w[cycle] = weighting factor for the appropriate test
cycle, as shown in Table 1 of this section.
m[cycle] = CO2 mass emissions over each test
cycle (other than idle).
D[cycle] = the total driving distance for the indicated
duty cycle. Use 2.842 miles for the transient cycle, and use 13.429
miles for both of the highway cruise cycles.
mi[cycle]-idle = CO2 emission rate at idle.

    Example: Class 7 vocational vehicle meeting the Phase 2
standards based on the Regional duty cycle.
PL = 5.6 tons
vmoving = 38.41 mi/hr
wtransient = 20% = 0.20
wdrive-idle = 0% = 0
wparked-idle = 25% = 0.25
w55 = 24% = 0.24
w65 = 56% = 0.56
mtransient = 4083 g
m55 = 13834 g
m65 = 17018 g
Dtransient = 2.8449 miles
D55 = 13.429 miles
D65 = 13.429 miles
midrive-idle = 4188 g/hr
miparked-idle = 3709 g/hr
[GRAPHIC] [TIFF OMITTED] TR25OC16.087

    (c) Weighting factors apply for each type of vehicle and for each
duty cycle as follows:
    (1) GEM applies weighting factors for specific types of tractors as
shown in Table 1 of this section.
    (2) GEM applies weighting factors for vocational vehicles as shown
in Table 1 of this section. Modeling for Phase 2 vocational vehicles
depends on characterizing vehicles by duty cycle to apply proper
weighting factors and average speed values. Select either Urban,
Regional, or Multi-Purpose as the most appropriate duty cycle for
modeling emission results with each vehicle configuration, as specified
in Sec. Sec.  1037.140 and 1037.150.
    (3) Table 1 follows:

                                              Table 1 of Sec.   1037.510--Weighting Factors for Duty Cycles
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                        Distance-weighted                       Time-weighted \1\              Average
                                                            --------------------------------------------------------------------------------    speed
                                                                            55 mi/hr      65 mi/hr                                           during non-
                                                              Transient      cruise        cruise      Drive idle  Parked idle    Non-idle   idle cycles
                                                                            (percent)     (percent)    (percent)    (percent)    (percent)   (mi/hr) \2\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Day Cabs...................................................           19            17            64  ...........  ...........  ...........  ...........
Sleeper Cabs...............................................            5             9            86  ...........  ...........  ...........  ...........
Heavy-haul tractors........................................           19            17            64  ...........  ...........  ...........  ...........
Vocational--Regional.......................................           20            24            56            0           25           75        38.41
Vocational--Multi-Purpose (2b-7)...........................           54            29            17           17           25           58        23.18
Vocational--Multi-Purpose (8)..............................           54            23            23           17           25           58        23.27
Vocational--Urban (2b-7)...................................           92             8             0           15           25           60        16.25
Vocational--Urban (8)......................................           90            10             0           15           25           60        16.51
Vocational with conventional powertrain (Phase 1 only).....           42            21            37  ...........  ...........  ...........  ...........
Vocational Hybrid Vehicles (Phase 1 only)..................           75             9            16  ...........  ...........  ...........  ...........
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Note that these drive idle and non-idle weighting factors do not reflect additional drive idle that occurs during the transient cycle. The transient
  cycle does not include any parked idle.
\2\ These values apply even for vehicles not following the specified speed traces.

    (d) For transient testing, compare actual second-by-second vehicle
speed with the speed specified in the test cycle and ensure any
differences are consistent with the criteria as specified in 40 CFR
1066.425. If the speeds do not

conform to these criteria, the test is not valid and must be repeated.
    (e) Run test cycles as specified in 40 CFR part 1066. For testing
vehicles equipped with cruise control over the highway cruise cycles,
use the vehicle's cruise control to control the vehicle speed. For
vehicles equipped with adjustable vehicle speed limiters, test the
vehicle with the vehicle speed limiter at its highest setting.
    (f) For Phase 1, test the vehicle using its adjusted loaded vehicle
weight, unless we determine this would be unrepresentative of in-use
operation as specified in 40 CFR 1065.10(c)(1).
    (g) For hybrid vehicles, correct for the net energy change of the
energy storage device as described in 40 CFR 1066.501.

Sec.  1037.515  Determining CO2 emissions to show compliance
for trailers.

    This section describes a compliance approach for trailers that is
consistent with the modeling for vocational vehicles and tractors
described in Sec.  1037.520, but is simplified consistent with the
smaller number of trailer parameters that affect CO2
emissions. Note that the calculated CO2 emission rate,
eCO2, is equivalent to the value that would result from
running GEM with the same input values.
    (a) Compliance equation. Calculate CO2 emissions for
demonstrating compliance with emission standards for each trailer
configuration.
    (1) Use the following equation:
    [GRAPHIC] [TIFF OMITTED] TR25OC16.088

Where:

Ci = constant values for calculating CO2
emissions from this regression equation derived from GEM, as shown
in Table 1 of this section. Let C5 = 0.988 for trailers
that have automatic tire inflation systems with all wheels, and let
C5 = 0.990 for trailers that have tire pressure
monitoring systems with all wheels (or a mix of the two systems);
otherwise, let C5 1.
TRRL = tire rolling resistance level as specified in paragraph (b)
of this section.
[Delta]CdA = the [Delta]CdA value for the
trailer as specified in paragraph (c) of this section.
WR = weight reduction as specified in paragraph (d) or (e) of this
section.

                Table 1 of Sec.   1037.515--Regression Coefficients for Calculating CO2 Emissions
----------------------------------------------------------------------------------------------------------------
                Trailer category                        C1              C2              C3              C4
----------------------------------------------------------------------------------------------------------------
Long dry box van................................            76.1            1.67           -5.82        -0.00103
Long refrigerated box van.......................            77.4            1.75           -5.78        -0.00103
Short dry box van...............................           117.8            1.78           -9.48        -0.00258
Short refrigerated box van......................           121.1            1.88           -9.36        -0.00264
----------------------------------------------------------------------------------------------------------------

    (2) The following is an example for calculating the mass of
CO2 emissions, eCO2, from a long dry box van that
has a tire pressure monitoring system for all wheels, an aluminum
suspension assembly, aluminum floor, and is designated as Bin IV:

C1 = 76.1
C2 = 1.67
TRRL = 4.6 kg/tonne
C3 = -5.82
[Delta]CdA = 0.7 m\2\
C4 = -0.00103
WR = 655 lbs
C5 = 0.990
eCO2 = (76.1 + 1.67 + (-5.82 [middot]0.7) + (-0.00103
[middot]655)) [middot]0.990
eCO2 = 78.24 g/ton-mile
    (b) Tire rolling resistance. Use the procedure specified in Sec.
1037.520(c) to determine the tire rolling resistance level for your
tires. Note that you may base tire rolling resistance levels on
measurements performed by tire manufacturers, as long as those
measurements meet this part's specifications.
    (c) Drag area. You may use [Delta]CdA values approved
under Sec.  1037.211 for device manufacturers if your trailers are
properly equipped with those devices. Determine [Delta]CdA
values for other trailers based on testing. Measure CdA and
determine [Delta]CdA values as described in Sec.
1037.526(a). You may use [Delta]CdA values from one trailer
configuration to represent any number of additional trailers based on
worst-case testing. This means that you may apply [Delta]CdA
values from your measurements to any trailer models of the same
category with drag area at or below that of the tested configuration.
For trailers in the short dry box vans and short refrigerated box vans
that are not 28 feet long, apply the [Delta]CdA value
established for a comparable 28-foot trailer model; you may use the
same devices designed for 28-foot trailers or you may adapt those
devices as appropriate for the different trailer length, consistent
with good engineering judgment. For example, 48-foot trailers may use
longer side skirts than the skirts that were tested with a 28-foot
trailer. Trailer and device manufacturers may seek preliminary approval
for these adaptations. Determine bin levels based on
[Delta]CdA test results as described in the following table:

  Table 2 of Sec.   1037.515--Bin Determinations for Trailers Based on
                        Aerodynamic Test Results
                          [[Delta]CdA in m\2\]
------------------------------------------------------------------------
                                                            and use the
    If a trailer's measured       designate the trailer      following
      [Delta]CdA is . . .                as . . .            value for
                                                            [Delta]CdA
------------------------------------------------------------------------
<=0.09.........................  Bin I..................             0.0
0.10-0.39......................  Bin II.................             0.1
0.40-0.69......................  Bin III................             0.4
0.70-0.99......................  Bin IV.................             0.7

1.00-1.39......................  Bin V..................             1.0
1.40-1.79......................  Bin VI.................             1.4
>1.80..........................  Bin VII................             1.8
------------------------------------------------------------------------

    (d) Weight reduction. Determine weight reduction for a trailer
configuration by summing all applicable values, as follows:
    (1) Determine weight reduction for using lightweight materials for
wheels as described in Sec.  1037.520(e).
    (2) Apply weight reductions for other components made with light-
weight materials as shown in the following table:

       Table 3 of Sec.   1037.515--Weight Reductions for Trailers
                                [pounds]
------------------------------------------------------------------------
                                                              Weight
           Component                     Material            reduction
                                                             (pounds)
------------------------------------------------------------------------
Structure for Suspension         Aluminum...............             280
 Assembly \1\.
Hub and Drum (per axle)........  Aluminum...............              80
Floor \2\......................  Aluminum...............             375
Floor \2\......................  Composite (wood and                 245
                                  plastic).
Floor Crossmembers \2\.........  Aluminum...............             250
Landing Gear...................  Aluminum...............              50
Rear Door......................  Aluminum...............             187
Rear Door Surround.............  Aluminum...............             150
Roof Bows......................  Aluminum...............             100
Side Posts.....................  Aluminum...............             300
Slider Box.....................  Aluminum...............             150
Upper Coupler Assembly.........  Aluminum...............             430
------------------------------------------------------------------------
\1\ For tandem-axle suspension sub-frames made of aluminum, apply a
  weight reduction of 280 pounds. Use good engineering judgment to
  estimate a weight reduction for using aluminum sub-frames with other
  axle configurations.
\2\ Calculate a smaller weight reduction for short trailers by
  multiplying the indicated values by 0.528 (28/53).

    (e) Off-cycle. You may apply the off-cycle provisions of Sec.
1037.610 to trailers as follows:
    (1) You may account for weight reduction based on measured values
instead of using paragraph (d) of this section. Quantify the weight
reduction by measuring the weight of a trailer in a certified
configuration and comparing it to the weight of an equivalent trailer
without weight-reduction technologies. This qualifies as A to B testing
under Sec.  1037.610. Use good engineering judgment to select an
equivalent trailer representing a baseline configuration. Use the
calculated weight reduction in Eq. 1037.515-1 to calculate the
trailer's CO2 emission rate.
    (2) If your off-cycle technology reduces emissions in a way that is
proportional to measured emissions as described in Sec.
1037.610(b)(1), multiply the trailer's CO2 emission rate by
the appropriate improvement factor.
    (3) If your off-cycle technology does not yield emission reductions
that are proportional to measured emissions, as described in Sec.
1037.610(b)(2), calculate an adjusted CO2 emission rate for
your trailers by subtracting the appropriate off-cycle credit.
    (4) Note that these off-cycle provisions do not apply for trailers
subject to design standards.

Sec.  1037.520  Modeling CO2 emissions to show compliance
for vocational vehicles and tractors.

    This section describes how to use the Greenhouse gas Emissions
Model (GEM) (incorporated by reference in Sec.  1037.810) to show
compliance with the CO2 standards of Sec. Sec.  1037.105 and
1037.106 for vocational vehicles and tractors. Use GEM version 2.0.1 to
demonstrate compliance with Phase 1 standards; use GEM Phase 2, Version
3.0 to demonstrate compliance with Phase 2 standards. Use good
engineering judgment when demonstrating compliance using GEM. See Sec.
1037.515 for calculation procedures for demonstrating compliance with
trailer standards.
    (a) General modeling provisions. To run GEM, enter all applicable
inputs as specified by the model.
    (1) GEM inputs apply for Phase 1 standards as follows:
    (i) Model year and regulatory subcategory (see Sec.  1037.230).
    (ii) Coefficient of aerodynamic drag or drag area, as described in
paragraph (b) of this section (tractors only).
    (iii) Steer and drive tire rolling resistance, as described in
paragraph (c) of this section.
    (iv) Vehicle speed limit, as described in paragraph (d) of this
section (tractors only).
    (v) Vehicle weight reduction, as described in paragraph (e) of this
section (tractors only for Phase 1).
    (vi) Automatic engine shutdown systems, as described in Sec.
1037.660 (only for Class 8 sleeper cabs). Enter a GEM input value of
5.0 g/ton-mile, or an adjusted value as specified in Sec.  1037.660.
    (2) For Phase 2 vehicles, the GEM inputs described in paragraphs
(a)(1)(i) through (v) of this section continue to apply. Note that the
provisions related to vehicle speed limiters and automatic engine
shutdown systems are available for vocational vehicles in Phase 2. The

rest of this section describes additional GEM inputs for demonstrating
compliance with Phase 2 standards. Simplified versions of GEM apply for
limited circumstances as follows:
    (i) You may use default engine fuel maps for glider kits as
described in Sec.  1037.635.
    (ii) If you certify vehicles to the custom-chassis standards
specified in Sec.  1037.105(h), run GEM by identifying the vehicle type
and entering ``NA'' instead of what would otherwise apply for, tire
revolutions per mile, engine information, transmission information,
drive axle ratio, axle efficiency, and aerodynamic improvement as
specified in paragraphs (c)(1), (f), (g)(1), (g)(3), (i), and (m) of
this section, respectively. Incorporate other GEM inputs as specified
in this section.
    (b) Coefficient of aerodynamic drag and drag area for tractors.
Determine the appropriate drag area, CdA, for tractors as
described in this paragraph (b). Use the recommended method or an
alternate method to establish a value for CdA expressed in
m\2\ to one decimal place, as specified in Sec.  1037.525. Where we
allow you to group multiple configurations together, measure
CdA of the worst-case configuration.
    (1) Except as specified in paragraph (b)(2) of this section,
determine the Phase 1 bin level for your vehicle based on measured
CdA values as shown in the following tables:CdA

                      Table 1 of Sec.   1037.520--Cd Inputs for Phase 1 High-Roof Tractors
----------------------------------------------------------------------------------------------------------------
                                                                                If your
                                                                                measured
                 Tractor type                              Bin level                [Delta]CdA     Then your Cd
                                                                                (m\2\) is . .  input is . . .
                                                                                .
----------------------------------------------------------------------------------------------------------------
High-Roof Day Cabs...........................  Bin I............................          >= 8.0            0.79
                                               Bin II...........................         7.1-7.9            0.72
                                               Bin III..........................         6.2-7.0            0.63
                                               Bin IV...........................         5.6-6.1            0.56
                                               Bin V............................          <= 5.5            0.51
High-Roof Sleeper Cabs.......................  Bin I............................          >= 7.6            0.75
                                               Bin II...........................         6.8-7.5            0.68
                                               Bin III..........................         6.3-6.7            0.60
                                               Bin IV...........................         5.6-6.2            0.52
                                               Bin V............................           <=5.5            0.47
----------------------------------------------------------------------------------------------------------------

                Table 2 of Sec.   1037.520--Cd Inputs for Phase 1 Low-Roof and Mid-Roof Tractors
----------------------------------------------------------------------------------------------------------------
                                                                                If your
                                                                                measured CdA    Then your Cd
                 Tractor type                              Bin level               (m\2\) is . .  input is . . .
                                                                                .
----------------------------------------------------------------------------------------------------------------
Low-Roof Day and Sleeper Cabs................  Bin I............................          >= 5.1            0.77
                                               Bin II...........................          <= 5.0            0.71
Mid-Roof Day and Sleeper Cabs................  Bin I............................          >= 5.6            0.87
                                               Bin II...........................          <= 5.5            0.82
----------------------------------------------------------------------------------------------------------------

    (2) For Phase 1 low- and mid-roof tractors, you may instead
determine your drag area bin based on the drag area bin of an
equivalent high-roof tractor. If the high-roof tractor is in Bin I or
Bin II, then you may assume your equivalent low- and mid-roof tractors
are in Bin I. If the high-roof tractor is in Bin III, Bin IV, or Bin V,
then you may assume your equivalent low- and mid-roof tractors are in
Bin II.
    (3) For Phase 2 tractors other than heavy-haul tractors, determine
bin levels and CdA inputs as follows:
    (i) Determine bin levels for high-roof tractors based on
aerodynamic test results as described in the following table:

                     Table 3 of Sec.   1037.520--Bin Determinations for Phase 2 High-Roof Tractors Based on Aerodynamic Test Results
                                                                      [CdA in m\2\]
--------------------------------------------------------------------------------------------------------------------------------------------------------
              Tractor type                     Bin I          Bin II          Bin III         Bin IV           Bin V          Bin VI          Bin VII
--------------------------------------------------------------------------------------------------------------------------------------------------------
Day Cabs................................           >=7.2         6.6-7.1         6.0-6.5         5.5-5.9         5.0-5.4         4.5-4.9           <=4.4
Sleeper Cabs............................           >=6.9         6.3-6.8         5.7-6.2         5.2-5.6         4.7-5.1         4.2-4.6           <=4.1
--------------------------------------------------------------------------------------------------------------------------------------------------------

    (ii) For low- and mid-roof tractors, you may either use the same
bin level that applies for an equivalent high-roof tractor as shown in
Table 3 of this section, or you may determine your bin level based on
aerodynamic test results as described in Table 4 of this section.

               Table 4 of Sec.   1037.520--Bin Determinations for Phase 2 Low-Roof and Mid-Roof Tractors Based on Aerodynamic Test Results
                                                                      [CdA in m\2\]
--------------------------------------------------------------------------------------------------------------------------------------------------------
              Tractor type                     Bin I          Bin II          Bin III         Bin IV           Bin V          Bin VI          Bin VII
--------------------------------------------------------------------------------------------------------------------------------------------------------
Low-Roof Cabs...........................           >=5.4         4.9-5.3        44.5-4.8         4.1-4.4         3.8-4.0         3.5-3.7           <=3.4
Mid-Roof Cabs...........................           >=5.9         5.5-5.8         5.1-5.4         4.7-5.0         4.4-4.6         4.1-4.3           <=4.0
--------------------------------------------------------------------------------------------------------------------------------------------------------

    (iii) Determine the CdA input according to the tractor's
bin level as described in the following table:

                                        Table 5 of Sec.   1037.520--Phase 2 CdA Tractor Inputs Based on Bin Level
--------------------------------------------------------------------------------------------------------------------------------------------------------
              Tractor type                     Bin I          Bin II          Bin III         Bin IV           Bin V          Bin VI          Bin VII
--------------------------------------------------------------------------------------------------------------------------------------------------------
High-Roof Day Cabs......................            7.45            6.85            6.25            5.70            5.20            4.70            4.20
High-Roof Sleeper Cabs..................            7.15             655            5.95            5.40            4.90            4.40            3.90
Low-Roof Cabs...........................            6.00            5.60            5.15            4.75            4.40            4.10            3.80
Mid-Roof Cabs...........................            7.00            6.65            6.25            5.85            5.50            5.20            4.90
--------------------------------------------------------------------------------------------------------------------------------------------------------

    (4) Note that, starting in model year 2027, GEM internally reduces
CdA for high-roof tractors by 0.3 m\2\ to simulate adding a
rear fairing to the standard trailer.
    (c) Tire revolutions per mile and rolling resistance. You must have
a tire revolutions per mile (TRPM) and a tire rolling resistance level
(TRRL) for each tire configuration. For purposes of this section, you
may consider tires with the same SKU number to be the same
configuration. Determine TRRL input values separately for drive and
steer tires; determine TRPM only for drive tires.
    (1) Use good engineering judgment to determine a tire's revolutions
per mile to the nearest whole number as specified in SAE J1025
(incorporated by reference in Sec.  1037.810). Note that for tire sizes
that you do not test, we will treat your analytically derived
revolutions per mile the same as test results, and we may perform our
own testing to verify your values. We may require you to test a sample
of additional tire sizes that we select.
    (2) Measure tire rolling resistance in kg per metric ton as
specified in ISO 28580 (incorporated by reference in Sec.  1037.810),
except as specified in this paragraph (c). Use good engineering
judgment to ensure that your test results are not biased low. You may
ask us to identify a reference test laboratory to which you may
correlate your test results. Prior to beginning the test procedure in
Section 7 of ISO 28580 for a new bias-ply tire, perform a break-in
procedure by running the tire at the specified test speed, load, and
pressure for 60  2 minutes.
    (3) For each tire design tested, measure rolling resistance of at
least three different tires of that specific design and size. Perform
the test at least once for each tire. Calculate the arithmetic mean of
these results to the nearest 0.1 kg/tonne and use this value or any
higher value as your GEM input for TRRL. You must test at least one
tire size for each tire model, and may use engineering analysis to
determine the rolling resistance of other tire sizes of that model.
Note that for tire sizes that you do not test, we will treat your
analytically derived rolling resistances the same as test results, and
we may perform our own testing to verify your values. We may require
you to test a small sub-sample of untested tire sizes that we select.
    (4) If you obtain your test results from the tire manufacturer or
another third party, you must obtain a signed statement from the party
supplying those test results to verify that tests were conducted
according to the requirements of this part. Such statements are deemed
to be submissions to EPA.
    (5) For tires marketed as light truck tires that have load ranges
C, D, or E, use as the GEM input TRRL multiplied by 0.87.
    (6) For vehicles with at least three drive axles or for vehicles
with more than three axles total, use good engineering judgment to
combine tire rolling resistance into three values (steer, drive 1, and
drive 2) for use in GEM. This may require performing a weighted average
of tire rolling resistance from multiple axles based on the typical
load on each axle.
    (7) For vehicles with a single rear axle, enter ``NA'' as the TRRL
value for drive axle 2.
    (d) Vehicle speed limit. If the vehicles will be equipped with a
vehicle speed limiter, input the maximum vehicle speed to which the
vehicle will be limited (in miles per hour rounded to the nearest 0.1
mile per hour) as specified in Sec.  1037.640. Use good engineering
judgment to ensure the limiter is tamper resistant. We may require you
to obtain preliminary approval for your designs.
    (e) Vehicle weight reduction. Develop a weight-reduction as a GEM
input as described in this paragraph (e). Enter the sum of weight
reductions as described in this paragraph (e), or enter zero if there
is no weight reduction. For purposes of this paragraph (e), high-
strength steel is steel with tensile strength at or above 350 MPa.
    (1) Vehicle weight reduction inputs for wheels are specified
relative to dual-wide tires with conventional steel wheels. For
purposes of this paragraph (e)(1), an aluminum alloy qualifies as
light-weight if a dual-wide drive wheel made from this material weighs
at least 21 pounds less than a comparable conventional steel wheel. The
inputs are listed in Table 6 of this section. For example, a tractor or
vocational vehicle with aluminum steer wheels and eight (4 x 2) dual-
wide aluminum drive wheels would have an input of 210 pounds (2 x 21 +
8 x 21).

       Table 6 of Sec.   1037.520--Wheel-Related Weight Reductions
------------------------------------------------------------------------
                                  Weight reduction--  Weight reduction--
   Weight-reduction technology      Phase 1 (lb per     Phase 2 (lb per
                                        wheel)              wheel)
------------------------------------------------------------------------
Wide-Base Single Drive Tire
 with: \1\
    Steel Wheel.................                  84                  84
    Aluminum Wheel..............                 139                 147
    Light-Weight Aluminum Alloy                  147                 147
     Wheel......................
Wide-Base Single Trailer Tire
 with: \1\
    Steel Wheel.................  ..................                  84
    Aluminum or Aluminum Alloy    ..................                 131
     Wheel......................
Steer Tire, Dual-wide Drive
 Tire, or Dual-wide Trailer Tire
 with:
    High-Strength Steel Wheel...                   8                   8
    Aluminum Wheel..............                  21                  25
    Light-Weight Aluminum Alloy                   30                  25
     Wheel......................
------------------------------------------------------------------------
\1\ The weight reduction for wide-base tires accounts for reduced tire
  weight relative to dual-wide tires.

    (2) Weight reduction inputs for tractor components other than
wheels are specified in the following table:

     Table 7 of Sec.   1037.520--Nonwheel-Related Weight Reductions From Alternative Materials for Tractors
                                                    [Pounds]
----------------------------------------------------------------------------------------------------------------
                                                                                High-strength
                  Weight reduction technologies                      Aluminum          steel       Thermoplastic
----------------------------------------------------------------------------------------------------------------
Door............................................................              20               6  ..............
Roof............................................................              60              18  ..............
Cab rear wall...................................................              49              16  ..............
Cab floor.......................................................              56              18  ..............
Hood Support Structure System...................................              15               3  ..............
Hood and Front Fender...........................................  ..............  ..............              65
Day Cab Roof Fairing............................................  ..............  ..............              18
Sleeper Cab Roof Fairing........................................              75              20              40
Aerodynamic Side Extender.......................................  ..............  ..............              10
Fairing Support Structure System................................              35               6  ..............
Instrument Panel Support Structure..............................               5               1  ..............
Brake Drums--Drive (set of 4)...................................             140              74  ..............
Brake Drums--Non Drive (set of 2)...............................              60              42  ..............
Frame Rails.....................................................             440              87  ..............
Crossmember--Cab................................................              15               5  ..............
Crossmember--Suspension.........................................              25               6  ..............
Crossmember--Non Suspension (3).................................              15               5  ..............
Fifth Wheel.....................................................             100              25  ..............
Radiator Support................................................              20               6  ..............
Fuel Tank Support Structure.....................................              40              12  ..............
Steps...........................................................              35               6  ..............
Bumper..........................................................              33              10  ..............
Shackles........................................................              10               3  ..............
Front Axle......................................................              60              15  ..............
Suspension Brackets, Hangers....................................             100              30  ..............
Transmission Case...............................................              50              12  ..............
Clutch Housing..................................................              40              10  ..............
Fairing Support Structure System................................              35               6  ..............
Drive Axle Hubs (set of 4)......................................              80              20  ..............
Non Drive Hubs (2)..............................................              40               5  ..............
Two-piece driveshaft............................................              20               5  ..............
Transmission/Clutch Shift Levers................................              20               4  ..............
----------------------------------------------------------------------------------------------------------------

    (3) Weight-reduction inputs for vocational-vehicle components other
than wheels are specified in the following table:

Table 8 of Sec.   1037.520--Nonwheel-Related Weight Reductions From Alternative Materials for Phase 2 Vocational
                                                    Vehicles
                                                    [Pounds]
----------------------------------------------------------------------------------------------------------------
                                                                                Vehicle type
               Component                        Material         -----------------------------------------------
                                                                     Light HDV      Medium HDV       Heavy HDV
----------------------------------------------------------------------------------------------------------------
Axle Hubs--Non-Drive..................  Aluminum................                40                            40
----------------------------------------------------------------------------------------------------------------
Axle Hubs--Non-Drive..................  High Strength Steel.....                 5                             5
Axle--Non-Drive.......................  Aluminum................                60                            60
Axle--Non-Drive.......................  High Strength Steel.....                15                            15
Brake Drums--Non-Drive................  Aluminum................                60                            60
Brake Drums--Non-Drive................  High Strength Steel.....                42                            42
Axle Hubs--Drive......................  Aluminum................                40                            80
Axle Hubs--Drive......................  High Strength Steel.....                10                            20
Brake Drums--Drive....................  Aluminum................                70                           140
Brake Drums--Drive....................  High Strength Steel.....                37                            74
Suspension Brackets, Hangers..........  Aluminum................                67                           100
----------------------------------------------------------------------------------------------------------------
Suspension Brackets, Hangers..........  High Strength Steel.....                20                            30
----------------------------------------------------------------------------------------------------------------
Crossmember--Cab......................  Aluminum................              10              15              15
Crossmember--Cab......................  High Strength Steel.....               2               5               5
Crossmember--Non-Suspension...........  Aluminum................              15              15              15
Crossmember--Non-Suspension...........  High Strength Steel.....               5               5               5
Crossmember--Suspension...............  Aluminum................              15              25              25
Crossmember--Suspension...............  High Strength Steel.....               6               6               6
Driveshaft............................  Aluminum................              12              40              50
Driveshaft............................  High Strength Steel.....               5              10              12
Frame Rails...........................  Aluminum................             120             300             440
Frame Rails...........................  High Strength Steel.....              40              40              87
----------------------------------------------------------------------------------------------------------------

    (4) Apply vehicle weight inputs for changing technology
configurations as follows:
    (i) For Class 8 tractors or for Class 8 vocational vehicles with a
permanent 6 x 2 axle configuration, apply a weight reduction input of
300 pounds. This does not apply for coach buses certified to custom-
chassis standards under Sec.  1037.105(h).
    (ii) For Class 8 tractors with 4 x 2 axle configuration, apply a
weight reduction input of 400 pounds.
    (iii) For tractors with installed engines with displacement below
14.0 liters, apply a weight reduction of 300 pounds.
    (iv) For tractors with single-piece driveshafts with a total length
greater than 86 inches, apply a weight reduction of 43 pounds for steel
driveshafts and 63 pounds for aluminum driveshafts.
    (5) You may ask to apply the off-cycle technology provisions of
Sec.  1037.610 for weight reductions not covered by this paragraph (e).
    (f) Engine characteristics. Enter information from the engine
manufacturer to describe the installed engine and its operating
parameters as described in 40 CFR 1036.510. The fuel-mapping
information must apply for the vehicle's GVWR; for example, if you
install a medium heavy-duty engine in a Class 8 vehicle, the engine
must have additional fuel-mapping information for the heavier vehicle.
Note that you do not need fuel consumption at idle for tractors.
    (g) Vehicle characteristics. Enter the following information to
describe and the vehicle and its operating parameters:
    (1) Transmission make, model, and type. Also identify the gear
ratio for every available forward gear to two decimal places, and
identify the lowest gear involving a locked torque converter, if
applicable. For vehicles with a manual transmission, GEM applies a 2%
emission increase relative to automated manual transmissions. If your
vehicle has a dual-clutch transmission, use good engineering judgment
to determine if it can be accurately represented in GEM as an automated
manual transmission. We may require you to perform a powertrain test
with dual-clutch transmissions to show that they can be properly
simulated as an automated manual transmission.
    (2) Drive axle configuration. Select a drive axle configuration to
represent your vehicle for modeling.
    (i) 4 x 2: One drive axle and one non-drive axle.
    (ii) 6 x 2: One drive axle and two non-drive axles.
    (iii) 6 x 4: Two or more drive axles, or more than three total
axles. Note that this includes, for example, a vehicle with two drive
axles out of four total axles (otherwise known as an 8x4
configuration).
    (iv) 6 x 4D: An axle that can automatically switch between 6 x 2
and 6 x 4 configuration. When the axle is in the 6 x 2 configuration
the input and output of the disconnectable axle must be mechanically
disconnected from the drive shaft and the wheels to qualify.
    (3) Drive axle ratio, ka. If a vehicle is designed with
two or more user-selectable axle ratios, use the drive axle ratio that
is expected to be engaged for the greatest driving distance. If the
vehicle does not have a drive axle, such as a hybrid vehicle with
direct electric drive, let ka = 1.
    (4) GEM inputs associated with powertrain testing include
powertrain family, transmission calibration identifier, test data from
Sec.  1037.550, and the powertrain test configuration (dynamometer
connected to transmission output or wheel hub). You do not need to
identify or provide inputs for transmission gear ratios, fuel map data,
or engine torque curves, which would otherwise be required under
paragraph (f) of this section.
    (h) Idle-reduction technologies. Identify whether your vehicle has
qualifying idle-reduction technologies, subject to the qualifying
criteria in Sec.  1037.660, as follows:
    (1) Stop-start technology and automatic engine shutdown systems

apply for vocational vehicles. See paragraph (j) of this section for
automatic engine shutdown systems for tractors.
    (2) Neutral idle applies for tractors and vocational vehicles.
    (i) Axle and transmission efficiency. You may use axle efficiency
maps as described in Sec.  1037.560 and transmission efficiency maps as
described in Sec.  1037.565 to replace the default values in GEM. If
you obtain your test results from the axle manufacturer, transmission
manufacturer, or another third party, you must obtain a signed
statement from the party supplying those test results to verify that
tests were conducted according to the requirements of this part. Such
statements are deemed to be submissions to EPA.
    (j) Additional reduction technologies. Enter input values in GEM as
follows to characterize the percentage CO2 emission
reduction corresponding to certain technologies and vehicle
configurations, or enter 0:
    (1) Intelligent controls. Enter 2 for tractors with predictive
cruise control. This includes any cruise control system that
incorporates satellite-based global-positioning data for controlling
operator demand. For other vehicles, enter 1.5 if they have neutral
coasting, unless good engineering judgment indicates that a lower
percentage should apply.
    (2) Accessory load. Enter the following values related to accessory
loads; if more than one item applies, enter the sum of those values:
    (i) If vocational vehicles have electrically powered pumps for
steering, enter 0.5 for vocational vehicles certified with the Regional
duty cycle, and enter 1 for tractors and other vocational vehicles.
    (ii) If tractors have electrically powered pumps for both steering
and engine cooling, enter 1.
    (iii) If vehicles have a high-efficiency air conditioning
compressor, enter 0.5 for tractors and vocational Heavy HDV, and enter
1 for other vocational vehicles. This includes mechanically powered
compressors meeting the specifications described in 40 CFR 86.1868-
12(h)(5), and all electrically powered compressors.
    (3) Tire-pressure systems. Enter 1.2 for vehicles with automatic
tire inflation systems on all axles (1.1 for Multi-Purpose and Urban
vocational vehicles). Enter 1.0 for vehicles with tire pressure
monitoring systems on all axles (0.9 for Multi-Purpose and Urban
vocational vehicles). If vehicles use a mix of the two systems, treat
them as having only tire pressure monitoring systems.
    (4) Extended-idle reduction. Enter values as shown in the following
table for sleeper cabs equipped with idle-reduction technology meeting
the requirements of Sec.  1037.660 that are designed to automatically
shut off the main engine after 300 seconds or less:

      Table 9 of Sec.   1037.520--GEM Input Values for AES Systems
------------------------------------------------------------------------
                                               GEM input values
             Technology              -----------------------------------
                                         Adjustable     Tamper-resistant
------------------------------------------------------------------------
Standard AES system.................                 1                 4
With diesel APU.....................                 3                 4
With battery APU....................                 5                 6
With automatic stop-start...........                 3                 3
Fuel-operated heater................                 2                 3
------------------------------------------------------------------------

    (5) Other. Additional GEM inputs may apply as follows:
    (i) Enter 1.7 and 0.9, respectively, for school buses and coach
buses that have at least seven available forward gears.
    (ii) If we approve off-cycle technology under Sec.  1037.610 in the
form of an improvement factor, enter the improvement factor expressed
as a percentage reduction in CO2 emissions. (Note: In the
case of approved off-cycle technologies whose benefit is quantified as
a g/ton-mile credit, apply the credit to the GEM result, not as a GEM
input value.)
    (k) Vehicles with hybrid power take-off. For vocational vehicles,
determine the delta PTO emission result of your engine and hybrid power
take-off system as described in Sec.  1037.540.
    (l) [Reserved]
    (m) Aerodynamic improvements for vocational vehicles. For
vocational vehicles certified using the Regional duty cycle, enter
[Delta]CdA values to account for using aerodynamic devices
as follows:
    (1) Enter 0.2 for vocational vehicles with an installed rear
fairing if the vehicle is at least 7 m long with a minimum frontal area
of 8 m\2\.
    (2) For vehicles at least 11 m long with a minimum frontal area of
9 m\2\, enter 0.5 if the vehicle has both skirts and a front fairing,
and enter 0.3 if it has only one of those devices.
    (3) You may determine input values for these or other technologies
based on aerodynamic measurements as described in Sec.  1037.527.
    (n) Alternate fuels. For fuels other than those identified in GEM,
perform the simulation by identifying the vehicle as being diesel-
fueled if the engine is subject to the compression-ignition standard,
or as being gasoline-fueled if the engine is subject to the spark-
ignition standards. Correct the engine or powertrain fuel map for mass-
specific net energy content as described in 40 CFR 1036.535(b).

Sec.  1037.525  Aerodynamic measurements for tractors.

    This section describes a methodology for quantifying aerodynamic
drag for use in determining input values for tractors as described in
Sec.  1037.520.
    (a) General provisions. The GEM input for a tractor's aerodynamic
performance is a Cd value for Phase 1 and a CdA
value for Phase 2. The input value is measured or calculated for a
tractor in a specific test configuration with a trailer, such as a
high-roof tractor with a box van meeting the requirements for the
standard trailer.
    (1) Aerodynamic measurements may involve any of several different
procedures. Measuring with different procedures introduces variability,
so we identify the coastdown method in Sec.  1037.528 as the primary
(or reference) procedure. You may use other procedures with our advance
approval as described in paragraph (d) of this section, but we require
that you adjust your test results from other test methods to correlate
with coastdown test results. All adjustments must be consistent with
good engineering judgment. Submit information describing how you
quantify aerodynamic drag from coastdown testing, whether or not you
use an alternate method.
    (2) Test high-roof tractors with a standard trailer as described in
Sec.  1037.501(g)(1). Note that the standard

trailer for Phase 1 tractors is different from that of later model
years. Note also that GEM may model a different configuration than the
test configuration, but accounts for this internally. Test low-roof and
mid-roof tractors without a trailer; however, you may test low-roof and
mid-roof tractors with a trailer to evaluate off-cycle technologies.
    (b) Adjustments to correlate with coastdown testing. Adjust
aerodynamic drag values from alternate methods to be equivalent to the
corresponding values from coastdown measurements as follows:
    (1) Determine the functional relationship between your alternate
method and coastdown testing. Unless good engineering judgment dictates
otherwise, assume that coastdown drag is proportional to drag measured
using alternate methods. This means you may apply a constant adjustment
factor, Falt-aero, for a given alternate drag measurement
method using the following equation, where the effective yaw angle,
[psi]eff, is assumed to be zero degrees for Phase 1 and is
determined from coastdown test results for Phase 2:
[GRAPHIC] [TIFF OMITTED] TR25OC16.089

    (2) Determine Falt-aero by performing coastdown testing
and applying your alternate method on the same vehicles. Consider all
applicable test data including data collected during selective
enforcement audits. Where you have test results from multiple vehicles
expected to have the same Falt-aero, you may either average
the Falt-aero values or select any greater value. Unless we
approve another vehicle, one vehicle must be a Class 8 high-roof
sleeper cab with a full aerodynamics package pulling a standard
trailer. Where you have more than one tractor model meeting these
criteria, use the tractor model with the highest projected sales. If
you do not have such a tractor model, you may use your most comparable
tractor model with our prior approval. In the case of alternate methods
other than those specified in this subpart, good engineering judgment
may require you to determine your adjustment factor based on results
from more than the specified minimum number of vehicles.
    (3) Measure the drag area using your alternate method for a Phase 2
tractor used to determine Falt-aero with testing at yaw
angles of 0[deg], 1[deg], 3[deg], 4.5[deg], 6[deg], and 9[deg] (you may
include additional angles), using direction conventions described in
Figure 2 of SAE J1252 (incorporated by reference in Sec.  1037.810).
Also, determine the drag area at the coastdown effective yaw angle,
CdAeffective-yaw-alt, by taking the average drag
area at [psi]eff and -[psi]eff for your vehicle
using the same alternate method.
    (4) For Phase 2 testing, determine separate values of
Falt-aero for a minimum of one high-roof day cab and one
high-roof sleeper cab for 2021, 2024, and 2027 model years based on
testing as described in paragraph (b)(2) of this section (six tests
total). For any untested tractor models, apply the value of
Falt-aero from the tested tractor model that best represents
the aerodynamic characteristics of the untested tractor model,
consistent with good engineering judgment. Testing under this paragraph
(b)(4) continues to be valid for later model years until you change the
tractor model in a way that causes the test results to no longer
represent production vehicles. You must also determine unique values of
Falt-aero for low-roof and mid-roof tractors if you
determine CdA values based on low or mid-roof tractor
testing as shown in Table 4 of Sec.  1037.520. For Phase 1 testing, if
good engineering judgment allows it, you may calculate a single,
constant value of Falt-aero for your whole product line by
dividing the coastdown drag area, CdAcoastdown,
by CdAalt.
    (5) Determine Falt-aero to at least three decimal
places. For example, if your coastdown testing results in a drag area
of 6.430, but your wind tunnel method results in a drag area of 6.200,
Falt-aero would be 1.037 (or a higher value you declare).
    (6) If a tractor and trailer cannot be configured to meet the gap
requirements, test with the trailer positioned as close as possible to
the specified gap dimension and use good engineering judgment to
correct the results to be equivalent to a test configuration meeting
the specified gap dimension.
    (c) Yaw sweep corrections. Aerodynamic features can have a
different effectiveness for reducing wind-averaged drag than is
predicted by zero-yaw drag. The following procedures describe how to
determine a tractor's CdA values to account for wind-
averaged drag and differences from coastdown testing:
    (1) For Phase 2 testing with an alternate method, apply the
following method using your alternate method for aerodynamic testing:
    (i) For all testing, calculate the wind-averaged drag area from the
alternate method, CdAwa-alt, using an average of
measurements at -4.5 and +4.5 degrees.
    (ii) Determine your wind-averaged drag area,
CdAwa, rounded to one decimal place, using the
following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.090

    (2) For Phase 2 coastdown test results, apply the following method:
    (i) For all coastdown testing, determine your effective yaw angle
from coastdown, CdAeffective-yaw-coastdown.
    (ii) Use an alternate method to calculate the ratio of the wind-
averaged drag area (using an average of measurements at -4.5 and +4.5
degrees, CdAwa-alt) to the drag area at the
effective yaw angle, CdAeffective-yaw.
    (iii) Determine your wind-averaged drag area,
CdAwa, rounded to one decimal place, using the
following equation:

[GRAPHIC] [TIFF OMITTED] TR25OC16.091

    (3) Different approximations apply for Phase 1. For Phase 1
testing, you may correct your zero-yaw drag area as follows if the
ratio of the zero-yaw drag area divided by yaw-sweep drag area for your
vehicle is greater than 0.8065 (which represents the ratio expected for
a typical Class 8 high-roof sleeper cab):
    (i) Determine the zero-yaw drag area,
CdAzero-yaw, and the yaw-sweep drag area for your
vehicle using the same alternate method as specified in this subpart.
Measure the drag area for 0[deg], -6[deg], and +6[deg]. Use the
arithmetic mean of the -6[deg] and +6[deg] drag areas as the 6[deg] drag area, CdA6.
    (ii) Calculate your yaw-sweep correction factor, CFys,
using the following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.092

    (iii) Calculate your corrected drag area for determining the
aerodynamic bin by multiplying the measured zero-yaw drag area by
CFys, as determined using Eq. 1037.525-4, as applicable. You
may apply the correction factor to drag areas measured using other
procedures. For example, apply CFys to drag areas measured
using the coastdown method. If you use an alternate method, apply an
alternate correction, Falt-aero, and calculate the final
drag area using the following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.093

    (iv) You may ask us to apply CFys to similar vehicles
incorporating the same design features.
    (v) As an alternative, you may calculate the wind-averaged drag
area according to SAE J1252 (incorporated by reference in Sec.
1037.810) and substitute this value into Eq. 1037.525-4 for the 6[deg] drag area.
    (d) Approval of alternate methods. You must obtain preliminary
approval before using any method other than coastdown testing to
quantify aerodynamic drag. We will approve your request if you show
that your procedures produce data that are the same as or better than
coastdown testing with respect to repeatability and unbiased
correlation. Note that the correlation is not considered to be biased
if there is a bias before correction, but you remove the bias using
Falt-aero. Send your request for approval to the Designated
Compliance Officer. Keep records of the information specified in this
paragraph (d). Unless we specify otherwise, include this information
with your request. You must provide any information we require to
evaluate whether you may apply the provisions of this section. Include
additional information related to your alternate method as described in
Sec. Sec.  1037.530 through 1037.534. If you use a method other than
those specified in this subpart, include all the following information,
as applicable:
    (1) Official name/title of the procedure.
    (2) Description of the procedure.
    (3) Cited sources for any standardized procedures that the method
is based on.
    (4) Description and rationale for any modifications/deviations from
the standardized procedures.
    (5) Data comparing the procedure to the coastdown reference
procedure.
    (6) Additional information specified for the alternate methods
described in Sec. Sec.  1037.530 through 1037.534 as applicable to this
method (e.g., source location/address, background/history).

Sec.  1037.526  Aerodynamic measurements for trailers.

    This section describes a methodology for determining aerodynamic
drag area, CdA for use in determining input values for box
vans as described in Sec. Sec.  1037.515 and 1037.520.
    (a) A trailer's aerodynamic performance for demonstrating
compliance with standards is based on a [Delta]CdA value
relative to a baseline trailer. Determine these [Delta]CdA
values by performing A to B testing, as follows:
    (1) Determine a baseline CdA value for a standard
tractor pulling a test trailer representing a production configuration;
use a 53-foot test trailer to represent long trailers and a 28-foot
test trailer to represent short trailers. Repeat this testing with the
same tractor and the applicable baseline trailer. For testing long
trailers, the baseline trailer is a trailer meeting the specifications
for a Phase 1 standard trailer in Sec.  1037.501(g)(1); for testing
refrigerated box vans, use a baseline trailer with an installed HVAC
unit that properly represents a baseline configuration correlated with
the production configuration. For testing short trailers, use a 28-foot
baseline trailer with a single axle that meets the same specifications
as the Phase 1 standard trailer, except as needed to accommodate the
reduced trailer length.
    (2) Use good engineering judgment to perform paired tests that
accurately demonstrate the reduction in aerodynamic drag associated
with the improved design. For example, the gap dimension should be the
same for all paired tests, and effective yaw angle

between paired tests should differ by no more than 1.0[deg].
    (3) Measure CdA in m\2\ to two decimal places. Calculate
[Delta]CdA by subtracting the drag area for the test trailer
from the drag area for the baseline trailer.
    (b) The default method for measuring is the wind-tunnel procedure
as specified in Sec.  1037.530. You may test using alternate methods as
follows:
    (1) If we approve it in advance, you may instead use one of the
alternate methods specified in Sec. Sec.  1037.528 through 1037.532,
consistent with good engineering judgment, which may require that you
adjust your test results from the alternate test method to correlate
with the primary method. If you request our approval to determine
[Delta]CdA using an alternate method, you must submit
additional information as described in paragraph (d) of this section.
    (2) The principles of 40 CFR 1065.10(c)(1) apply for aerodynamic
test methods. Specifically, we may require that you use coastdown
measurements if we determine that certain technologies are not suited
to evaluation with wind-tunnel testing or CFD, such as nonrigid
materials whose physical characteristics change in scaled-model
testing. You may similarly reference 40 CFR 1065.10(c)(1) in your
request to use coastdown testing as an alternate method.
    (c) The following provisions apply for combining multiple devices
under this section for the purpose of certifying trailers:
    (1) If the device manufacturer establishes a [Delta]CdA
value in a single test with multiple aerodynamic devices installed,
trailer manufacturers may use that [Delta]CdA value directly
for the same combination of aerodynamic devices installed on production
trailers.
    (2) Trailer manufacturers may combine [Delta]CdA values
for aerodynamic devices that are not tested together, as long as each
device does not significantly impair the effectiveness of another,
consistent with good engineering judgment. To approximate the overall
benefit of multiple devices, calculate a composite
[Delta]CdA value for multiple aerodynamic devices by
applying the full [Delta]CdA value for the device with the
greatest aerodynamic improvement, adding the second-highest
[Delta]CdA value multiplied by 0.9, and adding any other
[Delta]CdA values multiplied by 0.8.
    (d) You must send us a description of your plan to perform testing
under this section before you start testing. We will evaluate whether
plans for wind-tunnel testing meet the specifications of Sec.
1037.530, and will tell you if you may or must use any other method to
determine drag coefficients. We will approve your request to use an
alternate method if you show that your procedures produce data that are
the same as or better than wind-tunnel testing with respect to
repeatability and unbiased correlation. Note that the correlation is
not considered to be biased if there is a bias before correction, but
you apply a correction to remove the bias. Send your testing plan to
the Designated Compliance Officer. Keep records of the information
specified in this paragraph (d). Unless we specify otherwise, include
this information with your request. You must provide any information we
require to evaluate whether you may apply the provisions of this
section. Include additional information related to your alternate
method as described in Sec. Sec.  1037.528 through 1037.534.

Sec.  1037.527  Aerodynamic measurements for vocational vehicles.

    This section describes a methodology for determining aerodynamic
drag area, CdA, for use in determining input values for
vocational vehicles as described in Sec.  1037.520. This measurement is
optional.
    (a) Determine [Delta]CdA values by performing A to B
testing as described for trailers in Sec.  1037.526, with any
appropriate adjustments, consistent with good engineering judgment.
    (b) [Reserved]

Sec.  1037.528  Coastdown procedures for calculating drag area (CdA).

    The coastdown procedures in this section describe how to calculate
drag area, CdA, for Phase 2 tractors, trailers, and
vocational vehicles, subject to the provisions of Sec. Sec.  1037.525
through 1037.527. These procedures are considered the primary
procedures for tractors, but alternate procedures for trailers. Follow
the provisions of Sections 1 through 9 of SAE J2263 (incorporated by
reference in Sec.  1037.810), with the clarifications and exceptions
described in this section. Several of these exceptions are from SAE
J1263 (incorporated by reference in Sec.  1037.810). The coastdown
procedures in 40 CFR 1066.310 apply instead of the provisions of this
section for Phase 1 tractors.
    (a) The terms and variables identified in this section have the
meaning given in SAE J1263 (incorporated by reference in Sec.
1037.810) and J2263 unless specified otherwise.
    (b) To determine CdA values for a tractor, perform
coastdown testing with a tractor-trailer combination using the
manufacturer's tractor and a standard trailer. To determine
CdA values for a trailer, perform coastdown testing with a
tractor-trailer combination using a standard tractor. Prepare tractors
and trailers for testing as follows:
    (1) Install instrumentation for performing the specified
measurements.
    (2) After adding vehicle instrumentation, verify that there is no
brake drag or other condition that prevents the wheels from rotating
freely. Do not apply the parking brake at any point between this
inspection and the end of the measurement procedure.
    (3) Install tires mounted on steel rims in a dual configuration
(except for steer tires). The tires must--
    (i) Be SmartWay-Verified or have a coefficient of rolling
resistance at or below 5.1 kg/metric ton.
    (ii) Have accumulated at least 2,000 miles but have no less than 50
percent of their original tread depth, as specified for truck cabs in
SAE J1263.
    (iii) Not be retreads or have any apparent signs of chunking or
uneven wear.
    (iv) Be size 295/75R22.5 or 275/80R22.5.
    (v) Be inflated to the proper tire pressure as specified in
Sections 6.6 and 8.1 of SAE J2263.
    (vi) Be of the same tire model for a given axle.
    (4) Perform an inspection or wheel alignment for both the tractor
and the trailer to ensure that wheel position is within the
manufacturer's specifications.
    (c) The test condition specifications described in Sections 7.1
through 7.4 of SAE J1263 apply, with the following exceptions and
additional provisions:
    (1) We recommend that you not perform coastdown testing if winds
are expected to exceed 6.0 mi/hr.
    (2) The average of the component of the wind speed parallel to the
road must not exceed 6.0 mi/hr. This constraint is in addition to those
in Section 7.3 of SAE J1263.
    (3) If road grade is greater than 0.02% over the length of the test
surface, you must determine elevation as a function of distance along
the length of the test surface and incorporate this into the analysis.
    (4) Road grade may exceed 0.5% for limited portions of the test
surface as long as it does not affect coastdown results, consistent
with good engineering judgment.
    (5) The road surface temperature must be at or below 50 [deg]C. Use
good engineering judgment to measure road surface temperature.
    (d) CdA calculations are based on measured speed values
while the vehicle coasts down through a high-

speed range from 70 to 60 mi/hr, and through a low-speed range from 20
to 10 mi/hr. Disable any vehicle speed limiters that prevent travel
above 72 mi/hr. Measure vehicle speed at a minimum recording frequency
of 10 Hz, in conjunction with time-of-day data. Determine vehicle speed
using either of the following methods:
    (1) Complete coastdown runs. Operate the vehicle at a top speed
above 72.0 mi/hr and allow the vehicle to coast down to 8.0 mi/hr or
lower. Collect data for the high-speed range over a test segment that
includes speeds from 72.0 down to 58.0 mi/hr, and collect data for the
low-speed range over a test segment that includes speeds from 22.0 down
to 8.0 mi/hr.
    (2) Split coastdown runs. Collect data during a high-speed
coastdown while the vehicle coasts through a test segment that includes
speeds from 72.0 mi/hr down to 58.0 mi/hr. Similarly, collect data
during a low-speed coastdown while the vehicle coasts through a test
segment that includes speeds from 22.0 mi/hr down to 8.0 mi/hr. Perform
one high-speed coastdown segment or two consecutive high-speed
coastdown segments in one direction, followed by the same number of
low-speed coastdown segments in the same direction, and then perform
that same number of measurements in the opposite direction. You may not
split runs as described in Section 9.3.1 of SAE J2263 except as allowed
under this paragraph (d)(2).
    (e) Measure wind speed, wind direction, air temperature, and air
pressure at a recording frequency of 10 Hz, in conjunction with time-
of-day data. Use at least one stationary electro-mechanical anemometer
and suitable data loggers meeting SAE J1263 specifications, subject to
the following additional specifications for the anemometer placed along
the test surface:
    (1) You must start a coastdown measurement within 24 hours after
completing zero-wind and zero-angle calibrations.
    (2) Place the anemometer at least 50 feet from the nearest tree and
at least 25 feet from the nearest bush (or equivalent features).
Position the anemometer adjacent to the test surface, near the midpoint
of the length of the track, between 2.5 and 3.0 body widths from the
expected location of the test vehicle's centerline as it passes the
anemometer. Record the location of the anemometer along the test track,
to the nearest 10 feet.
    (3) Mount the anemometer at a height that is within 6 inches of
half the test vehicle's body height.
    (4) The height of vegetation surrounding the anemometer may not
exceed 10% of the anemometer's mounted height, within a radius equal to
the anemometer's mounted height.
    (f) Measure air speed and relative wind direction (yaw angle)
onboard the vehicle at a minimum recording frequency of 10 Hz, in
conjunction with time-of-day data, using an anemometer and suitable
data loggers that meet the requirements of Sections 5.4 of SAE J2263.
The yaw angle must be measured to a resolution and accuracy of 0.5[deg]. Mount the anemometer such that it measures air speed at
1.5 meters above the top of the leading edge of the trailer. If
obstructions at the test site do not allow for this mounting height,
then mount the anemometer such that it measures air speed at least 0.85
meters above the top of the leading edge of the trailer.
    (g) Perform the following calculations to filter and correct
measured data:
    (1) For any measured values not identified as outliers, use those
measured values directly in the calculations specified in this section.
Filter air speed, yaw angle, wind speed, wind direction, and vehicle
speed measurements to replace outliers for every measured value as
follows:
    (i) Determine a median measured value to represent the measurement
point and the measurements 3 seconds before and after that point. In
the first and last three seconds of the coastdown run, use all
available data to determine the median measured value. The measurement
window for determining the median value will accordingly include 61
measurements in most cases, and will always include at least 31
measurements (for 10 Hz recording frequency).
    (ii) Determine the median absolute deviation corresponding to each
measurement window from paragraph (g)(1)(i) of this section. This
generally results from calculating 61 absolute deviations from the
median measured value and determining the median from those 61
deviations. Calculate the standard deviation for each measurement
window by multiplying the median absolute deviation by 1.4826;
calculate three standard deviations by multiplying the median absolute
deviation by 4.4478. Note that the factor 1.4826 is a statistical
constant that relates median absolute deviations to standard
deviations.
    (iii) A measured value is an outlier if the measured value at a
given point differs from the median measured value by more than three
standard deviations. Replace each outlier with the median measured
value from paragraph (g)(1)(i) of this section. This technique for
filtering outliers is known as the Hampel method.
    (2) For each high-speed and each low-speed segment, correct
measured air speed using the wind speed and wind direction measurements
described in paragraph (e) of this section as follows:
    (i) Calculate the theoretical air speed, vair,th, for
each 10-Hz set of measurements using the following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.094

Where:

w = filtered wind speed.
v = filtered vehicle speed.
[oslash]w = filtered wind direction. Let
[oslash]w = 0[deg] for air flow in the first travel
direction, with values increasing counterclockwise. For example, if
the vehicle starts by traveling eastbound, then [oslash]w
= 270[deg] means a wind from the south.
[oslash]veh = the vehicle direction. Use
[oslash]veh = 0[deg] for travel in the first direction,
and use [oslash]veh = 180[deg] for travel in the opposite
direction.

    Example:
w = 7.1 mi/hr
v = 64.9 mi/hr
[oslash]w = 47.0[deg]
[oslash]veh = 0[deg]

[GRAPHIC] [TIFF OMITTED] TR25OC16.095

vair,th = 69.93 mi/hr

    (ii) Perform a linear regression using paired values of
vair,th and measured air speed, vair,meas, to
determine the air-speed correction coefficients, [alpha]0
and [alpha]1, based on the following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.096

    (iii) Correct each measured value of air speed using the following
equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.097

    (3) Correct measured air direction using the wind speed and wind
direction measurements described in paragraph (e) of this section as
follows:
    (i) Calculate the theoretical air direction,
[psi]air,th, using the following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.098

    Example:
w = 7.1 mi/hr
v = 64.9 mi/hr
[oslash]w = 47.0[deg]
[oslash]veh = 0[deg]
[GRAPHIC] [TIFF OMITTED] TR25OC16.099

[psi]air,th = 4.26[deg]

    (ii) Perform a linear regression using paired values of
[psi]air,th and measured air direction,
[psi]air,meas, to determine the air-direction correction
coefficients, [beta]0 and [beta]1, based on the
following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.100

    (iii) Correct each measured value of air direction using the
following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.101

    (h) Determine drag area, CdA, using the following
procedure instead of the procedure specified in Section 10 of SAE
J1263:
    (1) Calculate the vehicle's effective mass, Me, to
account for rotational inertia by adding 56.7 kg to the measured
vehicle mass, M, (in kg) for each tire making road contact.
    (2) Operate the vehicle and collect data over the high-speed range
and low-speed range as specified in paragraph (d)(1) or (2) of this
section. If the vehicle has a speed limiter that prevents it from
exceeding 72 mi/hr, you must disable the speed limiter for testing.
    (3) Calculate mean vehicle speed at each speed start point (70 and
20 mi/hr) and end point (60 and 10 mi/hr) as follows:
    (i) Calculate the mean vehicle speed to represent the start point
of each speed range as the arithmetic average of measured speeds
throughout the speed interval defined as 2.00 mi/hr above the nominal
starting speed point to 2.00 mi/hr below the nominal starting speed
point, expressed to at least two decimal places. Determine the
timestamp corresponding to the starting point of each speed range as
the time midpoint of the 2.00 mi/hr speed interval.
    (ii) Repeat the calculations described in paragraph (h)(3)(i) of
this section corresponding to the end point speed (60 or 10 mi/hr) to
determine the time at which the vehicle reaches the end speed, and the
mean vehicle speed representing the end point of each speed range.
    (iii) If you incorporate grade into your calculations, use the
average values for the elevation and distance traveled over each
interval.
    (4) Calculate the road-load force, F, for each speed range using
the following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.102

Where:

Me = the vehicle's effective mass.
v = average vehicle speed at the start or end of each speed range,
as described in paragraph (h)(3) of this section.
t = timestamp at which the vehicle reaches the starting or ending
speed expressed to at least one decimal place.
M = the vehicle's measured mass.
ag = acceleration of Earth's gravity, as described in 40
CFR 1065.630.
h = average elevation at the start or end of each speed range
expressed to at least two decimal places.
D = distance traveled on the road surface from a fixed reference
location along the road to the start or end of each speed range
expressed to at least one decimal place.

    Example:
Me = 17,129 kg (18 tires in contact with the road
surface)
vstart = 69.97 mi/hr = 31.28 m/s
vend = 59.88 mi/hr = 26.77 m/s
tstart = 3.05 s
tend = 19.11 s
M = 16,108 kg
ag = 9.8061 m/s\2\
hstart = 0.044 m
hend = 0.547 m
Dstart = 706.8 ft = 215.4 m
Dend = 2230.2 ft = 697.8 m
[GRAPHIC] [TIFF OMITTED] TR25OC16.103

F = 4645.5 N

    (5) For tractor testing, calculate the drive-axle spin loss force
at high and low speeds, Fspin[speed], and determine
[Delta]Fspin as follows:
    (i) Use the results from the axle efficiency test described in
Sec.  1037.560 for the drive axle model installed in the tractor being
tested for this coastdown procedure.
    (ii) Perform a second-order regression of axle power loss in W from
only the zero-torque test points with wheel speed, fnwheel,
in r/s from the axle efficiency test to determine coefficients
c0, c1, and c2.
[GRAPHIC] [TIFF OMITTED] TR25OC16.104

    (iii) Calculate Fspin[speed] using the following
equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.105

Where:

vseg[speed] = the mean vehicle speed of all vehicle speed
measurements in each low-speed and high-speed segment.
TRPM = tire revolutions per mile for the drive tire model installed
on the tractor being tested according to Sec.  1037.520(c)(1).

    Example:
vseghi = 28.86 m/s
vseglo = 5.84 m/s
TRPM = 508 r/mi = 0.315657 r/m
c0 = -206.841 W
c1 = 239.8279 W[middot]s/r
c2 = 21.27505 W[middot]s\2\/r\2\
[GRAPHIC] [TIFF OMITTED] TR25OC16.106

Fspinhi = 129.7 N
Fspinlo = 52.7 N

    (iv) Calculate [Delta]Fspin using the following
equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.107

    Example:
[Delta]Fspin = 129.7-52.7 = 77.0 N

    (6) For tractor testing, calculate the tire rolling resistance
force at high and low speeds for steer, drive, and trailer axle
positions, FTRR[speed,axle], and determine
[Delta]FTRR as follows:
    (i) Conduct a stepwise coastdown tire rolling resistance test with
three tires for each tire model installed on the vehicle using SAE
J2452 (incorporated by reference in Sec.  1037.810) for the following
test points (which replace the test points in Table 3 of SAE J2452):

     Table 1 of Sec.   1037.528--Stepwise Coastdown Test Points for
       Determining Tire Rolling Resistance as a Function of Speed
------------------------------------------------------------------------
                                                             Inflation
                 Step #                     Load (% of    pressure (% of
                                               max)            max)
------------------------------------------------------------------------
1.......................................              20             100
2.......................................              55              70
3.......................................              85             120
4.......................................              85             100
5.......................................             100              95
------------------------------------------------------------------------

    (ii) Calculate FTRR[speed,axle] using the following
equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.108

Where:

nt,[axle] = number of tires at the axle position.
P[axle] = the inflation pressure set and measured on the
tires at the axle position at the beginning of the coastdown test.
L[axle] = the load over the axle at the axle position on
the coastdown test vehicle.
[alpha][axle], [beta][axle],
a[axle], b[axle], and c[axle] =
regression coefficients from SAE J2452 that are specific to axle
position.

    Example:
nt,steer = 2
Psteer = 758.4 kPa
Lsteer = 51421.2 N
[alpha]steer = -0.2435
[beta]steer = 0.9576
asteer = 0.0434
bsteer = 5.4[middot]10-\5\
csteer = 5.53[middot]10-\7\
nt,drive = 8
Pdrive = 689.5 kPa
Ldrive = 55958.4 N
[alpha]drive = -0.3146
[beta]drive = 0.9914
adrive = 0.0504
bdrive = 1.11[middot]10-\4\
cdrive = 2.86[middot]10-\7\
nt,trailer = 8
Ptrailer = 689.5 kPa
Ltrailer = 45727.5 N
[alpha]trailer = -0.3982
[beta]trailer = 0.9756
atrailer = 0.0656
btrailer = 1.51[middot]10-\4\
ctrailer = 2.94[middot]10-\7\
vseghi = 28.86 m/s = 103.896 km/hr
vseglo = 5.84 m/s = 21.024 km/hr

[GRAPHIC] [TIFF OMITTED] TR25OC16.109

FTRRhi,steer = 365.6 N
FTRRhi,drive = 431.4 N
FTRRhi,trailer = 231.7 N
FTRRlo,steer = 297.8 N
FTRRlo,drive = 350.7 N
FTRRlo,trailer = 189.0 N

    (iii) Calculate FTRR[speed] by summing the tire rolling
resistance calculations at a given speed for each axle position and
determine [Delta]FTRR as follows:
[GRAPHIC] [TIFF OMITTED] TR25OC16.110

    Example:
FTRRhi = 365.6 + 431.4 + 231.7 = 1028.7 N
FTRRlo = 297.8 + 350.7 + 189.0 = 837.5 N

    (iv) Adjust FTRR[speed] to the ambient temperature
during the coastdown segment as follows:
[GRAPHIC] [TIFF OMITTED] TR25OC16.111

Where:

Tseg[speed] = the average ambient temperature during the
low or high speed segments.

    Example:
FTRRhi = 1028.7 N
FTRRlo = 837.5 N
Tseghi = 25.5 [deg]C
Tseglo = 25.1 [deg]C
FTRRhi,adj = 1028.7[middot][1 + 0.006[middot](24-25.5)] =
1019.4 N
FTRRlo,adj = 837.5[middot][1 + 0.006[middot](24-25.1)] =
832.0 N

    (v) Determine [Delta]FTRR as follows:
    [GRAPHIC] [TIFF OMITTED] TR25OC16.112

    Example:
[Delta]FTRR = 1019.4 - 832.0 = 187.4 N

    (7) For trailer testing, determine [Delta]FTRR using a
default value adjusted to the ambient temperature instead of performing
a rolling resistance test, as follows:
[GRAPHIC] [TIFF OMITTED] TR25OC16.113

Where:

[Delta]FTRR,def = default rolling resistance force speed
adjustment; Use 215 N for long box vans and 150 N for short box
vans.
Tcoast = the average ambient temperature during both low
and high speed segments.

    Example:
[Delta]FTRR,def = 215 N
Tcoast = 25.5 [deg]C
[Delta]FTRR = 215[middot][1 + 0.0006[middot](24-25.5)] =
213.1 N

    (8) Square the air speed measurements and calculate average squared
air speed during each speed range for each
run,v2air,hi and v2air,lo.
    (9) Average the Flo and v2air,lo
values for each pair of runs in opposite directions. If running
complete coastdowns as described in paragraph (d)(1) or one high-speed
segment per direction as described in paragraph (d)(2), average every
two Flo and v2air,lo values. If
running two high-speed segments per direction as described in paragraph
(d)(2), average every four Flo and
v2air,lo values. Use these values as
Flo,pair and v2air,lo,pair in the
calculations in this paragraph (h) to apply to each of the two or four
high-speed segments from the same runs as the low-speed segments used
to determine Flo,pair and
v2air,lo,pair.
    (10) Calculate average air temperature T and air pressure
Pact during each high-speed run.
    (11) Calculate drag area, CdA, in m\2\ for each high-
speed segment using the following equation, expressed to at least three
decimal places:

[GRAPHIC] [TIFF OMITTED] TR25OC16.114

Where:

Fhi = road load force at high speed determined from Eq.
1037.528-7.
Flo,pair = the average of Flo values for a
pair of opposite direction runs calculated as described in paragraph
(h)(9) of this section.
[Delta]Fspin = the difference in drive-axle spin loss
force between high-speed and low-speed coastdown segments. This is
described in paragraph (h)(5) of this section for tractor testing.
Let [Delta]Fspin = 110 N for trailer testing.
[Delta]FTRR = the difference in tire rolling resistance
force between high-speed and low-speed coastdown segments as
described in paragraphs (h)(6) or (7) of this section.
v2air,lo,pair = the average of
v2air,lo values for a pair of opposite
direction runs calculated as described in paragraph (h)(9) of this
section.
R = specific gas constant = 287.058 J/(kg[middot]K).
T = mean air temperature expressed to at least one decimal place.
Pact = mean absolute air pressure expressed to at least
one decimal place.

    Example:
Fhi = 4645.5 N
Flo,pair = 1005.0 N
[Delta]Fspin = 77.0 N
[Delta]FTRR = 187.4 N
v2air,hi = 933.4 m\2\/s\2\
v2air,lo,pair = 43.12 m\2\/s\2\
R = 287.058 J/(kg[middot]K)
T = 285.97 K
Pact = 101.727 kPa = 101727 Pa
[GRAPHIC] [TIFF OMITTED] TR25OC16.115

CdA = 6.120 m\2\

    (12) Calculate your final CdA value from the high-speed
segments as follows:
    (i) Eliminate all points where there were known equipment problems
or other measurement problems.
    (ii) Of the remaining points, calculate the median of the absolute
value of the yaw angles, [psi]med, and eliminate all
CdA values that differ by more than 1.0[deg] from
[psi]med.
    (iii) Of the remaining points, calculate the mean and standard
deviation of CdA and eliminate all values that differ by
more than 2.0 standard deviations from the mean value.
    (iv) There must be at least 24 points remaining. Of the remaining
points, recalculate the mean yaw angle. Round the mean yaw angle to the
nearest 0.1[deg]. This final result is the effective yaw angle,
[psi]eff, for coastdown testing.
    (v) For the same set of points, recalculate the mean
CdA. This is the final result of the coastdown test,
CdAeffective-yaw-coastdown.
    (i) [Reserved]
    (j) Include the following information in your application for
certification:
    (1) The name, location, and description of your test facilities,
including background/history, equipment and capability, and track and
facility elevation, along with the grade and size/length of the track.
    (2) Test conditions for each test result, including date and time,
wind speed and direction, ambient temperature and humidity, vehicle
speed, driving distance, manufacturer name, test vehicle/model type,
model year, applicable family, tire type and rolling resistance, weight
of tractor-trailer (as tested), and driver identifier(s).
    (3) Average CdA and yaw angle results and all the
individual run results (including voided or invalid runs).

Sec.  1037.530  Wind-tunnel procedures for calculating drag area (CdA).

    The wind-tunnel procedure specified in this section is considered
to be the primary procedure for trailers, but is an alternate procedure
for tractors.
    (a) You may measure drag areas consistent with published SAE
procedures as described in this section using any wind tunnel
recognized by the Subsonic Aerodynamic Testing Association, subject to
the provisions of Sec. Sec.  1037.525 through 1037.527. If your wind
tunnel does not meet the specifications described in this section, you
may ask us to approve it as an alternate method under Sec.  1037.525(d)
or Sec.  1037.526(d). All wind tunnels and wind tunnel tests must meet
the specifications described in SAE J1252 (incorporated by reference in
Sec.  1037.810), with the following exceptions and additional
provisions:
    (1) The Overall Vehicle Reynolds number,
Rew, must be at least 1.0[middot]10\6\.
Tests for Reynolds effects described in Section 7.1 of SAE J1252 are
not required.
    (2) For full-scale wind tunnel tractor testing, use good
engineering judgment to select a trailer that is a reasonable
representation of the trailer used for reference coastdown testing. For
example, where your wind tunnel is not long enough to test the tractor
with a standard 53 foot box van, it may be appropriate to use a shorter
box van. In such a case, the correlation developed using the shorter
trailer would only be valid for testing with the shorter trailer.
    (3) For reduced-scale wind tunnel testing, use a one-eighth or
larger scale model of a tractor and trailer that is sufficient to
simulate airflow through the radiator inlet grill and across an engine
geometry that represents engines commonly used in your test vehicle.
    (b) Open-throat wind tunnels must also meet the specifications of
SAE J2071 (incorporated by reference in Sec.  1037.810).
    (c) To determine CdA values for certifying tractors,
perform wind-tunnel testing with a tractor-trailer combination using
the manufacturer's tractor and a standard trailer. To determine
CdA values for certifying trailers, perform wind-tunnel
testing with a tractor-trailer combination using a standard tractor.
Use a moving/rolling floor if the facility has one. For Phase 1
tractors, conduct the wind tunnel tests at a zero yaw angle. For Phase
2 vehicles, conduct the wind tunnel tests by measuring the drag area at
yaw angles of +4.5[deg] and -4.5[deg] and calculating the average of
those two values.
    (d) In your request to use wind-tunnel testing for tractors, or in
your application for certification for trailers, describe how you meet
all the specifications that apply under this section, using terminology
consistent with SAE J1594 (incorporated by reference in Sec.
1037.810). If you request our approval to use wind-tunnel testing even
though you do not meet all the specifications of this section, describe
how your method nevertheless qualifies

as an alternate method under Sec.  1037.525(d) or 1037.526(d) and
include all the following information:
    (1) Identify the name and location of the test facility for your
wind-tunnel method.
    (2) Background and history of the wind tunnel.
    (3) The wind tunnel's layout (with diagram), type, and construction
(structural and material).
    (4) The wind tunnel's design details: The type and material for
corner turning vanes, air settling specification, mesh screen
specification, air straightening method, tunnel volume, surface area,
average duct area, and circuit length.
    (5) Specifications related to the wind tunnel's flow quality:
Temperature control and uniformity, airflow quality, minimum airflow
velocity, flow uniformity, angularity and stability, static pressure
variation, turbulence intensity, airflow acceleration and deceleration
times, test duration flow quality, and overall airflow quality
achievement.
    (6) Test/working section information: Test section type (e.g.,
open, closed, adaptive wall) and shape (e.g., circular, square, oval),
length, contraction ratio, maximum air velocity, maximum dynamic
pressure, nozzle width and height, plenum dimensions and net volume,
maximum allowed model scale, maximum model height above road, strut
movement rate (if applicable), model support, primary boundary layer
slot, boundary layer elimination method, and photos and diagrams of the
test section.
    (7) Fan section description: Fan type, diameter, power, maximum
rotational speed, maximum speed, support type, mechanical drive, and
sectional total weight.
    (8) Data acquisition and control (where applicable): Acquisition
type, motor control, tunnel control, model balance, model pressure
measurement, wheel drag balances, wing/body panel balances, and model
exhaust simulation.
    (9) Moving ground plane or rolling road (if applicable):
Construction and material, yaw table and range, moving ground length
and width, belt type, maximum belt speed, belt suction mechanism,
platen instrumentation, temperature control, and steering.
    (10) Facility correction factors and purpose.

Sec.  1037.532  Using computational fluid dynamics to calculate drag
area (CdA).

    This section describes how to use commercially available
computational fluid dynamics (CFD) software to determine CdA
values, subject to the provisions of Sec. Sec.  1037.525 through
1037.527. This is considered to be an alternate method for both
tractors and trailers.
    (a) For Phase 2 vehicles, use SAE J2966 (incorporated by reference
in Sec.  1037.810), with the following clarifications and exceptions:
    (1) Vehicles are subject to the requirement to meet standards based
on the average of testing at yaw angles of +4.5[deg] or -4.5[deg];
however, you may submit your application for certification with CFD
results based on only one of those yaw angles.
    (2) For CFD code with a Navier-Stokes based solver, follow the
additional steps in paragraph (d) of this section. For Lattice-
Boltzmann based CFD code, follow the additional steps in paragraph (e)
of this section.
    (3) Simulate a Reynolds number of 5.1 million and an air speed of
65 mi/hr.
    (4) Perform the General On-Road Simulation (not the Wind Tunnel
Simulation).
    (5) Use a free stream turbulence intensity of 0.0%.
    (6) Choose time steps that can accurately resolve intrinsic flow
instabilities, consistent with good engineering judgment.
    (7) The result must be drag area (CdA), not drag
coefficient (Cd), based on an air speed of 65 mi/hr.
    (8) Submit information as described in paragraph (g) of this
section.
    (b) For Phase 1 tractors, apply the procedures as specified in
paragraphs (c) through (f) of this section. Paragraphs (c) through (f)
of section apply for Phase 2 vehicles only as specified in paragraph
(a) of this section.
    (c) To determine CdA values for certifying a tractor,
perform CFD modeling based on a tractor-trailer combination using the
manufacturer's tractor and a standard trailer. To determine
CdA values for certifying a trailer, perform CFD modeling
based on a tractor-trailer combination using a standard tractor.
Perform all CFD modeling as follows:
    (1) Specify a blockage ratio at or below 0.2% to simulate open-road
conditions.
    (2) Assume zero yaw angle.
    (3) Model the tractor with an open grill and representative back
pressures based on available data describing the tractor's pressure
characteristics.
    (4) Enable the turbulence model and mesh deformation.
    (5) Model tires and ground plane in motion to simulate a vehicle
moving forward in the direction of travel.
    (6) Apply the smallest cell size to local regions on the tractor
and trailer in areas of high flow gradients and smaller-geometry
features (e.g., the A-pillar, mirror, visor, grille and accessories,
trailer-leading edge, trailer-trailing edge, rear bogey, tires, and
tractor-trailer gap).
    (7) Simulate a vehicle speed of 55 mi/hr.
    (d) Take the following steps for CFD code with a Navier-Stokes
formula solver:
    (1) Perform an unstructured, time-accurate analysis using a mesh
grid size with a total volume element count of at least 50 million
cells of hexahedral and/or polyhedral mesh cell shape, surface elements
representing the geometry consisting of no less than 6 million
elements, and a near-wall cell size corresponding to a y+ value of less
than 300.
    (2) Perform the analysis with a turbulence model and mesh
deformation enabled (if applicable) with boundary layer resolution of
95%. Once the results reach this resolution, demonstrate
the convergence by supplying multiple, successive convergence values
for the analysis. The turbulence model may use k-epsilon (k-[egr]),
shear stress transport k-omega (SST k-[omega]), or other commercially
accepted methods.
    (e) For Lattice-Boltzmann based CFD code, perform an unstructured,
time-accurate analysis using a mesh grid size with total surface
elements of at least 50 million cells using cubic volume elements and
triangular and/or quadrilateral surface elements with a near-wall cell
size of no greater than 6 mm on local regions of the tractor and
trailer in areas of high flow gradients and smaller geometry features,
with cell sizes in other areas of the mesh grid starting at twelve
millimeters and increasing in size from this value as the distance from
the tractor and trailer increases.
    (f) You may ask us to allow you to perform CFD analysis using
parameters and criteria other than those specified in this section,
consistent with good engineering judgment. In your request, you must
demonstrate that you are unable to perform modeling based on the
specified conditions (for example, you may have insufficient computing
power, or the computations may require inordinate time), or you must
demonstrate that different criteria (such as a different mesh cell
shape and size) will yield better results. In your request, you must
also describe your recommended alternative parameters and criteria, and
describe how this approach will produce results that adequately
represent a vehicle's in-use performance. We may require that you
supply data demonstrating that your selected parameters and criteria
will

provide a sufficient level of detail to yield an accurate analysis. If
you request an alternative approach because it will yield better
results, we may require that you perform CFD analysis using both your
recommended criteria and parameters and the criteria and parameters
specified in this section to compare the resulting key aerodynamic
characteristics, such as pressure profiles, drag build-up, and
turbulent/laminar flow at key points around the tractor-trailer
combination.
    (g) Include the following information in your request to determine
CdA values using CFD:
    (1) The name of the software.
    (2) The date and version number of the software.
    (3) The name of the company producing the software and the
corresponding address, phone number, and Web site.
    (4) Identify whether the software uses Navier-Stokes or Lattice-
Boltzmann equations.
    (5) Describe the input values you will use to simulate the
vehicle's aerodynamic performance for comparing to coastdown results.

Sec.  1037.534  Constant-speed procedure for calculating drag area
(CdA).

    This section describes how to use constant-speed aerodynamic drag
testing to determine CdA values, subject to the provisions
of Sec.  1037.525. This is considered to be an alternate method for
tractors.
    (a) Test track. Select a test track that meets the specifications
described in Sec.  1037.528(c)(3).
    (b) Ambient conditions. At least two tests are required. For one of
the tests, ambient conditions must remain within the specifications
described in Sec.  1037.528(c) throughout the preconditioning and
measurement procedure. The other tests must also meet those
specifications except for the wind conditions. The wind conditions must
be such that 80 percent of the values of yaw angle,
[psi]air, from the 50 mi/hr and 70 mi/hr test segments are
between 4[deg] and 10[deg] or between -4[deg] and -10[deg].
    (c) Vehicle preparation. Perform testing with a tractor-trailer
combination using the manufacturer's tractor and a standard trailer.
Prepare tractors and trailers for testing as described in Sec.
1037.528(b). Install measurement instruments meeting the requirements
of 40 CFR part 1065, subpart C, that have been calibrated as described
in 40 CFR part 1065, subpart D, as follows:
    (1) Measure torque at each of the drive wheels using a hub torque
meter or a rim torque meter. If testing a tractor with two drive axles,
you may disconnect one of the drive axles from receiving torque from
the driveshaft, in which case you would measure torque at only the
wheels that receive torque from the driveshaft. Set up instruments to
read engine rpm for calculating rotational speed at the point of the
torque measurements, or install instruments for measuring the
rotational speed of the wheels directly.
    (2) Install instrumentation to measure vehicle speed at 10 Hz, with
an accuracy and resolution of 0.1 mi/hr. Also install instrumentation
for reading engine rpm from the engine's onboard computer.
    (3) Mount an anemometer on the trailer as described in Sec.
1037.528(f).
    (4) Fill the vehicle's fuel tanks so they are at maximum capacity
at the start of the measurement procedure.
    (5) Measure the weight over each axle to the nearest 20 kg, with a
full fuel tank, including the driver and any passengers that will be in
the vehicle during the test.
    (d) Measurement procedure. The measurement sequence consists of
vehicle preconditioning followed by stabilization and measurement over
five consecutive constant-speed test segments with three different
speed setpoints (10, 50, and 70 mi/hr). Each test segment is divided
into smaller increments for data analysis.
    (1) Precondition the vehicle and zero the torque meters as follows:
    (i) If you are using rim torque meters, zero the torque meters by
lifting each instrumented axle and recording torque signals for at
least 30 seconds, and then drive the vehicle at 50 mi/hr for at least
30 minutes.
    (ii) If you are using any other kind of torque meter, drive the
vehicle at 50 mi/hr for at least 30 minutes, and then allow the vehicle
to coast down from full speed to a complete standstill while the clutch
is disengaged or the transmission is in neutral, without braking. Zero
the torque meters within 60 seconds after the vehicle stops moving by
recording the torque signals for at least 30 seconds, and directly
resume vehicle preconditioning at 50 mi/hr for at least 1.25 mi.
    (iii) You may calibrate instruments during the preconditioning
drive.
    (2) Perform testing as described in paragraph (d)(3) of this
section over a sequence of test segments at constant vehicle speed as
follows:
    (i) 30030 seconds in each direction at 10 mi/hr.
    (ii) 45030 seconds in each direction at 70 mi/hr.
    (iii) 45030 seconds in each direction at 50 mi/hr.
    (iv) 45030 seconds in each direction at 70 mi/hr.
    (v) 45030 seconds in each direction at 50 mi/hr.
    (vi) 30030 seconds in each direction at 10 mi/hr.
    (3) When the vehicle preconditioning described in paragraph (d)(1)
of this section is complete, stabilize the vehicle at the specified
speed for at least 200 meters and start taking measurements. The test
segment starts when you start taking measurements for all parameters.
    (4) During the test segment, continue to operate the vehicle at the
speed setpoint, maintaining constant speed and torque within the ranges
specified in paragraph (e) of this section. Drive the vehicle straight
with minimal steering; do not change gears. Perform measurements as
follows during the test segment:
    (i) Measure the rotational speed of the driveshaft, axle, or wheel
where the torque is measured, or calculate it from engine rpm in
conjunction with gear and axle ratios, as applicable.
    (ii) Measure vehicle speed in conjunction with time-of-day data.
    (iii) Measure ambient conditions, air speed, and air direction as
described in Sec.  1037.528(e) and (f). Correct air speed and air
direction as described in paragraphs (f)(1) and (2) of this section.
    (5) You may divide a test segment into multiple passes by
suspending and resuming measurements. Stabilize vehicle speed before
resuming measurements for each pass as described in paragraph (d)(3) of
this section. Analyze the data from multiple passes by combining them
into a single sequence of measurements for each test segment.
    (6) Divide measured values into even 10 second increments. If the
last increment for each test segment is less than 10 seconds, disregard
measured values from that increment for all calculations under this
section.
    (e) Validation criteria. Analyze measurements to confirm that the
test is valid. Analyze vehicle speed and drive torque by calculating
the mean speed and torque values for each successive 1 second
increment, for each successive 10 second increment, and for each test
segment. The test is valid if the data conform to all the following
specifications:
    (1) Vehicle speed. The mean vehicle speed for the test segment must
be within 1.00 mi/hr of the speed setpoint. In addition, for testing at
50 mi/hr and 70 mi/hr, all ten of the 1 second mean vehicle speeds used
to calculate a corresponding 10 second mean vehicle speed must be
within 0.2 mi/hr of that 10 second mean vehicle speed.
Perform

the same data analysis for testing at 10 mi/hr, but apply a validation
threshold of 0.1 mi/hr.
    (2) Drive torque. All ten of the 1 second mean torque values used
to calculate a corresponding 10 second mean torque value must be within
50% of that 10 second mean torque value.
    (3) Torque drift. Torque meter drift may not exceed 1%.
Determine torque meter drift by repeating the procedure described in
paragraph (d)(1) of this section after testing is complete, except that
driving the vehicle is necessary only to get the vehicle up to 50 mi/hr
as part of coasting to standstill.
    (f) Calculations. Analyze measured data for each time segment after
time-aligning all the data. Use the following calculations to determine
CdA:
    (1) Onboard air speed. Correct onboard anemometer measurements for
air speed using onboard measurements and measured ambient conditions as
described in Sec.  1037.528(f), except that you must first divide the
test segment into consecutive 10 second increments. Disregard data from
the final increment of the test segment if it is less than 10 seconds.
This analysis results in the following equation for correcting air
speed measurements:
[GRAPHIC] [TIFF OMITTED] TR25OC16.116

    (2) Yaw angle. Correct the onboard anemometer measurements for air
direction for each test segment as follows:
    (i) Calculate arithmetic mean values for vehicle speed, v, wind
speed, w, and wind direction, [phiv]w, over each 10 second
increment for each test segment. Disregard data from the final
increment of the test segment if it is less than 10 seconds.
    (ii) Calculate the theoretical air direction,
[psi]air,th, for each 10 second increment using the
following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.117

Where:

[phiv]veh = the vehicle direction, as described in Sec.
1037.528(f)(2).

    Example:
w = 7.1 mi/hr
v = 69.9 mi/hr
[phiv]w = 47.0[deg]
[phiv]veh = 0[deg]
[GRAPHIC] [TIFF OMITTED] TR25OC16.118

[psi]air,th = 3.97[deg]

    (iii) Perform a linear regression using paired values of
[psi]air,th and measured air direction,
[psi]air,meas, from each 10 second increment for all 50 mi/
hr and 70 mi/hr test segments to determine the air-direction correction
coefficients, [beta]0 and [beta]1, based on the
following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.119

    (iv) For all 50 mi/hr and 70 mi/hr test segments, correct each
measured value of air direction using the following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.120

    (3) Road load force. (i) Average the sum of the corrected torques,
the average of the wheel speed measurements, and the vehicle speed over
every 10 second increment to determine, Ttotal,
fnwheel, and v.
    (ii) Calculate a mean road load force, FRL[speed], for
each 10 second increment using the following equation:

[GRAPHIC] [TIFF OMITTED] TR25OC16.121

Where:

Ttotal = mean of all corrected torques at a point in
time.
v = mean vehicle speed.
fnwheel = mean wheel speed.
M = the measured vehicle mass.
ag = acceleration of Earth's gravity, as described in 40
CFR 1065.630.
hinc = elevation at the start or end of each 10 second
increment expressed to at least two decimal places.
Dinc = distance traveled on the road surface from a fixed
reference location along the road to the start or end of each 10
second increment, expressed to at least one decimal place.

    Example:
Ttotal = 2264.9 N[middot]m
v = 31.6 m/s
fnwheel =598.0 r/min
M = 16508 kg
ag = 9.8061 m/s\2\
hinc,start = 0.044 m
hinc,end = 0.574 m
Dinc,start = 215.4 m
Dinc,end = 697.8 m
[GRAPHIC] [TIFF OMITTED] TR25OC16.122

FRL70 = 4310.6 N

    (4) Determination of drag area. Calculate a vehicle's drag area as
follows:
    (i) Calculate the mean road load force from all 10 second
increments from the 10 mi/hr test segments from the test that was
within the wind limits specified in Sec.  1037.528(c),
FRL10,test. This value represents the mechanical drag force
acting on the vehicle.
    (ii) Calculate the mean aerodynamic force for each 10 second
increment, Faero[speed], from the 50 mi/hr and 70 mi/hr test
segments by subtracting FRL10,test from
FRL[speed].
    (iii) Average the corrected air speed and corrected yaw angle over
every 10 second segment from the 50 mi/hr and 70 mi/hr test segments to
determine vair and [psi]air.
    (iv) Calculate CdA for each 10 second increment from the
50 mi/hr and 70 mi/hr test segments using the following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.123

Where:

CdAi[speed] = the mean drag area for each 10
second increment, i.
Faero[speed] = mean aerodynamic force over a given 10
second increment = FRL[speed] - FRL10,test.
vair[speed] = mean aerodynamic force over a given 10
second increment.
R = specific gas constant = 287.058 J/(kg[middot]K).
T = mean air temperature.
Pact = mean absolute air pressure.

    Example:
FRL70 = 4310.6 N
FRL10,test = 900.1 N
Faero70 = 4310.6 - 900.1 = 3410.5 N
v2air70 = 1089.5 m\2\/s\2\
R = 287.058 J/(kg[middot]K)
T = 293.68 K
Pact = 101300 Pa
[GRAPHIC] [TIFF OMITTED] TR25OC16.124

CdAi70 = 5.210 m\2\

    (v) Plot all CdA values from the 50 mi/hr and 70 mi/hr
test segments against the corresponding values for corrected yaw angle
for each 10 second increment. Create a regression based on a fourth-
order polynomial regression equation of the following form:
[GRAPHIC] [TIFF OMITTED] TR25OC16.125

    (vi) Determine CdAwa-alt as the average of
CdA values at 4.5[deg] and -4.5[deg] by applying Eq.
1037.534-7 at those angles.
    (g) Documentation. Keep the following records related to the
constant-speed procedure for calculating drag area:
    (1) The measurement data for calculating CdA as
described in this section.
    (2) A general description and pictures of the vehicle tested.
    (3) The vehicle's maximum height and width.
    (4) The measured vehicle mass.
    (5) Mileage at the start of the first test segment and at the end
of the last test segment.
    (6) The date of the test, the starting time for the first test
segment, and the ending time for the last test segment.
    (7) The transmission gear used for each test segment.
    (8) The data describing how the test was valid relative to the
specifications and criteria described in paragraphs (b) and (e) of this
section.
    (9) A description of any unusual events, such as a vehicle passing
the test vehicle, or any technical or human errors that may have
affected the CdA determination without invalidating the
test.

Sec.  1037.540  Special procedures for testing vehicles with hybrid
power take-off.

    This section describes optional procedures for quantifying the
reduction in greenhouse gas emissions for vehicles as a result of
running power take-off (PTO) devices with a hybrid energy delivery
system. See Sec.  1037.550 for powertrain testing requirements that
apply for drivetrain hybrid systems. The procedures are written to test
the PTO by ensuring that the engine produces all of the energy with no
net change in stored energy (charge-sustaining), and for plug-in hybrid
vehicles, also allowing for drawing down the stored energy (charge-
depleting). The full charge-sustaining test for the hybrid vehicle is
from a fully charged renewable energy storage system (RESS) to a
depleted RESS and then back to a fully charged RESS. You must include
all hardware for the PTO system. You may ask us to modify the
provisions of this section to allow testing hybrid vehicles other than
electric-battery hybrids, consistent with good engineering judgment.
For plug-in hybrids, use a utility factor to properly weight charge-
sustaining and charge-depleting operation as described in paragraph
(f)(3) of this section.
    (a) Select two vehicles for testing as follows:
    (1) Select a vehicle with a hybrid energy delivery system to
represent the range of PTO configurations that will be covered by the
test data. If your test data will represent more than one PTO
configuration, use good engineering judgment to select the
configuration with the maximum number of PTO circuits that has the
smallest potential reduction in greenhouse gas emissions.
    (2) Select an equivalent conventional vehicle as specified in Sec.
1037.615.
    (b) Measure PTO emissions from the fully warmed-up conventional
vehicle as follows:
    (1) Without adding a restriction, instrument the vehicle with
pressure transducers at the outlet of the hydraulic pump for each
circuit. Perform pressure measurements with a frequency of at least 1
Hz.
    (2) Operate the PTO system with no load for at least 15 seconds.
Measure gauge pressure and record the average value over the last 10
seconds (pmin). For hybrid PTO systems the measured pressure
with no load is typically zero. Apply maximum operator demand to the
PTO system until the pressure relief valve opens and pressure
stabilizes; measure gauge pressure and record the average value over
the last 10 seconds (pmax).
    (3) Denormalize the PTO duty cycle in Appendix II of this part
using the following equation:
[GRAPHIC] [TIFF OMITTED] TR25OC16.126

Where:

prefi = the reference pressure at each point i in the PTO
cycle.
pi = the normalized pressure at each point i in the PTO
cycle (relative to pmax).
pmax = the mean maximum pressure measured in paragraph
(b)(2) of this section.
pmin = the mean minimum pressure measured in paragraph
(b)(2) of this section.

    (4) If the PTO system has two circuits, repeat paragraph (b)(2) and
(3) of this section for the second PTO circuit.
    (5) Install a system to control pressures in the PTO system during
the cycle.
    (6) Start the engine.
    (7) Depending on the number of circuits the PTO system has, operate
the vehicle over one or concurrently over both of the denormalized PTO
duty cycles in Appendix II of this part. Measure emissions during
operation over each duty cycle using the provisions of 40 CFR part
1066.
    (8) Measured pressures must meet the cycle-validation
specifications in the following table for each test run over the duty
cycle:

  Table 1 of Sec.   1037.540--Statistical Criteria for Validating Each
                      Test Run Over the Duty Cycle
------------------------------------------------------------------------
               Parameter \1\                          Pressure
------------------------------------------------------------------------
Slope, a1.................................  0.950 <= a1 <= 1.030.
Absolute value of intercept,                <= 2.0% of maximum mapped
 [verbar]a0[verbar].                         pressure.
Standard error of estimate, SEE...........  <= 10% of maximum mapped
                                             pressure.
Coefficient of determination, r\2\........  >= 0.970.
------------------------------------------------------------------------
\1\ Determine values for specified parameters as described in 40 CFR
  1065.514(e) by comparing measured values to denormalized pressure
  values from the duty cycle in Appendix II of this part.

    (c) Measure PTO emissions from the fully warmed-up hybrid vehicle
as follows:
    (1) Perform the steps in paragraphs (b)(1) through (5) of this
section.
    (2) Prepare the vehicle for testing by operating it as needed to
stabilize the RESS at a full state of charge (or equivalent for non-
electric RESS).
    (i) For plug-in hybrid electric vehicles, we recommend charging the
battery with an external electrical source.
    (ii) For other vehicles, we recommend running back-to-back PTO
tests until engine operation is initiated to charge the RESS. The RESS
should be fully charged once engine operation stops. The ignition
should remain in the ``on'' position.
    (3) Turn the vehicle and PTO system off while the sampling system
is being prepared.
    (4) Turn the vehicle and PTO system on such that the PTO system is

functional, whether it draws power from the engine or a battery.
    (5) Operate the vehicle over one or both of the denormalized PTO
duty cycles without turning the vehicle off, until the engine starts
and then shuts down. This may require running multiple repeats of the
PTO duty cycles. For non-PHEV systems the test cycle is completed once
the engine shuts down. For plug-in hybrid systems, continue running
until the PTO hybrid is running in a charge-sustaining mode such that
the ``End of Test'' requirements defined in 40 CFR 1066.501 are met.
Measure emissions as described in paragraph (b)(7) of this section. Use
good engineering judgment to minimize the variability in testing
between the two types of vehicles.
    (6) For plug-in hybrid electric vehicles, follow 40 CFR 1066.501 to
divide the test into charge-depleting and charge-sustaining operation.
    (7) Apply cycle-validation criteria as described in paragraph
(b)(8) of this section to both charge-sustaining and charge-depleting
operation.
    (d) Calculate the equivalent distance driven based on operating
time for each section of the PTO portion of the test as applicable by
determining the time of the test and applying the conversion factor in
paragraph (d)(4) of this section. For testing where fractions of a
cycle were run (for example, where three cycles are completed and the
halfway point of a fourth PTO cycle is reached before the engine starts
and shuts down again), calculate the time of the test,
ttest, as follows:
    (1) Add up the time run for all complete tests.
    (2) For fractions of a test, use the following equation to
calculate the time:
[GRAPHIC] [TIFF OMITTED] TR25OC16.127

Where:

i = an indexing variable that represents one recorded value.
N = number of measurement intervals.
pcircuit-1,i = normalized pressure command from circuit 1
of the PTO cycle for each point, i, starting from i = 1.
pcircuit-2,i = normalized pressure command from circuit 2
of the PTO cycle for each point, i, starting from i = 1. Let
pcircuit-2 = 0 if there is only one circuit.
pcircuit-1 = the mean normalized pressure command from
circuit 1 over the entire PTO cycle.
pcircuit-2 = the mean normalized pressure command from
circuit 2 over the entire PTO cycle. Let pcircuit-2 = 0
if there is only one circuit.
[Delta]t = the time interval between measurements. For example, at
100 Hz, [Delta]t = 0.0100 seconds.

    (3) Sum the time from the complete cycles and from the partial
cycle.
    (4) Divide the total PTO operating time from paragraph (d)(3) of
this section by a conversion factor of 0.0144 hr/mi for Phase 1 and
0.0217 hr/mi for Phase 2 to determine the equivalent distance driven.
The conversion factors are based on estimates of average vehicle speed
and PTO operating time as a percentage of total engine operating time;
the Phase 2 conversion factor is calculated from an average speed of
27.1 mi/hr and PTO operation 37% of engine operating time, as follows:
[GRAPHIC] [TIFF OMITTED] TR25OC16.128

    (e) For Phase 1, calculate combined cycle-weighted emissions of the
four duty cycles for vocational vehicles, for both the conventional and
hybrid PTO vehicle tests, as follows:
    (1) Calculate the CO2 emission rates in grams per test
without rounding for both the conventional vehicle and the charge-
sustaining and charge-depleting portions of the test for the hybrid
vehicle as applicable.
    (2) Divide the CO2 mass from the PTO cycle by the
distance determined in paragraph (d)(4) of this section and the
standard payload to get the CO2 emission rate in g/ton-mile.
For plug-in hybrid electric vehicles follow paragraph (f)(3) of this
section to calculate utility factor weighted CO2 emissions
in g/ton-mile.
    (3) Calculate the g/ton-mile emission rate for the driving portion
of the test specified in Sec.  1037.510 and add this to the
CO2 g/ton-mile emission rate for the PTO portion of the
test.
    (4) Follow the provisions of Sec.  1037.615 to calculate
improvement factors and benefits for advanced technologies.
    (f) For Phase 2, calculate the delta PTO fuel results for input
into GEM during vehicle certification as follows:
    (1) Calculate fuel consumption in grams per test,
mfuelPTO, without rounding, as described in 40 CFR
1036.540(d)(4) and (5) for both the conventional vehicle and the
charge-sustaining and charge-depleting portions of the test for the
hybrid vehicle as applicable.
    (2) Divide the fuel mass by the applicable distance determined in
paragraph (d)(4) of this section and the appropriate standard payload
to determine the fuel rate in g/ton-mile.
    (3) For plug-in hybrid electric vehicles calculate the utility
factor weighted fuel consumption in g/ton-mile, as follows:
    (i) Determine the utility factor fraction for the PTO system from
the table in Appendix V of this part using interpolation based on the
total time of the charge-depleting portion of the test as determined in
paragraphs (c)(6) and (d)(3) of this section.
    (ii) Weight the emissions from the charge-sustaining and charge-
depleting portions of the test using the following equation:

[GRAPHIC] [TIFF OMITTED] TR25OC16.129

Where:

mPTO,CD = mass of fuel per ton-mile while in charge-
depleting mode.
UFtCD = utility factor fraction at time tCD as
determined in paragraph (f)(3)(i) of this section.
mPTO,CS = mass of fuel per ton-mile while in charge-
sustaining mode.

    (4) Calculate the difference between the conventional PTO emissions
result and the hybrid PTO emissions result for input into GEM.
    (g) If the PTO system has more than two circuits, apply the
provisions of this section using good engineering judgment.

Sec.  1037.550  Powertrain testing.

    (a) This section describes how to determine engine fuel maps using
a measurement procedure that involves testing an engine coupled with a
powertrain to simulate vehicle operation. Engine fuel maps are part of
demonstrating compliance with Phase 2 vehicle standards under this part
1037; this fuel-mapping information may come from different types of
testing as described in 40 CFR 1036.510.
    (b) Perform powertrain testing to establish measured fuel-
consumption rates over applicable duty cycles for several different
vehicle configurations. The following general provisions apply:
    (1) Measure NOX emissions for each sampling period in
grams. You may perform these measurements using a NOX
emission-measurement system that meets the requirements of 40 CFR part
1065, subpart J. Include these measured NOX values any time
you report to us your greenhouse gas emissions or fuel consumption
values from testing under this section. If a system malfunction
prevents you from measuring NOX emissions during a test
under this section but the test otherwise gives valid results, you may
consider this a valid test and omit the NOX emission
measurements; however, we may require you to repeat the test if we
determine that you inappropriately voided the test with respect to
NOX emission measurement.
    (2) This section uses engine parameters and variables that are
consistent with 40 CFR part 1065.
    (3) While this section includes the detailed equations, you need to
develop your own driver model and vehicle model; we recommend that you
use the MATLAB/Simulink code provided at www.epa.gov/otaq/climate/gem.htm.
    (c) Select an engine and powertrain for testing as described in
Sec.  1037.231.
    (d) Set up the engine according to 40 CFR 1065.110. The default
test configuration involves connecting the powertrain's transmission
output shaft directly to the dynamometer. You may instead set up the
dynamometer to connect at the wheel hubs if your powertrain
configuration requires it, such as for hybrid powertrains, or if you
want to represent the axle performance with powertrain test results. If
you connect at the wheel hubs, input your test results into GEM to
reflect this.
    (e) Cool the powertrain during testing so temperatures for intake-
air, oil, coolant, block, head, transmission, battery, and power
electronics are within their expected ranges for normal operation. You
may use auxiliary coolers and fans.
    (f) Set the dynamometer to operate in speed-control mode. Record
data as described in 40 CFR 1065.202. Command and control dynamometer
speed at a minimum of 5 Hz. If you choose to command the dynamometer at
a slower rate than the calculated dynamometer speed setpoint, use good
engineering judgment to subsample the calculated setpoints for use in
commanding the dynamomemter speed setpoint. Design a vehicle model to
use the measured torque and calculate the dynamometer speed setpoint at
a rate of at least 100 Hz, as follows:
    (1) Calculate the dynamometer's angular speed target,
[fnof]nref,dyno, based on the simulated linear speed of the
tires:
[GRAPHIC] [TIFF OMITTED] TR25OC16.130

Where:

ka[speed] = drive axle ratio as determined in paragraph
(h) of this section.
vrefi = simulated vehicle reference speed. Use the
unrounded result for calculating [fnof]nrefi,dyno.
r[speed] = tire radius as determined in paragraph (h) of
this section.
[GRAPHIC] [TIFF OMITTED] TR25OC16.131

Where:

i = a time-based counter corresponding to each measurement during
the sampling period. Let vref1 = 0; start calculations at
i = 2. A 10-minute sampling period will generally involve 60,000
measurements.
T = instantaneous measured torque.

E[fnof][fnof]axle = axle efficiency. Use
E[fnof][fnof]axle = 0.955 for T > 0, and use
E[fnof][fnof]axle = 1/0.955 for T < 0. To calculate
[fnof]nrefi,dyno for a dynamometer connected at the wheel
hubs, as described in paragraph (f)(2) of this section, use
E[fnof][fnof]axle = 1.0.
M = vehicle mass for a vehicle class as determined in paragraph (h)
of this section.
g = gravitational constant = 9.81 m/s\2\.
Crr = coefficient of rolling resistance for a vehicle
class as determined in paragraph (h) of this section.
Gi-1 = the percent grade interpolated at distance,