--------------------------------------------------------------------------------------------------------------------------------------------------------
SET \a\...................................              17               1                             1           0.030             455           0.024
FTP.......................................              20               2                            12           0.141             514           0.076
LLC.......................................              29               3                            35           0.245             617           0.132
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Using the weighting factors in our finalized test procedures (40 CFR 1036.510).

   Table III-8--Stage 3 Engine Emissions at 600,000 Mile Equivalent Test Point Without Adjustments for IRAF or
                                               Crankcase Emissions
----------------------------------------------------------------------------------------------------------------
                                                 NOX (mg/
                  Duty cycle                      hp-hr)   PM (mg/hp- NMHC (mg/  CO (g/hp-  CO2 (g/hp- N2O (g/hp-
                                                              hr)       hp-hr)      hr)        hr)        hr)
----------------------------------------------------------------------------------------------------------------
SET \a\.......................................         24          1          1      0.015        460      0.030
FTP...........................................         27          1          9      0.144        519      0.058
LLC...........................................         33          4         16      0.153        623      0.064
----------------------------------------------------------------------------------------------------------------
\a\ Using the weighting factors in our finalized test procedures (40 CFR 1036.510).

   Table III-9--Stage 3 Engine Emissions at 800,000 Mile Equivalent Test Point Without Adjustments for IRAF or
                                               Crankcase Emissions
----------------------------------------------------------------------------------------------------------------
                                                 NOX (mg/
                  Duty cycle                      hp-hr)   PM (mg/hp- NMHC (mg/  CO (g/hp-  CO2 (g/hp- N2O (g/hp-
                                                              hr)       hp-hr)      hr)        hr)        hr)
----------------------------------------------------------------------------------------------------------------
SET \a\.......................................         30          2          1      0.023        458      0.028
FTP...........................................         37          1         14      0.149        520      0.092
LLC...........................................         34          1         40      0.205        629      0.125
----------------------------------------------------------------------------------------------------------------
\a\ Using the weighting factors in our finalized test procedures (40 CFR 1036.510).

 Table III-10--Stage 3 Engine Emissions at Interpolated at 650,000 Mile Equivalent Without Adjustments for IRAF
                                             or Crankcase Emissions
----------------------------------------------------------------------------------------------------------------
                                                 NOX (mg/
                  Duty cycle                      hp-hr)   PM (mg/hp- NMHC (mg/  CO (g/hp-  CO2 (g/hp- N2O (g/hp-
                                                              hr)       hp-hr)      hr)        hr)        hr)
----------------------------------------------------------------------------------------------------------------
SET \a\.......................................         26          1          1      0.017        460      0.030
FTP...........................................         30          1         10      0.145        519      0.067
LLC...........................................         33          3         22      0.166        625      0.079
----------------------------------------------------------------------------------------------------------------
\a\ Using the weighting factors in our finalized test procedures (40 CFR 1036.510).

    In addition to evaluating the feasibility of the new criteria
pollutant standards, we also evaluated how CO2 was impacted
on the CARB Stage 3 engine (which is the same engine that was used for
EPA's Stage 3 engine with modifications to the aftertreatment system
and engine calibration to lower NOX emissions). We did this
by evaluating how CO2 emissions changed from the base engine
over the SET, FTP, and LLC, as well as the fuel mapping test procedures
defined in 40 CFR 1036.535 and 1036.540. For all three cycles the CARB
Stage 3 engine emitted CO2 with no measurable difference
compared to the base 2017 Cummins X15 engine. Specifically, we compared
the CARB Stage 3 engine including the 0-hour (degreened) aftertreatment
with the 2017 Cummins X15 engine including degreened aftertreatment and
found the percent reduction in CO2 was

0 percent for the SET, 1 percent for the FTP, and 1 percent for the
LLC.\273\
---------------------------------------------------------------------------

    \273\ See Chapter 3 of the RIA for the CO2 emissions
of the 2017 Cummins X15 engine and the CARB Stage 3 engine.
---------------------------------------------------------------------------

    We note that while the data from the EPA Stage 3 engine (the same
engine as the CARB Stage 3 engine but after SwRI made changes to the
thermal management strategies) at the equivalent age of 435,000 miles
showed an increase in CO2 emissions for the SET, FTP, and
LLC of 0.6, 0.7 and 1.3 percent respectively, which resulted in the
CO2 emissions for the EPA Stage 3 engine being higher than
the 2017 Cummins X15 engine, this is not directly comparable because
the baseline 2017 Cummins X15 aftertreatment had not been aged to an
equivalent of 435,000 miles.\274\ As discussed in Chapter 3 of the RIA,
aging the EPA Stage 3 engine included exposing the aftertreatment to
ash, that increased the back pressure on the engine, which contributed
to the increase in CO2 emissions from the EPA Stage 3
engine. We would expect the same increase in backpressure and in
CO2 emissions from the 2017 Cummins X15 engine if the
aftertreatment of the 2017 Cummins X15 engine was aged to an equivalent
of 435,000 miles.
---------------------------------------------------------------------------

    \274\ As part of the agency's diesel demonstration program, we
didn't age the aftertreatment of the base 2017 Cummins X15 engine
since the focus of this program was to demonstrate emissions
performance of future technologies and due to resource constraints.
Thus, there isn't data directly comparable to the baseline engine at
each aging step.
---------------------------------------------------------------------------

    To evaluate how the technology on the CARB Stage 3 engine compares
to the 2017 Cummins X15 engine with respect to the HD GHG Phase 2
vehicle CO2 standards, both engines were tested on the fuel
mapping test procedures defined in 40 CFR 1036.535 and 1036.540. These
test procedures define how to collect the fuel consumption data from
the engine for use in GEM. For these tests the CARB Stage 3 engine was
tested with the development aged aftertreatment.\275\ The fuel maps
from these tests were run in GEM and the results from this analysis
showed that the EPA and CARB Stage 3 engine emitted CO2 at
the same rate as the 2017 Cummins X15 engine. The details of this
analysis are described in Chapter 3.1 of the RIA.
---------------------------------------------------------------------------

    \275\ The CARB Stage 3 0-hour (degreened) aftertreatment could
not be used for these tests, because it had already been aged past
the 0-hour point when these tests were conducted.
---------------------------------------------------------------------------

    The technologies included in the EPA Stage 3 engine were selected
to both demonstrate the lowest criteria pollutant emissions and have a
negligible effect on GHG emissions. Manufactures may choose to use
other technologies to meet the final standards, but manufacturers will
still also need to comply with the GHG standards that apply under HD
GHG Phase 2. We have, therefore, not projected an increase in GHG
emissions resulting from compliance with the final standards.
---------------------------------------------------------------------------

    \276\ See RIA Chapter 3 for the details of the cost for the
aftertreatment and CDA, which are the drivers for why the
incremental direct manufacturing cost is lowest for Medium HDE.
    \277\ See Table III-3 for the final useful life values and
Section IV.B.1 for the final emissions warranty periods.
---------------------------------------------------------------------------

    Table III-11 summarizes the incremental direct manufacturing costs
for the final standards, from the baseline costs shown in Table III-15.
These values include aftertreatment system, closed crankcase, and CDA
costs. As discussed in Chapter 7 of the RIA, the direct manufacturing
costs include the technology costs plus some costs to improve the
durability of the technology through regulatory useful life. The
details of this analysis can be found in Chapters 3 and 7 of the
RIA.\276\ The cost of the final standards and useful life periods are
further accounted for in the indirect costs as discussed in Chapter 7
of the RIA.\277\

 Table III-11--Incremental Direct Manufacturing Cost of Final Standards
      for the Aftertreatment, Closed Crankcase, and CDA Technology
                                [2017 $]
------------------------------------------------------------------------
                                           Medium
               Light HDE                    HDE     Heavy HDE  Urban bus
------------------------------------------------------------------------
$1,957.................................     $1,817     $2,316     $1,850
------------------------------------------------------------------------

b. Baseline Emissions and Cost
    The basis for our baseline technology assessment is the data
provided by manufacturers in the heavy-duty in-use testing program.
This data encompasses in-use operation from nearly 300 Light HDE,
Medium HDE, and Heavy HDE vehicles. Chapter 5 of the RIA describes how
the data was used to update the MOVES model emissions rates for HD
diesel engines. Chapter 3 of the RIA summarizes the in-use emissions
performance of these engines.
    We also evaluated the certification data submitted to the agency.
The data includes test results adjusted for IRAF and FEL that includes
adjustments for deterioration and margin. The certification data,
summarized in Table III-12 and Table III-13, shows that manufacturers
vary in their approach to how much margin is built into the FEL. Some
manufactures have submitted certification data with zero emissions
(with rounding), which results in a margin at 100 percent of the FEL,
while other manufacturers have margin that is less than 25 percent of
the FEL.

                            Table III-12--Summary of Certification Data for FTP Cycle
----------------------------------------------------------------------------------------------------------------
                                                           NOX (g/hp- PM (g/hp-   NMHC (g/  CO (g/hp-  N2O (g/hp-
                                                              hr)        hr)       hp-hr)      hr)        hr)
----------------------------------------------------------------------------------------------------------------
Average..................................................       0.13       0.00       0.01       0.18       0.07
Minimum..................................................       0.05       0.00       0.00       0.00       0.04
Maximum..................................................       0.18       0.00       0.04       1.10       0.11
----------------------------------------------------------------------------------------------------------------

                            Table III-13--Summary of Certification Data for SET Cycle
----------------------------------------------------------------------------------------------------------------
                                                           NOX (g/hp- PM (g/hp-   NMHC (g/  CO (g/hp-  N2O (g/hp-
                                                              hr)        hr)       hp-hr)      hr)        hr)
----------------------------------------------------------------------------------------------------------------
Average..................................................       0.11       0.00       0.01       0.00       0.06
Minimum..................................................       0.00       0.00       0.00       0.00       0.00
Maximum..................................................       0.18       0.00       0.04       0.20       0.11
----------------------------------------------------------------------------------------------------------------

    In addition to analyzing the on-cycle certification data submitted
by manufacturers, we tested three modern HD diesel engines on an engine
dynamometer and analyzed the data. These engines were a 2018 Cummins
B6.7, 2018 Detroit DD15 and 2018 Navistar A26. These engines were
tested on cycles that range in power demand from the creep mode of the
Heavy Heavy-Duty Diesel Truck (HHDDT) schedule to the HD SET cycle
defined in 40 CFR 1036.510. Table III-14 summarizes the range of
results from these engines on the SET, FTP, and LLC. As described in
Chapter 3 of the RIA, the emissions of current production heavy-duty
engines vary from engine to engine but the largest difference in NOX
between engines is seen on the LLC.

                   Table III-14--Range of NOX Emissions From MY2018 Heavy-Duty Diesel Engines
----------------------------------------------------------------------------------------------------------------
                                                   SET in 40 CFR   SET in 40 CFR
                  NOX (g/hp-hr)                       86.1333        1036.510      FTP composite        LLC
----------------------------------------------------------------------------------------------------------------
Minimum.........................................            0.01            0.01            0.10            0.35
Maximum.........................................            0.12            0.05            0.15            0.81
Average.........................................            0.06            0.03            0.13            0.59
----------------------------------------------------------------------------------------------------------------

    Table III-15 summarizes the baseline sales-weighted total
aftertreatment cost of Light HDEs, Medium HDEs, Heavy HDEs and urban
bus engines. The details of this analysis can be found in Chapters 3
and 7 of the RIA.

                         Table III-15--Baseline Direct Manufacturing Aftertreatment Cost
                                                    [2017 $]
----------------------------------------------------------------------------------------------------------------
                          Light HDE                               Medium HDE       Heavy HDE        Urban bus
----------------------------------------------------------------------------------------------------------------
$2,585.......................................................          $2,536           $3,761           $2,613
----------------------------------------------------------------------------------------------------------------

C. Summary of Compression-Ignition Off-Cycle Standards and Off-Cycle
Test Procedures

    In this Section 0, we describe the final off-cycle standards and
test procedures that will apply for model year 2027 and later heavy-
duty compression-ignition engines. The final off-cycle standards and
test procedures cover the range of operation included in the duty cycle
test procedures and operation that is outside of the duty cycle test
procedures for each regulated pollutant (NOX, HC, CO, and
PM). As described in Section III.C.1, our current not-to-exceed (NTE)
test procedures were not designed to capture and control low-load
operation. In contrast to the current NTE approach that evaluates
engine operation within the NTE zone and excludes operation out of the
NTE zone, we are finalizing a moving average window (MAW) approach that
divides engine operation into two categories (or ``bins'') based on the
time-weighted average engine power of each MAW of engine data. See
Section III.C.2 for a discussion of the derivation of the final off-
cycle standards for each bin. For bin 1, the NOX emission
standard is 10.0 g/hr. The final off-cycle standards for bin 2 are
shown in Table III-16.

             Table III-16--Final Off-Cycle Bin 2 Standards for Light HDE, Medium HDE, and Heavy HDE
----------------------------------------------------------------------------------------------------------------
                        NOX (mg/hp-hr)                          HC (mg/hp-hr)    PM (mg/hp-hr)     CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
58 \a\.......................................................             120              7.5                9
----------------------------------------------------------------------------------------------------------------
\a\ An interim NOX compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy
  HDE. Manufacturers will add the compliance allowance to the NOX standard that applies for each duty cycle and
  for off-cycle testing, with both field testing and laboratory testing.

    The proposed rule provided an extensive discussion of the rationale
and information supporting the proposed off-cycle standards (87 FR
17472, March 28, 2022). Chapters 2 and 3 of the RIA include additional
information including background on applicable test procedures and the
full feasibility analysis for compression-ignition engines. See also
section 11.3 of the Response to Comments for a detailed discussion of
the comments and how they have informed this final rule.

1. Existing NTE Standards and Need for Changes to Off-Cycle Test
Procedures

    Heavy-duty CI engines are currently subject to Not-To-Exceed (NTE)
standards that are not limited to specific test cycles, which means
they can be evaluated not only in the laboratory but also in-use. NTE
standards and test procedures are generally referred to as ``off-
cycle'' standards and test procedures. These off-cycle emission
standards are 1.5 (1.25 for CO) times the laboratory certification
standard for NOX, HC, PM and CO and can be found in 40 CFR
86.007-11.\278\ NTE standards have been successful in broadening the
types of operation for which manufacturers design their emission
controls to remain effective, including steady cruise operation.
However, there remains a significant proportion of vehicle operation
not covered by NTE standards.
---------------------------------------------------------------------------

    \278\ As noted in Section IV.G, manufacturers choosing to
participate in the existing or final averaging, banking, and trading
program agree to meet the family emissions limit (FEL) declared
whenever the engine is tested over the applicable duty- or off-cycle
test procedure. The FELs serves as the emission standard for
compliance testing instead of the standards specified in 40 CFR
86.007-11 or 40 CFR 1036.104(a); thus, the existing off-cycle
standards are 1.5 (1.25 for CO) times the FEL for manufacturers who
choose to participate in ABT.

---------------------------------------------------------------------------

    Compliance with an NTE standard is based on emission test data
(whether collected in a laboratory or in use) analyzed pursuant to 40
CFR 86.1370 to identify NTE events, which are intervals of at least 30
seconds when engine speeds and loads remain in the NTE control area or
``NTE zone''. The NTE zone excludes engine operation that falls below
certain torque, power, and speed values.\279\ The NTE procedure also
excludes engine operation that occurs in certain ambient conditions
(i.e., high altitudes, high intake manifold humidity), or when
aftertreatment temperatures are below 250 [deg]C. Collected data is
considered a valid NTE event if it occurs within the NTE zone, lasts at
least 30 seconds, and does not occur during any of the exclusion
conditions (ambient conditions or aftertreatment temperature).
---------------------------------------------------------------------------

    \279\ Specifically, engine operations are excluded if they fall
below 30 percent of maximum torque, 30 percent of maximum power, or
15 percent of the European Stationary Cycle speed.
---------------------------------------------------------------------------

    The purpose of the NTE test procedure is to measure emissions
during engine operation conditions that could reasonably be expected to
occur during normal vehicle use; however, only data in a valid NTE
event is then compared to the NTE emission standard. Our analysis of
existing heavy-duty in-use vehicle test data indicates that less than
ten percent of a typical time-based dataset are part of valid NTE
events, and hence subject to the NTE standards; the remaining test data
are excluded from consideration. We also found that emissions are high
during many of the excluded periods of operation, such as when the
aftertreatment temperature drops below the 250 [deg]C exclusion
criterion. Our review of in-use data indicates that extended time at
low load and idle operation results in low aftertreatment temperatures,
which in turn lead to diesel engine SCR-based emission control systems
not functioning over a significant fraction of real-world
operation.\280\ \281\ \282\ Test data collected as part of EPA's
manufacturer-run in-use testing program indicate that low-load
operation could account for greater than 50 percent of the
NOX emissions from a vehicle over a given workday.\283\
---------------------------------------------------------------------------

    \280\ Hamady, Fakhri, Duncan, Alan. ``A Comprehensive Study of
Manufacturers In-Use Testing Data Collected from Heavy-Duty Diesel
Engines Using Portable Emissions Measurement System (PEMS)''. 29th
CRC Real World Emissions Workshop, March 10-13, 2019.
    \281\ Sandhu, Gurdas, et al. ``Identifying Areas of High
NOX Operation in Heavy-Duty Vehicles''. 28th CRC Real-
World Emissions Workshop, March 18-21, 2018.
    \282\ Sandhu, Gurdas, et al. ``In-Use Emission Rates for MY
2010+ Heavy-Duty Diesel Vehicles''. 27th CRC Real-World Emissions
Workshop, March 26-29, 2017.
    \283\ Sandhu, Gurdas, et al. ``Identifying Areas of High
NOX Operation in Heavy-Duty Vehicles''. 28th CRC Real-
World Emissions Workshop, March 18-21, 2018.
---------------------------------------------------------------------------

    For example, 96 percent of tests in response to 2014, 2015, and
2016 EPA in-use testing orders passed with NOX emissions for
valid NTE events well below the 0.3 g/hp-hr NOX NTE
standard. When we used the same data to calculate NOX
emissions over all operation measured, not limited to valid NTE events,
the NOX emissions were more than double those within the
valid NTE events (0.5 g/hp-hr).\284\ The results were even higher when
we analyzed the data to consider only NOX emissions that
occur during low load events.
---------------------------------------------------------------------------

    \284\ Hamady, Fakhri, Duncan, Alan. ``A Comprehensive Study of
Manufacturers In-Use Testing Data Collected from Heavy-Duty Diesel
Engines Using Portable Emissions Measurement System (PEMS)''. 29th
CRC Real World Emissions Workshop, March 10-13, 2019.
---------------------------------------------------------------------------

    EPA and others have compared the performance of US-certified
engines and those certified to European Union emission standards and
concluded that the European engines' NOX emissions are lower
in low-load conditions, but comparable to US-certified engines subject
to MY 2010 standards under city and highway operation.\285\ This
suggests that manufacturers are responding to the European
certification standards by designing their emission controls to perform
well under low-load operations, as well as highway operations.
---------------------------------------------------------------------------

    \285\ Rodriguez, F.; Posada, F. ``Future Heavy-Duty Emission
Standards An Opportunity for International Harmonization''. The
International Council on Clean Transportation. November 2019.
Available online: https://theicct.org/sites/default/files/publications/Future%20_HDV_standards_opportunity_20191125.pdf.
---------------------------------------------------------------------------

    The European Union ``Euro VI'' emission standards for heavy-duty
engines require manufacturers to check for ``in-service conformity'' by
operating their engines over a mix of urban, rural, and motorway
driving on prescribed routes using portable emission measurement system
(PEMS) equipment to measure emissions.\286\ \287\ Compliance is
determined using a work-based windows approach where emissions data are
evaluated over segments or ``windows.'' A window consists of
consecutive 1 Hz data points that are summed until the engine performs
an amount of work equivalent to the European transient engine test
cycle (World Harmonized Transient Cycle).
---------------------------------------------------------------------------

    \286\ COMMISSION REGULATION (EU) No 582/2011, May 25, 2011.
Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:02011R0582-20180118&from=EN.
    \287\ COMMISSION REGULATION (EU) 2018/932, June 29, 2018.
Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32018R0932&from=EN.
---------------------------------------------------------------------------

    EPA is finalizing new off-cycle test procedures similar to the
European Euro VI in-service conformity program, with key distinctions
that build upon the Euro VI approach, as discussed in the following
section. This new approach will require manufacturers to account for a
relatively larger proportion of engine operation and thereby further
ensure that real-world emissions meet the off-cycle standards.
2. Off-Cycle Standards and Test Procedures
    We are replacing the NTE test procedures and standards (for
NOX, PM, HC and CO) for model year 2027 and later engines.
Under the final new off-cycle standards and test procedures, engine
operation and emissions test data must be assessed in test intervals
that consist of 300-second moving average windows (MAWs) of continuous
engine operation. Our evaluation accounts for our current understanding
that shorter windows are more sensitive to measurement variability and
longer windows make it difficult to distinguish between duty cycles. In
contrast to the current NTE approach that divides engine operation into
two categories (in the NTE zone and out of the NTE zone), this approach
will divide engine operation into two categories (or ``bins'') based on
the time-weighted average engine power of each MAW of engine data, with
some limited exclusions from the two bins, as described in more detail
in the following discussion.
    In the NPRM, we requested comment on the proposed off-cycle
standards and test procedures, including the 300 second length of the
window. We first note that commenters broadly agree that the current
NTE methodology should be revised, and that a MAW structure is
preferable for off-cycle standards. Some commenters were concerned that
individual seconds of data would be ``smeared,'' with the same 1-Hz
data appearing in both bins as the 300 second windows are placed in the
appropriate bin. We are finalizing the window length that we proposed,
as the 300 second length provides an adequate averaging time to smooth
any anomalous emission events and we anticipate that the final bin
structure described in Section III.C.2.i. should also help address
these concerns. See Response to Comments Section 11.1 through 11.3 for
further details on these comments and EPA's response to these comments.
    Although this program has similarities to the European Euro VI
approach, we are not limiting our off-

cycle standards and test procedures to operation on prescribed routes.
Our current NTE program is not limited to prescribed routes, and we
would consider it an unnecessary step backward to change that aspect of
the procedure.
    In Section IV.G, we discuss the final rule updates to the ABT
program to account for these new off-cycle standards.
i. Moving Average Window Operation Bins
    The final bin structure includes two bins of operation that
represent two different domains of emission performance. Bin 1
represents extended idle operation and other very low load operation
where engine exhaust temperatures may drop below the optimal
temperature for aftertreatment function. Bin 2 represents higher power
operation including much of the operation currently covered by the NTE.
Operation in bin 2 naturally involves higher exhaust temperatures and
catalyst efficiencies. Because this approach divides 300 second windows
into bins based on time-averaged engine power of the window, any of the
bins could include some idle or high-power operation. Like the duty
cycle standards, we believe more than a single standard is needed to
apply to the entire range of operation that heavy-duty engines
experience. A numerical standard that is technologically feasible under
worst case conditions such as idle would necessarily be much higher
than the levels that are achievable when the aftertreatment is
functioning optimally. Section III.C.2.iii includes the final numeric
off-cycle standards.
    Given the challenges of measuring engine power directly in-use, we
are using the CO2 emission rate (grams per second) as a
surrogate for engine power in defining the bins for an engine. We are
further normalizing CO2 emission rates relative to the
nominal maximum CO2 rate of the engine. So, if an engine
with a maximum CO2 emission rate of 50 g/sec was found to be
emitting CO2 at a rate of 10 g/sec, its normalized
CO2 emission rate would be 20 percent. The maximum
CO2 rate is defined as the engine's rated maximum power
multiplied by the engine's CO2 family certification level
(FCL) for the FTP certification cycle.
    In the proposal, we requested comment on whether the maximum
CO2 mass emission rate should instead be determined from the
steady-state fuel mapping procedure in 40 CFR 1036.535 or the torque
mapping procedure defined in 40 CFR 1065.510. After considering
comments, EPA is finalizing the use of the CO2 emission rate
as a surrogate for engine power with the proposed approach to
determining the maximum CO2 mass emission rate. We have two
main reasons for finalizing the determination of maximum CO2
mass emission rate as proposed. First, the FTP FCL and maximum engine
power are already reported to the EPA, so no new requirements are
needed under the finalized approach. Second, our assessment of the
finalized approach has shown that this approach for the determination
of maximum CO2 mass emission rate matches well with the
other options we requested comment on. EPA believes that using the
CO2 emission rate will automatically account for additional
fuel usage not directly used for driveshaft torque and minimizes
concerns about the accuracy and data alignment in the use of broadcast
torque. EPA acknowledges that there is some small variation in
efficiency, and thus CO2 emissions rates, among engines.
However, the test procedure accounts for improvements to the engine
efficiency by using the FTP FCL to convert CO2 specific
NOX to work specific NOX. This is because the FTP
FCL captures the efficiency of the engine over a wide range of
operation, from cold start, idle and steady-state higher power
operation. Furthermore, the FTP FCL can also capture the CO2
improvements from hybrid technology when the powertrain test option
described in preamble Section III.B.2.v is utilized.
    The bins are defined as follows:
     Bin 1: 300 second windows with normalized average
CO2 rate <=6 percent.
     Bin 2: 300 second windows with normalized average
CO2 rate >6 percent.
    The bin cut point of six percent is near the average power of the
low-load cycle. In the NPRM, we proposed a three-bin structure and
requested comment on the proposed number of bins and the value of the
cut point(s). After considering comments, EPA agrees with commenters to
the extent the commenters recommend combining the proposed bins 2 and 3
into a single ``non-idle'' bin 2. Results from the EPA Stage 3 real
world testing indicate that emissions in bins 2 and 3 (expressed as
emissions/normalized CO2) are substantially similar,
minimizing the advantage of separating these modes of operation. See
Response to Comments Section 11.1 for further details on these comments
and EPA's response to these comments.
    To ensure that there is adequate data in each of the bins to
compare to the off-cycle standards, the final requirements specify that
there must be a minimum of 2,400 moving average windows in bin 1 and
10,000 moving average windows in bin 2. In the NPRM, we proposed a
minimum of 2,400 windows for all bins and requested comment on the
appropriate minimum number of windows required to sufficiently reduce
variability in the results while not requiring an unnecessary number of
shift days to be tested to meet the requirement. EPA received comments
both supporting the proposed 2,400 window minimum and supporting an
increase to 10,000 windows total for the non-idle bins (now a single
bin 2 in this final rule). After considering comments, we believe
requiring a minimum of 10,000 windows in final bin 2 to define a valid
test is appropriate. Analysis of data from the EPA Stage 3 off-cycle
test data has shown that emissions are stable after 6,000 windows of
data at moderate temperatures but NOX emissions under low
ambient temperatures need closer to 10,000 windows to be stable. EPA
believes the larger number of required windows will better characterize
the emissions performance of the engine.
    If during the first shift day any of the bins do not include at
least the minimum number of windows, then the engine will need to be
tested for additional day(s) until the minimum requirement is met.
Additionally, the engine can be idled at the end of the shift day to
meet the minimum window count requirement for the idle bin. This is to
ensure that even for duty cycles that do not include significant idle
operation the minimum window count requirement for the idle bin can be
met without testing additional days.
    We received comments on the timing and duration of the optional
end-of-day idle. After considering comments, the final requirements
specify that the ability to add idle time is restricted to the end of
the shift day, and manufacturers may extend this end-of-day idle period
to be as long as they choose. Additional idle in the middle of the
shift day is contrary to the intent of real-world testing, and the end
of the shift day is the only realistic time to add windows. Since idle
times of varying lengths are encountered in real-world operation, we do
not think that requiring a specific length of idle time would
necessarily make the resulting data set more representative.
    As described further in section III.C.2.ii, after consideration of
comment, EPA is including requirements in 40 CFR 1036.420 that specify
that during the end-of-day idle period, when testing vehicles with
automated engine shutdown features, manufacturers will be required to
override the automated shutdown feature where possible. This will
ensure

that the test data will contain at least 2,400 windows in the idle bin,
which otherwise would be unobtainable. For automated shutdown features
that cannot be overridden, the manufacturer may populate the bin with
zero emission values for idle until exactly 2,400 windows are achieved.
ii. Off-Cycle Test Procedures
    The final off-cycle test procedures include measuring off-cycle
emissions using the existing test procedures that specify measurement
equipment and the process of measuring emissions during testing in 40
CFR part 1065. Part 1036, subpart E contains the process for recruiting
test vehicles, how to test over the shift day, how to evaluate the
data, what constitutes a valid test, and how to determine if an engine
family passes. Measurements may use either the general laboratory test
procedures or the field-testing procedures in 40 CFR part 1065, subpart
J. However, we are finalizing special calculations for bin 2 in 40 CFR
1036.530 that will supersede the brake-specific emission calculations
in 40 CFR part 1065. The test procedures require second-by-second
measurement of the following parameters:

 Molar concentration of CO2 (ppm)
 Molar concentration of NOX (ppm)
 Molar concentration of HC (ppm)
 Molar concentration of CO (ppm)
 Concentration of PM (g/m\3\)
 Exhaust flow rate (m\3\/s)

    Mass emissions of CO2 and each regulated pollutant are
separately determined for each 300-second window and are binned based
on the normalized CO2 rate for each window.
    Additionally, EPA agrees with commenters that the maximum allowable
engine coolant temperature at the start of the day should be raised to
40 degrees Celsius and we are finalizing this change in 40 CFR
1036.530. In the NPRM, we proposed 30 [deg]C which is 86 [deg]F. It is
possible that ambient temperatures in some regions of the United States
won't drop below this overnight. We are therefore finalizing 40 [deg]C
which is 104 [deg]F as this should ensure that high overnight ambient
temperatures do not prevent a manufacturer from testing a vehicle.
    The standards described in Section III.C.2.iii are expressed in
units of g/hr for bin 1 and mg/hp-hr for bin 2. However, unlike most of
our exhaust standards, the hp-hr values for the off-cycle standards do
not refer to actual brake work. Rather, they refer to nominal
equivalent work calculated proportional to the CO2 emission
rate. Thus, in 40 CFR 1036.530 the NOX emissions (``e'') in
g/hp-hr are calculated as:
[GRAPHIC] [TIFF OMITTED] TR24JA23.000

    The final requirements include a limited number of exclusions (six
total) in 40 CFR 1036.530(c)(3) that exclude some data from being
subject to the off-cycle standards. The first exclusion in 40 CFR
1036.530(c)(3)(i) is for data collected during periodic PEMS zero and
span drift checks or calibrations, where the emission analyzers and/or
flow meter are not available to measure emissions during that time and
these checks/calibrations are needed to ensure the robustness of the
data.
    The second exclusion in 40 CFR 1036.530(c)(3)(ii) is for data
collected anytime the engine is off during the course of the shift day,
with modifications from proposal that (1) this exclusion does not
include engine off due to automated stop-start, and (2) specific
requirements for vehicles with stop-start technology. In the NPRM, we
proposed excluding data for vehicles with stop-start technology when
the engine was off and requested comment on the appropriateness of this
exclusion. We received comment suggesting provisions for vehicles
equipped with automated stop-start technology. After considering
comments, EPA has included in the final rule requirements applicable
when testing vehicles with automatic engine shutdown (AES) and/or stop-
start technology. Under the final requirements, the manufacturer shall
disable AES and/or stop-start if it is not tamper resistant as
described in 40 CFR 1036.415(g), 1036.420(c), and 1036.530(c)(3). If
stop-start is tamper resistant, the 1-Hz emission rate for all GHG and
criteria pollutants shall be set to zero when AES and/or stop-start is
active and the engine is off, and these data are included in the normal
windowing process (i.e., the engine-off data are not treated as
exclusions). If at the end of the shift day there are not 2,400 windows
in bin 1 for a vehicle with AES and/or stop-start technology, the
manufacturer must populate the bin with additional windows with the
emission rate for each GHG and criteria pollutant set to zero to
achieve exactly 2,400 idle bin windows. This process accounts for
manufacturers who implement a start/stop mode that cannot be overridden
and applies the windowing and binning process in a way that is similar
to the process applied to a conventionally idling vehicle.
    The third exclusion in 40 CFR 1036.530(c)(3)(iii) is for data
collected during infrequent regeneration events. The data collected for
the test order may not collect enough operation to properly weight the
emissions rates during an infrequent regeneration event with emissions
that occur without an infrequent regeneration event.
    The fourth exclusion in 40 CFR 1036.530(c)(3)(iv) is for data
collected when ambient temperatures are below 5 [deg]C (this aspect
includes some modifications from proposal), or when ambient
temperatures are above the altitude-based value determined using
Equation 40 CFR 1036.530-1. The colder temperatures can significantly
inhibit the engine's ability to maintain aftertreatment temperature
above the minimum operating temperature of the SCR catalyst while the
higher temperature conditions at altitude can limit the mass airflow
through the engine, which can adversely affect the engine's ability to
reduce engine out NOX through the use of exhaust gas
recirculation (EGR). In addition to affecting EGR, the air-fuel ratio
of the engine can decrease under high load, which can increase exhaust
temperatures above the conditions where the SCR catalyst is most
efficient at reducing NOX. However, we also do not want to
select temperature limits that overly exclude operation, such as
setting a cold temperature limit so high that it excludes important
initial cold start operation from all tests, or a number of return to
service events. These are important operational regimes, and the MAW
protocol is intended to capture emissions over the entire operation of
the vehicle. The final rule strikes an appropriate balance between
these considerations.
    In the NPRM, we proposed excluding data when ambient temperatures
were below -7 [deg]C and requested comment on the appropriateness of
this exclusion. Several comments disagreed with the proposed low
temperature exclusion level and recommended a higher

temperature of 20 [deg]C as well as additional exemptions for coolant
and oil temperatures, and recommended low temperature exclusion
temperatures that ranged from 20 to 70 [deg]C. After considering
comments, we adjusted the final ambient temperature exclusion to 5
[deg]C. We have additionally incorporated a temperature-based
adjustment to the final numerical NOX standards, as
described in Section III.C.iii. However, we have not incorporated
exclusions based on coolant and oil temperatures. These changes are
supported by data recently generated from testing at SwRI with the EPA
Stage 3 engine at low temperatures over the CARB Southern Route Cycle
and Low Load Cycle. This testing consisted of operation of the engine
over the duty-cycle with the test cell ambient temperature set at 5
[deg]C with air flow moving over the aftertreatment system to simulate
the airflow over the aftertreatment during over the road operation. The
results indicated that there were cold ambient air temperature effects
on aftertreatment temperature that reduced NOX reduction
efficiency, which supports that the temperature should be increased.
With these changes, our analysis, as described in section III.C, shows
that the off-cycle standards are achievable for MY 2027 and later
engines down to 5 [deg]C, taking into account the temperature-based
adjustment to the final numerical standards. We have concerns about
whether the off-cycle standards could be met below 5 [deg]C after
taking a closer look at all data regarding real world effects and based
on this we are exempting data from operation below 5 [deg]C from being
subject to the standards.
    The fifth exclusion in 40 CFR 1036.530(c)(3)(v) is for data
collected where the altitude is greater than 5,500 feet above sea level
for the same reasons as for the high temperatures at altitude
exclusion.
    The sixth exclusion in 40 CFR 1036.530(c)(3)(vi) is for data
collected when any approved Auxiliary Emission Control Device (AECD)
for emergency vehicles are active because the engines are allowed to
exceed the emission standards while these AECDs are active.
    To reduce the influence of environmental conditions on the accuracy
and precision of the PEMS for off-cycle in-use testing, we are adding
additional changes to those proposed in requirements in 40 CFR
1065.910(b). These requirements are to minimize the influence of
temperature, electromagnetic frequency, shock, and vibration on the
emissions measurement. If the design of the PEMS or the installation of
the PEMS does not minimize the influence of these environmental
conditions, the final requirements specify that the PEMS must be
installed in an environmental chamber during the off-cycle test to
minimize these effects.
iii. Off-Cycle Standards
    For NOX, we are finalizing separate standards for
distinct modes of operation. To ensure that the duty-cycle
NOX standards and the off-cycle NOX standards are
set at the same relative stringency level, the bin 1 standard is
proportional to the Voluntary Idle standard discussed in Section
III.B.2.iv, and the bin 2 standard is proportional to a weighted
combination of the LLC standard discussed in Section III.B.2.iii and
the SET standard discussed in Section III.B.2.ii. For bin 1, the
NOX emission standard for all CI primary intended service
classes is 10.0 g/hr starting in model year 2027. For PM, HC and CO we
are not setting standards for bin 1 because the emissions from these
pollutants are very small under idle conditions and idle operation is
extensively covered by the SET, FTP, and LLC duty cycles discussed in
Section III.B.2. The combined NOX bin 2 standard is weighted
at 25 percent of the LLC standard and 75 percent of the SET standard,
reflecting the nominal flow difference between the two cycles. For HC,
the bin 2 standard is also set at values proportional to a 25 percent/
75 percent weighted combination of the LLC standard and the SET
standard.\288\ For PM and CO, the SET, FTP, and LLC standards are the
same numeric value, so bin 2 is proportional to that numeric standard.
The numerical values of the off-cycle standards for bin 2 are shown in
Table III-17.
---------------------------------------------------------------------------

    \288\ See Preamble Section III.B.2 for the HC standards for the
SET and LLC.
---------------------------------------------------------------------------

    The final numerical off-cycle bin 1 NOX standard reflect
a conformity factor of 1.0 times the Clean Idle standard discussed in
Section III.B.2.iv. The final numerical off-cycle bin 2 standards for
all pollutants reflect a conformity factor of 1.5 times the duty-cycle
standards set for the LLC and SET cycles discussed in Section
III.B.2.ii and Section III.B.2.iii. Additionally, as discussed in
Section III.B.2, the in-use NOX off-cycle standard for
Medium and Heavy HDE reflects an additional 15 mg/hp-hr NOX
allowance above the bin 2 standard. Similar to the duty cycle
standards, the off-cycle standards were set at a level that resulted in
at least 40 percent compliance margin for the EPA Stage 3 engine. We
requested and received comments on the appropriate scaling factors or
other approaches to setting off-cycle standards. After consideration of
the comments, we believe the final numerical standards are feasible and
appropriate for certification and in-use testing. We note that the
final standards are similar, but not identical to, the options proposed
in the NPRM. As with the duty cycle standards discussed in Preamble
Section III.B, the data from the EPA Stage 3 engine supported the most
stringent numeric standards we proposed under low-load operation and
the most stringent numeric standards we proposed for MY 2027 under high
load operation. More discussion of the feasibility of these standards
can be found in the following discussion and in Section III.C.3 and
Response to Comments Section 11.3.1.

                                     Table III-17--Off-Cycle Bin 2 Standards
----------------------------------------------------------------------------------------------------------------
                       NOX  (mg/hp-hr)                          HC (mg/hp-hr)    PM (mg/hp-hr)     CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
58 \a\.......................................................             120              7.5                9
----------------------------------------------------------------------------------------------------------------
\a\ An interim NOX compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy
  HDE. Manufacturers will add the compliance allowance to the NOX standard that applies for each duty cycle and
  for off-cycle Bin 2, for both in-use field testing and laboratory testing as described in 40 CFR 1036, subpart
  E. Note, the NOX compliance allowance doesn't apply to confirmatory testing described in 40 CFR 1036.235(c) or
  selective enforcement audits described in 40 CFR part 1068.

    In the proposal, we requested comment on the in-use test conditions
over which engines should be required to comply with the standard,
asking commentors to take into consideration any tradeoffs that broader
or narrower

conditions might have on the stringency of the standard we set. After
considering comments on low ambient air temperature and the available
data from the low-temperature Stage 3 testing at SwRI described in
section III.C.2.ii, we are also incorporating an adjustment to the
numerical off-cycle bin 1 and bin 2 standards for NOX as a
function of ambient air temperature below 25 [deg]C. The results
demonstrated higher NOX emissions at low temperatures,
indicating that standards should be numerically higher to account for
real-world temperature effects on the aftertreatment system. To
determine the magnitude of this adjustment, we calculated the increase
in the Stage 3 engine NOX emissions over the CARB Southern
Route Cycle at low temperature over the NOX emissions at 25
[deg]C. These values were linearly extrapolated to determine the
projected increase at 5 [deg]C versus 25 [deg]C. Table III-18 presents
the numerical value of each off-cycle bin 1 and bin 2 NOX
standard at both 25 [deg]C and 5 [deg]C.
    Under the final requirements in 40 CFR 1036.104, the ambient
temperature adjustment is applied based on the average 1-Hz ambient air
temperature during the shift day for all data not excluded under 40 CFR
1036.530(c), calculated as the time-averaged temperature of all
included data points. If this average temperature is 25 [deg]C or
above, no adjustment to the standard is made. If the average
temperature is below 25 [deg]C, the applicable NOX standard
is calculated using the equations in Table 3 to paragraph (a)(3) of 40
CFR 1036.104 Table III-18 for the appropriate service class and bin.

                      Table III-18--Temperature Adjustments to the Off-Cycle NOX Standards
----------------------------------------------------------------------------------------------------------------
                                                                         NOX        NOX
                                                                       standard   standard
           Service class                Applicability         Bin       at 25       at 5       Applicable unit
                                                                        [deg]C     [deg]C
----------------------------------------------------------------------------------------------------------------
All...............................  All..................          1         10     \a\ 15  g/hr.
Light HDE.........................  Certification & In-            2         58    \a\ 102  mg/hp-hr.
                                     use.
Medium and Heavy HDE..............  Certification........          2         58    \a\ 102  mg/hp-hr.
Medium and Heavy HDE..............  In-Use...............          2     \a\ 73    \a\ 117  mg/hp-hr.
----------------------------------------------------------------------------------------------------------------
\a\ The Bin 1 and Bin 2 ambient temperature adjustment and the NOX compliance allowance for in-use testing do
  not scale with the FELFTPNOx.

3. Feasibility of the Diesel (Compression-Ignition) Off-Cycle Standards
i. Technologies
    As a starting point for our determination of the appropriate
numeric levels of the off-cycle emission standards, we considered
whether manufacturers could meet the duty-cycle standard corresponding
to the type of engine operation included in a given bin,\289\ as
follows:
---------------------------------------------------------------------------

    \289\ See preamble Section III.B.3 for details on EPA's
assessment of the feasibility of the duty-cycle standards.
---------------------------------------------------------------------------

     Bin 1 operation is generally similar to operation at idle
and the lower speed portions of the LLC.
     Bin 2 operation is generally similar to operation over the
LLC, the FTP and much of the SET.
    An important question is whether the off-cycle standards would
require technology beyond what we are projecting would be necessary to
meet the duty-cycle standards. As described in this section, we do not
expect the off-cycle standards to require different technologies.
    This is not to say that we expect manufacturers to be able to meet
these standards with no additional work. Rather, we project that the
off-cycle standards can be met primarily through additional effort to
calibrate the duty-cycle technologies to function properly over the
broader range of in-use conditions. We also recognize that
manufacturers can choose to include additional technology, if it
provided a less expensive or otherwise preferred option.
    When we evaluated the technologies discussed in Section III.B.3.i
with emissions controls that were designed to cover a broad range of
operation, it was clear that we should set the off-cycle standards to
higher numerical values than the duty-cycle standards to take into
account the broader operations covered by the off-cycle test
procedures. Section III.C.3.ii explains how the technology and controls
performed when testing with the off-cycle test procedures over a broad
range of operation. The data presented in Section III.C.3.ii shows that
even though there are similarities in the operation between the duty
cycles (SET, FTP, and LLC) and the off-cycle bins 1 and 2, the broader
range of operation covered by the off-cycle test procedure results in a
broader range of emissions performance, which justifies setting the
numeric off-cycle standards higher than the corresponding duty cycle
standards for equivalent stringency. In addition to this, the off-cycle
test procedures and standards cover a broader range of ambient
temperature and pressure, which can also increase the emissions from
the engine as discussed in Section III.C.2.ii.
ii. Summary of Feasibility Analysis
    To identify appropriate numerical levels for the off-cycle
standards, we evaluated the performance of the EPA Stage 3 engine in
the laboratory on five different cycles that were created from field
data of HD engines that cover a range of off-cycle operation. These
cycles are the CARB Southern Route Cycle, Grocery Delivery Truck Cycle,
Drayage Truck Cycle, Euro-VI ISC Cycle (EU ISC) and the Advanced
Collaborative Emissions Study (ACES) cycle. The CARB Southern Route
Cycle is predominantly highway operation with elevation changes
resulting in extended motoring sections followed by high power
operation. The Grocery Delivery Truck Cycle represents goods delivery
from regional warehouses to downtown and suburban supermarkets and
extended engine-off events characteristic of unloading events at
supermarkets. Drayage Truck Cycle includes near dock and local
operation of drayage trucks, with extended idle and creep operation.
Euro-VI ISC Cycle is modeled after Euro VI ISC route requirements with
a mix of 30 percent urban, 25 percent rural and 45 percent highway
operation. ACES Cycle is a 5-mode cycle developed as part of ACES
program. Chapter 3 of the RIA includes figures that show the engine
speed, engine torque and vehicle speed of the cycles.
    The engine was initially calibrated to minimize NOX
emissions for the dynamometer duty cycles (SET, FTP, and LLC). It was
then further calibrated to achieve more optimal performance over off-
cycle operation. The test results shown in Table III-19 provide a
reasonable basis for evaluating the feasibility of controlling off-
cycle emissions to a useful life of 435,000 miles and 800,000 miles.
Additionally,

the engine tested did not include the SCR catalyst volume that is
included in our cost analysis and that we determined should enable
lower bin 2 NOX emissions, further supporting that the final
standards are feasible. Additionally, the 800,000 mile aged
aftertreatment was tested over the CARB Southern Route Cycle with an
ambient temperature between 2 [deg]C and 9 [deg]C (6.8 [deg]C average),
the average of which is slightly above the 5 [deg]C minimum ambient
temperature that the final requirements specify as the level below
which test data are excluded.\290\ The summary of the results is in
Chapter 3 of the RIA. For Light HDE standards, we looked at the data at
the equivalent of 435,000 miles.\291\ For the Medium and Heavy HDE
standards we looked at the data at the equivalent of 800,000
miles.\292\
---------------------------------------------------------------------------

    \290\ The low ambient temperature exclusion was raised from the
proposed level of -7 [deg]C to 5 [deg]C, since engines can continue
to use EGR to reduce NOX without the use of an EGR cooler
bypass at and above 5 [deg]C. See RIA Chapter <IP_ADDRESS>.2 for a
summary of data from the EPA Stage 3 engine with three different
idle calibrations.
    \291\ See Section III.B.3.ii for an explanation on why we
determined data at the equivalent of 435,000 miles was appropriate
for determining the feasibility of the Light HDE standards.
    \292\ Similar to our reasoning in Section III.B.3.ii for using
the interpolated data at the equivalent of 650,000 miles to
determine the feasibility of the duty cycle standards for Medium and
Heavy HDE, we determined the data at the equivalent of 800,000 was
appropriate for determining the feasibility of the Medium and Heavy
HDE off-cycle standards. The one difference is that emission data
was not collected at the equivalent of 600,000 miles. Therefore, we
used the data at the equivalent of 800,000 miles (rather than
assuming the emissions performance changed linearly and
interpolating the emissions from the data at the equivalent of
435,000 and 800,000 miles) to determine the emissions performance at
the equivalent of 650,000 miles. We think it's appropriate to use
the data at the equivalent of 800,000 miles (rather than the
interpolated data at the equivalent of 650,000 miles) to account for
uncertainties in real world performance, particularly given the
significant increases in useful life, decreases in the numeric
levels of the standards, and the advanced nature of the
technologies.

                         Table III-19--EPA Stage 3 NOX Emissions Off-Cycle Operation Without Adjustments for Crankcase Emissions
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                           CARB southern  Grocery deliv.
   Equivalent miles, ambient T ([deg]C)                Bin No.              route cycle        cycle           ACES           EU ISC          Drayage
--------------------------------------------------------------------------------------------------------------------------------------------------------
435,000, 25 [deg]C........................  1 (g/hr)....................             0.7             1.0             0.9             0.4             0.3
                                            2 (mg/hp-hr)................              32              21              20              31              19
800,000, 25 [deg]C........................  1 (g/hr)....................             0.7             3.3             1.5             0.4             1.1
                                            2 (mg/hp-hr)................              47              32              34              32              28
                                                                                ---------------------------------------------------------------
800,000, 2 to 9 [deg]C....................  1 (g/hr)....................             1.4                            Not tested
                                                                                ---------------------------------------------------------------
                                            2 (mg/hp-hr)................              87                            Not tested
--------------------------------------------------------------------------------------------------------------------------------------------------------

a. Bin 1 Evaluation
    Bin 1 includes the idle operation and some of the lower speed
operation that occurs during the FTP and LLC. However, it also includes
other types of low-load operation observed with in-use vehicles, such
as operation involving longer idle times than occur in the LLC. To
ensure that the bin 1 standard is feasible, we set the idle bin
standard at the level projected to be achievable engine-out with
exhaust temperatures below the aftertreatment light-off temperature. As
can be seen from the results in Table III-19, the EPA Stage 3 engine
performed well below the bin 1 NOX standards. The summary of
the results is located in Chapter 3 of the RIA.
    For bin 1 we are finalizing NOX standard at a level
above what we have demonstrated because there are conditions in the
real world that may prevent the emissions control technology from being
as effective as demonstrated with the EPA Stage 3 engine. For example,
under extended idle operation the EGR rate may need to be reduced to
maintain engine durability. Under extended idle operation with cold
ambient temperatures, the aftertreatment system can lose NOX
reduction efficiency which can also increase NOX emissions.
Taking this under consideration, as well as other factors, we believe
that the final bin 1 NOX standard in Table III-17 is the
lowest achievable standard in MY 2027.
b. Bin 2 Evaluations
    As can be seen see from the results in Table III-19, the
NOX emissions from the Stage 3 engine in bin 2 were below
the final off-cycle standards for each of the off-cycle duty-cycles.
The HC and CO emissions measured for each of these off-cycle duty
cycles were well below the final off-cycle standards for bin 2. PM
emissions were not measured during the off-cycle tests, but based on
the effectiveness of DPFs over all engine operation as seen with the
SET, FTP, and LLC, our assessment is that the final PM standards in Bin
2 are feasible. The summary of the results is located in Chapter 3 of
the RIA.
    For bin 2, all the 25 [deg]C off-cycle duty cycles at a full useful
life of 800,000 miles had emission results below the NOX
certification standard of 58 mg/hp-hr shown in Table III-19.
Additionally, the CARB Southern Route Cycle run at ambient temperatures
under 10 [deg]C had emission results below the Heavy HDE NOX
in-use off-cycle standard of 106 mg/hp-hr which is the standard at 10
[deg]C as determined from Equation 40 CFR 1036.104-2. While this cycle
was run at temperatures above the minimum ambient temperature exclusion
limit of 5 [deg]C that we are finalizing, we expect actual HDIUT
testing to be less severe than the demonstration. Nonetheless, since
the results of the low ambient temperature testing demonstrated higher
NOX emissions at low temperatures, as shown in Table III-19,
we have finalized standards that are numerically higher at lower
temperatures to account for real-world temperature effects on the
aftertreatment system.
    In the NPRM, we requested comment on the numerical values of the
off-cycle standards, as well as the overall structure of the off-cycle
program. We received comments recommending both lower and higher
numerical standards than were proposed. After considering comments, we
believe the off-cycle standards that we are finalizing are appropriate
and feasible values. See Response to Comments Section 11.3.1 for
further details on these comments and EPA's response to these comments.
4. Compliance and Flexibilities for Off-Cycle Standards
    Given the similarities of the off-cycle standards and test
procedures to the current NTE requirements that we are

replacing starting in MY 2027, we evaluated the appropriateness of
applying the current NTE compliance provisions to the off-cycle
standards we are finalizing and determined which final compliance
requirements and flexibilities are applicable to the new final off-
cycle standards, as discussed immediately below.
i. Relation of Off-Cycle Standards To Defeat Devices
    CAA section 203 prohibits bypassing or rendering inoperative a
certified engine's emission controls. When the engine is designed or
modified to do this, the engine is said to have a defeat device. With
today's engines, the greatest risks with respect to defeat devices
involve manipulation of the engine's electronic controls. EPA refers to
an element of design that manipulates emission controls as an Auxiliary
Emission Control Device (AECD).\293\ Unless explicitly permitted by
EPA, AECDs that reduce the effectiveness of emission control systems
under conditions which may reasonably be expected to be encountered in
normal vehicle operation and use are prohibited as defeat devices under
current 40 CFR 86.004-2.
---------------------------------------------------------------------------

    \293\ 40 CFR 86.082-2 defines Auxiliary Emission Control Device
(AECD) to mean ``any element of design which senses temperature,
vehicle speed, engine RPM, transmission gear, manifold vacuum, or
any other parameter for the purpose of activating, modulating,
delaying, or deactivating the operation of any part of the emission
control system.''
---------------------------------------------------------------------------

    For certification, EPA requires manufacturers to identify and
describe all AECDs.\294\ For any AECD that reduces the effectiveness of
the emission control system under conditions which may reasonably be
expected to be encountered in normal vehicle operation and use,
manufacturers must provide a detailed justification.\295\ We are
migrating the definition of defeat device from 40 CFR 86.004-2 to 40
CFR 1036.115(h) and clarifying that an AECD is not a defeat device if
such conditions are substantially included in the applicable procedure
for duty-cycle testing as described in 40 CFR 1036, subpart F. Such
AECDs are not treated as defeat devices because the manufacturer shows
that their engines are able to meet standards during duty-cycle testing
while the AECD is active. The AECD might reduce the effectiveness of
emission controls, but not so much that the engine fails to meet the
standards that apply.
---------------------------------------------------------------------------

    \294\ See 40 CFR 86.094-21(b)(1)(i)(A).
    \295\ See definition of ``defeat device'' in 40 CFR 86.004-2.
---------------------------------------------------------------------------

    We do not extend this same treatment to off-cycle testing, for two
related reasons. First, we can have no assurance that the AECD is
adequately exercised during any off-cycle operation to support the
conclusion that the engine will consistently meet emission standards
over all off-cycle operation. Second, off-cycle testing may involve
operation over an infinite combination of engine speeds and loads, so
excluding AECDs from consideration as defeat devices during off-cycle
testing would make it practically impossible to conclude that an engine
has a defeat device.
    If an engine meets duty-cycle standards and the engine has no
defeat devices, we should be able to expect engines to achieve a
comparable level of emission control for engine operation that is
different than what is represented by the certification duty cycles.
The off-cycle standards and measurement procedures allow for a modest
increase in emissions for operation that is different than the duty
cycle, but manufacturers may not change emission controls to increase
emissions to the off-cycle standard if those controls were needed to
meet the duty-cycle standards. The finalized off-cycle standards are
set at a level that is feasible under all operating conditions, so we
expect that under much of the engine operation the emissions are well
below the final off-cycle standards.
ii. Heavy-Duty In-Use Testing Program
    Under the current manufacturer-run heavy-duty in-use testing
(HDIUT) program, EPA annually selects engine families to evaluate
whether engines are meeting current emissions standards. Once we submit
a test order to the manufacturer to initiate testing, it must contact
customers to recruit vehicles that use an engine from the selected
engine family. The manufacturer generally selects five unique vehicles
that have a good maintenance history, no malfunction indicators on, and
are within the engine's regulatory useful life for the requested engine
family. The tests require use of portable emissions measurement systems
(PEMS) that meet the requirements of 40 CFR part 1065, subpart J.
Manufacturers collect data from the selected vehicles over the course
of a day while they are used for their normal work and operated by a
regular driver, and then submit the data to EPA. Compliance is
currently evaluated with respect to the NTE standards.
    With some modifications from proposal, we are continuing the HDIUT
program, with compliance with respect to the new off-cycle standards
and test procedures added to the program beginning with MY 2027
engines. As proposed, we are not carrying forward the Phase 2 HDIUT
requirements in 40 CFR 86.1915 once the NTE phases out after MY 2026.
Under the current NTE based off-cycle test program, if a manufacturer
is required to test ten engines under Phase 1 testing and less than
eight fully comply with the vehicle pass criteria in 40 CFR 86.1912, we
could require the manufacturer to initiate Phase 2 HDIUT testing which
would require manufacturers to test an additional 10 engines. After
consideration of comments, we are generally finalizing our overall long
term HDIUT program's engine testing steps and pass/fail criteria as
proposed; however, EPA believes that an interim approach in the initial
two years of the program is appropriate, as manufacturers transition to
the final standards, test procedures, and requirements, while still
providing overall compliance assurance during that transition. More
specifically, we are finalizing that compliance with the off-cycle
standards would be determined by testing a maximum of fifteen engines
for MYs 2027 and MY 2028 under the interim provisions, and ten engines
for MYs 2029 and later. As noted in the proposal, the testing of a
maximum of ten engines was the original limit under Phase 1 HDIUT
testing in 40 CFR 86.1915. Similar to the current Phase 1 HDIUT
requirements in 40 CFR 86.1912, the finalized 40 CFR 1036.425 and
finalized interim provision in 40 CFR 1036.150(z) require initially
testing five engines. Various outcomes are possible based on the
observed number of vehicle passes or failures from manufacturer-run in-
use testing, as well as other supplemental information. Under the
interim provisions for MYs 2027 and 2028, if four of the first test
vehicles meet the off-cycle standards, testing stops, and no other
action is required of the manufacturer for that diesel engine family.
For MYs 2029 and later, if five of the first test vehicles meet the
off-cycle standards, testing stops, and no other action is required of
the manufacturer for that diesel engine family. For MYs 2027 and 2028,
if two of those engines do not comply fully with the off-cycle bin
standards, the manufacturer would then test five additional engines for
a total of ten. For MYs 2029 and later, if one of those engines does
not comply fully with the off-cycle bin standards, the manufacturer
would then test a sixth engine. For MYs 2027 and 2028, if eight of the
ten engines tested pass, testing stops, and no other action is required
of the manufacturer for that diesel engine family under the program for
that model

year. For MYs 2029 and later, if five of the six engines tested pass,
testing stops, and no other action is required of the manufacturer for
that diesel engine family under the program for that model year. For
MYs 2027 and 2028, if three or more of the first ten engines tested do
not pass, the manufacturer may test up to five additional engines until
a maximum of fifteen engines have been tested. For MYs 2029 and later,
when two or more of the first six engines tested do not pass, the
manufacturer must test four additional engines until a total of ten
engines have been tested. If the arithmetic mean of the emissions from
the ten, or up to fifteen under the interim provisions, engine tests
determined in Sec.  1036.530(g), or Sec.  1036.150(z) under the interim
provisions, is at or below the off-cycle standard for each pollutant,
the engine family passes and no other action is required of the
manufacturer for that diesel engine family. If the arithmetic mean of
the emissions from the ten, or up to fifteen under the interim
provisions, engines for either of the two bins for any of the
pollutants is above the respective off-cycle bin standard, the engine
family fails and the manufacturer must join EPA in follow-up
discussions to determine whether any further testing, investigations,
data submissions, or other actions may be warranted. Under the final
requirements, the manufacturer may accept a fail result for the engine
family and discontinue testing at any point in the sequence of testing
the specified number of engines.
    We received comment on the elimination of Phase 2 testing. See
Response to Comment Section 11.5.1 for further information on these
comments and EPA's response to these comments. As noted in the
preceding paragraphs, we are finalizing elimination of Phase 2 testing.
However, we also are clarifying what happens when an engine family
fails under the final program. In such a case, three outcomes are
possible. First, we may ultimately decide not to take further action if
no nonconformity is indicated after a thorough evaluation of the causes
or conditions that caused vehicles in the engine family to fail the
off-cycle standards, and a review of any other supplemental information
obtained separately by EPA or submitted by the manufacturer shows that
no significant nonconformity exists. Testing would then stop, and no
other action would be required of the manufacturer for that diesel
engine family under the program for that year. Second, we may seek some
form of remedial action from the manufacturer based on our evaluation
of the test results and review of other supplemental information.
Third, and finally, in situations where a significant nonconformity is
observed during testing, we may order a recall action for the diesel
engine family in question if the manufacturer does not voluntarily
initiate an acceptable remedial action.
    In the NPRM, we proposed allowing manufacturers to test a minimum
of 2 engines using PEMS, in response to a test order program, provided
they measure, and report in-use data collected from the engine's on-
board NOX measurement system. EPA received comments
expressing concerns on the feasibility of this alternate in-use testing
option. Given meaningful uncertainties in whether technological
advancement of measurement capabilities of these sensors will occur by
MY 2027, at this time, EPA is not including the proposed option in 40
CFR 1036.405(g) and not finalizing this alternative test program option
in this action. The final in-use option for manufacturers to show
compliance with the off-cycle standard will require the use of
currently available PEMS to measure criteria pollutant emissions, with
the sampling and measurement of emission concentrations in a manner
similar to the current NTE in-use test program as described in 40 CFR
part 1036, subpart E, and Section III.C of this preamble. See Response
to Comment Section 11.5.3 for further information on these comments and
EPA's response to these comments.
    In the NPRM, we proposed to not carry forward the provision in 40
CFR 86.1908(a)(6) that considers an engine misfueled if operated on a
biodiesel fuel blend that is either not listed as allowed or otherwise
indicated to be an unacceptable fuel in the vehicle's owner or operator
manual. We also proposed in 40 CFR 1036.415(c)(1) to allow vehicles to
be tested for compliance with the new off-cycle standards on any
commercially available biodiesel fuel blend that meets the
specifications for ASTM D975 or ASTM D7467.
    We received comments on these proposed requirements. After
considering the comments, we have altered provisions in the final rule
from what was proposed. EPA agrees with the commenters' recommendation
to restrict in-use off-cycle standards testing on vehicles that have
been fueled with biodiesel to those that are either expressly allowed
in the vehicle's owner or operator manual or not otherwise indicated as
an unacceptable fuel in the vehicle's owner or operator manual or in
the engine manufacturer's published fuel recommendations. EPA believes,
as explained in section IV.H of this preamble, that data show biodiesel
is compliant with ASTM D975, D7467 and D6751, that the occurrence of
metal contamination in the fuel pool is extremely low, and that the
metal content of biodiesel is low. However, EPA understands that
manufacturers have little control over the quality of fuel that their
engines will encounter over years of in-use operation.\296\ To address
uncertainties, EPA is modifying the proposed approach to in-use off-
cycle standards testing and will allow manufacturers to continue to
exempt engines from in-use off-cycle standards testing if the engine is
being operated on biofuel that exceeds the manufacturers maximum
allowable biodiesel percentage usable in their engines, as specified in
the engine owner's manual. See 40 CFR 1036.415(c)(1).
---------------------------------------------------------------------------

    \296\ At this time, as explained in the proposed rule, EPA did
not propose and is not taking final action to regulate biodiesel
blend metal content because the available data does not indicate
that there is widespread off-specification biodiesel blend stock or
biodiesel blends in the marketplace. EPA also notes that the request
to set a maximum nationwide biodiesel percentage of 20 percent is
outside the scope of this final rule.
---------------------------------------------------------------------------

    EPA requested comment on a process for a manufacturer to receive
EPA approval to exempt test results from in-use off-cycle standards
testing from being considered for potential recall if an engine
manufacturer can show that the vehicle was historically fueled with
biodiesel blends whose B100 blendstock did not meet the ASTM D6751-20a
limit for Na, K, Ca, and/or Mg metal (metals which are a byproduct of
biodiesel production) or contaminated petroleum based fuels (i.e. if
the manufacturer can show that the vehicle was misfueled), and the
manufacturer can show that misfueling lead to degradation of the
emission control system performance. 40 CFR 1068.505 describes how
recall requirements apply for engines that have been properly
maintained and used. Given the risk of metal contamination from
biofuels and in some rare cases petroleum derived fuels, EPA will be
willing to engage with any information manufacturers can share to
demonstrate that the fueling history caused an engine to be
noncompliant based on improper maintenance or use. It is envisioned
that this engagement would include submission by the manufacturer of a
comparison of the degraded emission control system to a representative
compliant system of similar miles with respect to content of the
contaminant, including an analysis of the level of the poisoning agents
on the catalysts in the engine's aftertreatment system. This

process addresses concerns expressed by a commentor who stated that it
would be difficult if not impossible for a manufacturer to provide
``proof of source'' of the fuel contamination that led to the
degradation in catalyst performance. This clarifies that the
manufacturer must only determine the amount of poisoning agent present
versus a baseline aftertreatment system.
    In the NPRM, we requested comment on the need to measure PM
emissions during in-use off-cycle testing of engines that comply with
MY 2027 or later standards if they are equipped with a DPF. PEMS
measurement is more complicated and time-consuming for PM measurements
than for gaseous pollutants such as NOX and eliminating it
for some or all of in-use off-cycle standards testing would provide
significant cost savings. We received comments both in support of and
in opposition to continuing to require measurement of PM during in-use
off-cycle standards testing. After considering these comments, EPA
believes that historic test results from the manufacturer run in-use
test program indicate that there is not a PM compliance problem for
properly maintained engines. Additionally, we believe that removing the
requirement for in-use off-cycle PM standards testing will not lead
manufacturers to stop using wall flow DPF technology to meet the PM
standards. Therefore, EPA is not including the proposed requirement for
manufacturers to measure PM in the final 40 CFR 1036.415(d)(1) but is
modifying that requirement from proposal to include a final provision
in this paragraph that EPA may request PM measurement and that
manufacturers must provide that measurement if EPA requests it.
Generally, EPA expects that test orders issued by EPA under 40 CFR
1036.405 will not include a requirement to measure PM.
    Furthermore, EPA received comments on the subject of the need to
measure NMHC emissions during in-use off-cycle testing of engines that
comply with MY 2027 or later standards. After considering comments, EPA
believes that historic test results from the manufacturer run in-use
test program indicate that there is not an NMHC compliance problem for
properly maintained engines. EPA is not including the proposed
requirement for manufacturers to measure NMHC in the final 40 CFR
1036.415(d)(1) but is modifying that requirement from proposal to
include a provision in this paragraph that EPA may request NMHC
measurement and that manufacturers must provide that measurement if EPA
requests it. Generally, EPA expects that test orders issued by EPA
under 40 CFR 1036.405 will not include a requirement to measure NMHC.
See Response to Comment Section 11.5.5 for further information on these
comments and EPA's response to comments on the subject of in-use off-
cycle standards PM and NMHC testing.
iii. PEMS Accuracy Margin
    EPA worked with engine manufacturers on a joint test program to
establish measurement allowance values to account for the measurement
uncertainty associated with in-use testing in the 2007-time frame for
gaseous emissions and the 2010-time frame for PM emissions to support
NTE in-use testing.\297\ \298\ \299\ PEMS measurement allowance values
in 40 CFR 86.1912 are 0.01 g/hp-hr for HC, 0.25 g/hp-hr for CO, 0.15 g/
hp-hr for NOX, and 0.006 g/hp-hr for PM. We are maintaining
the same values for HC, CO, and PM in this rulemaking. For
NOX we are finalizing an off-cycle NOX accuracy
margin (formerly known as measurement allowance) that is 5 percent of
the off-cycle standard for a given bin. This final accuracy margin is
supported by PEMS accuracy margin work at SwRI. The SwRI PEMS accuracy
margin testing was done on the Stage 3 engine, which was tested over
five field cycles with three different commercially available PEMS.
EPA's conclusion after assessing the results of that study, was that
accuracy margins set at 0.4 g/hr for bin 1 and 5 mg/hp-hr for bin 2
were appropriate.
---------------------------------------------------------------------------

    \297\ Feist, M.D.; Sharp, C.A; Mason, R.L.; and Buckingham, J.P.
Determination of PEMS Measurement Allowances for Gaseous Emissions
Regulated Under the Heavy-Duty Diesel Engine In-Use Testing Program.
SwRI 12024, April 2007.
    \298\ Feist, M.D.; Mason, R.L.; and Buckingham, J.P. Additional
Analyses of the Monte Carlo Model Developed for the Determination of
PEMS Measurement Allowances for Gaseous Emissions Regulated Under
the Heavy-Duty Diesel Engine In-Use Testing Program. SwRI[supreg]
12859. July 2007.
    \299\ Khalek, I.A.; Bougher, T.L.; Mason, R.L.; and Buckingham,
J.P. PM-PEMS Measurement Allowance Determination. SwRI Project
03.14936.12. June 2010.
---------------------------------------------------------------------------

    The accuracy margins we are finalizing differ from the 10 percent
of the standard margin proposed in the NPRM, which was based on an
earlier study by JRC. This SwRI PEMS accuracy margin study was on-going
at the time the NPRM was published, and the results were only available
post-NPRM publication.\300\ However, the NPRM did note that we would
consider the results of the SwRI PEMS study when they became available,
and that the final off-cycle bin NOX standards could be
higher or lower than what we proposed. EPA requested and received
comments on the value of the PEMS accuracy margin for NOX;
some commenters encouraged EPA to account for the SwRI PEMS accuracy
work that was carried out on the Stage 3 engine. We initially planned
to consider the results of this work and this was further supported
through recommendations by some commentors; thus, we believe that
incorporating the results of the latest study to determine an off-cycle
NOX accuracy margin is appropriate. The SwRI PEMS study is
further discussed in RIA Chapter 2. The study consisted of testing the
Stage 3 engine with three commercially available PEMS units over 19
different tests. These tests were 6 to 9 hours long, covering a wide
range of field operation. In addition, the Stage 3 engine was tested in
three different configurations to cover the range of emissions levels
expected from an engine both meeting and failing the final standards.
We believe, based on this robust data set that was evaluating using the
finalized test procedures, the SwRI study provides a more accurate
assessment of PEMS measurement uncertainty from field testing of heavy-
duty engines than what was determined from the JRC study that we relied
on in the proposal for the proposed 10 percent margin. See Response to
Comment Section 11.6 for further information on these comments and
EPA's response to these comments.
---------------------------------------------------------------------------

    \300\ The data and the results from the study were added to the
public docket prior to the signing of the final rule.
---------------------------------------------------------------------------

    It should be noted that our off-cycle test procedures already
include a linear zero and span drift correction over at least the shift
day, and we are finalizing requirements for at least hourly zero drift
checks over the course of the shift day on purified air. We believe
that the addition of these checks and the additional improvements we
implemented helped facilitate a measurement error that is lower than
the analytically derived JRC value of 10 percent.\301\
---------------------------------------------------------------------------

    \301\ Giechaskiel B., Valverde V., Clairotte M. 2020 Assessment
of Portable Emissions Measurement Systems (PEMS) Measurement
Uncertainty. JRC124017, EUR 30591 EN. https://publications.europa.eu/en/publications.
---------------------------------------------------------------------------

    We are updating 40 CFR 1065.935 to require hourly zeroing of the
PEMS analyzers using purified air for all analyzers. We are also
updating the drift limits for NOX analyzers to improve data
quality. Specifically, for NOX analyzers, we are requiring
an hourly or more frequent zero verification limit of 2.5 ppm, a zero-
drift limit over the entire shift day of 10 ppm, and a span drift limit
between the beginning and end of the shift day or more frequent span
verification(s) of 4 percent of the

measured span value. In the NPRM, we requested comment on the test
procedure updates in 40 CFR 1065.935 and any changes that would reduce
the PEMS measurement uncertainty. We received no comments on this topic
other than a few minor edits and are finalizing these updates with
minor edits for clarification.
iv. Demonstrating Off-Cycle Standards for Certification
    Consistent with current certification requirements in 40 CFR
86.007-21(p)(1), we are finalizing a new paragraph in 40 CFR
1036.205(p) that requires manufacturers to provide a statement in their
application for certification that their engine complies with the off-
cycle standards, along with testing or other information to support
that conclusion. We are finalizing this provision as proposed.

D. Summary of Spark-Ignition HDE Exhaust Emission Standards and Test
Procedures

    This section summarizes the exhaust emission standards, test
procedures, and other requirements and flexibilities we are finalizing
for certain spark-ignition (SI) heavy-duty engines. The exhaust
emission provisions in this section apply for SI engines installed in
vehicles above 14,000 lb GVWR and incomplete vehicles at or below
14,000 lb GVWR, but do not include engines voluntarily certified to or
installed in vehicles subject to 40 CFR part 86, subpart S.
    As described in this Section III.D, Spark-ignition HDE
certification will continue to be based on emission performance in lab-
based engine dynamometer testing, which will include a new SET duty
cycle to address high load operation. High load temperature protection
and idle emission control requirements are also added to supplement our
current FTP and new SET duty cycles. We are also lengthening the useful
life and emissions-related warranty periods for all heavy-duty engines,
including Spark-ignition HDE, as detailed in Sections IV.A and IV.B.1
of this preamble.
    The final exhaust emission standards in 40 CFR 1037.104 apply
starting in MY 2027. This final rule includes new standards over the
FTP duty cycle currently used for certification, as well as new
standards over the SET duty cycle to ensure manufacturers of Spark-
ignition HDE are designing their engines to address emissions in during
operation that is not covered by the FTP. The new standards are shown
in Table III-20.

                                                            Table III-20--Final Duty Cycle Emission Standards for Spark-Ignition HDE
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Model year 2026 and earlier \a\                                    Model year 2027 and later
                                                                 -------------------------------------------------------------------------------------------------------------------------------
                           Duty cycle                              NOX  (mg/hp-                                                    NOX  (mg/hp-
                                                                        hr)        HC (mg/hp-hr)   PM (mg/hp-hr)   CO (g/hp-hr)         hr)        HC (mg/hp-hr)   PM (mg/hp-hr)   CO (g/hp-hr)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SET.............................................................  ..............  ..............  ..............  ..............              35              60               5            14.4
FTP.............................................................             200             140              10            14.4              35              60               5             6.0
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Current emission standards for NOX, HC, and PM were converted from g/hp-hr to mg/hp-hr to compare with the final standards.

    Our proposal included two options of fuel-neutral standards that
applied the same numerical standards across all primary intended
service classes. The proposed NOX and PM standards for the
SET and FTP duty cycles were based on the emission performance of
technologies evaluated in our HD CI engine technology demonstration
program.\302\ We based the proposed SET and FTP standards for HC and CO
on HD SI engine performance.
---------------------------------------------------------------------------

    \302\ Our assessment of the projected technology package for
compression-ignition engines is based on both CARB's and EPA's
technology demonstration programs. See Section III.B for a
description of those technologies and test programs.
---------------------------------------------------------------------------

    Three organizations specifically expressed support for adopting the
standards of proposed Option 1 for Spark-ignition HDE. The final
standards are based largely on the emission levels of proposed Option
1, with some revisions to account for a single-step program, starting
in MY 2027. Some organizations commented that the proposed SI standards
were challenging enough to need the flexibility of ABT for HC and CO.
Consistent with the proposal for this rule, we are finalizing an ABT
program for NOX credits only and are discontinuing the
current options for manufacturers to generate HC and PM credits. We did
not request comment on and are not finalizing an option for
manufacturers to generate credits for CO. See Section IV.G of this
preamble and section 12 of the Response to Comments document for more
information on the final ABT program.
    We are remaining generally consistent with a fuel neutral approach
in the final SET and FTP standards, with the exception of CO for Spark-
ignition HDE over the new SET duty cycle. We expand on our rationale
for this deviation from fuel neutrality in Section III.D.1 where we
also describe our rationale for the final program, including a summary
of the feasibility demonstration, available data, and comments
received.
    After considering comments, we are revising three other proposed
provisions for Spark-ignition HDE as described in Section . Two new
requirements in 40 CFR 1036.115(j) focus on ensuring catalyst
efficiency at low loads and proper thermal management at high loads. We
are finalizing, with additional clarification, a new OBD flexibility
for ``sister vehicles''. We did not propose and are not finalizing
separate off-cycle standards, manufacturer-run in-use testing
requirements, or a low-load duty cycle for Spark-ignition HDE at this
time.\303\
---------------------------------------------------------------------------

    \303\ See section 3 of the Response to Comments document for
more information.
---------------------------------------------------------------------------

    The proposed rule provided an extensive discussion of the rationale
and information supporting the proposed standards (87 FR 17479, March
28, 2022). The RIA includes additional information related to the range
of technologies to control criteria emissions, background on applicable
test procedures, and the full feasibility analysis for Spark-ignition
HDE. See also section 3 of the Response to Comments for a detailed
discussion of the comments and how they have informed this final rule.
1. Basis of the Final Exhaust Emission Standards and Test Procedures
    EPA conducted a program with SwRI to better understand the
emissions performance limitations of current heavy-duty SI engines as
well as investigate the feasibility of advanced three-way catalyst
aftertreatment and technologies and strategies to meet our proposed
exhaust emission standards.\304\ Our demonstration included the use of
advanced catalyst

technologies artificially aged to the equivalent of 250,000 miles and
engine downspeeding. Our feasibility analyses for the exhaust emission
standards are based on the SwRI demonstration program. Feasibility of
the FTP standards is further supported by compliance data submitted by
manufacturers for the 2019 model year. We also support the feasibility
of the SET standards using engine fuel mapping data from a test program
performed by the agency as part of the HD GHG Phase 2 rulemaking. See
Chapter 3.2 of the RIA for more details related to the SwRI
demonstration program and the two supporting datasets.
---------------------------------------------------------------------------

    \304\ Ross, M. (2022). Heavy-Duty Gasoline Engine Low
NOX Demonstration. Southwest Research Institute. Final
Report EPA Contract 68HERC20D0014.
---------------------------------------------------------------------------

    Results from our SI HDE technology demonstration program (see Table
III-21 and Table III-22) show that the NOX standards based
on our CI engine feasibility analysis are also feasible for SI HDEs
over the SET and FTP duty cycles. The NOX standard was
achieved in this test program by implementing an advanced catalyst with
minor catalyst system design changes, and NOX levels were
further improved with engine down-speeding. The emission control
strategies that we evaluated did not specifically target PM emissions,
but we note that PM emissions remained low in our demonstration. We
project SI HDE manufacturers will maintain near-zero PM levels with
limited effort. The following sections discuss the feasibility of the
HC and CO standards over each of the duty cycles and the basis for our
final numeric standards' levels.
i. Federal Test Procedure and Standards for Spark-Ignition HDE
    After considering comments, we are finalizing FTP standards that
differ from our proposed options for Spark-ignition HDE. We are
finalizing standards of 35 mg/hp-hr NOX, 5 mg/hp-hr PM, 60
mg/hp-hr HC, and 6.0 g/hp-hr CO over the FTP duty cycle in a single
step for MY 2027 and later engines. The NOX and HC standards
match the MY 2027 step of proposed Option 1; the PM and CO standards
match the MY 2031 step of Option 1. All of these standards were
demonstrated to be technologically feasible in EPA's SI engine test
program.
    As shown in Table III-21, use of advanced catalysts provided
NOX emission levels over the FTP duty cycle well below
today's standards and below the certification levels of some of the
best performing engines certified in recent years.\305\ Engine down-
speeding further decreased CO emissions while maintaining
NOX, NMHC, and PM control. Engine down-speeding also
resulted in a small improvement in fuel consumption over the FTP duty
cycle, with fuel consumption being reduced from 0.46 to 0.45 lb/hp-hr.
See Chapter 3.2.3 of the RIA for an expanded description of the test
program and results.
---------------------------------------------------------------------------

    \305\ As presented in Chapter 3.2 of the RIA, MY 2019 gasoline-
fueled HD SI engine certification results included NOX
levels ranging from 40 to 240 mg/hp-hr at a useful life of 110,000
miles. MY 2019-2021 alternative-fueled (CNG, LPG) HD SI engine
certification results included NOx levels ranging from 6 to 70 mg/
hp-hr at the same useful life.

    Table III-21--Exhaust Emission Results From FTP Duty Cycle Testing in the HD SI Technology Demonstration
----------------------------------------------------------------------------------------------------------------
                                                   NOX  (mg/hp-
                                                        hr)        PM (mg/hp-hr)   HC (mg/hp-hr)   CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
Current Standards MY 2026 and earlier...........             200              10             140            14.4
Final Standards MY 2027 and later...............              35               5              60               6
Test Program Base Engine with Advanced Catalyst               19             4.8              32             4.9
 \a\............................................
Test Program Down-sped Engine with Advanced                   18             4.5              35            0.25
 Catalyst \b\...................................
----------------------------------------------------------------------------------------------------------------
\a\ Base engine's manufacturer-stated maximum test speed is 4715 RPM; advanced catalyst aged to 250,000 miles.
\b\ Down-sped engine's maximum test speed lowered to 4000 RPM; advanced catalyst aged to 250,000 miles.

    All SI HDEs currently on the market use a three-way catalyst (TWC)
to simultaneously control NOX, HC, and CO emissions.\306\ We
project most manufacturers will continue to use TWC technology and will
also adopt advanced catalyst washcoat technologies and refine their
existing catalyst thermal protection (fuel enrichment) strategies to
prevent damage to engine and catalyst components over the longer useful
life period we have finalized. We expect manufacturers, who design and
have full access to the engine controls, could achieve similar emission
performance as we demonstrated by adopting other, more targeted
approaches, including a combination of calibration changes, optimized
catalyst location, and fuel control strategies that EPA was unable to
evaluate in our demonstration program due to limited access to
proprietary engine controls.
---------------------------------------------------------------------------

    \306\ See Chapter 1.2 of the RIA for a detailed description of
the TWC technology and other strategies HD SI manufacturers use to
control criteria emissions.
---------------------------------------------------------------------------

    In the proposal we described how the FTP duty cycle did not
sufficiently incentivize SI HDE manufacturers to address fuel
enrichment and the associated CO emissions that are common under higher
load operations in the real-world. In response to our proposed rule,
one manufacturer shared technical information with us regarding an SI
engine architecture under development that is expected to reduce or
eliminate enrichment and the associated CO emissions.\307\ The company
indicated that the low CO emissions may come at the expense of HC
emission reduction in certain operation represented by the FTP duty
cycle, and reiterated their request for an 80 mg/hp-hr HC standard, as
was stated in their written comments. We are not finalizing an HC
standard of 80 mg/hp-hr as requested in comment. For the FTP duty
cycle, the EPA test program achieved HC levels more than half of the
requested level without compromising NOX or CO emission
control (see Table III-21), which clearly demonstrates feasibility.
---------------------------------------------------------------------------

    \307\ U.S. EPA. Stakeholder Meeting Log. December 2022.
---------------------------------------------------------------------------

    While we demonstrated emission levels below the final standards of
60 mg HC/hp-hr and 35 mg NOX/hp-hr over the FTP duty cycle
in our SI HDE testing program, we expect manufacturers to apply a
compliance margin to their certification test results to account for
uncertainties, such as production variation. Additionally, we believe
manufacturers would have required additional lead time to implement the
demonstrated emission levels broadly across all heavy-duty SI engine
platforms for the final useful life periods. Since we are finalizing a
single-step program starting in MY 2027, as discussed in Section
III.A.3 of this preamble, we continue to consider 60 mg HC/hp-hr and 35
mg NOX/hp-hr the appropriate level of the standards for

that model year, as proposed in the MY 2027 step of proposed Option 1.
ii. Supplemental Emission Test and Standards for Spark-Ignition HDE
    The existing SET duty cycle, currently only applicable to CI
engines, is a ramped modal cycle covering 13 steady-state torque and
engine speed points that is intended to exercise the engine over
sustained higher load and higher speed operation. Historically, in
light of the limited range of applications and sales volumes of SI
heavy-duty engines, especially compared to CI engines, we believed the
FTP duty cycle was sufficient to represent the high-load and high-speed
operation of SI engine-powered heavy-duty vehicles. As the market for
SI engines increases for use in larger vehicle classes, these engines
are more likely to operate under extended high-load conditions. To
address these market shifts, we proposed to apply the SET duty cycle
and new SET standards to Spark-ignition HDE, starting in model year
2027. This new cycle would ensure that emission controls are properly
functioning in the high load and speed conditions covered by the SET.
    We are finalizing the addition of the SET duty cycle for the Spark-
ignition HDE primary intended service class, as proposed.\308\ We
requested comment on revisions we should consider for the CI-based SET
procedure to adapt it for SI engines. We received no comments on
changes to the procedure itself and the SET standards for Spark-
ignition HDE are based on the same SET procedure as we are finalizing
for heavy-duty CI engines. After considering comments, we are
finalizing SET standards that differ from our proposed options for
Spark-ignition HDE.
---------------------------------------------------------------------------

    \308\ See our updates to the SET test procedure in 40 CFR
1036.505.
---------------------------------------------------------------------------

    The EPA HD SI technology demonstration program evaluated emission
performance over the SET duty cycle. As shown in Table III-22, the
NOX and NMHC emissions over the SET duty cycle were
substantially lower than the emissions from the FTP duty cycle (see
Table III-21). Lower levels of NMHC were demonstrated, but at the
expense of increased CO emissions in those higher load operating
conditions. Engine down-speeding improved CO emissions significantly,
while NOX, NMHC, and PM remained low.\309\ The considerably
lower NOX and HC in our SET duty cycle demonstration results
leave enough room for manufacturers to calibrate the tradeoff in TWC
emission control of NOX, HC, and CO to continue to fine-tune
CO. See Chapter 3.2 of the RIA for an expanded description of the test
program and results.
---------------------------------------------------------------------------

    \309\ Engine down-speeding also resulted in a small improvement
in brake specific fuel consumption over the SET duty cycle reducing
from 0.46 to 0.44 lb/hp-hr.

    Table III-22--Exhaust Emission Results From SET Duty Cycle Testing in the HD SI Technology Demonstration
----------------------------------------------------------------------------------------------------------------
                                                   NOX  (mg/hp-
                                                        hr)        PM (mg/hp-hr)   HC (mg/hp-hr)   CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
Final Standards MY 2027 and later...............              35               5              60            14.4
Test Program Base Engine with Advanced Catalyst                8           \c\ 7               6            36.7
 \a\............................................
Test Program Down-sped Engine with Advanced                    5               3               1            7.21
 Catalyst \b\...................................
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\a\ Base engine's manufacturer-stated maximum test speed is 4715 RPM; advanced catalyst aged to 250,000 miles.
\b\ Down-sped engine's maximum test speed lowered to 4000 RPM; advanced catalyst aged to 250,000 miles.
\c\ As noted in Chapter 3.2 of the RIA, the higher PM value was due to material separating from the catalyst mat
  during the test and is not indicative of the engine's ability to control engine-generated PM emissions at the
  higher load conditions of the SET.

    Similar to our discussion related to the FTP standards, we expect
manufacturers, who design and have full access to the engine controls,
could achieve emission levels comparable to or lower than our
feasibility demonstration over the SET duty cycle by adopting other
approaches, including a combination of calibration changes, optimized
catalyst location, and fuel control strategies that EPA was unable to
evaluate due to limited access to proprietary engine controls. In fact,
we are aware of advanced engine architectures that can reduce or
eliminate enrichment, and the associated CO emissions, by maintaining
closed loop operation.\310\
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    \310\ See Chapter 1 of the RIA for a description of fuel
enrichment, when engine operation deviates from closed loop, and its
potential impact on emissions.
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    We proposed Spark-ignition HDE standards for HC and CO emissions on
the SET cycle that were numerically equivalent to the respective
proposed FTP standards. Our intent was to ensure that SI engine
manufacturers utilize emission control hardware and calibration
strategies to control emissions during high load operation to levels
similar to the FTP duty cycle.\311\ We retain this approach for HC,
but, after considering comments, the final CO standard is revised from
that proposed. One commenter indicated that manufacturers would need CO
credits to achieve the proposed standards. Another commenter suggested
that EPA underestimated the modifications manufacturers would need to
make to fully transition away from the fuel enrichment strategies they
currently use to protect their engines. The same commenter requested
that EPA delay the SET to start in model year 2031 or temporarily
exclude the highest load points over the test to provide additional
lead time for manufacturers.
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    \311\ Test results presented in Chapter 3.2 of the RIA indicate
that these standards are achievable when the engine controls limit
fuel enrichment and maintain closed loop control of the fuel-air
ratio.
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    We are not finalizing an option for manufacturers to generate CO
credits. We believe a delayed implementation of SET, as requested,
would further delay manufacturers' motivation to focus on high load
operation to reduce enrichment and the associated emissions reductions
that would result. Additionally, our objective for adding new standards
over the SET duty cycle is to capture the prolonged, high-load
operation not currently represented in the FTP duty cycle, and the
commenter's recommendation to exclude the points of highest load would
be counter to that objective.
    We agree with commenters that the new SET duty cycle and standards
will be a challenge for heavy-duty SI manufacturers but maintain that
setting a feasible technology-forcing CO standard is consistent with
our authority under the CAA. After further considering the comments and
assessing CO data from the EPA heavy-duty SI test program, the final
new CO standard we

are adopting is less stringent than proposed to provide manufacturers
additional margin for ensuring compliance with that pollutant's
standard over the new test procedure for Spark-ignition HDE. Given this
final standard, we determined that neither ABT or more lead time are
appropriate or required. The Spark-ignition HDE standard for CO
emissions on the SET duty-cycle established in this final rule is
numerically equivalent to the current FTP standard of 14.4 g/hp-hr.
2. Other Provisions for Spark-Ignition HDE
    This Section III.D.2 describes other provisions we proposed and are
finalizing with revisions from proposal in this rule. The following
three provisions address information manufacturers will share with EPA
as part of their certification and we are adding clarification where
needed after considering comments. See also section 3 of the Response
to Comments for a detailed discussion of the comments summarized in
this section and how they have informed the updates we are finalizing
for these three provisions.
Idle Control for Spark-Ignition HDE
    We proposed to add a new paragraph at 40 CFR 1036.115(j)(1) to
require manufacturers to show how they maintain a catalyst bed
temperature of 350 [deg]C in their application for certification or get
approval for an alternative strategy that maintains low emissions
during idle. As described in Chapter 3.2 of the RIA, prolonged idling
events may allow the catalyst to cool and reduce its efficiency,
resulting in emission increases until the catalyst temperatures
increase. Our recent HD SI test program showed idle events that extend
beyond four minutes allow the catalyst to cool below the light-off
temperature of 350 [deg]C. The current heavy-duty SET and FTP duty
cycles do not include sufficiently long idle periods to represent these
real-world conditions where the exhaust system cools below the
catalyst's light-off temperature.
    We continue to believe that a 350 [deg]C lower bound for catalysts
will sufficiently ensure emission control is maintained during idle
without additional manufacturer testing. We are finalizing the 350
[deg]C target and the option for manufacturers to request approval for
a different strategy, as proposed. We are revising the final
requirement from our proposal to also allow manufacturers to request
approval of a temperature lower than 350 [deg]C, after considering
comments that requested that we replace the 350 [deg]C temperature with
the more generic ``light-off temperature'' to account for catalysts
with other formulations or locations relative to the engine.
i. Thermal Protection Temperature Modeling Validation
    The existing regulations require manufacturers to report any
catalyst protection strategy that reduces the effectiveness of emission
controls as an AECD in their application for certification.\312\ The
engine controls used to implement these strategies often rely on a
modeling algorithm to predict high exhaust temperatures and to disable
the catalyst, which can change the emission control strategy and
directly impact real world emissions. The accuracy of these models used
by manufacturers is critical in both ensuring the durability of the
emission control equipment and preventing excessive emissions that
could result from unnecessary or premature activation of thermal
protection strategies.
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    \312\ See 40 CFR 86.094-21(b)(1)(i) and our migration of those
provisions to final 40 CFR 1036.205(b).
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    To ensure that a manufacturer's model accurately estimates the
temperatures at which thermal protection modes are engaged, we proposed
a validation process during certification in a new paragraph 40 CFR
1036.115(j)(2) to demonstrate the model performance.
    Several commenters opposed the proposed requirement that
manufacturers demonstrate a 5 [deg]C accuracy between modelled and
actual exhaust and emission component temperatures and expressed
concern with the ability to prove correlation at this level and lack of
details on the procedure for measuring the temperatures. Our final,
revised approach still ensures EPA has the information needed to
appropriately assess a manufacturer's AECD strategy, without a specific
accuracy requirement.
    Our final 40 CFR 1036.115(j)(2) clarifies that the new validation
process is a requirement in addition to the requirements for any SI
engine applications for certification that include an AECD for thermal
protection.\313\ Instead of the proposed 5 [deg]C accuracy requirement,
a manufacturer will describe why they rely on any AECDs, instead of
other engine designs, for thermal protection of catalyst or other
emission-related components. They will also describe the accuracy of
any modeled or measured temperatures used to activate the AECD. Instead
of requiring manufacturers to submit second-by-second data upfront in
the application for certification to demonstrate a specific accuracy
requirement is met, the final requirement gives EPA discretion to
request the information at certification. We note that our final
revised requirements apply the same validation process for modeled and
measured temperatures that activate an AECD and that this requirement
would not apply if manufacturers certify their engines without an AECD
for enrichment as thermal protection.
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    \313\ These requirements are in place today under existing 40
CFR 86.094-21(b)(1)(i), which have been migrated to 40 CFR
1036.205(b) in this final rule.
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ii. OBD Flexibilities
    In recognition that there can be some significant overlap in the
technologies and emission control systems adopted for products in the
chassis-certified and engine-certified markets, we proposed an OBD
flexibility to limit the data requirements for engine-certified
products that use the same engines and generally share similar emission
controls (i.e., are ``sister vehicles'') with chassis-certified
products. Specifically, in a new 40 CFR 1036.110(a)(2), we proposed to
allow vehicle manufacturers the option to request approval to certify
the OBD of their SI, engine-certified products using data from similar
chassis-certified Class 2b and Class 3 vehicles that meet the
provisions of 40 CFR 86.1806-17.
    Two organizations commented in support of the proposed OBD
flexibility and with one suggesting some revisions to the proposed
regulatory language. The commenter suggested that the expression `share
essential design characteristics' was too vague, and requested EPA
provide more specific information on what EPA will use to make their
determination. We disagree that more specific information is needed. We
are relying on the manufacturers to identify the design characteristics
and justify their request as part of the certification process. We are
adjusting the final regulatory text to clarify how the vehicles above
and below 14,000 lbs GVWR must use the same engine and share similar
emission controls, but are otherwise finalizing this OBD flexibility as
proposed.

E. Summary of Spark-Ignition HDV Refueling Emission Standards and Test
Procedures

    All sizes of complete and incomplete heavy-duty vehicles have been
subject to evaporative emission standards for many years. Similarly,
all sizes of complete heavy-duty vehicles are subject to refueling
standards. We most

recently applied the refueling standards to complete heavy-duty
vehicles above 14,000 pounds GVWR starting with model year 2022 (81 FR
74048, Oct. 25, 2016).
    We proposed to amend 40 CFR 1037.103 to apply the same refueling
standard of 0.20 grams hydrocarbon per gallon of dispensed fuel to
incomplete heavy-duty vehicles above 14,000 pounds GVWR starting with
model year 2027 over a useful life of 150,000 miles or 15 years
(whichever comes first). We further proposed to apply the same testing
and certification procedures that currently apply for complete heavy-
duty vehicles. We are adopting this standard and testing and
certification procedures as proposed, with some changes to the proposed
rule as noted in this section. As noted in 40 CFR 1037.103(a)(2), the
standards apply for vehicles that run on gasoline, other volatile
liquid fuels, and gaseous fuels.
    The proposed rule provided an extensive discussion of the history
of evaporative and refueling standards for heavy-duty vehicles, along
with rationale and information supporting the proposed standards (87 FR
17489, March 28, 2022). The RIA includes additional information related
to control technology, feasibility, and test procedures. See also
section 3 of the Response to Comments for a detailed discussion of the
comments and the changes we made to the proposed rule.
    Some commenters advocated for applying the refueling standards also
to incomplete heavy-duty vehicles at or below 14,000 pounds GVWR.
Specifically, some manufacturers commented that they would need a
phase-in schedule that allowed more lead time beyond the proposed MY
2027 start of the refueling standards for incomplete vehicles above
14,000 pounds GVWR, and that EPA should consider a longer phase-in that
also included refueling standards for incomplete vehicles at or below
14,000 pounds GVWR. In EPA's judgment, the design challenge for meeting
the new refueling standards will mainly involve larger evaporative
canisters, resizing purge valves, and recalibrating for higher flow of
vapors from the evaporative canister into the engine's intake. Four
years of lead time is adequate for designing, certifying, and
implementing these design solutions. We are therefore finalizing the
proposed start of refueling standards in MY 2027 for all incomplete
heavy-duty vehicles above 14,000 pounds GVWR.
    At the same time, as manufacturers suggested, expanding the scope
of certification over a longer time frame may be advantageous for
implementing design changes across their product line in addition to
the environmental gain from applying refueling controls to a greater
number of vehicles. We did not propose refueling standards for vehicles
at or below 14,000 pounds GVWR and we therefore do not adopt such
standards in this final rule. However, the manufacturers' suggestion to
consider a package of changes to both expand the scope of the standards
and increase the lead time for meeting standards has led us to adopt an
optional alternative phase-in. Under the alternative phase-in
compliance pathway, instead of certifying all vehicles above 14,000
pounds GVWR to the refueling standard in MY 2027, manufacturers can opt
into the alternate phase-in that applies for all incomplete heavy-duty
vehicles, regardless of GVWR. The alternative phase-in starts at 40
percent of production in MYs 2026 and 2027, followed by 80 percent of
production in MYs 2028 and 2029, ramping up to 100 percent of
production in MY 2030. Phase-in calculations are based on projected
nationwide production volume of all incomplete heavy-duty vehicles
subject to refueling emission standards under 40 CFR 86.1813-17.
Specifying the phase-in schedule in two-year increments allows
manufacturers greater flexibility for integrating emission controls
across their product line.
    Manufacturers may choose either schedule of standards; however,
they must satisfy at least one of the two. That is, if manufacturers do
not certify all their incomplete heavy-duty vehicles above 14,000
pounds GVWR to the refueling standards in MY 2027, the alternate phase-
in schedule described in 40 CFR 86.1813-17(b) becomes mandatory to
avoid noncompliance. Conversely, if manufacturers do not meet the
alternative phase-in requirement for MY 2026, they must certify all
their incomplete heavy-duty vehicles above 14,000 pounds GVWR to the
refueling standard in MY 2027 to avoid noncompliance. See the final 40
CFR 86.1813-17(b) for the detailed specifications for the alternative
phase-in schedule.
    We received several comments suggesting that we adjust various
aspects of the testing and certification procedures for heavy-duty
vehicles meeting the evaporative and refueling standards. Consideration
of these comments led us to include some changes from proposal for the
final rule. First, we are revising 40 CFR 1037.103 to add a reference
to the provisions from 40 CFR part 86, subpart S, that are related to
the refueling standards. This is intended to make clear that the
overall certification protocol from 40 CFR part 86, subpart S, applies
for heavy-duty vehicles above 14,000 pounds GVWR (see also existing 40
CFR 1037.201(h)). This applies, for example, for durability procedures,
useful life, and information requirements for certifying vehicles.