Through comments received on our ANPR, we have heard from manufacturers
that given the challenge of implementing the third step of the HD GHG
rules in MY 2027, they believe it would take closer to four years to
adequately fine-tune and validate their products for a second step of
more stringent criteria pollutant control that also extends useful
life.\300\ In response to this concern, and the general request by
suppliers and environmental stakeholders for a nationally aligned
criteria pollutant program, we are proposing MY 2031 for the final step
of the proposed Option 1 standards to provide four additional years for
manufacturers to design and build engines that will meet the proposed
second step of the Option 1 standards and associated compliance
provisions.\301\ A MY 2031 final step would also align with the
Omnibus.\302\ We request comment on the general approach of a two-step
versus one-step program, and the advantages or disadvantages of the
proposed Option 1 two-step approach that EPA should consider in
developing the final rule. For instance, we seek commenters' views on
whether the Agency should adopt a first step of standards but defer any
second step of standards to a planned future rulemaking on heavy-duty
GHG emissions instead of adopting a second step of standards in this
rulemaking.\303\ We also request comment on whether there are
additional factors that we should consider when setting standards out
to the MY 2031 timeframe.
---------------------------------------------------------------------------

    \300\ See comments from Volvo. Docket ID: EPA-HQ-OAR-2019-0055-
0463.
    \301\ See comments from MECA, MEMA and Union of Concerned
Scientists. Docket ID: EPA-HQ-OAR-2019-0055-0463.
    \302\ California Air Resources Board. Heavy-Duty Omnibus
Regulation. Available online: https://ww2.arb.ca.gov/rulemaking/2020/hdomnibuslownox.
    \303\ As noted in the Executive Summary and discussed in
Sections XI and XIII, this proposal is consistent with E.O. 14037,
which also directs EPA to consider undertaking a separate rulemaking
to establish new GHG emission standards for heavy-duty engines and
vehicles to begin as soon as MY 2030.
---------------------------------------------------------------------------

    As explained in Section III.B.3, we have evaluated and considered
the costs of these technologies in our assessment of the proposed
Options 1 and 2 standards. The proposed Options 1 and 2 standards are
achievable without increasing the overall fuel consumption and
CO2 emissions of the engine for each of the duty cycles
(FTP, SET, and LLC) and the fuel mapping test procedures defined in 40
CFR 1036.535 and 1036.540, as discussed in the Chapter 3 of the draft
RIA.\304\ Finally,

the proposed Options 1 and 2 standards would have no negative impact on
safety, based on the existing use of these technologies in light-duty
vehicles and heavy-duty engines on the road today.
---------------------------------------------------------------------------

    \304\ The proposed ORVR requirements discussed in Section
III.E.2 would reduce fuel consumed from gasoline fuel engines, but
these fuel savings would not be measured on the duty cycles since
the test procedures for these tests measure tailpipe emissions and
do not measure emissions from refueling. We describe our estimate of
the fuel savings in Chapter 7.2.2 of the draft RIA.
---------------------------------------------------------------------------

B. Summary of Proposed Compression-Ignition Exhaust Emission Standards
and Proposed Duty Cycle Test Procedures

1. Current Duty Cycle Test Procedures and Standards
    Current criteria pollutant standards must be met by compression-
ignition engines over both the Federal Test Procedure (FTP) \305\ and
the Supplemental Emission Test (SET) duty cycles. The FTP duty cycles,
which date back to the 1970s, are composites of a cold-start and a hot-
start transient duty cycle designed to represent urban driving. There
are separate duty cycles for both SI and CI engines. The cold-start
emissions are weighted by one-seventh and the hot-start emissions are
weighted by six-sevenths.\306\ The SET is a more recent duty cycle for
diesel engines that is a continuous cycle with ramped transitions
between the thirteen steady-state modes.\307\ The SET does not include
engine starting and is intended to represent fully warmed-up operating
modes not emphasized in the FTP, such as more sustained high speeds and
loads.
---------------------------------------------------------------------------

    \305\ EPA specifies different FTP duty cycles for compression-
ignition and spark-ignition engines.
    \306\ See 40 CFR 86.007-11 and 40 CFR 86.008-10.
    \307\ See 40 CFR 86.1362.
---------------------------------------------------------------------------

    Emission standards for criteria pollutants are currently set to the
same numeric value for FTP and SET test cycles. Manufacturers of
compression-ignition engines have the option to participate in our
averaging, banking, and trading (ABT) program for NOX and PM
as discussed in Section IV.G.\308\ These pollutants are subject to
family emission limit (FEL) caps of 0.50 g/hp-hr for NOX and
0.02 g/hp-hr for PM.\309\
---------------------------------------------------------------------------

    \308\ See 40 CFR 86.007-15.
    \309\ See 40 CFR 86.007-11.

 Table III-1--Current Diesel-Cycle Engine Standards Over the FTP and SET
                               Duty Cycles
------------------------------------------------------------------------
 NOX \a\  (g/hp-
       hr)          PM \b\ (g/hp-hr)    HC (g/hp-hr)      CO (g/hp-hr)
------------------------------------------------------------------------
         0.20               0.01              0.14              15.5
------------------------------------------------------------------------
\a\ Engine families participating in the ABT program are subject to a
  FEL cap of 0.50 g/hp-hr for NOX.
\b\ Engine families participating in the ABT program are subject to a
  FEL cap of 0.02 g/hp-hr for PM.

    EPA developed powertrain and hybrid powertrain test procedures for
the HD GHG Phase 2 Heavy-Duty Greenhouse Gas rulemaking (81 FR 73478,
October 25, 2016) with updates in the HD Technical Amendments rule (86
FR 34321, June 29, 2021).\310\ The powertrain and hybrid powertrain
tests allow manufacturers to directly measure the effectiveness of the
engine, the transmission, the axle and the integration of these
components as an input to the Greenhouse gas Emission Model (GEM) for
compliance with the greenhouse gas standards. As part of the technical
amendments, EPA allowed the powertrain test procedure to be used beyond
the current GEM drive cycles to include the FTP and SET engine-based
test cycles and to facilitate hybrid powertrain testing (40 CFR
1036.505 and 1036.510 and 40 CFR 1037.550).
---------------------------------------------------------------------------

    \310\ See 40 CFR 1037.550.
---------------------------------------------------------------------------

    These heavy-duty diesel-cycle engine standards are applicable for a
useful life period based on the primary intended service class of the
engine.\311\ For certification, manufacturers must demonstrate that
their engines will meet these standards throughout the useful life by
performing a durability test and applying a deterioration factor (DF)
to their certification value.\312\
---------------------------------------------------------------------------

    \311\ 40 CFR 86.004-2.
    \312\ See 40 CFR 86.004-26(c) and (d) and 86.004-28(c) and (d).
---------------------------------------------------------------------------

    Additionally, manufacturers must adjust emission rates for engines
with exhaust aftertreatment to account for infrequent regeneration
events accordingly.\313\ To account for variability in these
measurements, as well as production variability, manufacturers
typically add margin between the DF and infrequent regeneration
adjustment factor (IRAF) adjusted test result, and the family emission
limit (FEL). A summary of the margins manufacturers have included for
MY 2019 and newer engines is summarized in Chapter 3.1.2 of the draft
RIA.
---------------------------------------------------------------------------

    \313\ See 40 CFR 1036.501(d).
---------------------------------------------------------------------------

2. Proposed Test Procedures and Standards
    EPA is proposing new NOX, PM, HC, and CO emission
standards for heavy-duty compression-ignition engines that will be
certified under 40 CFR part 1036.314 315 We are proposing
updates to emission standards for our existing laboratory test cycles
(i.e., FTP and SET) and proposing NOX, PM, HC and CO
emission standards based on a new low-load test cycle (LLC) as
described below.\316\ The proposed standards for NOX, PM,
and HC are in units of milligrams/horsepower-hour instead of grams/
horsepower-hour because using units of milligrams better reflects the
precision of the new standards, rather than adding multiple zeros after
the decimal place. Making this change would require updates to how
manufacturers report data to the EPA in the certification application,
but it does not require changes to the test procedures that define how
to determine emission values. We describe compression-ignition engine
technology packages that demonstrate the feasibility of achieving these
proposed Options 1 and 2 standards in Section III.B.3.ii and provide
additional details in Chapters 2 and 3 of the draft RIA for this
rulemaking.
---------------------------------------------------------------------------

    \314\ See proposed 40 CFR 1036.104.
    \315\ See proposed 40 CFR 1036.605 and Section XII.B of this
preamble for a discussion of our proposal for engines installed in
specialty vehicles.
    \316\ See proposed 40 CFR 1036.104.
---------------------------------------------------------------------------

    As part of this rulemaking, we are proposing two options to
increase the useful life for each engine class as described in Section
IV.A. The proposed Options 1 and 2 emission standards outlined in this
section would apply for the longer useful life periods and
manufacturers would be responsible for demonstrating that their engines
will meet these standards as part of the proposed revisions to
durability requirements described in Section IV.F. In Section IV.G, we
discuss our proposed updates to the ABT program to account for our
proposal of three laboratory cycles (FTP, SET and LLC) with unique
standards.
    As discussed in Section III.B.2, the proposal includes two sets of
standards: Proposed Option 1 and proposed Option

2. As described in Section III.B.3.ii, we believe the technology
packages evaluated for this proposal can achieve our proposed Options 1
and 2 duty-cycle standards. For Option 1, we are proposing the
standards in two steps in MY 2027 and MY 2031, because the proposed
Option 1 program includes not only numerical updates to existing
standards but also other new and revised standards and compliance
provisions such as a new duty-cycle procedure and standards, revised
off-cycle procedures and standards, longer useful life periods, and
other proposed requirements that, when considered collectively, merit a
phased approach to lead time. As discussed in Section I.G and in
Section III.B.4, we also present an alternative set of standards
(Alternative) that we also considered. The Alternative is more
stringent than either the proposed Option 1 MY 2031 standards or
proposed Option 2 because the Alternative has shorter lead time, lower
numeric NOX emission standards and longer useful life
periods. We note that we currently are unable to conclude that the
Alternative is feasible in the MY 2027 timeframe over the useful life
periods in this Alternative in light of deterioration in the emission
control technologies that we have evaluated to date, and we expect that
we would need additional supporting data or other information in order
to determine that the Alternative is feasible in the MY 2027 timeframe
to consider adopting it in the final rule.
    The proposed options for NOX standards were derived to
consider the range of options that may potentially be appropriate to
adopt to achieve the maximum feasible emissions reductions from heavy-
duty diesel engines considering lead time, stability, cost, energy and
safety. To accomplish this, we evaluated what operation made up the
greatest part of the inventory as discussed in Section VI.B and what
technologies could be used to reduce emissions in these areas. As
discussed in Section I, we project that emissions from operation at low
power, medium-to-high power, and mileages beyond the current regulatory
useful life of the engine would account for the majority of heavy-duty
highway emissions in 2045. To achieve reductions in these three areas
we identified options for cycle-specific standards to ensure that the
maximum achievable reductions are seen across the operating range of
the engine. As described in Section IV, we are proposing to increase
both the regulatory useful life and the emission-related warranty
periods to ensure these proposed standards are met for a greater
portion of the engine's operational life.
    To achieve the goal of reducing emissions across the operating
range of the engine, we are proposing two options for standards for
three duty cycles (FTP, SET and LLC). In proposing these standards, we
assessed the performance of the best available aftertreatment systems,
which are more efficient at reducing NOX emissions at the
higher exhaust temperatures that occur at high engine power, than they
are at reducing NOX emissions at low exhaust temperatures
that occur at low engine power. To achieve the maximum NOX
reductions from the engine at maximum power, the aftertreatment system
was designed to ensure that the downstream selective catalytic
reduction (SCR) catalyst was properly sized, diesel exhaust fluid (DEF)
was fully mixed with the exhaust gas ahead of the SCR catalyst and the
diesel oxidation catalyst (DOC) was designed to provide a molar ratio
of NO to NO2 of near one. To reduce emissions under low
power operation and under cold-start conditions, we selected standards
for proposed Option 1, for the LLC and the FTP that would achieve an 80
to 90 percent, or more, reduction in emissions under these operating
conditions as compared to current standards. The proposed Options 1 and
2 standards are achievable by utilizing cylinder deactivation (CDA),
dual-SCR aftertreatment configuration and heated diesel exhaust fluid
(DEF) dosing. To reduce emissions under medium to high power, we
selected standards for proposed Option 1, for the SET that would
achieve a greater than 80 percent reduction in emissions under these
operating conditions. The proposed Options 1 and 2 SET standards are
achievable by utilizing improvements to the SCR formulation, SCR
catalyst sizing, and improved mixing of DEF with the exhaust. Further
information about these technologies can be found in Chapters 1 and 3
of the draft RIA.
    For the proposed Options 1 and 2 PM standards, they were set at a
level to maintain the current emissions performance of diesel engines.
For the proposed Options 1 and 2 standards for HC and CO, they were
generally set at a level that is achievable by spark-ignition engines.
Each of these standards are discussed in more detail in the following
sections.
    In proposed Option 1 for MY 2031 and later Heavy HDE, we are
proposing NOX standards at an intermediate useful life (IUL)
of 435,000 miles as discussed later in Section III.B.2. We believe that
the proposed Option 1 useful life for these engines of 800,000 miles
justifies the need for standards at IUL. It could be many years after
the engines are on the road before EPA could verify that the engines
meet the standards out to useful life if there is no IUL standard. As
discussed further in Section III.B.3.ii.a, IUL standards ensure that
the emissions from the engine are as low as feasible for the entire
useful life and provides an intermediate check on emission performance
deterioration over the UL.
    As discussed in Section III.B.3, we have assessed the feasibility
of the proposed Options 1 and 2 standards for compression-ignition
engines by testing a Heavy HDE equipped with cylinder CDA technology
and dual-SCR aftertreatment configuration with heated DEF dosing. The
demonstration work consisted of two phases. The first phase of the
demonstration was led by CARB and is referred to as CARB Stage 3. In
this demonstration the aftertreatment was chemically- and
hydrothermally-aged to the equivalent of 435,000 miles. During this
aging the emissions performance of the engine was assessed after the
aftertreatment was degreened, at the equivalent of 145,000 miles,
290,000 miles and 435,000 miles. The second phase of the demonstration
was led by EPA and is referred to as the EPA Stage 3 engine. In this
phase, improvements were made to the aftertreatment by replacing the
zone-coated catalyzed soot filter with a separate DOC and diesel
particulate filter (DPF) that were chemically- and hydrothermally-aged
to the equivalent of 800,000 miles and improving the mixing of the DEF
with exhaust prior to the downstream SCR catalyst. The EPA Stage 3
engine was tested at an age equivalent to 435,000 and 600,000 miles.
The EPA Stage 3 engine will be tested at an age equivalent of 800,000
miles. Additionally, we plan to test a second aftertreatment system
referred to as ``Team A'' which is also a dual-SCR aftertreatment
configuration with heated DEF dosing, but has greater SCR catalyst
volume and a different catalyst washcoat formulation.
i. FTP
    We are proposing new emission standards for testing over the FTP
duty-cycle as shown in Table III-2.\317\ These brake-specific FTP
standards would apply across the primary intended service classes over
the useful life periods shown in Table III-3. These Options 1 and 2
standards have been shown to be feasible for compression-ignition
engines based on testing of the

CARB Stage 3 and EPA Stage 3 engine with a chemically- and
hydrothermally-aged aftertreatment system.\318\ At the time of this
proposal, the catalyst was aged to an equivalent of 800,000 miles, but
the test data at the equivalent of 800,000 miles was not yet available.
EPA will continue to assess the feasibility of the proposed standards
as additional demonstration data becomes available during the course of
this rulemaking. For example, the EPA Stage 3 engine, and EPA's Team A
demonstration engine will be aged to and tested at the equivalent of
800,000 miles.\319\ A summary of the data used for EPA's feasibility
analysis can be found in Section III.B.3. To provide for additional
margin, in our technology cost analysis we increased the SCR catalyst
volume from what was used on the EPA and CARB Stage 3 engine. We are
proposing to continue an averaging, banking, and trading (ABT) program
for NOX credits as a flexibility for manufacturers. Our
proposal includes targeted revisions to the current ABT program,
including new provisions to clarify how FELs apply for additional duty
cycles, lower FEL caps for NOX and restrictions for using
NOX emission credits (see Section IV.G for details on the
ABT program).
---------------------------------------------------------------------------

    \317\ See 40 CFR 1036.510 for FTP duty-cycle test procedure.
    \318\ See Section III.B.2 for a description of the engine.
    \319\ Data will be added to the public docket once it becomes
available.

                                   Table III-2--Proposed Compression-Ignition Engine Standards Over the FTP Duty Cycle
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                NOX \a\
                                                    Model year                Primary intended service class   (mg/hp-   PM (mg/hp- HC (mg/hp- CO (g/hp-
                                                                                hr)        hr)        hr)        hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Proposed Option 1....................  2027-2030...........................  All HD Engines.................         35          5         60        6.0
                                       2031 and later......................  Light HDE and Medium HDE.......         20          5         40        6.0
                                       2031 and later......................  Heavy HDE through IUL..........         20          5         40        6.0
                                       2031 and later......................  Heavy HDE from IUL to FUL......         40          5         40        6.0
Proposed Option 2....................  2027 and later......................  All HD Engines.................         50          5         40        6.0
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Engine families participating in the ABT program would be subject to a NOX FEL cap, discussed in Section IV.G.3.

 Table III-3--Proposed Useful Life Periods for Heavy-Duty Compression-Ignition Primary Intended Service Classes
----------------------------------------------------------------------------------------------------------------
                          Current                        Proposed Option 1                   Proposed Option 2
                 -----------------------------------------------------------------------------------------------
Primary intended                               MY 2027-2030              MY 2031+
  service class  -----------------------------------------------------------------------------------------------
                     Miles       Years       Miles       Years       Miles       Years       Miles       Years
----------------------------------------------------------------------------------------------------------------
Light HDE \a\...      110,000         10      190,000         12      270,000         15      250,000         10
Medium HDE......      185,000         10      270,000         11      350,000         12      325,000         10
Heavy HDE \b\...      435,000         10      600,000         11  800,000 \c\         12      650,000         10
----------------------------------------------------------------------------------------------------------------
\a\ Current useful life period for Light HDE for GHG emission standards is 15 years or 150,000 miles. See 40 CFR
  1036.108(d).
\b\ Proposed Option 1 includes an hours-based useful life for Heavy HDE of 32,000 operating hours for model year
  2027 through 2030, and 40,000 operating hours for model year 2031 and later.
\c\ For MY 2031 and later Heavy HDE under proposed Option 1, we are proposing intermediate useful life periods
  of 435,000 miles, 10 years, or 22,000 hours, whichever comes first. See Section III for a discussion of the
  Option 1 standards we propose to apply for the intermediate and full useful life periods.

    The proposed Options 1 and 2, 5 mg/hp-hr (0.005 g/hp-hr) FTP
standard for PM is intended to ensure that there is not an increase in
PM emissions from future engines. As summarized in Section
III.B.3.ii.b, manufacturers are submitting certification data to the
agency for current production engines well below the proposed PM
standard over the FTP duty cycle. Lowering the standard to 5 mg/hp-hr
would ensure that future engines will maintain the low level of PM
emissions of the current engines. Taking into account measurement
variability of the PM measurement test procedure in the proposed PM
standards, we believe that PM emissions from current diesel engines are
at the lowest feasible level for MY 2027 and later engines. We request
comment on whether 5 mg/hp-hr provides enough margin for particular
engine designs. For example, would 6 or 7 mg/hp-hr be a more
appropriate standard to maintain current PM emissions levels while
providing enough margin to account for the measurement variability of
the PM measurement test procedure.
    We are proposing two options HC and CO standards based on the
feasibility demonstration for SI engines. As summarized in Section
III.B.3.ii.b, manufacturers are submitting data to the agency that show
emissions performance for current production CI engines is well below
the current and proposed standards. Keeping standards at the same value
for all fuels is consistent with the agency's approach to previous
criteria pollutant standards. See Section III.C for more information on
how the numeric values of these two options for proposed HC and CO
standards were determined.
    In the ANPR, we requested comment on changing the weighting factors
for the FTP cycle for heavy-duty engines. The current FTP weighting of
cold-start and hot-start emissions was promulgated in 1980 (45 FR 4136,
January 21, 1980). It reflects the overall ratio of cold and hot
operation for heavy-duty engines generally and does not distinguish by
engine size or intended use. Specifically, we asked if FTP weighting
factors should vary by engine class and any challenges manufacturers
may encounter to implement changes to the weighting factors. We did not
receive any comments to change the weighting and received comments from
Roush and MECA that the current weighting factors are appropriate.
After considering these comments, we are not proposing any changes to
the weighting factors.

ii. SET
    We are proposing new emissions standards for the SET test procedure
as shown in Table III-4 over the same useful life periods shown in
Table III-3. Consistent with our current standards, we are proposing
the same numeric values for the standards over the FTP and SET duty
cycles, and the brake-specific SET standards apply across engine
classes (primary intended service class). As with the FTP cycle, the
Options 1 and 2 standards have been shown to be feasible for
compression-ignition engines based on testing of the CARB Stage 3 and
EPA Stage 3 engines with a chemically- and hydrothermally-aged
aftertreatment system. At the time of this proposal, the catalyst was
aged to an equivalent of 800,000 miles, but the test data at the
equivalent of 800,000 miles was not yet available. EPA will continue to
assess the feasibility of the proposed standards as additional data
becomes available. To provide additional margin for meeting the SET
standards, we have accounted for additional SCR catalyst volume in our
cost analysis. A summary of the data used for EPA's feasibility
analysis can be found in Section III.B.3.

                                   Table III-4--Proposed Compression-Ignition Engine Standards Over the SET Duty Cycle
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                NOX (mg/
                                                    Model year                Primary intended service class    hp-hr)   PM (mg/hp- HC (mg/hp- CO (g/hp-
                                                                                hr)        hr)        hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Proposed Option 1....................  2027-2030...........................  All HD Engines.................         35          5         60        6.0
                                       2031 and later......................  Light HDE and Medium HDE.......         20          5         40        6.0
                                       2031 and later......................  Heavy HDE through IUL..........         20          5         40        6.0
                                       2031 and later......................  Heavy HDE from IUL to FUL......         40          5         40        6.0
Proposed Option 2....................  2027 and later......................  All HD Engines.................         50          5         40        6.0
--------------------------------------------------------------------------------------------------------------------------------------------------------

    As with the proposed PM standards for the FTP (see Section
III.B.2.i), the proposed Options 1 and 2 P.M. standards for SET is
intended to ensure that there is not an increase in PM emissions from
future engines. We request comment on whether 5 mg/hp-hr provides
enough margin for particular engine designs. For example, would 6 or 7
mg/hp-hr be a more appropriate standard to maintain current PM
emissions levels while providing enough margin to account for the
measurement variability of the PM measurement test procedure. As with
the options for proposed HC and CO standards for the FTP (see Section
III.B.2.i), we are proposing two options for standards for HC and CO
based on the feasibility demonstration for SI engines (see Section
III.C).
    We have also observed an industry trend toward engine down-
speeding--that is, designing engines to do more of their work at lower
engine speeds where frictional losses are lower. To better reflect this
trend in our duty cycle testing, in the HD GHG Phase 2 final rule, we
promulgated new SET weighting factors for measuring CO2
emissions (81 FR 73550, October 25, 2016). Since we believe these new
weighting factors better reflect in-use operation of current and future
heavy-duty engines, we are proposing to apply these new weighting
factors to criteria pollutant measurement, as show in Table III-5, for
NOX and other criteria pollutants as well. To assess the
impact of the new test cycle on criteria pollutant emissions, we
analyzed data from the EPA Stage 3 engine that was tested on both
versions of the SET. The data summarized in Section III.B.3.ii.a show
that the NOX emissions from the EPA Stage 3 engine at an
equivalent of 435,000 miles are slightly lower using the proposed SET
weighting factors in 40 CFR 1036.505 versus the current SET procedure
in 40 CFR 86.1362. The lower emissions using the proposed SET cycle
weighting factors are reflected in the stringency of the proposed
Options 1 and 2 SET standards.

           Table III-5 Proposed Weighting Factors for the SET
------------------------------------------------------------------------
                                                               Weighting
                         Speed/% load                            factor
                                                                  (%)
------------------------------------------------------------------------
Idle.........................................................         12
A, 100.......................................................          9
B, 50........................................................         10
B, 75........................................................         10
A, 50........................................................         12
A, 75........................................................         12
A, 25........................................................         12
B, 100.......................................................          9
B, 25........................................................          9
C, 100.......................................................          2
C, 25........................................................          1
C, 75........................................................          1
C, 50........................................................          1
                                                              ----------
    Total....................................................        100
Idle Speed...................................................         12
    Total A Speed............................................         45
    Total B Speed............................................         38
    Total C Speed............................................          5
------------------------------------------------------------------------

iii. LLC
    EPA is proposing the addition of a low-load test cycle and standard
that would require CI engine manufacturers to demonstrate that the
emission control system maintains functionality during low-load
operation where the catalyst temperatures have historically been found
to be below their operational temperature (see Chapter 2.2.2 of the
draft RIA). We believe the addition of a low-load cycle would
complement the expanded operational coverage of our proposed off-cycle
testing requirements (see Section III.C).
    During ``Stage 2'' of their Low NOX Demonstration
program, SwRI and NREL developed several candidate cycles with average
power and duration characteristics intended to test current diesel
engine emission controls under three low-load operating conditions:
Transition from high- to low-load, sustained low-load, and transition
from low- to high-load.\320\ In September 2019, CARB selected the 92-
minute ``LLC Candidate #7'' as the low load cycle they adopted for
their Low NOX Demonstration program and subsequent Omnibus
regulation.321 322
---------------------------------------------------------------------------

    \320\ California Air Resources Board. ``Heavy-Duty Low
NOX Program Public Workshop: Low Load Cycle
Development''. Sacramento, CA. January 23, 2019. Available online:
https://ww3.arb.ca.gov/msprog/hdlownox/files/workgroup_20190123/02-llc_ws01232019-1.pdf.
    \321\ California Air Resources Board. Heavy-Duty Omnibus
Regulation. Available online: https://ww2.arb.ca.gov/rulemaking/2020/hdomnibuslownox.
    \322\ California Air Resources Board. ``Heavy-Duty Low
NOX Program: Low Load Cycle'' Public Workshop. Diamond
Bar, CA. September 26, 2019. Available online: https://ww3.arb.ca.gov/msprog/hdlownox/files/workgroup_20190926/staff/03_llc.pdf.
---------------------------------------------------------------------------

    We are proposing to adopt CARB's Omnibus LLC as a new test cycle,
the LLC. This cycle is described in Chapter 2 of the draft RIA for this
rulemaking and test procedures are specified in the proposed 40 CFR
1036.512. The proposed LLC includes applying the accessory loads
defined in the HD GHG Phase 2 rule. These accessory loads are 1.5, 2.5
and 3.5 kW for Light HDE,

Medium HDE, and Heavy HDE engines, respectively. To allow vehicle level
technologies to be recognized on this cycle we are proposing the
powertrain test procedure to include the LLC. More information on the
powertrain test procedure can be found in Section III.A.2.v. For the
determination of IRAF for the LLC, we are proposing the test procedures
defined in 40 CFR 1036.522, which is the same test procedure that is
used for the FTP and SET. We believe that the IRAF test procedures that
apply to the FTP and SET are appropriate for the LLC, but we request
comment on whether to modify how the regeneration frequency value in 40
CFR 1065.680 is determined, to account for the fact that a regeneration
frequency value is needed for three duty cycles and not just two.
    Our proposed Options 1 and 2 emission standards for this proposed
LLC are presented in Table III-6. The brake-specific LLC standards
would apply across engine classes. As with the FTP cycle, the data from
the EPA Stage 3 demonstration engine with an aged aftertreatment system
shows that these proposed Options 1 and 2 standards are feasible with
available margins between the data and the proposed standards. In fact,
the margin between the proposed Option 1 MY 2031 standards and the
Stage 3 engine data is the largest on the LLC, suggesting that a lower
numeric NOX standard would be feasible at 435,000 and
600,000 miles than included in the proposed Option 1 IUL NOX
standard. The summary of this data can be found in Section III.B.3.
    We request comment on the addition of a low-load test cycle and
standard, as well as the proposed accessory loads, or other engine
operation a low-load cycle should encompass, if finalized.

                                   Table III-6--Proposed Compression-Ignition Engine Standards Over the LLC Duty Cycle
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                          Primary intended service    NOX (mg/hp-   PM (mg/hp-   HC (mg/hp-   CO (g/hp-
                                                Model year                          class                 hr)          hr)          hr)          hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Proposed Option 1.................  2027-2030.........................  All HD Engines..............           90            5          140          6.0
                                    2031 and later....................  Light HDE and Medium HDE....           50            5           60          6.0
                                    2031 and later....................  Heavy HDE through IUL.......           50            5           60          6.0
                                    2031 and later....................  Heavy HDE from IUL to FUL...          100            5           60          6.0
Proposed Option 2.................  2027 and later....................  All HD Engines..............          100            5           60          6.0
--------------------------------------------------------------------------------------------------------------------------------------------------------

    The proposed LLC standards for PM are based on the effectiveness of
the diesel particulate filter (DPF) to reduce PM emissions across the
operating range of the engine, including under low loads. We request
comment on whether 5 mg/hp-hr provides enough margin for particular
engine designs. For example, would 6 or 7 mg/hp-hr be a more
appropriate standard for the LLC to maintain current PM emissions
levels while providing enough margin to account for the measurement
variability of the PM measurement test procedure. Since we are not
proposing standards on the LLC for SI engines, the data from the CARB
and EPA Stage 3 engine discussed in Section III.B.3 were used to assess
the feasibility of the proposed CO and HC standards. For both proposed
Option 1 and Option 2 standards, we are proposing the same numeric
standards for CO on the LLC as we have respectively proposed in Option
1 and Option 2 for the FTP and SET cycles. This is because the
demonstration data of the EPA Stage 3 engine shows that CO emissions on
the LLC are in similar to CO emissions from the FTP and SET. For the
proposed Options 1 and 2 for HC standards on the LLC, we are proposing
standards that are different than the standards of the FTP and SET
cycles, to reflect the performance of the EPA Stage 3 engine on the
LLC. The data discussed in Section III.B.3 of the preamble shows that
the proposed Options 1 and 2 standards are feasible for both current
and future new engines.
iv. Idle
    CARB currently has an idle test procedure and accompanying standard
of 30 g/h of NOX for diesel engines to be ``Clean Idle
Certified''.\323\ In the Omnibus rule the CARB lowered the
NOX standard to 10 g/h for MY 2024 to MY 2026 engines and 5
g/h for MY 2027 and beyond. In the ANPR, we requested comment on the
need or appropriateness of setting a federal idle standard for diesel
engines. We received comments supporting action by EPA to adopt
California's Clean Idle NOX standard as a voluntary emission
standard for federal certification.\324\ For proposed Option 1 we are
proposing an optional idle standard in 40 CFR 1036.104(b) and a new
test procedure in 40 CFR 1036.514, based on CARB's test procedure,\325\
to allow compression-ignition engine manufacturers to voluntarily
choose to certify (i.e., it would be optional for a manufacturer to
include the idle standard in an EPA certification but once included the
idle standard would become mandatory and full compliance would be
required) to an idle NOX standard of 30.0 g/hr for MY 2023,
10.0 g/hr for MY 2024 to MY 2026 and 5.0 g/hr for MY 2027 and beyond.
As part of this optional idle standard, we are proposing to require
that the brake-specific HC, CO, and PM emissions during the Clean Idle
test may not exceed measured emission rates from the idle segments of
the FTP or the idle mode in the SET, in addition to meeting the
applicable idle NOX standard.\326\ For proposed Option 2 we
are proposing an idle NOX standard of 10.0 g/hr for MY 2027
and beyond. We request comment on whether EPA should make the idle
standards mandatory instead of voluntary for MY 2027 and beyond, as
well as whether EPA should set clean idle standards for HC, CO, and PM
emissions (in g/hr) rather than capping the idle emissions for those
pollutants based on the measured emission levels during the idle
segments of the FTP or the idle mode in the SET. We request comment on
the need for EPA to define a label that would be put on the vehicles
that are certified to the optional idle standard.
---------------------------------------------------------------------------

    \323\ 13 CCR 1956.8 (a)(6)(C)--Optional NOX idling
emission standard.
    \324\ See comments from CARB, Volvo, and Union of Concerned
Scientists, and Eaton. Docket ID: EPA-HQ-OAR-2019-0055-0463.
    \325\ 86.1360-2007.B.4, California Exhaust Emission Standards
and Test Procedures for 2004 and Subsequent Model Heavy-Duty Diesel
Engines and Vehicles, April 18, 2019.
    \326\ See 40 CFR 1036.104(b).
---------------------------------------------------------------------------

v. Powertrain
    EPA recently finalized a separate rulemaking that included an
option for manufacturers to certify a hybrid powertrain to the FTP and
SET greenhouse gas engine standards by using a powertrain test
procedure (86 FR 34321, June 29, 2021).\327\ In this

rulemaking, we similarly propose to allow manufacturers to certify
hybrid powertrains, BEVs, and FCEVs to criteria pollutant emissions
standards by using the powertrain test procedure. In this section we
describe how manufacturers could apply the powertrain test procedure to
certify hybrid powertrains, and, separately, BEVs or FCEVs.
---------------------------------------------------------------------------

    \327\ The powertrain test procedure was established in the GHG
Phase 1 rulemaking but the recent rulemaking included adjustments to
apply the test procedure to the engine test cycles.
---------------------------------------------------------------------------

a. Development of Powertrain Test Procedures
    Powertrain testing allows manufacturers to demonstrate emission
benefits that cannot be captured by testing an engine alone on a
dynamometer. For hybrid engines and powertrains, powertrain testing
captures when the engine operates less or at lower power levels due to
the use of the hybrid powertrain function; for BEVs and FCEVs
powertrain testing allows the collection of data on work produced,
energy used and other parameters that would normally be collected for
an engine during a dynamometer test. However, powertrain testing
requires the translation of an engine test procedure to a powertrain
test procedure. Chapter 2 of the draft RIA describes how we translated
the FTP, proposed SET for criteria pollutants, and proposed LLC engine
test cycles to the proposed powertrain test cycles.\328\ The two
primary goals of this process were to make sure that the powertrain
version of each test cycle was equivalent to each respective engine
test cycle in terms of positive power demand versus time and that the
powertrain test cycle had appropriate levels of negative power demand.
To achieve this goal, over 40 engine torque curves were used to create
the powertrain test cycles. We request comment on ways to further
improve the proposed powertrain test procedures, including approaches
to apply the proposed procedures to powertrains that include a
transmission as part of the certified configuration to make the idle
accessory load more representative.
---------------------------------------------------------------------------

    \328\ As discussed in Section III.B.1, as part of the technical
amendments rulemaking, EPA allowed the powertrain test procedure to
be used for GHG emission standards on the FTP and SET engine-based
test cycles. In this rulemaking we are proposing to allow the
powertrain test procedure to be used for criteria emission standards
on these test cycles and the proposed LLC. As discussed in Section
2.ii, we are proposing new weighting factors for the engine-based
SET procedure for criteria pollutant emissions, which would be
reflected in the SET powertrain test cycle.
---------------------------------------------------------------------------

b. Testing Hybrid Engines and Hybrid Powertrains
    As noted in the introduction of this Section III, we are proposing
to clarify in 40 CFR 1036.101 that manufacturers may optionally test
the hybrid engine and hybrid powertrain to demonstrate compliance. We
propose that the powertrain test procedures specified in 40 CFR
1036.505 and 1036.510, which were previously developed for
demonstrating compliance with GHG emission standards on the SET and FTP
test cycles, are applicable for demonstrating compliance with criteria
pollutant standards on the SET and FTP test cycles. In addition, for
GHG emission standards we are proposing updates to 40 CFR 1036.505 and
1036.510 to further clarify how to carry out the test procedure for
plug-in hybrids. We have done additional work for this rulemaking to
translate the proposed LLC to a powertrain test procedure, and we are
proposing that manufacturers could similarly certify hybrid engines and
hybrid powertrains to criteria pollutant emission standards on the
proposed LLC using the proposed test procedures defined in 40 CFR
1036.512.
    We thus propose to allow manufacturers to use the powertrain test
procedures to certify hybrid engine and powertrain configurations to
all MY 2027 and later criteria pollutant engine standards. We also
propose to allow manufacturers to begin using powertrain test
procedures to certify hybrid configurations to criteria pollutant
standards in MY 2023. Manufacturers could choose to use either the SET
duty-cycle in 40 CFR 86.1362 or the proposed SET in 40 CFR 1036.505 in
model years prior to 2027.329 330
---------------------------------------------------------------------------

    \329\ We proposing to allow either the SET duty-cycle in 40 CFR
86.1362 or 40 CFR 1036.505 because the duty cycles are similar and
as shown in Chapter 3.1.2 of the Draft RIA the criteria pollutant
emissions level of current production engines is similar between the
two cycles.
    \330\ Prior to MY 2027, only manufacturers choosing to
participate in the Early Adoption Incentive Program would need to
conduct LLC powertrain testing (see Section IV.H for details on the
Early Adoption Incentive Program).
---------------------------------------------------------------------------

    We are proposing to allow these procedures starting in MY 2023 for
plug-in hybrids and, to maintain consistency with the requirements for
LD plug-in hybrids, we are proposing that the applicable criteria
pollutant standards must be met under the worst case condition, which
is achieved by testing and evaluating emission under both charge
depleting and charge sustaining operation. This is to ensure that under
all drive cycles the powertrain meets the criteria pollutant standards
and is not based on an assumed amount of zero emissions range. We are
proposing changes to the test procedures defined in 40 CFR 1036.505 and
1036.510 to clarify how to weight together the charge depleting and
charge sustaining greenhouse gas emissions for determining the
greenhouse gas emissions of plug-in hybrids for the FTP and SET duty
cycles. This weighting would be done using an application specific
utility factor curve that is approved by EPA. We are also proposing to
not apply the cold and hot weighting factors for the determination of
the FTP composite emission result for greenhouse gas pollutants because
the charge depleting and sustaining test procedures proposed in 40 CFR
1036.510 include both cold and hot start emissions by running repeat
FTP cycles back-to-back. By running back-to-back FTPs, the proposed
test procedure captures both cold and hot emissions and their relative
contribution to daily greenhouse gas emissions per unit work, removing
the need for weighting the cold and hot emissions. We request comment
on our proposed approach to the FTP duty cycle for plug-in hybrids and
the proposed approach to the determination of the FTP composite
emissions result, including whether EPA should instead include cold and
hot weighting factors for the latter. If you comment that EPA should
include the cold and hot weighting factors, we request that you also
include an example of how these calculations would be carried out with
such an approach (how the calculations would include both the weighting
of charge sustaining and charge depleting emissions in conjunction with
the weighting of the cold and hot emissions results).
    We propose to limit this test procedure to hybrid powertrains to
avoid having two different testing pathways for non-hybrid engines for
the same standards. On the other hand, there may be other technologies
where the emissions performance is not reflected on the engine test
procedures, so we request comment on whether this test procedure should
be available to other powertrains, and if so how to define those
powertrains.
    Finally, for all pollutants, we request comment on if we should
remove 40 CFR 1037.551 or limit the use of it to only selective
enforcement audits (SEA). 40 CFR 1037.551 was added as part of the
Heavy-Duty Phase 2 GHG rulemaking to provide flexibility for an SEA or
a confirmatory test, by allowing just the engine of the powertrain to
be tested. Allowing just the engine to be tested over the engine speed
and torque cycle that was recorded during the powertrain test enables
the testing to be conducted in more widely available engine dynamometer
test cells, but this

flexibility could increase the variability of the test results. If you
submit comment in support of removing or limiting the use of 40 CFR
1037.551 to just SEA, we request that you include data supporting your
comment.
c. Testing Battery-Electric and Fuel Cell Electric Vehicles
    As noted in the introduction to this Section III, and detailed in
Section IV.I, we are proposing to recognize the zero tailpipe emission
benefits of BEV and FCEV technologies by allowing manufacturers to
generate NOX emission credits with these technologies.\331\
We are further proposing that manufacturers who choose to generate
NOX emission credits from BEVs or FCEVs would be required to
conduct testing to measure work produced over a defined duty-cycle
test, and either useable battery energy (UBE) for BEVs or fuel cell
voltage (FCV) for FCEVs (see Section IV.I for details).
---------------------------------------------------------------------------

    \331\ See Section IV.I, proposed 40 CFR 1037.616, and proposed
40 CFR 1036.741 for details on the proposed NOX emission
credits for BEVs and FCEVs. Briefly, manufacturers would generate
vehicle emissions credits, which would then be fungible between
vehicle and engine certification programs, such that NOX
credits generated through the vehicle program could be applied to
the proposed engine ABT program described in Section IV.G and
specified in proposed 40 CFR 1036.705.
---------------------------------------------------------------------------

    To conduct the testing necessary for generating NOX
emission credits from BEVs or FCEVs, we are proposing that
manufacturers would use the powertrain test procedures for the FTP,
proposed SET and proposed LLC. Specifically, for BEVs, manufacturers
would run a series of powertrain FTP, SET and LLC tests over a defined
sequence referred to as a ``Multicycle Test'' (MCT), which is specified
in proposed 40 CFR 1037.552. For FCEVs, manufacturers would operate the
powertrain over an FTP, SET, and LLC and determine the average fuel
cell voltage (FCV) by taking the average of the FCV when the fuel cell
current is between 55 percent and 65 percent of rated fuel cell
current, as specified in proposed 40 CFR 1037.554.\332\
---------------------------------------------------------------------------

    \332\ The MCT for BEVs (specified in 40 CFR 1037.552) and FCEVs
(specified in 40 CFR 1037.554) use the same foundational powertrain
test procedures for the FTP, SET, and LLC test cycles; however, the
MCT for BEVs includes additional iterations of the test cycles that
are needed to deplete the battery and measure UBE, while the MCT for
FCEVs includes the measurement of FCV, rather than UBE.
---------------------------------------------------------------------------

    The MCT for BEVs consists of a fixed number of dynamic drive cycles
combined with constant-speed driving phases. The heavy-duty transient
cycle (HDTC) described in current 40 CFR 1036.510(a)(4), LLC described
in proposed 40 CFR 1036.512, and SET described in proposed 40 CFR
1036.505 are used to determine the energy consumption associated with
specific and established driving patterns. These dynamic drive cycles
make up a combined 57.92 miles of driving distance. The constant speed
cycles (CSC), which are located in the middle and the end of the test,
are intended to: Reduce test duration by depleting the battery more
rapidly than the established certification drive schedules; improve the
robustness of the energy determination by minimizing the impact of
drive style variation; and prevent inconsistent triggering of end-of-
test criteria that can occur at high power-demand points when a BEV is
following a dynamic drive schedule at low states-of-charge.
    The CSC middle phase is located after the initial run through two
HDTCs, one LLC, and one SET. This CSC depletes the battery and allows
determination of the vehicle's performance on the HDTC, LLC, and SET
for both high and low states of charge. The distance traveled during
the CSC middle phase that is determined by this procedure ensures that
the second run through two HDTCs, one LLC, and one SET is conducted at
a substantially lower state of charge. The target distance traveled
over the CSC end phase is 20 percent or less of the total driven
distance for the combined initial and second runs through the HDTC,
LLC, or SET cycles.
    The MCT for FCEVs consists of running a powertrain on the FTP, LLC,
and SET to determine the FCV when the fuel cell current (FCC) is
between 55 percent and 65 percent of rated FCC. Work is also measured
during the second HDTC in the FTP and used in the determination of the
FCEV conversion factor (CF) value for credit generation in proposed 40
CFR 1037.616.
    We request comment on our proposed approach to powertrain testing
for BEVs and FCEVs, and specifically whether any modifications of the
FTP, SET and LLC powertrain test cycles would be needed for BEVs and
FCEVs. We further request comment on whether the MCT, as defined in
proposed 40 CFR 1037.552, would require modifications to accurately
measure work produced over the FTP cycle or the measure of UBE. We
request comment on whether the procedure in proposed 40 CFR 1037.554 is
appropriate for determining FCV. Finally, we request comment on if
current 40 CFR 1036.527 should be used to determine rated FCC.
vi. Closed Crankcase
    During combustion, gases can leak past the piston rings sealing the
cylinder and into the crankcase. These gases are called blowby gases
and generally include unburned fuel and other combustion products.
Blowby gases that escape from the crankcase are considered crankcase
emissions (see 40 CFR 86.402-78). Current regulations restrict the
discharge of crankcase emissions directly into the ambient air. Blowby
gases from gasoline engine crankcases have been controlled for many
years by sealing the crankcase and routing the gases into the intake
air through a positive crankcase ventilation (PCV) valve. However, in
the past there have been concerns about applying a similar technology
for diesel engines. For example, high PM emissions venting into the
intake system could foul turbocharger compressors. As a result of this
concern, diesel-fueled and other compression-ignition engines equipped
with turbochargers (or other equipment) were not required to have
sealed crankcases (see 40 CFR 86.007-11(c)). For these engines,
manufacturers are allowed to vent the crankcase emissions to ambient
air as long as they are measured and added to the exhaust emissions
during all emission testing to ensure compliance with the emission
standards.
    Because all new highway heavy-duty diesel engines on the market
today are equipped with turbochargers, they are not required to have
closed crankcases under the current regulations. Manufacturer
compliance data indicate approximately one-third of current highway
heavy-duty diesel engines have closed crankcases, indicating that some
heavy-duty engine manufacturers have developed systems for controlling
crankcase emissions that do not negatively impact the turbocharger. EPA
is proposing provisions in 40 CFR 1036.115(a) to require a closed
crankcase ventilation system for all highway compression-ignition
engines to prevent crankcase emissions from being emitted directly to
the atmosphere starting for MY 2027 engines.\333\ These emissions could
be routed upstream of the aftertreatment system or back into the intake
system. Unlike many other standards, this standard is a design standard
rather than a performance standard.
---------------------------------------------------------------------------

    \333\ We are proposing to move the current crankcase emissions
provisions to a new paragraph (u) in the interim provisions of 40
CFR 1036.150, which would apply through model year 2026.
---------------------------------------------------------------------------

    Our reasons for proposing a requirement for closed crankcases are
twofold. While the exception in the current regulations for certain
compression-ignition engines requires manufacturers to quantify their
engines'

crankcase emissions during certification, they report non-methane
hydrocarbons in lieu of total hydrocarbons. As a result, methane
emissions from the crankcase are not quantified. Methane emissions from
diesel-fueled engines are generally low; however, they are a concern
for compression-ignition-certified natural gas-fueled heavy-duty
engines because the blowby gases from these engines have a higher
potential to include methane emissions. EPA proposed to require that
all natural gas-fueled engines have closed crankcases in the Heavy-Duty
Phase 2 GHG rulemaking, but opted to wait to finalize any updates to
regulations in a future rulemaking, where we could then propose to
apply these requirements to natural gas-fueled engines and to the
diesel fueled engines that many of the natural gas-fueled engines are
based off of (81 FR 73571, October 25, 2016).
    In addition to our concern of unquantified methane emissions, we
believe another benefit to closed crankcases would be better in-use
durability. We know that the performance of piston seals reduces as the
engine ages, which would allow more blowby gases and could increase
crankcase emissions. While crankcase emissions are included in the
durability tests that estimate an engine's deterioration, those tests
were not designed to capture the deterioration of the crankcase. These
unquantified age impacts continue throughout the operational life of
the engine. Closing crankcases could be a means to ensure those
emissions are addressed long-term to the same extent as other exhaust
emissions.
    Chapter 1.1.4 of the draft RIA describes EPA's recent test program
to evaluate the emissions from open crankcase systems on two modern
heavy-duty diesel engines. Results suggest THC and CO emitted from the
crankcase can be a notable fraction of overall tailpipe emissions. By
closing the crankcase, those emissions would be rerouted to the engine
or aftertreatment system to ensure emission control.
3. Feasibility of the Diesel (Compression-Ignition) Engine Standards
i. Summary of Technologies Considered
    Our proposed Options 1 and 2 standards for compression-ignition
engines are based on the performance of technology packages described
in Chapters 1 and 3 of the draft RIA for this rulemaking. Specifically,
we are evaluating the performance of next-generation catalyst
formulations in a dual SCR catalyst configuration with a smaller SCR
catalyst as the first substrate in the aftertreatment system for
improved low-temperature performance, and a larger SCR catalyst
downstream of the diesel particulate filter to improve NOX
conversion efficiency during high power operation and to allow for
passive regeneration of the particulate filter.\334\ Additionally, the
technology package includes CDA that reduces the number of active
cylinders, resulting in increased exhaust temperatures for improved
catalyst performance under light-load conditions and can be used to
reduce fuel consumption and CO2 emissions. The technology
package also includes the use of a heated DEF injector for the upfront
SCR catalyst; the heated DEF injector allows DEF injection at
temperatures as low as approximately 140 [deg]C. The heated DEF
injector also improves the mixing of DEF and exhaust gas within a
shorter distance than with unheated DEF injectors, which enables the
aftertreatment system to be packaged in a smaller space. Finally, the
technology package includes hardware needed to close the crankcase of
diesel engines.
---------------------------------------------------------------------------

    \334\ As described in Chapter 3 of the draft RIA, we are
evaluating 3 different aftertreatment systems that contain different
catalyst formulation.
---------------------------------------------------------------------------

ii. Summary of Feasibility Analysis
a. Projected Technology Package Effectiveness and Cost
    Based upon preliminary data from EPA's diesel demonstration
research and the CARB Heavy-duty Low NOX Stage 3 Research
Program (see Chapter <IP_ADDRESS> and Chapter <IP_ADDRESS> of the draft RIA),
Heavy HDE NOX reductions of 90 percent from current
NOX standards are technologically feasible when using CDA or
other valvetrain-related air control strategies in combination with
dual SCR systems. EPA has continued to evaluate aftertreatment system
durability via accelerated aging of advanced emissions control systems
as part of EPA's diesel engine demonstration program that is described
in Chapter 3 of the draft RIA. In assessing the feasibility of our
proposed standards, we have taken into consideration the proposed level
of the standards, the additional emissions from infrequent
regenerations, the proposed longer useful life, and lead time for
manufacturers.
    Manufacturers are required to design engines that meet the duty
cycle and off-cycle standards throughout their useful life. In
recognition that emissions performance will degrade over time,
manufacturers design their engines to perform significantly better than
the standards when first sold to ensure that the emissions are below
the standard throughout useful life even as the emissions controls
deteriorate. As discussed below and in Chapter 3 of the draft RIA,
manufacturer margins can range from less than 25 percent to 100 percent
of the FEL. For Option 1, for Heavy HDEs that have the longest proposed
useful life, we are proposing intermediate useful life standards that
ensure that engines do not degrade in performance down to the duty
cycle and off-cycle standards too quickly and allow for an intermediate
check on emissions performance deterioration over the useful life.
    To assess the feasibility of the proposed Option 1 MY 2031
standards for heavy HDE at the IUL of 435,000 miles, the data from the
EPA Stage 3 engine was used. As discussed in Section III.B.2 the EPA
Stage 3 engine includes improvements beyond the CARB Stage 3 engine,
namely replacing the zone-coated catalyzed soot filter with a separate
DOC and DPF and improving the mixing of the DEF with exhaust for the
downstream SCR. These improvements lowered the emissions on the FTP,
SET and LLC below what was measured with the CARB Stage 3 engine. The
emissions for the EPA Stage 3 engine on the FTP, SET and LLC aged to an
equivalent of 435,000 and 600,000 miles are shown in Table III-7 and
Table III-8. To assess the feasibility of the proposed Option 1
NOX standards for MY 2027 and MY 2031 for Heavy HDE at the
respective proposed Option 1 useful life periods, the data from the EPA
Stage 3 engine was used. The data from the EPA Stage 3 engine was used
because it included emission performance with the aftertreatment at the
equivalent age of 435,000 and 600,000 miles. Having data at multiple
points allowed us to use linear regression to project out the
performance of the EPA Stage 3 engine at 800,000 miles.\335\ To account
for the IRAF for both particulate matter and sulfur on the
aftertreatment system, we relied on an analysis by SwRI that is
summarized in Chapter 3 of the draft RIA. In this analysis SwRI
determined the IRAF at 2 mg/hp-hr for both the FTP and SET cycles and 5
mg/hp-hr for the LLC. Based on our analysis, the proposed Option 1 MY
2027 and MY 2031 emissions standards for Heavy HDE are feasible at the
respective proposed useful life periods. To provide for additional
margin, in our technology

cost analysis we increased the SCR catalyst volume from what was used
on the EPA and CARB Stage 3 engine. The increase in total SCR catalyst
volume relative to the EPA and CARB Stage 3 SCR was approximately 23.8
percent. We believe this further supports our conclusion that the
proposed Option 1 standards are achievable for the proposed useful life
of 800,000 miles for MY 2031 Heavy HDE. In addition to NOX,
the proposed Option 1 HC and CO standards are feasible for CI engines
on all three cycles. This is shown in Table III-7, where the
demonstrated HC and CO emissions results are below the proposed Option
1 standards discussed in Section III.B.2. The proposed Option 1
standards for PM of 5 mg/hp-hr for the FTP, SET and LLC, continue to be
feasible with the additional technology and control strategies needed
to meet the proposed Option 1 NOX standards, as seen by the
PM emissions results in Table III-7 below. As discussed in Section
III.B.2, taking into account measurement variability of the PM
measurement test procedure, we believe that PM emissions from current
diesel engines are at the lowest feasible level for MY 2027 and later
engines. We request comment on whether 5 mg/hp-hr provides enough
margin for particular engine designs or for any of the duty cycles
(FTP, SET, or LLC). For example, would 6 or 7 mg/hp-hr be a more
appropriate standard for the LLC to maintain current PM emissions
levels while providing enough margin to account for the measurement
variability of the PM measurement test procedure. In addition, we
request comment on if there are technologies that EPA could consider
that would enable a PM standard lower than 5 mg/hp-hr. Commenters
requesting a higher standard are encouraged to provide data supporting
such comments.
---------------------------------------------------------------------------

    \335\ See Chapter 3.1.3 of the draft RIA for our analysis on
projecting emissions performance beyond 600,000 miles.

    Table III-7--Stage 3 Engine Emissions at 435,000 Mile Equivalent Test Point Without Adjustments for IRAF
----------------------------------------------------------------------------------------------------------------
                                                 NOX (mg/  PM (mg/hp- NMHC (mg/  CO  (g/hp-  CO2  (g/   N2O  (g/
                  Duty cycle                      hp-hr)      hr)       hp-hr)      hr)       hp-hr)     hp-hr)
----------------------------------------------------------------------------------------------------------------
FTP...........................................         20          2         12      0.141        514      0.076
SET \a\.......................................         17          1          1      0.030        455      0.024
LLC...........................................         29          3         35      0.245        617      0.132
----------------------------------------------------------------------------------------------------------------
\a\ Using the weighting factors in our proposed test procedures (40 CFR 1036.505).

    Table III-8--Stage 3 Engine Emissions at 600,000 Mile Equivalent Test Point Without Adjustments for IRAF
----------------------------------------------------------------------------------------------------------------
                                                NOX  (mg/   PM  (mg/  NMHC  (mg/ CO  (g/hp-  CO2  (g/   N2O  (g/
                  Duty cycle                      hp-hr)     hp-hr)     hp-hr)      hr)       hp-hr)     hp-hr)
----------------------------------------------------------------------------------------------------------------
FTP...........................................         27          1          9      0.144        519      0.058
SET \a\.......................................         24          1          1      0.015        460      0.030
LLC...........................................         33          4         16      0.153        623      0.064
----------------------------------------------------------------------------------------------------------------
\a\ Using the weighting factors in our proposed test procedures (40 CFR 1036.505).

    As additional data is received from the EPA led demonstration
project, the demonstration data will inform whether the proposed Option
1 IUL standards for MY 2031 are needed. For example, if the
demonstration data shows much lower emissions for the first half of
useful life than for the second half of useful life, then this would
confirm our assumption that the proposed Option 1 IUL standard would
ensure that the emission reductions during the earlier portion of an
engine's useful life are achieved, while preserving sufficient margin
for deterioration during the second half of useful life. On the other
hand, if we find that the emissions values are relatively constant
through useful life, this may support that an IUL standard may not be
needed. This data will also inform whether the proposed Option 1 IUL
standard of 20 mg/hp-hr at 435,000 miles is appropriate for Heavy HDE
in MY 2031 and whether an IUL standard is also needed for MY 2027 to
account for deterioration out to the proposed Option 1 600,000-mile
useful life for MY 2027.
    Our analysis also shows that the proposed Option 2 standards could
be met starting in MY 2027 with CDA and dual-SCR with heated dosing
(see draft RIA Chapter 3 for details of our analysis) as shown in Table
III-7. The proposed Option 2 includes a higher (less stringent)
NOX emission level for all CI engine classes over the FTP
and SET compared to either step of our proposed Option 1 NOX
FTP and SET standards. The FTP and SET standards in proposed Option 2
for PM, HC, and CO are numerically equivalent to our proposed Option 1
MY 2031 standards. As shown in Table III-7, we currently have data
demonstrating that the proposed Option 2 standards could be met out to
600,000 miles. These data show the proposed Option 2 standards are
feasible through the proposed Option 2 useful life periods for Light
HDE, Medium HDEs. Our evaluation of the current data suggests that the
proposed Option 2 standards would also be feasible out to the proposed
Option 2 Heavy HDE useful life; we are continuing to collect data to
confirm our extrapolation of data out to the longer useful life
mileage. As discussed in Section IV.A, useful life mileages for
proposed Option 2 are higher than our MY 2027 proposed useful life, but
lower than our proposed Option 2 useful life values for MY 2031.
    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. To do this we evaluated how CO2
emissions changed from the base engine on the FTP, SET, and LLC, as
well as the fuel mapping test procedures defined in 40 CFR 1036.535 and
1036.540. For all three cycles the 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 for the FTP, SET and LLC, was 1, 0 and 1
percent

respectively.\336\ We note that after this data was taken SwRI made
changes to the thermal management strategies of the CARB Stage 3 engine
to improve NOX reduction at low SCR temperatures. The data
from the EPA Stage 3 engine at the equivalent age of 435,000 miles
includes these calibration changes, and although there was an increase
in CO2, which resulted in the CO2 emissions for
the EPA Stage 3 engine being higher than the 2017 Cummins X15 engine
for the FTP, SET and LLC of 0.6, 0.7 and 1.3 percent respectively, this
was not a direct comparison because the 2017 Cummins X15 aftertreatment
had not been aged to an equivalent of 435,000 miles. As discussed in
Chapter 3 of the draft 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. To evaluate how the technology on the
CARB Stage 3 engine compares to the 2017 Cummins X15 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.\337\ The fuel maps from these tests were run in GEM and
the results from this analysis showed that the Stage 3 engine emitted
CO2 at the same rate as the 2017 Cummins X15. The details of
this analysis are described in Chapter 3.1 of the draft RIA. The
technologies included in the EPA demonstration 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 proposed standards, but manufacturers
will still also need to comply with the GHG standards that apply under
HD GHG Phase 2.\338\ Because of this we have not projected an increase
in GHG emissions resulting from compliance with the proposed standards.
---------------------------------------------------------------------------

    \336\ See Chapter 3 of the draft RIA for the CO2
emissions of the 2017 Cummins X15 engine and the CARB Stage 3
engine.
    \337\ 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.
    \338\ As explained in Section XI, EPA is also proposing targeted
updates to the Phase 2 Heavy-Duty Greenhouse Gas Emissions program.
---------------------------------------------------------------------------

    Table III-9 summarizes the incremental technology costs for the
proposed Options 1 and 2 standards, from the baseline costs shown in
Table III-13. While the standards vary between the proposed Option 1
and the proposed Option 2 standards, we are evaluating the same
technologies to assess the feasibility of the two sets of standards.
These values include aftertreatment system and CDA costs. The details
of this analysis can be found in Chapter 3 of the draft RIA.
Differences in the useful life and warranty periods between the
proposed Options 1 and 2 are accounted for in the indirect costs as
discussed in Chapter 7.1.2 of the draft RIA.\339\
---------------------------------------------------------------------------

    \339\ See Table III-3 for the proposed useful life values and
Section IV.B.1 for the proposed emissions warranty periods for each
option.

Table III-9--Incremental Direct Manufacturing Cost of Proposed Options 1
        and 2 Standards for the Aftertreatment and CDA Technology
                                [2019 $]
------------------------------------------------------------------------
                                           Medium
               Light HDE                    HDE     Heavy HDE  Urban bus
------------------------------------------------------------------------
$1,685.................................     $1,648     $2,266     $1,684
------------------------------------------------------------------------

    As described in Chapter 3.1 of the draft RIA, we have estimated the
incremental technology cost for closed crankcase filtration systems for
all CI engines to be $37 (2017 $), noting that these technologies are
on some engines available in the market today.
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 LHD, MHD, and
HHD vehicles. Chapter 5 of the draft RIA describes how the data was
used to update the MOVES model emissions rates for HD diesel engines.
Chapter 3 of the draft 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-10, shows that manufacturers vary in their
approach to how much margin is built into the FEL. Some manufactures
have greater than 100 percent margin built into the FEL, while other
manufacturers have less than 25 percent.

                            Table III-10--Summary of Certification Data for FTP Cycle
----------------------------------------------------------------------------------------------------------------
                                                            NOX  (g/  PM  (g/hp- NMHC  (g/  CO  (g/hp-  N2O  (g/
                                                             hp-hr)      hr)       hp-hr)      hr)       hp-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-11--Summary of Certification Data for SET Cycle
----------------------------------------------------------------------------------------------------------------
                                                            NOX  (g/  PM  (g/hp- NMHC  (g/  CO  (g/hp-  N2O  (g/
                                                             hp-hr)      hr)       hp-hr)      hr)       hp-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 1036.505. Table III-12 summarizes the range of
results from these engines on the FTP, SET and LLC. As described in
Chapter 3 of the draft 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-12--Range of NOX Emissions From MY2017 to MY2019 Heavy-Duty
                             Diesel Engines
------------------------------------------------------------------------
                                           SET in     SET in
        NOX (g/hp-hr)            FTP       40 CFR     40 CFR      LLC
                              composite   86.1333    1036.505
------------------------------------------------------------------------
Minimum.....................       0.10       0.01       0.01       0.35
Maximum.....................       0.15       0.12       0.05       0.81
Average.....................       0.13       0.06       0.03       0.59
------------------------------------------------------------------------

    Table III-13 summarizes the baseline sales-weighted total
aftertreatment cost of Light HDE, Medium HDE, Heavy HDE and urban bus
engines. The details of this analysis can be found in Chapter 3 of the
draft RIA.

     Table III-13--Baseline Direct Manufacturing Aftertreatment Cost
                                [2019 $]
------------------------------------------------------------------------
                                           Medium
               Light HDE                    HDE     Heavy HDE  Urban bus
------------------------------------------------------------------------
$ 2,804................................    $ 2,877    $ 4,587    $ 2,929
------------------------------------------------------------------------

4. Potential Alternative
    We evaluated one alternative (the Alternative) to our proposed HD
CI exhaust emission standards (summarized in Table III-14, Table III-
15, and Table III-16). As discussed in this section and based on
information we have collected to date, we do not project that the
Alternative standards are feasible in the MY 2027 timeframe with the
technology we have evaluated (Table III-9).
    The Alternative we considered includes lower (more stringent)
numeric NOX emission levels for Heavy HDEs, and lower HC
emission levels for all CI engine classes, combined with longer useful
life periods and shorter lead time compared to the proposed Option 1 MY
2031 standards. As shown in Table III-7, the test data we currently
have from the EPA Stage 3 engine is not sufficient to conclude that the
Alternative standards would be feasible in the MY 2027 timeframe.
Specifically, our data suggest that the numeric level of the FTP and
SET NOX emission standards would be very challenging to meet
through 435,000 miles (see draft RIA Chapter 3.1). For Light HDEs and
Medium HDEs, these data suggest that to meet the combination of numeric
levels of the NOX emission standards and useful life periods
of the Alternative, it may be appropriate for EPA to consider providing
manufacturers with additional lead time, beyond the MY 2027
implementation date of the Alternative. For Heavy HDEs, our
extrapolation of the data from 600,000 miles through the 850,000 miles
useful life period of the Alternative suggests that the numeric level
of the NOX emission control in the Alternative could not be
maintained through the Alternative useful life period (see draft RIA
Chapter 3.1 for details on available data and our evaluation). Wholly
different emission control technologies than we have evaluated to date
(i.e., not based on CDA and a dual SCR) would be needed to meet the
Alternative standards for Heavy HDEs; we request comment on this
conclusion and on the availability, or potential development and
timeline, of such additional technologies. We also note that the
Alternative is significantly more stringent than the CARB Omnibus
because of the combination of numeric level of the NOX
emission standards and useful life periods in the Alternative compared
to the CARB Omnibus. Specifically, for heavy HDEs, the Alternative
includes a 20 mg/hp-hr standard at a useful life of 850,000 miles,
whereas for MYs 2027 through 2030 the CARB Omnibus includes a 20 mg/hp-
hr standard at 435,000 miles and a 35 mg/hp-hr standard at 600,000
miles for heavy HDEs. Thus, the heavy HDE useful life period of the
Alternative is substantially longer than the CARB Omnibus useful life
periods that start in MY 2027, particularly when comparing the useful
life period for the 20 mg/hp-hr standard. Starting in MY 2031, the CARB
Omnibus NOX standard for heavy HDEs is 40 mg/hp-hr at a
useful life of 800,000 miles, which is again a higher numeric level of
the standard at a shorter useful life than the Alternative.

                         Table III-14--Proposed and Alternative Compression-Ignition Engine Standards for the FTP Test Procedure
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                NOX  (mg/   PM  (mg/   HC  (mg/  CO  (g/hp-
                                                    Model year                Primary intended service class    hp-hr)     hp-hr)     hp-hr)      hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Proposed Option 1....................  2027-2030...........................  All HD Engines.................         35          5         60        6.0
                                       2031 and later......................  Light HDE and Medium HDE.......         20          5         40        6.0
                                       2031 and later......................  Heavy HDE......................     40 \a\          5         40        6.0
Proposed Option 2....................  2027 and later......................  All HD Engines.................         50          5         40        6.0
Alternative..........................  2027 and later......................  All HD Engines.................         20          5         10        6.0
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Proposed Option 1 MY 2031 and later IUL NOX standard for Heavy HDE is 20 mg/hp-hr.

                         Table III-15--Proposed and Alternative Compression-Ignition Engine Standards for the SET Test Procedure
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                NOX  (mg/   PM  (mg/   HC  (mg/  CO  (g/hp-
                                                    Model year                Primary intended service class    hp-hr)     hp-hr)     hp-hr)      hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Proposed Option 1....................  2027-2030...........................  All HD Engines.................         35          5         60        6.0
                                       2031 and later......................  Light HDE and Medium HDE.......         20          5         40        6.0
                                       2031 and later......................  Heavy HDE......................     \a\ 40          5         40        6.0
Proposed Option 2....................  2027 and later......................  All HD Engines.................         50          5         40        6.0
Alternative..........................  2027 and later......................  All HD Engines.................         20          5         10        6.0
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Proposed Option 1 MY 2031 and later IUL NOX standard for Heavy HDE is 20 mg/hp-hr.

                         Table III-16--Proposed and Alternative Compression-Ignition Engine Standards for the LLC Test Procedure
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                NOX  (mg/   PM  (mg/   HC  (mg/  CO  (g/hp-
                                                    Model year                Primary intended service class    hp-hr)     hp-hr)     hp-hr)      hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Proposed Option 1....................  2027-2030...........................  All HD Engines.................         90          5        140        6.0
                                       2031 and later......................  Light HDE and Medium HDE.......         50          5         60        6.0
                                       2031 and later......................  Heavy HDE......................    \a\ 100          5         60        6.0
Proposed Option 2....................  2027 and later......................  All HD Engines.................        100          5         60        6.0
Alternative..........................  2027 and later......................  All HD Engines.................        100          5         60        6.0
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Proposed Option 1 MY 2031 and later IUL NOX standard for Heavy HDE is 50 mg/hp-hr.

    For the optional idle NOX standard, the Alternative
includes a standard of 10.0 g/hr for MY 2027 and beyond. The proposed
Options 1 and 2 standards generally represent the range of options,
including the standards, regulatory useful life and emission-related
warranty periods and lead time provided, that we are currently
considering in this rule, depending in part on any additional
information we receive on the feasibility, costs, and other impacts of
the proposed Options 1 and 2 standards. In order to consider adopting
the Alternative in the final rule, we would need additional data to
project that the Alternative is feasible for the MY 2027 time frame. As
discussed in Section III.B.5, we are soliciting comment on the
feasibility of the Alternative and other alternatives outside the range
of options covered by the proposed Options 1 and 2 standards.
5. Summary of Requests for Comment on the Stringency of the CI Duty
Cycle Standards
    We request comment on the following items related to the proposed
CI duty cycle standards. First, we request comment on the numeric value
of each proposed, or alternative, standard for each duty cycle and off-
cycle emissions and the proposed Option 1 two step, or the proposed
Option 2 one step, approach and implementation timetable, as well as
other standards or approaches recommended by the commenter, within the
approximate range of the proposed Options 1 and 2 standards. We request
comment, including relevant data and other information, on the
feasibility of the implementation model year, numeric levels of the
emission standards, and useful life and warranty periods included in
the Alternative, or other alternatives outside the range of options
covered by the proposed Options 1 and 2 standards. We request comment
on if a margin between the demonstrated emissions performance and the
proposed standards should be included and if so, we request comment on
if a specific margin should be used and what that value should be.
Commenters requesting a specific margin are encouraged to provide data
and analysis to support the numeric value of the margin(s).
    We request comment on whether a lower numeric standard for
NOX should be set for the LLC based on the emission levels
achieved with the CARB Stage 3 engine or EPA Stage 3 engine. We request
comment on whether EPA should make the idle standards mandatory for MY
2027 and beyond. We request comment on whether the test procedures
defined in 40 CFR 1036.522 for IRAF should be applied to the LLC or if
alternative procedures should be considered. We request comment on
whether the proposed PM standards of 5 mg/hp-hr for the FTP, SET and
LLC provide enough margin to account for the measurement variability of
the PM measurement test procedure, while ensuring that the PM emissions
from HD CI engines do not increase. We are requesting comment on
whether we should include HEV, BEV, and/or FCEV technologies in our
feasibility analysis for the final rule.
    As discussed in Section III.B.2.v, EPA requests comment on the
proposed powertrain test procedure, including any additional
requirements that are needed to ensure that the engine and respective
powertrain cycles are equivalent. We request comment on other
improvements that could be made specifically to make the idle accessory
load more representative for powertrains that include a transmission as
part of the certified configuration. EPA requests comment on whether
the powertrain test procedure option is needed for specific non-hybrid
powertrains where the engine test procedure is not representative of
in-use operation of the powertrain in a vehicle, and if so how should
we define these powertrains so that the powertrain test option is only
available for these powertrains. We request comment on our proposed
approach to powertrain testing for BEVs and FCEVs, and specifically
whether any modifications of the FTP, SET and LLC powertrain test
cycles would be needed for BEVs and FCEVs. We further request comment
on whether the MCT as defined in 40 CFR 1037.552 would require
modifications to accurately measure work produced over the FTP cycle or
the measure of useable battery energy (UBE). We request comment on
whether the procedure in 40 CFR 1037.554 is appropriate for determining
fuel cell voltage (FCV). In addition, we request

comment on if 40 CFR 1036.527 should be used to determine rated FCC.
    Finally, we request comment on whether the standards should be
expressed in units of milligrams per kilowatt-hour, so that each value
of the standards is in the international system of units (SI units), as
we have done for the HD nonroad and locomotive standards.

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

1. Current 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 limits
are 1.5 (1.25 for CO) times the laboratory certification standard or
family emission limit (FEL) for NOX, HC, PM and CO and can
be found in 40 CFR 86.007-11. 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 significant operation not covered by
NTE standards.
    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.\340\ 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).
---------------------------------------------------------------------------

    \340\ 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.\341\ \342\ \343\ 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.\344\
---------------------------------------------------------------------------

    \341\ 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.
    \342\ Sandhu, Gurdas, et al. ``Identifying Areas of High
NOX Operation in Heavy-Duty Vehicles''. 28th CRC Real-
World Emissions Workshop, March 18-21, 2018.
    \343\ 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.
    \344\ 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).\345\ The results were even higher when
we analyzed the data to consider only NOX emissions that
occur during low load events.
---------------------------------------------------------------------------

    \345\ 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.\346\ 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.
---------------------------------------------------------------------------

    \346\ 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.347 348 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).
---------------------------------------------------------------------------

    \347\ 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.
    \348\ 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 proposing an approach similar to the European in-use
program, with key distinctions that build upon the Euro VI approach, as
discussed below.
2. Proposed Off-Cycle Standards and Test Procedures
    As described in Section III.C.1, our current NTE test procedures
were not designed to capture low-load operation. We are proposing to
replace the NTE test procedures and standards (for NOX, PM,
HC and CO) for model year 2027 and later engines. Engine operation and
emissions test data would be assessed in 300-second moving average
windows (MAWs) of continuous engine operation.\349\ In contrast to the
current NTE approach that divides engine operation into two categories
(in the NTE zone and out of the NTE zone), the proposed approach would
divide engine operation into three categories (or ``bins'') based on
the time-weighted average engine power of each MAW of

engine data as described in more detail below.
---------------------------------------------------------------------------

    \349\ Our evaluation includes our current understanding that
shorter windows are more sensitive to measurement variability and
longer windows make it difficult to distinguish between duty cycles.
---------------------------------------------------------------------------

    Although the proposed program has similarities to the European
approach, we are not proposing to limit our standards 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 our proposed updates to the ABT program
to account for our proposal of unique off-cycle standards.
i. Bins
    We are proposing two options of off-cycle standards for three bins
of operation that 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). The three bins represent three different domains of emission
performance. The idle bin represents extended idle operation and other
very low load operation where engine exhaust temperatures may drop
below the optimal temperature for aftertreatment function. The medium/
high load bin represents higher power operation including much of the
operation currently covered by the NTE. Operation in the medium/high
load bin naturally involves higher exhaust temperatures and catalyst
efficiencies. The low load bin represents intermediate operation and
could include a large fraction of urban driving. Because the proposed
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 that
more than a single standard is needed to apply to the entire range of
operation that heavy-duty engines experience. A numerical standard that
would be 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. Similarly,
since the low load bin will consist of operation either between the
idle and medium/high load bins or be an average of the operation in the
two bins, the work specific emissions of the low load bin will
generally be lower than the idle bin and higher than the medium/high
load bin. Section III.C.2.iii includes the proposed Options 1and 2 off-
cycle standards.
    Given the challenges of measuring engine power directly in-use, we
are proposing to use the CO2 emission rate (grams per
second) as a surrogate for engine power in defining the bins for an
engine. We are further proposing to normalize 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. We are
proposing that the maximum CO2 rate be defined as the
engine's rated maximum power multiplied by the engine's family
certification level (FCL) for the FTP certification cycle. We request
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. We propose the bins to be defined as follows:

 Idle bin: 300 second windows with normalized average
CO2 rate <= 6 percent
 Low-load bin: 300 second windows with normalized average
CO2 rate > 6 percent and <= 20 percent
 Medium/high-load bin: 300 second windows with normalized
average CO2 rate > 20 percent

    The proposed bin cut points of six and twenty percent are near the
average power of the proposed low-load cycle and the FTP, respectively.
We request comment on whether the cut points should be defined at
different power levels or if other metrics should be used to define the
bins. We also request comment on whether it would be more appropriate
to divide in-use operation into two bins rather than three bins and, if
so, what the cut point should be.
    To ensure that there is adequate data in each of the bins to
compare to the off-cycle standards, we are proposing a minimum of 2,400
moving average windows per bin. We are proposing that if during the
first shift day each of the bins does not include at least 2,400
windows, then the engine would need to be tested for additional day(s)
until the minimum requirement is met. We are also proposing that 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 request comment on whether 2,400 windows is
the appropriate minimum to sufficiently reduce variability in the
results while not requiring an unnecessary number of shift-days to be
tested to meet the requirement.
ii. Off-Cycle Test Procedures
    We are proposing to measure off-cycle emissions using the existing
test procedures that specify measurement equipment and the process of
measuring emissions during field testing in 40 CFR part 1065. We are
proposing in part 1036 subpart F 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 in 40 CFR 1065, or the field test procedures in 40 CFR part
1065, subpart J. However, we are proposing special calculations for low
load and medium/high load bins in 40 CFR 1036.515 that would supersede
the brake-specific emission calculations in 40 CFR part 1065. The
proposed test procedures would 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/m3)
 Exhaust flow rate (m3/s)

    Mass emissions of CO2 and each regulated pollutant would
be separately determined for each 300-second window and would be binned
based on the normalized CO2 rate for each window.
    The standards described in Section III.C.2.iii are expressed in
units of g/hr for the idle bin and g/hp-hr for the low and medium/high
load bins. 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, we are proposing in 40 CFR
1036.515 that the NOX emissions (``e'') in g/hp-hr would be
calculated as:
[GRAPHIC] [TIFF OMITTED] TP28MR22.000

    We are proposing a limited number of exclusions that would exclude
some data from being subject to the off-cycle standards. The first
exclusion is for data collected during periodic PEMS zero and span
drift checks or calibrations, where the emission analyzers are not
available to measure emissions during that time and these checks/
calibrations are needed to ensure the robustness of the data. Data
would also be excluded anytime the engine is off during the course of
the shift-day, including engine off due to automated start/stop, as no
exhaust emissions are being generated by the engine while it is not
operating. We are also proposing to exclude data when ambient
temperatures are below -7 [deg]C, or when ambient temperatures are
above the altitude-based value determined using Equation 40 CFR
1036.515-1. 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. Data would also be excluded for operation at
altitudes greater than 5,500 feet above sea level for the same reasons
as for high temperatures at altitude. We would also exclude data 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. Data collected during
infrequent regeneration events would also be excluded due to the fact
that the data collected may not include enough operation during the
infrequent regeneration to properly weight the emissions rates during
an infrequent regeneration event with emissions that occur without an
infrequent regeneration event. We request comment on the
appropriateness of these exclusions and whether other exclusions should
be included. We request comment on whether emissions during infrequent
regeneration should be included in determining compliance with the
proposed off-cycle standards and if so, how these emissions should be
included such that the emissions are properly weighted with the
emissions when infrequent regenerations are not occuring. While data is
excluded when any approved ACEDs for emergency vehicles are active,
data generated while other approved ACEDs are active may not be
excluded from the emissions calculations under the proposed 40 CFR
1036.515.
    To reduce the influence of environmental conditions on the accuracy
and precision of the PEMS, we are proposing additional requirements in
40 CFR 1065.910(b). These requirements are to minimize the influence of
temperature, pressure, 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 PEMS must be installed in an environmental
chamber during the off-cycle test.
iii. Off-Cycle Standards
    For NOX and HC, we are proposing separate standards for
distinct modes of operation. To ensure that the proposed duty-cycle
NOX standards and the proposed off-cycle NOX
standards are set at the same relative stringency level for each
option, the idle bin standard is proportional to the voluntary Idle
standard discussed in Section III.B.2.iv, the low load bin standard is
proportional to the proposed LLC standard discussed in Section
III.B.2.iii and the medium/high load bin standard is proportional to
the proposed SET standard discussed in Section III.B.2.ii. For HC for
each option the proposed low load bin standards are set at values
proportional to the LLC standard and the medium/high load bin standard
is proportional to the SET proposed standard. For PM and CO for each
option the standards for the FTP, SET and LLC are the same numeric
value, so the low load and medium/high load bin have the same
standards. The proposed Options 1 and 2 off-cycle standards for the low
load and medium/high load bin are shown in Table III-17. For the idle
bin, the proposed Option 1 NOX emission standard for all CI
primary intended service classes is 10.0 g/hr starting in model years
2027 through 2030 and 7.5 g/hr starting in model year 2031. For
proposed Option 2, the idle bin NOX standard for all CI
primary intended service classes is 15.0 g/hr starting in model year
2027. For PM, HC and CO we are not proposing standards for the idle bin
because the emissions from these pollutants are very small under idle
conditions and idle operation is extensively covered by the FTP, SET
and LLC duty cycles discussed in Section III.B.2. We request comment on
appropriate scaling factors or other approaches to setting off-cycle
standards. Finally, we request comment on whether there is a continued
need for measurement allowances in an in-use program such as described
below. A discussion of the measurement allowance values can be found in
Section III.C.5.iii.

                                        Table III-17--Proposed Off-Cycle Low Load and Medium/High Load Standards
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                NOX (mg/hp-   PM (mg/hp-    HC (mg/hp-
               Option/MY                Primary intended service class             Bin                 hr)           hr)           hr)      CO (g/hp-hr)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Proposed Option 1.....................  All HD Engines................  Low load................           180            10           280            12
MY 2027-2030                            ..............................  Medium/high load........            70  ............           120  ............
Proposed Option 1.....................  Light HDE and Medium HDE......  Low load................            75             8            90             9
                                                                        Medium/high load........            30  ............            60  ............
MY 2031 and later.....................  Heavy HDE.....................  Low load................       \a\ 150             8            90             9
                                                                        Medium/high load........        \b\ 60  ............            60  ............
Proposed Option 2.....................  All HD Engines................  Low load................           150             8            90             9
MY 2027 and later                       ..............................  Medium/high load........            75  ............            60  ............
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Proposed Option 1 2031 and later low load bin IUL NOX standard is 75 mg/hp-hr for Heavy HDE.
\b\ Proposed Option 1 2031 and later medium/high load bin IUL NOX standard is 30 mg/hp-hr for Heavy HDE.

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 our proposed 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,
as follows:
     Idle bin operation is generally similar to operation at
idle and the lower speed portions of the LLC.
     Low load bin operation is generally similar to operation
over the LLC and the FTP.
     Medium/high load bin operation is generally similar to
operation over the FTP and much of the SET.
    An important question is whether the proposed off-cycle standards
would require technology beyond what we are projecting would be
necessary to meet the duty-cycle standards. As described below, we do
not expect our proposed Options 1 and 2 off-cycle standards to require
different technologies. However, the proposed Option 1 standard for the
medium/high load bin would likely require manufacturers to increase the
volume of the SCR catalyst.
    This is not to say that we expect manufacturers to be able to meet
these proposed Options 1 and 2 standards with no additional work.
Rather, we project that the proposed Options 1 and 2 off-cycle
standards could 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 could 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 for the off-cycle
test procedures being proposed. 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 (LLC, FTP, and SET) and the off-cycle
bins (Idle bin, Low load bin, and Medium/high load bin), the broader
range of operation covered by the off-cycle test procedure results in a
broader range in emissions performance, which justifies the need for
higher off-cycle standards than the corresponding duty cycle standards.
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. Commenters supporting lower or higher numerical standards
are encouraged to consider the proposed level of the standards in the
full context of the test procedures and compliance provisions. See
Section III.C.6.
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 dominantly 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 draft 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 proposed duty cycles (FTP, SET, and LLC). It was then
further calibrated to achieve more optimal performance over the off-
cycle operation. Although the engine did not include the SCR catalyst
volume that is included in our cost analysis and that would enable
lower medium/high load bin NOX emissions, the test results
shown in Table III-18 provide a reasonable basis for evaluating the
feasibility of controlling off-cycle emissions to a useful life of
435,000 miles. Using this data along with the data from the CARB Stage
3 that was measured at multiple points in the age of the aftertreatment
to project out the emissions level to 800,000 miles, the proposed
Options 1 and 2 off-cycle NOX standards at each respective
useful life value are shown to be feasible. The summary of the results
is in Chapter 3 of the draft RIA.

                           Table III-18--EPA Stage 3 NOX Emissions Off-Cycle Operation
----------------------------------------------------------------------------------------------------------------
                                                      Grocery
               Bin                CARB  southern     delivery          ACES           EU ISC          Drayage
                                       route           cycle
----------------------------------------------------------------------------------------------------------------
Idle bin (g/hr).................             0.7             1.0             0.9             0.4             0.3
Low load bin (mg/hp-hr).........              41              25              29              25              15
Medium/high load bin (mg/hp-hr).              30              18              16              33              23
----------------------------------------------------------------------------------------------------------------

a. Idle Bin Evaluation
    The proposed idle bin would include the idle operation and some of
the lower speed operation that occurs during the LLC and FTP. However,
it would also include 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 idle bin standard would be
feasible, we set the proposed Option 1 idle bin standard in MY 2027 and
MY 2031 at the level projected to be achievable engine-out with exhaust
temperatures below the light-off temperature. As can be seen see from
the results in Table III-18, the EPA Stage 3 engine performed well
below the proposed Options 1 and 2 NOX standards. The
summary of the results is located in Chapter 3 of the draft RIA.

b. Low and Medium/High Load Bin Evaluations
    As can be seen see from the results in Table III-18, the emissions
from the Stage 3 engine in the low load bin were below the proposed
Options 1 and 2 standards for each of the off-cycles standards. The HC
and CO emissions measured for each of these off-cycle duty cycles was
well below the proposed Options 1 and 2 off-cycle standards for the low
and medium/high load bins. The summary of the results is located in
Chapter 3 of the draft RIA.
    For the medium/high load bin, four of the five off-cycle duty
cycles had emission results below the proposed Option 1 NOX
standard for MY 2031 of 30 mg/hp-hr shown in Table III-17. As
mentioned, in Section III.B.2 the engine did not include the SCR
catalyst volume that is included in our cost analysis, so we will
continue to evaluate the emissions performance from the EPA Stage 3