to conduct additional testing in order
to better understand the causes of the emission increases with air conditioning.

INVENTORY IMPLICATIONS

Test Result Implications
   The primary purpose of the driving surveys and emission testing described above was to evaluate
the need for regulatory revisions.  Much of the work, however, has  clear implications for mobile
source emission inventories.   The test  results suggest that emission estimates for  in-use driving
behavior are likely to be understated. Current approaches to estimating  start emissions are also likely
to underestimate in-use emission levels. Air conditioning and road grade both appear to result in
substantial emission increases.  Air-conditioning had the greatest impact on  NOx; for ozone non-
attainment areas this may be of great concern since air conditioning usage is likely to be greatest
during periods of peak ozone formation.   Road grade seems to be primarily a CO issue, which is
likely to be important to CO nonattainment areas which feature significant grades.
   Table  3 presents our preliminary estimate of the in-use impacts for these four  components. A
rough adjustment (test results were cut in half) was made to the upper end of the  road grade estimate
range in recognition that vehicles spend as much time going down as going up a grade.  In the case
of air conditioning,  the test results were reduced by 40 percent in an attempt to account for air
conditioning usage (in addition, the CO result is listed as a range starting from zero in recognition
that most  areas do not have  summertime CO exceedences). Both adjustments are admittedly crude
and future work is needed in developing activity factors.  Included at the bottom of the table is the
potential impact on future emission inventories associated with  the assumed adoption of intermediate
soak standards; such standards would actually cause a decrease in future inventories compared to
current inventory assessments.

Other Inventory Implications
   As the principal focus of this project is to evaluate the need for regulatory revisions to the FTP,
only modern technology, properly operating  vehicles that are representative of future vehicle
production have been tested.   In addition, because of work being done in other areas to improve the
evaporative emission test procedures, no evaporative emission testing was conducted.  Thus, there are
several in-use factors that were not included in EPA's test program that may also  significantly impact
emission inventories.
   Current Vehicle Fleet.  The emission impact on older vehicles in the current in-use vehicle fleet
is likely to be different than the test results presented from modern, properly operating vehicles.
Carburetors and, to a lessor extent,  single-point injection systems offer less precise fuel control than
the multi-point injection systems on all but two of the eight test vehicles.  It is likely that these older

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                                               8

fuel systems will have larger gram/mile increases during the higher speed, higher load, and more
variable cycles representative of in-use driving behavior.  On the other  hand, these older vehicles
also have higher emissions during normal operation and vehicle starts and tend to have a higher
incident of malfunctions; all of which raise the baseline emissions compared to modern,  multi-point
fuel injected vehicles. Thus, the emission impact on a percentage increase basis may be smaller for
older  vehicles, even though the grams/mile increase is likely to be larger.
   Evaporative Emissions.  One of the most significant findings of the instrumented vehicle driving
surveys is that in-use  trip lengths are much shorter and there are more trips per day than previously
thought.  This is likely due to stops taken for errands and short hops between stores.  These factors
may have a very large impact on hot soak evaporative emissions. The larger number of trips  results
in more hot soak evaporative events that the canister must absorb, and the short trips suggests that
the vehicle does not have as much time to purge the canister between events. This combination may
cause in-use hot soak emissions to be much higher than is currently modelled (as an aside,  it  should
be noted that this may also increase the cost and/or reduce the effectiveness of catalyst preheaters).
The high proportion of intermediate soaks,  instead of long soaks, and high number of trips  per day
may also impact diurnal  evaporative emissions and the relative distribution of hot soak and diurnal
emissions.
   In conclusion, results from of the FTP Review Project suggest a number of in-use driving modes
or factors which are not  adequately accounted for in current emission inventories. Further work,
focused exclusively on emission inventories, is needed to build on these early findings.

Positions and opinions advanced in this paper are those of the authors and not necessarily
those of the Environmental Protection Agency,
References

  1.    Federal Test Procedure Review Project: Preliminary Technical Report, EPA 420-R-93-007; U.S.
       Environmental Protection Agency, May 1993.

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Table 1.  Description of vehicles in FTP Test Program

Vehicle                  Displacement    Weight/Power       Fuel System
                         (Liters)          (ETW/Net HP)

1992 Ford Crown Victoria    4.6               21.05               MFI
1991 Honda Accord          2.2               27.00               MFI
1992 Dodge Dakota          5.2               17.39               MFI
1991 GMC Sonoma          2.8               27.00               TBI
1993 Dodge Intrepid         3.3               24.21               MFI
1993 Mercedes 400SEL      4.2               16.67               MFI
1992 VW Golf              1.8               27.50               MFI
1993 Saturn SL              1.9               32.35               TBI

MFI=multi-point fuel injection
TBI=throttle body injection
Table 2.  In-use weighting factors for hot, stabilized driving

                       Fraction of total distance   Fraction of total time
                              (grams/mile)           (grams/minute)
FTP
  Bag 1                          0.48                   0.368
  Bag 2                          0.52                   0.632

In-use
  Start                           0.24                   0.296
  Remnant                       0.48                   0.581
  Non-FTP high speed             0.264                  0.105
  Non-FTP high accel             0.016                  0.018

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Table 3. Preliminary estimates of emission inventory impact (grams/mile)

In-use driving
Soak/start effects
A/C operation
Road grade
Total

Intermediate soak
standards*
HC
0.05
0.05
0.02
0 - 0.02
0.12 - 0.14

(0.04)
CO
2.6
0.4
0- 1.4
0 - 1.6
3.0 - 6.0

(0.2)
NOx
0.06
0.10
0.12
0 - 0.06
0.28 - 0.34

(0.03)
*Potential reduction in future emission inventories associated with assumed adoption of intermediate
soak standards.

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Figure 1.  In-use driving  cycles
     60
     50
         Start = 0 to 257 seconds


         Remnant = 258 to 1494 seconds
                                               Start and remnant cycles
     40  -
   a.
     30
   CL
  DO
     20  I-
     10  >-
                                                    1
                                                                                 ,v
                 100    200    300    400    500    600   700   800   900   1000   1100   1200  1300  1400
                                                   Time (seconds)
   Q.


  O
   u
80  r

    |
70  1-


60  ;-


50


40


30


20


10
                                                   Non-FTP cycle
           0     100    200   300    400   500    600    700    800    900   1000   1100   1200   1300   1400
                                                   Time (seconds)

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Figure 2. Comparison of unweighted emissions from individual in-use and FTP driving cycles (hot stabilized)


                                                      HC
      045
      30
       0 4-
             505
            505
             505
 Bag2
Start
Remnant
High
accel
High spd
Bag2
Start
Remnant
                                                       NOx
 High
 accel
 High spd
Bag2
Start
Remnant
 High
 accel
High spd
                                          I grams/mile   E3 grams/minute
                                                                           0 14
                                                                                                      0.35

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Figure 3. Comparison of weighted emissions for in-use and FTP driving cycles (hot stabilized)
       0.300
   0)
   C 0.100
   (0

   O
      0.000
                      HC
NOx
CO
                                   0
                               FTP
 In-Use

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Figure 4. Comparison of weighted emissions for In-use and FTP driving cycles by vehicle (hot stabilized)
                                                  HC
       0.25
             Crown Vic  Accord
Dakota   Sonoma
Intrepid   Mercedes
           Benz
Golf
Saturn
                                                  CO
             Crown Vic   Accord     Dakota    Sonoma   Intrepid
                             Mercedes
                               Benz
                     Golf
         Saturn
                                                 NOx
            Crown Vic   Accord     Dakota   Sonoma    Intrepid
                            Mercedes
                              Benz
                     Golf
         Saturn
                                        FTP Cycle ii In-Use

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Figure 5.  In-use driving modes contribution to emission increase (percent of total increase)
                  HC
                                CO
             10%
         18%
            31%
41%
                          16%
                                                  45%
                                                                13%
                                     NOx
                                19%
                              23%
                                             37%
                                      21%
               Remnant   H Start       ^ High speed   High accel

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Figure 6. Comparison of soak and start emissions from FTP and in-use operation.
                                                   HC
                  Crown Vic
 Intrepid
 Saturn
Average
                                                  CO
    o>
                Crown Vic
Intrepid
Saturn
Average
                                                   NOx
                  Crown Vic
 Intrepid
 Saturn
 Average
                                              FTP
                   In-Use
Note:  Emissions are for the first 3.6 miles only (48% of all driving)

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Figure 7.  Comparison of soak and start emissions for insulated and uninsulated catalysts (in-use start cycle)
                                                     HC
    o>
                  Crown Vic
 Intrepid
 Saturn
Average
    0)
                                                    CO
                 Crown Vic
Intrepid
Saturn
Average
                                                     NOx
                  Crown Vic
 Intrepid
 Saturn
Average
                                         Uninsulated  H3 Insulated
Note: Emissions are for the first 1.4 miles (24% of all driving)

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Figure 8.  Summary of road grade and air conditioning emission impact (in-use driving cycles)
                                                 HC
                                                         Saturn
                                   Average
                                                 CO
    0)
    2
    o
                    Crown Vic
Accord
Saturn
Average
                                                 NOx
    o>
                                                         Saturn
                                   Average
                Baseline
 W/ A/C turned on  M W/ 2% road grade
                        U.S. Environmental Protection Agency
                        Region 5, Library (p|_- 12J)
                        77 West Jackson Boulevard, 12th Floor
                        Chicago, IL  60604-3590

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