effects on vegetation. VOCs, some of which are considered air toxics,
have long been suspected to play a role in vegetation damage.\206\ In
laboratory experiments, a wide range of tolerance to VOCs has been
observed.\207\ Decreases in harvested seed pod weight have been
reported for the more sensitive plants, and some studies have reported
effects on seed germination, flowering, and fruit ripening. Effects of
individual VOCs or their role in conjunction with other stressors
(e.g., acidification, drought, temperature extremes) have not been well
studied. In a recent study of a mixture of VOCs including ethanol and
toluene on herbaceous plants, significant effects on seed production,
leaf water content, and photosynthetic efficiency were reported for
some plant species.\208\
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    \206\ U.S. EPA. (1991). Effects of organic chemicals in the
atmosphere on terrestrial plants. EPA/600/3-91/001.
    \207\ Cape J.N., I.D. Leith, J. Binnie, J. Content, M. Donkin,
M. Skewes, D.N. Price, A.R. Brown, A.D. Sharpe. (2003). Effects of
VOCs on herbaceous plants in an open-top chamber experiment.
Environ. Pollut. 124:341-343.
    \208\ Cape J.N., I.D. Leith, J. Binnie, J. Content, M. Donkin,
M. Skewes, D.N. Price, A.R. Brown, A.D. Sharpe. (2003). Effects of
VOCs on herbaceous plants in an open-top chamber experiment.
Environ. Pollut. 124:341-343.
---------------------------------------------------------------------------

    Research suggests an adverse impact of vehicle exhaust on plants,
which has in some cases been attributed to aromatic compounds and in
other cases to NOX.209 210 211 The impacts of
VOCs on plant reproduction may have long-term implications for
biodiversity and survival of native species near major roadways. Most
of the studies of the impacts of VOCs on vegetation have focused on
short-term exposure and few studies have focused on long-term effects
of VOCs on vegetation and the potential for metabolites of these
compounds to affect herbivores or insects.
---------------------------------------------------------------------------

    \209\ Viskari E-L. (2000). Epicuticular wax of Norway spruce
needles as indicator of traffic pollutant deposition. Water, Air,
and Soil Pollut. 121:327-337.
    \210\ Ugrekhelidze D., F. Korte, G. Kvesitadze. (1997). Uptake
and transformation of benzene and toluene by plant leaves. Ecotox.
Environ. Safety 37:24-29.
    \211\ Kammerbauer H., H. Selinger, R. Rommelt, A. Ziegler-Jons,
D. Knoppik, B. Hock. (1987). Toxic components of motor vehicle
emissions for the spruce Picea abies. Environ. Pollut. 48:235-243.
---------------------------------------------------------------------------

III. Test Procedures and Standards

    In applying heavy-duty criteria pollutant emission standards, EPA
divides engines primarily into two types: Compression ignition (CI)
(primarily diesel-fueled engines) and spark-ignition (SI) (primarily
gasoline-fueled engines). The CI standards and requirements also apply
to the largest natural gas engines. Battery-electric and fuel-cell
vehicles are also subject to criteria pollutant standards and
requirements. Criteria pollutant exhaust emission standards apply for
four criteria pollutants: Oxides of nitrogen (NOX),
particulate matter (PM), hydrocarbons (HC), and carbon monoxide
(CO).\212\ In this Section III we describe new emission standards that
will apply for these pollutants starting in MY 2027. We also describe
new and updated test procedures we are finalizing in this rule.
---------------------------------------------------------------------------

    \212\ Reference to hydrocarbon (HC) standards includes
nonmethane hydrocarbon (NMHC), nonmethane-nonethane hydrocarbon
(NMNEHC) and nonmethane hydrocarbon equivalent (NMHCE). See 40 CFR
86.007-11.
---------------------------------------------------------------------------

    Section III.A provides an overview of provisions that broadly apply
for this final rule. Section III.B and Section III.D include the new
laboratory-based standards and final updates to test procedures for
heavy-duty compression-ignition and spark-ignition engines,
respectively. Section III.C introduces the final off-cycle standards
and test procedures that apply for compression-ignition engines and
extend beyond the laboratory to on-the-road, real-world conditions.
Section III.E describes the new refueling standards we are finalizing
for certain heavy-duty spark-ignition engines. Each of these sections
describe the final new standards and their basis, as well as describe
the new test procedures and any updates to current test procedures, and
describe our rationale for the final program, including feasibility
demonstrations, available data, and comments received.

A. Overview

1. Migration and Clarifications of Regulatory Text
    As noted in Section I of this preamble, we are migrating our
criteria pollutant regulations for model year 2027 and later heavy-duty
highway engines from their current location in 40 CFR Part 86, subpart
A, to 40 CFR Part 1036.\213\ Consistent with this migration, the
compliance provisions discussed in this preamble refer to the
regulations in their new location in part 1036. In general, this
migration is not intended to change the compliance program specified in
part 86, except as specifically finalized in this rulemaking. EPA
submitted a memorandum to the docket describing how we proposed to
migrate

certification and compliance provisions into 40 CFR part 1036.\214\
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    \213\ As noted in the following sections, we are proposing some
updates to 40 CFR parts 1037, 1065, and 1068 to apply to other
sectors in addition to heavy-duty highway engines.
    \214\ Stout, Alan; Brakora, Jessica. Memorandum to docket EPA-
HQ-OAR-2019-0055. ``Technical Issues Related to Migrating Heavy-Duty
Highway Engine Certification Requirements from 40 CFR part 86,
subpart A, to 40 CFR part 1036''. March 2022.
---------------------------------------------------------------------------

i. Compression- and Spark-Ignition Engines Regulatory Text
    For many years, the regulations of 40 CFR part 86 have referred to
``diesel heavy-duty engines'' and ``Otto-cycle heavy-duty engines'';
however, as we migrate the heavy-duty provisions of 40 CFR part 86,
subpart A, to 40 CFR part 1036 in this rule, we proposed to refer to
these engines as ``compression-ignition'' (CI) and ``spark-ignition''
(SI), respectively, which are more comprehensive terms and consistent
with existing language in 40 CFR part 1037 for heavy-duty motor vehicle
regulations. We also proposed to update the terminology for the primary
intended service classes in 40 CFR 1036.140 to replace Heavy heavy-duty
engine with Heavy HDE, Medium heavy-duty engine with Medium HDE, Light
heavy-duty engine with Light HDE, and Spark-ignition heavy-duty engine
with Spark-ignition HDE.\215\ We received no adverse comment and are
finalizing these terminology changes, as proposed. This final rule
revises 40 CFR parts 1036 and 1037 to reflect this updated terminology.
Throughout this preamble, reference to diesel and Otto-cycle engines
and the previous service class nomenclature is generally limited to
discussions relating to current test procedures and specific
terminology used in 40 CFR part 86. Heavy-duty engines not meeting the
definition of compression-ignition or spark-ignition are deemed to be
compression-ignition engines for purposes of part 1036, per 40 CFR
1036.1(c) and are subject to standards in 40 CFR 1036.104.
---------------------------------------------------------------------------

    \215\ This new terminology for engines is also consistent with
the ``HDV'' terminology used for vehicle classifications in 40 CFR
1037.140.
---------------------------------------------------------------------------

ii. Heavy-Duty Hybrid Regulatory Text
    Similar to our updates to more comprehensive and consistent
terminology for CI and SI engines, as part of this rule we are also
finalizing three main updates and clarifications to regulatory language
for hybrid engines and hybrid powertrains. First, as proposed, we are
finalizing an updated definition of ``engine configuration'' in 40 CFR
1036.801; the updated definition clarifies that an engine configuration
includes hybrid components if it is certified as a hybrid engine or
hybrid powertrain. Second, we are finalizing, as proposed, a
clarification in 40 CFR 1036.101(b) that regulatory references in part
1036 to engines generally apply to hybrid engines and hybrid
powertrains. Third, we are finalizing as proposed that manufacturers
may optionally test the hybrid engine and powertrain together, rather
than testing the engine alone. The option to test hybrid engine and
powertrain together allows manufacturers to demonstrate emission
performance of the hybrid technology that are not apparent when testing
the engine alone. If the emissions results of testing the hybrid engine
and powertrain together show NOX emissions lower than the
final standards, then EPA anticipates that manufacturers may choose to
participate in the NOX ABT program in the final rule (see
preamble Section IV.G for details on the final ABT program).
    We requested comment on our proposed clarification in 40 CFR
1036.101(b) that manufacturers may optionally test the hybrid engine
and powertrain together, rather than testing the engine alone, and
specifically, whether EPA should require all hybrid engines and
powertrains to be certified together, rather than making it optional.
For additional details on our proposed updates and clarifications to
regulatory language for hybrid engines and hybrid powertrains, as well
as our specific requests for comment on these changes, see the proposed
rule preamble (87 FR 17457, March 28, 2022).
    Several commenters support the proposal to allow manufacturers to
certify hybrid powertrains with a powertrain test procedure, but urge
EPA to continue to allow manufacturers to certify hybrid systems using
engine dynamometer testing procedures. These commenters stated that the
powertrain dynamometer test procedures produce emission results that
are more representative of hybrid engine or powertrain on-road
operation than engine-only testing, however, commenters also stated the
proposed test cycles are not reflective of real-world applications
where hybrid technology works well and urged EPA to finalize different
duty-cycles. In contrast, one commenter pointed to data collected from
light-duty hybrid electric vehicles in Europe that the commenter stated
shows hybrid-electric vehicles (HEVs) emit at higher levels than
demonstrated in current certification test procedures; based on those
data the commenter stated that EPA should not allow HEVs to generate
NOX emissions credits. Separately, some commenters also
stated that requiring powertrain testing for hybrid engines or hybrid
powertrains certification would add regulatory costs or other
logistical challenges.
    After considering these comments, EPA has determined that
powertrain testing for hybrid systems should remain an option in this
final rule. This option allows manufacturers to demonstrate emission
performance of the hybrid technology, without requiring added test
burden or logistical constraints. We are therefore finalizing as
proposed the allowance for manufacturers to test the hybrid engine and
powertrain together. If testing the hybrid engine and hybrid powertrain
together results in NOX emissions that are below the final
standards, then manufacturers can choose to certify to a FEL below the
standard, and then generate NOX emissions credits as
provided under the final ABT program (see Section IV.G). We disagree
with one commenter who asserted that manufacturers should not be
allowed to generate NOX emissions credits from HEVs based on
data showing higher emissions from HEVs operating in the real-world
compared to certification test data in Europe. Rather, we expect the
powertrain test procedures we are finalizing will accurately reflect
NOX emissions from HEVs due to the specifications we are
including in the final test procedures, which differ from the
certification test procedures to which the commenter referred.\216\ See
preamble Section III.B.2.v for more details on the powertrain test
procedures that we are finalizing.
---------------------------------------------------------------------------

    \216\ We note that the data provided by the commenter was
specific to light-duty vehicles and evaluated CO2
emissions, not criteria pollutant emissions. EPA proposed and is
finalizing changes to the light-duty test procedures for HEVs; in
this Section III we focus on heavy-duty test procedures. See
preamble Section XI and RTC Section 32 for details on the light-duty
test procedures for HEVs.
---------------------------------------------------------------------------

    Similarly, we disagree with those commenters urging EPA to finalize
different duty-cycle tests to reflect hybrid real-world operations.
While the duty-cycles suggested by commenters would represent some
hybrid operations, they would not represent the duty-cycles of other
hybrid vehicle types. See Section 3 of the Response to Comments
document for additional details on our responses to comments on
different duty-cycles for hybrid vehicles, and responses to other
comments on hybrid engines and hybrid powertrains.
    In addition to our three main proposed updates and clarifications
to regulatory language for hybrid engines and hybrid powertrain, we
also proposed that manufacturers would certify a hybrid engine or
hybrid powertrain to criteria pollutant

standards by declaring a primary intended service class of the engine
configuration using the proposed, updated 40 CFR 1036.140.\217\ Our
proposal included certifying to the same useful life requirements of
the primary intended service class, which would provide truck owners
and operators with similar assurance of durability regardless of the
powertrain configuration they choose. Finally, we proposed an update to
40 CFR 1036.230(e) such that engine configurations certified as a
hybrid engine or hybrid powertrain may not be included in an engine
family with conventional engines, which is consistent with the current
provisions. We received no adverse comment and are finalizing as
proposed these updates to 40 CFR 1036.140 and 1036.230(e).
---------------------------------------------------------------------------

    \217\ The current provisions of 40 CFR 1036.140 distinguish
classes based on engine characteristics and characteristics of the
vehicles for which manufacturers intend to design and market their
engines.
---------------------------------------------------------------------------

iii. Heavy-Duty Zero Emissions Vehicles Regulatory Text
    As part of this final rule we are also updating and consolidating
regulatory language for battery-electric vehicles and fuel cell
electric vehicles (BEVs and FCEVs), collectively referred to as zero
emissions vehicles (ZEVs). For ZEVs, we are finalizing as proposed a
consolidation and update to our regulations as part of a migration of
heavy-duty vehicle regulations from 40 CFR part 86 to 40 CFR part 1037.
In the HD GHG Phase 1 rulemaking, EPA revised the heavy-duty vehicle
and engine regulations to make them consistent with our regulatory
approach to electric vehicles (EVs) under the light-duty vehicle
program. Specifically, we applied standards for all regulated criteria
pollutants and GHGs to all heavy-duty vehicle types, including
EVs.\218\ Starting in MY 2016, criteria pollutant standards and
requirements applicable to heavy-duty vehicles at or below 14,000
pounds gross vehicle weight rating (GVWR) in 40 CFR part 86, subpart S,
applied to heavy-duty EVs above 14,000 pounds GVWR through the use of
good engineering judgment (see current 40 CFR 86.016-1(d)(4)). Under
the current 40 CFR 86.016-1(d)(4), heavy-duty vehicles powered solely
by electricity are deemed to have zero emissions of regulated
pollutants; this provision also provides that heavy-duty EVs may not
generate NOX or PM emission credits.
---------------------------------------------------------------------------

    \218\ 76 FR 57106, September 15, 2011.
---------------------------------------------------------------------------

    As proposed, this final rule consolidates certification
requirements for ZEVs over 14,000 pounds GVWR in 40 CFR part 1037 such
that manufacturers of ZEVs over 14,000 pounds GVWR will certify to
meeting the emission standards and requirements of 40 CFR part 1037.
There are no criterial pollutant emission standards in 40 CFR part
1037, so we state in a new 40 CFR 1037.102, with revisions from the
proposed rule, that heavy-duty vehicles without propulsion engines are
subject to the same criteria pollutant emission standards that apply
for engines under 40 CFR part 86, subpart A, and 40 CFR part 1036. We
further specify in the final 40 CFR 1037.102 that ZEVs are deemed to
have zero tailpipe emissions of criteria pollutants. As discussed in
Section IV.G, we are choosing not to finalize our proposal to allow
manufacturers to generate NOX emission credits from ZEVs if
the vehicle met certain proposed requirements. We are accordingly
carrying forward in the final 40 CFR 1037.102 a provisions stating that
manufacturers may not generate emission credits from ZEVs. We are
choosing not to finalize the proposed durability requirements for ZEVs,
but we may choose in a future action to reexamine this issue. We are
finalizing as proposed to continue to not allow heavy-duty ZEVs to
generate PM emission credits since we are finalizing as proposed not to
allow any manufacturer to generate PM emission credits for use in MY
2027 and later under the final ABT program presented in Section IV.G.
    The provisions in existing and final 40 CFR 1037.5 defer to 40 CFR
86.1801-12 to clarify how certification requirements apply for heavy-
duty vehicles at or below 14,000 pounds GVWR. Emission standards and
certification requirements in 40 CFR part 86, subpart S, generally
apply for complete heavy-duty vehicles at or below 14,000 pounds GVWR.
We proposed to also apply emission standards and certification
requirements under 40 CFR part 86, subpart S, for all incomplete
vehicles at or below 14,000 pounds GVWR. We decided not to adopt this
requirement and are instead continuing to allow manufacturers to choose
whether to certify incomplete vehicles at or below 14,000 pounds GVWR
to the emission standards and certification requirements in either 40
CFR part 86, subpart S, or 40 CFR part 1037.
2. Numeric Standards and Test Procedures for Compression-Ignition and
Spark-Ignition Engines
    As summarized in preamble Section I.B and detailed in this preamble
Section III, we are finalizing numeric NOX standards and
useful life periods that are largely consistent with the most stringent
proposed option for MY 2027. The specific standards are summarized in
Section III.B, Section 0, Section III.D, and Section III.E. As required
by CAA section 202(a)(3), EPA is finalizing new NOX, PM, HC,
and CO emission standards for heavy-duty engines that reflect the
greatest degree of emission reduction achievable through the
application of technology that we have determined would be available
for MY 2027, and in doing so have given appropriate consideration to
additional factors, namely lead time, cost, energy, and safety. For all
heavy-duty engine classes, the final numeric NOX standards
for medium- and high-load engine operations match the most stringent
standards proposed for MY 2027; for low-load operations we are
finalizing the most stringent standard proposed for any model year (see
III.B.2.iii for discussion).\219\ For smaller heavy-duty engine service
classes (i.e., light and medium heavy-duty engines CI and SI heavy-duty
engines), the numeric standards are combined with the longest useful
life periods we proposed. For the largest heavy-duty engines (i.e.,
heavy heavy-duty engines), the final numeric standards are combined
with the longest useful life mileage that we proposed for MY 2027. The
final useful life periods for the largest heavy-duty engines are 50
percent longer than today's useful life periods, which will play an
important role in ensuring continued emissions control while the
engines operate on the road. The final numeric emissions standards and
useful life periods for all heavy-duty engines are based on further
consideration of data included in the proposal from our engine
demonstration programs that show the final emissions standards are
feasible at the final useful life periods applicable to these each
heavy-duty engine service class. Our assessment of the data available
at the time of proposal is further supported by our evaluation of
additional information and public comments stating that the proposed
standards are feasible. Our technical assessments are primarily based
on results from testing several diesel engine and aftertreatment
systems at Southwest Research Institute and at EPA's National Vehicle
and Fuel Emissions Laboratory (NVFEL), as well as heavy-duty gasoline
engine testing conducted at NVFEL; we also

considered heavy-duty engine certification data submitted to EPA by
manufacturers, ANPR and NPRM comments, and other data submitted by
industry stakeholders or studies conducted by EPA, as more specifically
identified in the sections that follow.
---------------------------------------------------------------------------

    \219\ As proposed, we are finalizing a new test procedure for
heavy-duty CI engines to demonstrate emission control when the
engine is operating under low-load and idle conditions; this new
test procedure does not apply to heavy-duty SI engines (see Section
III.B.2.iii for additional discussion).
---------------------------------------------------------------------------

    After further consideration of the data included in the proposal,
as well as information submitted by commenters and additional data we
collected since the time of proposal, we are finalizing two updates
from our proposed testing requirements in order to ensure the greatest
emissions reductions technically achievable are met throughout the
final useful life periods; these updates are tailored to the larger
engine classes (medium and heavy heavy-duty engines). First, we are
finalizing a requirement for manufacturers to demonstrate before heavy
heavy-duty engines are in-use that the emissions control technology is
durable through a period of time longer than the final useful life
mileage. For these largest engines with the longest useful life
mileages, the extended laboratory durability demonstration will better
ensure the final standards will be met throughout the regulatory useful
life under real-world operations where conditions are more variable.
Second, we are finalizing an interim in-use compliance allowance that
applies when EPA evaluates whether heavy or medium heavy-duty engines
are meeting the final standards after these engines are in use in the
real-world. When combined with the final useful life values, we believe
the interim in-use compliance allowance will address concerns raised in
comments from manufacturers that the more stringent proposed MY 2027
standards would not be feasible to meet over the very long useful life
periods of heavy heavy-duty engines, or under the challenging duty-
cycles of medium heavy-duty engines. This interim, in-use compliance
allowance is generally consistent with our past practice (for example,
see 66 FR 5114, January 18, 2001); also consistent with past practice,
the compliance allowance is included as an interim provision that we
may reassess in the future through rulemaking based on the performance
of emissions controls over the final useful life periods for medium and
heavy heavy-duty engines.\220\ To set standards that result in the
greatest emission reductions achievable for medium and heavy heavy-duty
engines, we considered additional data that we and others collected
since the time of the proposal; these data show the significant
technical challenge of maintaining very low NOX emissions
throughout very long useful life periods for heavy heavy-duty engines,
and greater amounts of certain aging mechanisms over the long useful
life periods of medium heavy-duty engines. In addition to these data,
in setting the standards we gave appropriate consideration to costs
associated with the application of technology to achieve the greatest
emissions reductions in MY 2027 (i.e., cost of compliance for
manufacturers associated with the standards \221\) and other statutory
factors, including energy and safety. We determined that for heavy
heavy-duty engines the combination of: (1) The most stringent MY 2027
standards proposed, (2) longer useful life periods compared to today's
useful life periods, (3) targeted, interim compliance allowance
approach to in-use compliance testing, and (4) the extended durability
demonstration for emissions control technologies is appropriate,
feasible, and consistent with our authority under the CAA to set
technology-forcing criteria pollutant standards for heavy-duty engines
for their useful life.\222\ Similarly, for medium heavy-duty engines we
determined that the combination of the first three elements (i.e., most
stringent MY 2027 standards proposed, increase in useful life periods,
and interim compliance allowance for in-use testing) is appropriate,
feasible, and consistent with our CAA authority to set technology-
forcing criteria pollutant standards for heavy-duty engines for their
useful life.
---------------------------------------------------------------------------

    \220\ We plan to closely monitor the in-use emissions
performance of model year 2027 and later engines to determine the
long-term need for the interim compliance allowance. For example, we
intend to analyze the data from the manufacturer run in-use testing
program to compare how engines age in the field compared to how they
age in the laboratory.
    \221\ More specifically, for this rule in setting the final
standards and consistent with CAA section 202(a)(3)(A), the cost of
compliance for manufacturers associated with the standards that EPA
gave appropriate consideration to includes the direct manufacturing
costs and indirect costs incurred by manufacturers associated with
meeting the final standards over the corresponding final useful life
values, given that this rule sets new more stringent standards
through both the numeric level of the standard and the length of the
useful life period.
    \222\ CAA section 202(a)(3)(A) is a technology-forcing provision
and reflects Congress' intent that standards be based on projections
of future advances in pollution control capability, considering
costs and other statutory factors. See National Petrochemical &
Refiners Association v. EPA, 287 F.3d 1130, 1136 (D.C. Cir. 2002)
(explaining that EPA is authorized to adopt ``technology-forcing''
regulations under CAA section 202(a)(3)); NRDC v. Thomas, 805 F.2d
410, 428 n.30 (D.C. Cir. 1986) (explaining that such statutory
language that ``seek[s] to promote technological advances while also
accounting for cost does not detract from their categorization as
technology-forcing standards''); see also Husqvarna AB v. EPA, 254
F.3d 195 (D.C. Cir. 2001) (explaining that CAA sections 202 and 213
have similar language and are technology-forcing standards). In this
context, the term ``technology-forcing'' has a specific legal
meaning and is used to distinguish standards that may require
manufacturers to develop new technologies (or significantly improve
existing technologies) from standards that can be met using existing
off-the-shelf technology alone. Technology-forcing standards such as
those in this final rule do not require manufacturers to use
specific technologies.
---------------------------------------------------------------------------

    In addition to the final standards for the defined duty cycle and
off-cycle test procedures, the final standards include several other
provisions for controlling emissions from specific operations in CI or
SI engines. First, we are finalizing, as proposed, to allow CI engine
manufacturers to voluntarily certify to idle standards using a new idle
test procedure that is based on an existing California Air Resources
Board (CARB) procedure.\223\
---------------------------------------------------------------------------

    \223\ 13 CCR 1956.8 (a)(6)(C)--Optional NOX idling
emission standard.
---------------------------------------------------------------------------

    We are also finalizing two options for manufacturers to control
engine crankcase emissions. Specifically, manufacturers will be
required to either: (1) As proposed, close the crankcase, or (2)
measure and account for crankcase emissions using an updated version of
the current requirements for an open crankcase. We believe that either
will ensure that the total emissions are accounted for during
certification testing and throughout the engine operation during useful
life. See Section III.B for more discussion on both the final idle and
crankcase provisions.
    For heavy-duty SI, we are finalizing as proposed a new refueling
emission standard for incomplete vehicles above 14,000 lb GVWR starting
in MY 2027.\224\ The final refueling standard is based on the current
refueling standard that applies to complete heavy-duty gasoline-fueled
vehicles. Consistent with the current evaporative emission standards
that apply for these same vehicles, we are finalizing a requirement
that manufacturers can use an engineering analysis to demonstrate that
they meet our final refueling standard. We are also adopting an
optional alternative phase-in compliance pathway that manufacturers can
opt into in lieu of being subject to this implementation date for all
incomplete heavy-duty vehicles above 14,000 pounds GVWR (see Section
III.E for details).
---------------------------------------------------------------------------

    \224\ Some vehicle manufactures sell their engines or
``incomplete vehicles'' (i.e., chassis that include their engines,
the frame, and a transmission) to body builders who design and
assemble the final vehicle.
---------------------------------------------------------------------------

    Consistent with our proposal, we are also finalizing several
provisions to

reduce emissions from a broader range of engine operating conditions.
First, we are finalizing new standards for our existing test procedures
to reduce emissions under medium- and high-load operations (e.g., when
trucks are traveling on the highway). Second, we are finalizing new
standards and a corresponding new test procedure to measure emissions
during low-load operations (i.e., the low-load cycle, LLC). Third, we
are finalizing new standards and updates to an existing test procedure
to measure emissions over the broader range of operations that occur
when heavy-duty engines are operating on the road (i.e., off-
cycle).\225\
---------------------------------------------------------------------------

    \225\ Duty-cycle test procedures measure emissions while the
engine is operating over precisely defined duty cycles in an
emissions testing laboratory and provide very repeatable emission
measurements. ``Off-cycle'' test procedures measure emissions while
the engine is not operating on a specified duty cycle; this testing
can be conducted while the engine is being driven on the road (e.g.,
on a package delivery route), or in an emission testing laboratory.
Both duty-cycle and off-cycle testing are conducted pre-production
(e.g., for certification) or post-production to verify that the
engine meets applicable duty-cycle or off-cycle emission standards
throughout useful life (see Section III for more discussion).
---------------------------------------------------------------------------

    The new, more stringent numeric standards for the existing
laboratory-based test procedures that measure emissions during medium-
and high-load operations will ensure significant emissions reductions
from heavy-duty engines. Without this final rule, these medium- and
high-load operations are projected to contribute the most to heavy-duty
NOX emissions in 2045.
    We are finalizing as proposed a new LLC test procedure, which will
ensure demonstration of emission control under sustained low-load
operations. After further consideration of data included in the
proposal, as well as additional information from the comments
summarized in this section, we are finalizing the most stringent
numeric standard for the LLC that we proposed for any model year. As
discussed in our proposal, data from our CI engine demonstration
program showed that the lowest numeric NOX standard proposed
would be feasible for the LLC throughout a useful life period similar
to the useful life we are finalizing for the largest heavy-duty
engines. After further consideration of this data, and additional
support from data collected since the time of proposal, we are
finalizing the most stringent standard proposed for any model year.
    We are finalizing new numeric standards and revisions to the
proposed off-cycle test procedure. We proposed updates to the current
off-cycle test procedure that included binning emissions measurements
based on the type of operation the engine is performing when the
measurement data is being collected. Specifically, we proposed that
emissions data would be grouped into three bins, based on if the engine
was operating in idle (Bin 1), low-load (Bin 2), or medium-to-high load
(Bin 3) operation. Given the different operational profiles of each of
the three bins, we proposed a separate standard for each bin. Based on
further consideration of data included in the proposal, as well as
additional support from our consideration of data provided by
commenters, we are finalizing off-cycle standards for two bins, rather
than three bins; correspondingly, we are finalizing a two-bin approach
for grouping emissions data collected during off-cycle test procedures.
Our evaluation of available information shows that two bins better
represent the differences in engine operations that influence emissions
(e.g., exhaust temperature, catalyst efficiency) and ensure sufficient
data is collected in each bin to allow for an accurate analysis of the
data to determine if emissions comply with the standard for each bin.
Preamble Section III.C further discusses the final off-cycle standards.
3. Implementation of the Final Program
    As discussed in this section, we have evaluated the final standards
in terms of technological feasibility, lead time, and stability, and
given appropriate consideration to cost, energy, and safety, consistent
with the requirements in CAA section 202(a)(3). The final standards are
based on data from our CI and SI engine feasibility demonstration
programs that was included in the proposal, and further supported by
information submitted by commenters and additional data we collected
since the time of proposal. Our evaluation of available data shows that
the final standards and useful life periods are feasible and will
result in the greatest emission reductions achievable for MY 2027,
pursuant to CAA section 202(a)(3), giving appropriate consideration to
cost, lead time, and other factors. We note that CAA section 202(a)(3)
neither requires that EPA consider all the statutory factors equally
nor mandates a specific method of cost analysis; rather EPA has
discretion in determining the appropriate consideration to give such
factors.\226\ As discussed in the Chapter 3 of the RIA, the final
standards are achievable without increasing the overall fuel
consumption and CO2 emissions of the engine (1) for each of
the duty cycles (SET, FTP, and LLC), and (2) for the fuel mapping test
procedures defined in 40 CFR 1036.535 and 1036.540.\227\ Finally, the
final standards will have no negative impact on safety, based on the
existing use of these technologies in light-duty and heavy-duty engines
on the road today (see section 3 of the Response to Comments document
for additional discussion on our assessment that the final standards
will have no negative impact on safety). This includes the safety of
closed crankcase systems, which we received comment on. As discussed in
Section 3 of the RTC, one commenter stated that requiring closed
crankcases could increase the chance of engine run away caused by
combustion of engine oil that could enter the intake from the closed-
crankcase system. We disagree with the commenter since closed crankcase
systems are used on engines today with no adverse effect on safety;
however, we are providing flexibility for manufactures to meet the
final standards regarding crankcase emissions (see preamble Section
III.B.2.vi for details).
---------------------------------------------------------------------------

    \226\ See, e.g., Sierra Club v. EPA, 325 F.3d 374, 378 (D.C.
Cir. 2003) (explaining that similar technology forcing language in
CAA section 202(l)(2) ``does not resolve how the Administrator
should weigh all [the statutory] factors in the process of finding
the `greatest emission reduction achievable' ''); Husqvarna AB v.
EPA, 254 F.3d 195, 200 (D.C. Cir. 2001) (explaining that under CAA
section 213's similar technology-forcing authority that ``EPA did
not deviate from its statutory mandate or frustrate congressional
will by placing primary significance on the `greatest degree of
emission reduction achievable' '' or by considering cost and other
statutory factors as important but secondary).
    \227\ The final ORVR requirements discussed in Section III.E
will reduce fuel consumed from gasoline fuel engines, but these fuel
savings will 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 of the RIA.
---------------------------------------------------------------------------

    While we have referenced a technology pathway for complying with
our standards (Chapter 3 of the RIA) that is consistent with CAA
section 202(a)(3), there are other technology pathways that
manufacturers may choose in order to comply with the performance-based
final standards. We did not rely on alternative technology pathways in
our assessment of the feasibility of the final standards, however,
manufacturers may choose from any number of technology pathways to
comply with the final standards (e.g., alternative fuels, including
biodiesel, renewable diesel, renewable natural gas, renewable propane,
or hydrogen in combination with relevant emissions aftertreatment
technologies, and electrification, including plug-in hybrid electric
vehicles, battery-electric or fuel cell

electric vehicles). As noted in Section I, we are finalizing a program
that will begin in MY 2027, which is the earliest year that standards
can begin to apply under CAA section 202(a)(3)(C).\228\ The final
NOX standards are a single-step program that reflect the
greatest emission reductions achievable starting in MY 2027, giving
appropriate consideration to costs and other factors. In this final
rule, we are focused on achieving the greatest emission reductions
achievable in the MY 2027 timeframe, and have applied our judgment in
determining the appropriate standards for MY 2027 under this authority
for a national program. As the heavy-duty industry continues to
transition to zero-emission technologies, EPA could consider additional
criteria pollutant standards for model years beyond 2027 in future
rules.
---------------------------------------------------------------------------

    \228\ Section 202(a)(3)(C) requires that standards under
202(a)(3)(A) apply no earlier than 4 years after promulgation, and
apply for no less than 3 model years.
---------------------------------------------------------------------------

    In the event that manufacturers start production of some engine
families sooner than four years from our final rule, we are finalizing
a provision for manufacturers to split the 2027 model year, with an
option for manufacturers to comply with the final MY 2027 standards for
all engines produced for that engine family in MY 2027. Specifically,
we are finalizing as proposed that a MY 2027 engine family that starts
production within four years of the final rule could comply with the
final MY 2027 standards for all engines produced for that engine family
in MY2027, or could split the engine family by production date in MY
2027 such that engines in the family produced prior to four years after
the date that the final rule is promulgated would continue to be
subject to the existing standards.229 230 The split model
year provision for MY 2027 provides assurance that all manufacturers,
regardless of when they start production of their engine families, will
have four years of lead time to the MY 2027 standards under this final
rule, while also maximizing emission reductions, which is consistent
with our CAA authority. This final rule is promulgated upon the date of
signature, upon which date EPA also provided this signed final rule to
manufacturers and other stakeholders by email and posted it on EPA's
public website.\231\
---------------------------------------------------------------------------

    \229\ See 40 CFR 86.007-11.
    \230\ 40 CFR 1036.150(t).
    \231\ This final rule will also be published in the Federal
Register, and the effective date runs from the date of publication
as specified in the DATES section. Note, non-substantive edits from
the Office of the Federal Register may appear in the published
version of the final rule.
---------------------------------------------------------------------------

4. Severability
    This final rule includes new and revised requirements for numerous
provisions under various aspects of the highway heavy-duty emission
control program, including numeric standards, test procedures,
regulatory useful life, emission-related warranty, and other
requirements. Further, as explained in Sections I and XI, it modernizes
and amends numerous other CFR parts for other standard-setting parts
for various specific reasons. Therefore, this final rule is a
multifaceted rule that addresses many separate things for independent
reasons, as detailed in each respective section of this preamble. We
intended each portion of this rule to be severable from each other,
though we took the approach of including all the parts in one
rulemaking rather than promulgating multiple rules to modernize each
part of the program.
    For example, the following portions of this rulemaking are mutually
severable from each other, as numbered: (1) The emission standards in
section III; (2) warranty in Section IV.B.1; (3) OBD requirements in
Section IV.C; (4) inducements requirements in Section IV.D; (5) ABT
program in Section IV.G; (6) the migration and clarification of
regulatory text in Section III.A; and (7) other regulatory amendments
discussed in Section XI. Each emission standard in Section III is also
severable from each other emission standard, including for each duty-
cycle, off-cycle, and refueling standard; each pollutant; and each
primary intended service class. For example, the NOX
standard for the FTP duty-cycle for Heavy HDE is severable from all
other emission standards. Each of the migration and clarification
regulatory amendments in Section III.A is also severable from all the
other regulatory amendments in that Section, and each of the regulatory
amendments in Section XI is also severable from all the other
regulatory amendments in that Section. If any of the above portions is
set aside by a reviewing court, then we intend the remainder of this
action to remain effective, and the remaining portions will be able to
function absent any of the identified portions that have been set
aside. Moreover, this list is not intended to be exhaustive, and should
not be viewed as an intention by EPA to consider other parts of the
rule not explicitly listed here as not severable from other parts of
the rule.

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

    EPA is finalizing new NOX, PM, HC, and CO emission
standards for heavy-duty compression-ignition engines that will be
certified under 40 CFR part 1036.232 233 We are finalizing
new emission standards for our existing laboratory test cycles (i.e.,
SET and FTP) and finalizing new NOX, PM, HC and CO emission
standards based on a new LLC, as described in this section.\234\ The
standards for NOX, PM, and HC are in units of milligrams/
horsepower-hour instead of the grams/horsepower-hour used for existing
standards 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 will 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.
---------------------------------------------------------------------------

    \232\ See 40 CFR 1036.104.
    \233\ See 40 CFR 1036.605 and Section XI.B of this preamble for
a discussion of engines installed in specialty vehicles.
    \234\ See 40 CFR 1036.104.
---------------------------------------------------------------------------

    The final duty cycle emission standards in 40 CFR 1037.104 apply
starting in model year 2027. This final rule includes new standards
over the SET and FTP duty cycles currently used for certification, as
well as new standards over a new LLC duty cycle to ensure manufacturers
of compression-ignition engines are designing their engines to address
emissions in during lower load operation that is not covered by the SET
and FTP. The new standards are shown in Table III-1.

            Table III-1--Final Duty Cycle Emission Standards for Light HDE, Medium HDE, and Heavy HDE
----------------------------------------------------------------------------------------------------------------
                                                                     Model year 2027 and later
                                                 ---------------------------------------------------------------
                   Duty cycle                     NOX \a\ mg/hp-
                                                        hr          HC mg/hp-hr     PM mg/hp-hr     CO g/hp-hr
----------------------------------------------------------------------------------------------------------------
SET and FTP.....................................              35              60               5             6.0

LLC.............................................              50             140               5             6.0
----------------------------------------------------------------------------------------------------------------
\a\ An interim NOX compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy
  HDE. Manufacturers will add the compliance allowance to the NOX standard that applies for each duty cycle and
  for off-cycle Bin 2, for both in-use field testing and laboratory testing as described in 40 CFR part 1036,
  subpart E. Note, the NOX compliance allowance doesn't apply to confirmatory testing described in 40 CFR
  1036.235(c) or selective enforcement audits described in 40 CFR part 1068.

    This Section III.B describes the duty cycle emission standards and
test procedures we are finalizing for compression-ignition engines. We
describe compression-ignition engine technology packages that
demonstrate the feasibility of achieving these standards in Section
III.B.3.ii. The proposed rule provided an extensive discussion of the
rationale and information supporting the proposed duty cycle standards
(87 FR 17460, March 28, 2022). Chapters 1, 2, and 3 of the RIA include
additional information related to the range of technologies to control
criteria emissions, background on applicable test procedures, and the
full feasibility analysis for compression-ignition engines. See also
section 3 of the Response to Comments for a detailed discussion of the
comments and how they have informed this final rule.
    As part of this rulemaking, we are finalizing an increase in the
useful life for each engine class as described in Section IV.A. The
emission standards outlined in this section will apply for the longer
useful life periods and manufacturers will be responsible for
demonstrating that their engines will meet these standards as part of
the revisions to durability requirements described in Section IV.F. In
Section IV.G, we discuss the updates to the ABT program, including
updates to account for the three laboratory cycles (SET, FTP, and LLC)
with unique standards.
1. Background on Existing Duty Cycle Test Procedures and Standards
    We begin by providing background information on the existing duty
cycle test procedures and standards as relevant to this final rule,
including the SET and FTP standards and test procedures, powertrain and
hybrid powertrain test procedures, test procedure adjustments to
account for production and measurement variability, and crankcase
emissions. Current criteria pollutant standards must be met by
compression-ignition engines over both the SET and FTP 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 FTP 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.\235\ 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.\236\
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.
---------------------------------------------------------------------------

    \235\ See 40 CFR 86.007-11 and 40 CFR 86.008-10.
    \236\ See 40 CFR 86.1362.
---------------------------------------------------------------------------

    Emission standards for criteria pollutants are currently set to the
same numeric value for SET and FTP test cycles, as shown in Table III-
2. Manufacturers of compression-ignition engines have the option under
the existing regulations to participate in our ABT program for
NOX and PM, as discussed in the background of Section
IV.G.\237\ These pollutants are subject to FEL caps under the existing
regulations of 0.50 g/hp-hr for NOX and 0.02 g/hp-hr for
PM.\238\
---------------------------------------------------------------------------

    \237\ See 40 CFR 86.007-15.
    \238\ See 40 CFR 86.007-11.

          Table III-2--Existing Part 86 Diesel-Cycle Engine Standards Over the SET and FTP Duty Cycles
----------------------------------------------------------------------------------------------------------------
                                                                   PM \b\ (g/hp-
                        NOX \a\ (g/hp-hr)                               hr)        HC (g/hp-hr)    CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
0.20............................................................            0.01            0.14            15.5
----------------------------------------------------------------------------------------------------------------
\a\ Engine families participating in the existing ABT program are subject to a FEL cap of 0.50 g/hp-hr for NOX.
\b\ Engine families participating in the existing 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 final
rule (86 FR 34321, June 29, 2021).\239\ 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 updated the powertrain test
procedure to allow use of test cycles beyond the current GEM vehicle
drive cycles, to include the SET and FTP engine-based test cycles and
to facilitate hybrid powertrain testing (40 CFR 1036.510, 1036.512, and
1037.550).
---------------------------------------------------------------------------

    \239\ 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.\240\ 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.\241\ Additionally, manufacturers must
adjust emission rates for engines with exhaust aftertreatment to
account for infrequent

regeneration events accordingly.\242\ To account for variability in
these measurements, as well as production variability, manufacturers
typically add margin between the DF plus infrequent regeneration
adjustment factor (IRAF) adjusted test result and the FEL. A summary of
the margins manufacturers have added for MY 2019 and newer engines is
summarized in Chapter 3.1.2 of the RIA.
---------------------------------------------------------------------------

    \240\ 40 CFR 86.004-2.
    \241\ See 40 CFR 86.004-26(c) and (d) and 86.004-28(c) and (d).
    \242\ See 40 CFR 1036.501(d).
---------------------------------------------------------------------------

    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. Chapter 1.1.4 of the RIA describes EPA's
recent test program to evaluate the emissions from open crankcase
systems on two modern heavy-duty diesel engines. Results suggest HC 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.
2. Test Procedures and Standards
    As described in Section III.B.3.ii, we have determined that the
technology packages evaluated for this final action can achieve the new
duty-cycle standards. We are finalizing a single set of standards that
take effect starting in MY 2027, including not only new numerical
standards for new and existing duty-cycles but also other new numerical
standards for revised off-cycles test procedures and compliance
provisions, longer useful life periods, and other requirements.
    The final standards were derived to achieve the maximum feasible
emissions reductions from heavy-duty diesel engines for MY 2027,
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
can 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 will 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 finalizing an increase
in the regulatory useful life periods for each heavy-duty engine class
to ensure these new standards are met for a greater portion of the
engine's operational life. Also as described in Section IV, we are
separately lengthening the warranty periods for each heavy-duty engine
class, which is expected to help to maintain the benefits of the
emission controls 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 finalizing standards for three duty cycles
(SET, FTP, and LLC). In finalizing these standards, we assessed the
performance of the best available aftertreatment systems under various
operating conditions. For example, we observed that these systems are
more effective 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. The final standards for the FTP
and LLC are 80 to 90 percent, or more, lower as compared to current
standards, which will contribute to reductions in emissions under low
power operation and under cold-start conditions. The standards are
achievable by utilizing cylinder deactivation (CDA), dual-SCR
aftertreatment configuration, closed crankcase, and heated diesel
exhaust fluid (DEF) dosing. To reduce emissions under medium to high
power, the final standards for the SET are greater than 80 percent
lower as compared to current standards. The 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 RIA.
    The final PM standards are set at a level that requires heavy-duty
engines to maintain the emissions performance of current diesel
engines. The final standards for HC and CO are set at levels that are
equivalent to the maximum emissions reductions achievable by spark-
ignition engines over the FTP, with the general intent of making the
final standards fuel neutral.243 244 Compared to current
standards, the final standards for the SET and FTP duty cycles are 50
percent lower for PM, 57 percent lower for HC, and 61 percent lower for
CO. Each of these standards are discussed in more detail in the
following sections.
---------------------------------------------------------------------------

    \243\ See Section III.D for a discussion of these standards as
they relate to Spark-ignition HDE.
    \244\ See 65 FR 6728 (February 10, 2000) and 79 FR 23454 (April
28, 2014) for more discussion on the principle of fuel neutrality
applied in recent rulemakings for light-duty vehicle criteria
pollutant standards.
---------------------------------------------------------------------------

    For Heavy HDE, we are finalizing NOX standards to a
useful life of 650,000 miles with a durability demonstration out to
750,000 miles, as discussed later in Section III.B.2. We recognize the
greater demonstration burden of a useful life of 650,000 miles for
these engines, and after careful analysis are updating our DF
demonstration provisions to include two options for an accelerated
aging demonstration. However, we also are taking into account that
extending a durability demonstration, given that it is conducted in the
controlled laboratory environment, will better ensure the final
standards will be met throughout the longer final regulatory useful
life mileage of 650,000 miles when these engines are operating in the
real-world where conditions are more variable. We are thus requiring
the durability demonstration to show that the emission control system
hardware is designed to comply with the NOX standards out to
750,000 miles. As discussed further in Section III.B, the aging
demonstration out to 750,000 miles in a controlled laboratory
environment ensures that manufacturers are designing Heavy HDE to meet
the

final standards out to the regulatory useful life of 650,000 miles once
the engine is in the real-world, while reducing the risk of greater
real world uncertainties impacting emissions at the longest useful life
mileages in the proposed rule. This approach both sets standards that
result in the maximum emission reductions achievable in MY 2027 while
addressing the technical issues raised by manufacturers regarding
various uncertainties in variability and the degradation of system
performance over time due to contamination of the aftertreatment from,
for example, fuel contamination (the latter of which is out of the
manufacturer's control).
    As discussed in Section III.B.3, we have assessed the feasibility
of the standards for compression-ignition engines by testing a Heavy
HDE equipped with cylinder CDA technology, closed crankcase, 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 \245\, 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, 600,000, and 800,000
miles. We also tested two additional aftertreatment systems, referred
to as ``System A'' and ``System B,'' which are each also a dual-SCR
aftertreatment configuration with heated DEF dosing. However, they each
have unique catalyst washcoat formulation and the ``System A''
aftertreatment has greater SCR catalyst volume. The details of these
aftertreatment systems, along with the test results, can be found in
RIA Chapter 3.
---------------------------------------------------------------------------

    \245\ Degreening is a process by which the catalyst is broken in
and is critical in order to obtain a stable catalyst prior to
assessing the catalyst's performance characteristics.
---------------------------------------------------------------------------

i. FTP
    We are finalizing new emission standards for testing over the FTP
duty cycle, as shown in Table III-3.\246\ These brake-specific FTP
standards apply across the Heavy HDE, Medium HDE, and Light HDE primary
intended service classes over the useful life periods shown in Table
III-4.\247\ The numeric levels of the NOX FTP standards at
the time of certification are consistent with the most stringent
proposed for MY 2027; as summarized in Section III.A.2 and detailed in
this Section III.B we are also finalizing an interim, in-use compliance
allowance for Medium and Heavy HDEs. The numeric level of the PM and CO
FTP standards are the same as proposed, and the numeric level of the HC
FTP standard is consistent with the proposed Option 1 standard starting
in MY 2027. These 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.\248\ The EPA Stage 3 engine, was aged to and
tested at the equivalent of 800,000 miles.\249\ EPA's System A
demonstration engine, was aged to and tested at the equivalent of
650,000 miles.\250\ The System B demonstration engine was not aged and
was only tested after it was degreened. A summary of the data used for
EPA's feasibility analysis can be found in Section III.B.3. See Section
III.B.3 for details on how we addressed compliance margin when setting
the standards, including discussion of the interim in-use testing
allowance for Medium and Heavy HDE for determining the interim in-use
testing standards for these primary intended service classes.
---------------------------------------------------------------------------

    \246\ See 40 CFR 1036.510 for the FTP duty-cycle test procedure.
    \247\ The same FTP duty-cycle standards apply for Spark-ignition
HDE as discussed in Section III.D.
    \248\ See Section III.B.2 for a description of the engine.
    \249\ For the EPA Stage 3 engine, the data at the equivalent of
435,000 and 600,000 miles were included in the preamble of the NPRM
and the data at the equivalent of 800,000 miles was added to the
docket on May 5th, 2022.
    \250\ Due to the timing of when the data from the System A
system were available, the data were added to the public docket
prior to the signing of the final rule.

            Table III-3--Final Compression-Ignition Engine Standards Over the SET and FTP Duty Cycles
----------------------------------------------------------------------------------------------------------------
                                                  NOX (mg/hp-hr)
                   Model year                                      HC (mg/hp-hr)   PM (mg/hp-hr)   CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
2027 and later..................................          \a\ 35              60               5             6.0
----------------------------------------------------------------------------------------------------------------
\a\ An interim NOX compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy
  HDE. Manufacturers will add the compliance allowance to the NOX standard that applies for each duty cycle and
  for off-cycle Bin 2, for both in-use field testing and laboratory testing as described in 40 CFR part 1036,
  subpart E. Note, the NOX compliance allowance doesn't apply to confirmatory testing described in 40 CFR
  1036.235(c) or selective enforcement audits described in 40 CFR part 1068.

      Table III-4--Useful Life Periods for Heavy-Duty Compression-Ignition Primary Intended Service Classes
----------------------------------------------------------------------------------------------------------------
                                            Current (Pre-MY 2027)                 Final MY 2027 and later
  Primary intended service class   -----------------------------------------------------------------------------
                                       Miles        Years        Hours        Miles        Years        Hours
----------------------------------------------------------------------------------------------------------------
Light HDE \a\.....................      110,000           10  ...........      270,000           15       13,000
Medium HDE........................      185,000           10  ...........      350,000           12       17,000
Heavy HDE.........................      435,000           10       22,000      650,000           11       32,000
----------------------------------------------------------------------------------------------------------------
\a\ Current useful life period for Light HDE for GHG emission standards is 15 years or 150,000 miles; we are not
  revising GHG useful life periods in this final rule. See 40 CFR 1036.108(d).

    As further discussed in Section III.B.3, taking into account
measurement variability of the PM measurement test procedure and the
low numeric level of the new PM standards, we believe PM emissions from
current diesel engines are at the lowest feasible level for standards
starting in MY 2027. As summarized in Section III.B.3.ii.b,
manufacturers are submitting certification data to the agency for
current production engines well below the existing PM standards over
the FTP duty cycle. Setting the new PM FTP standards lower than the
existing FTP PM standards, at 5 mg/hp-hr (0.005 g/hp-hr), ensures that
future engines will maintain the low level of PM emissions of the
current engines and not increase PM emissions. We received comment
stating that a 5 mg/hp-hr standard did not provide enough margin for
some engine designs and that a 7.5 mg/hp-hr would 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. The reason submitted in comment to justify the 7.5 mg/
hp-hr standard was that data from the Stage 3 testing at Southwest
Research Institute (SwRI) shows that in some conditions PM values
exceed the 5 mg/hp-hr emission standard. EPA took a further look at
this data and determined that the higher PM emission data points occur
immediately following DPF ash cleaning, and that the PM level returns
to a level well below the 5 mg/hp-hr standards shortly after return to
service once a soot cake layer reestablishes itself in the DPF. EPA
concluded from this assessment that these very short-term elevations in
PM that occur after required maintenance of the DPF should not be the
basis for the stringency of the PM standards and that the standards are
feasible.
    As noted earlier in this section, we are finalizing HC and CO FTP
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 that are well below the current standards. Keeping FTP
standards at the same value for all fuels is consistent with the
agency's approach to previous criteria pollutant standards. See Section
III.D for more information on how the numeric values of the HC and CO
standards were determined.
    In the NPRM, we did not propose any changes to 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. We received comment to
change the weighting factors to reduce the effect of the cold start
portion of the FTP on the composite FTP emission results or to add 300
seconds of idle before the first acceleration in the cold start FTP to
reduce the emissions impact of the cold start on the first
acceleration. Duty-cycles are an approximation of the expected real-
world operation of the engine and no duty cycle captures all aspects of
the real-world operation. Changing the cold/hot weighting factors would
not fully capture all aspects of what really occurs in-use, and there
is precedent in experience and historical approach with the current \1/
7\ cold and \6/7\ hot weighting factors. Adding 300 seconds of idle to
the beginning of the FTP would simply reduce the stringency of the
standard by reducing the impact of cold start emissions, as the 300
seconds of idle would allow the aftertreatment to light off prior to
the first major acceleration in the FTP. Although the case can be made
that many vehicles idle for some amount of time after start up, any
attempt to add idle time before the first acceleration is simply an
approximation and this ``one size fits all'' approach doesn't afford an
improvement over the current FTP duty-cycle, nor does it allow
determination of cold start emissions where the vehicle is underway
shortly after start up. After considering these comments we are also
not including any changes to the weighting factors for the FTP duty-
cycle in this final rule.
    For Heavy HDE, we are finalizing test procedures for the
determination of deterioration factors in 40 CFR 1036.245 that require
these engines to be aged to an equivalent of 750,000 miles, which is 15
percent longer than the regulatory useful life of those engines. As
explained earlier in this section, we are finalizing this requirement
for Heavy HDE to ensure the final NOX standard will be met
through the lengthy regulatory useful life of 650,000 miles. See
preamble Section IV.A for details on how we set the regulatory useful
life for Heavy HDE.
ii. SET
    We are finalizing new emissions standards for testing over the SET
duty-cycle as shown in Table III-3. These brake-specific SET standards
apply across the Heavy HDE, Medium HDE, and Light HDE primary intended
service classes, as well as the SI HDE primary intended service class
as discussed in Section III.D, over the same useful life periods shown
in Table III-4. The numeric levels of the NOX SET standards
at the time of certification are consistent with the most stringent
standard proposed for MY 2027.\251\ The numeric level of the CO SET
standard is consistent with the most stringent standard proposed for MY
2027 for all CI engine classes.\252\ The numeric level of the PM SET
standard is the same as proposed, and the numeric level of the HC SET
standard is consistent with the proposed Option 1 standard starting in
MY 2027. Consistent with our current standards, we are finalizing the
same numeric values for the standards over the SET and FTP duty cycles
for the CI engine classes. As with the FTP cycle, the 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. The EPA Stage 3 engine
was aged to and tested at the equivalent of 800,000 miles.\253\ EPA's
Team A demonstration engine was aged to and tested at the equivalent of
650,000 miles.\254\ See Section III.B.3 for details on how we addressed
compliance margin when setting the standards, including discussion of
the interim in-use testing allowance for Medium and Heavy HDEs for
determining the interim in-use testing standards for these primary
intended service classes. A summary of the data used for EPA's
feasibility analysis can be found in Section III.B.3.
---------------------------------------------------------------------------

    \251\ As discussed in Section III.B.3, we are finalizing an
interim, in-use compliance allowance that applies when Medium and
Heavy HDE are tested in-use.
    \252\ As explained in Section III.D.1.ii, the final Spark-
ignition HDE CO standard for the SET duty-cycle is 14.4 g/hp-hr.
    \253\ For the EPA Stage 3 engine, the data at the equivalent of
435,000 and 600,000 miles were included in the preamble of the NPRM
and the data at the equivalent of 800,000 miles was added to the
docket on May 5th, 2022.
    \254\ Due to the timing of when the data from the System A
system were available, the data were added to the public docket
prior to the signing of the final rule.
---------------------------------------------------------------------------

    As with the PM standards for the FTP (see Section III.B.2.i), and
as further discussed in Section III.B.3, taking into account
measurement variability of the PM measurement test procedure and the
low numeric level of the new PM standards, we believe PM emissions from
current diesel engines are at the lowest feasible level for standards
starting in MY 2027. Thus, the PM standard for the SET duty-cycle is
intended to ensure that there is not an increase in PM emissions from
future engines. We are finalizing new PM SET

standards of 5 mg/hp-hr for the same reasons outlined for the FTP in
Section III.B.2.i. Also similar to the FTP (see Section III.B.2.i), we
are finalizing HC and CO SET standards based on the feasibility
demonstration for SI engines (see Section III.D).
    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 finalizing application of 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
SET weighting factors in 40 CFR 1036.510 versus the current SET
procedure in 40 CFR 86.1362. The lower emissions using the SET cycle
weighting factors in 40 CFR 1036.510 are reflected in the stringency of
the final SET standards.

               Table III-5--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 finalizing the addition of new standards for testing over
the new low-load duty-cycle, that will 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 the catalyst's operational
temperature (see Chapter 2.2.2 of the RIA). We believe the addition of
this LLC will complement the expanded operational coverage of our new
off-cycle testing requirements (see Section III.C).
    During ``Stage 2'' of the CARB 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.\255\ 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.256 257
---------------------------------------------------------------------------

    \255\ 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.
    \256\ California Air Resources Board. Heavy-Duty Omnibus
Regulation. Available online: https://ww2.arb.ca.gov/rulemaking/2020/hdomnibuslownox.
    \257\ 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 adopting CARB's Omnibus LLC as a new duty-cycle, the LLC.
This cycle is described in Chapter 2 of the RIA for this rulemaking and
the test procedures are specified in 40 CFR 1036.514. The LLC includes
applying the accessory loads defined in the HD GHG Phase 2 rule, that
were based on data submitted to EPA as part of the development of the
HD GHG Phase 2. These accessory loads are 1.5, 2.5 and 3.5 kW for Light
HDE, Medium HDE, and Heavy HDE engines, respectively. As detailed
further in section 3 of the Response to Comments, we received comments
that EPA should revise the accessory loads. One commenter provided
specific recommendations for engines installed in tractors but in all
cases commenters didn't provide data to support their comments; after
consideration of these comments and further consideration of the basis
of the proposal, we are finalizing the accessory loads for the LLC as
proposed. To allow vehicle level technologies to be recognized on this
cycle, we are including a powertrain test procedure option for the LLC.
More information on the powertrain test procedure can be found in
Section III.B.2.v. IRAF determination for the LLC follows the test
procedures defined in 40 CFR 1036.580, which are the same test
procedures used for the SET and FTP. The IRAF test procedures that
apply to the SET and FTP in 40 CFR 1065.680 are appropriate for the LLC
as the procedures in 40 CFR 1065.680 were developed to work with any
engine-based duty-cycle. We are finalizing as proposed that, while the
IRAF procedures in 40 CFR 1036.580 and 1065.680 require that
manufacturers determine an IRAF for the SET, FTP, and LLC duty cycles,
manufacturers may omit the adjustment factor for a given duty cycle if
they determine that infrequent regeneration does not occur over the
types of engine operation contained in the duty cycle as described in
40 CFR 1036.580(c).
    The final emission standards for the LLC are presented in Table
III-6, over the useful life periods shown in Table III-4. The numeric
levels of the NOX LLC standards at the time of certification
are the most stringent proposed for any model year.\258\ The numeric
level of the PM and CO LLC standards are the same as proposed, and the
numeric level of the HC LLC standard is consistent with the proposed
Option 1 standard starting in MY 2027. As with the FTP cycle, these
standards have been shown to be feasible for compression-ignition
engines based on testing of the EPA Stage 3 demonstration engine with
chemically- and hydrothermally-aged aftertreatment system, and for the
LLC the data shows that the standards are feasible for all engine
service classes with available margins between the data and the
standards. The summary of this data along with how we addressed
compliance margin can be found in Section III.B.3, including discussion
of the interim in-use compliance allowance for Medium and Heavy HDEs
for determining the interim in-use

standards for these primary intended service classes.
---------------------------------------------------------------------------

    \258\ As summarized in Section III.A.2 and detailed in this
Section III.B we are also finalizing an interim, in-use compliance
allowance for medium and heavy heavy-duty engines.

                   Table III-6--Compression-Ignition Engine Standards Over the LLC Duty Cycle
----------------------------------------------------------------------------------------------------------------
                                                  NOX (mg/hp-hr)
                   Model year                                      PM (mg/hp-hr)   HC (mg/hp-hr)   CO (g/hp-hr)
----------------------------------------------------------------------------------------------------------------
2027 and later..................................          \a\ 50               5             140             6.0
----------------------------------------------------------------------------------------------------------------
\a\ An interim NOX compliance allowance of 15 mg/hp-hr applies for any in-use testing of Medium HDE and Heavy
  HDE. Manufacturers will add the compliance allowance to the NOX standard that applies for each duty cycle and
  for off-cycle Bin 2, for both in-use field testing and laboratory testing as described in 40 CFR part 1036,
  subpart E. Note, the NOX compliance allowance doesn't apply to confirmatory testing described in 40 CFR
  1036.235(c) or selective enforcement audits described in 40 CFR part 1068.

    We are finalizing an LLC PM standard of 5 mg/hp-hr for the same
reasons outlined for the FTP in Section III.B.2.i. We are finalizing HC
and CO standards based on data from the CARB and EPA Stage 3 engine
discussed in Section III.B.3. We are finalizing the same numeric
standard for CO on the LLC as we have for the SET and FTP cycles
because the demonstration data from the EPA Stage 3 engine shows that
CO emissions on the LLC are similar to CO emissions from the SET and
FTP. We are finalizing HC standards that are different than the
standards of the SET and FTP cycles, to reflect our assessment of the
performance of the EPA Stage 3 engine on the LLC. The data discussed in
Section III.B.3 of this preamble shows that the PM, HC, and CO
standards are feasible for both current and future new engines.
iv. Idle
    CARB currently has an optional idle test procedure and accompanying
standard of 30 g/hr of NOX for diesel engines to be ``Clean
Idle Certified.''.\259\ In the CARB Omnibus rule, the CARB lowered the
optional NOX standard to 10 g/hr for MY 2024 to MY 2026
engines and 5 g/hr for MY 2027 and beyond. In the NPRM, we proposed
optional NOX idle standards with a corresponding idle test
procedure, with potentially different numeric levels of the
NOX idle standards for MY 2023, MY 2024 to MY 2026 engines,
and for MY 2027 and beyond, that would 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). We proposed 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
mode in the SET or the idle segments of the FTP, in addition to meeting
the applicable idle NOX standard. We requested 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 mode in the SET or the idle segments of
the FTP. We also requested 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.
---------------------------------------------------------------------------

    \259\ 13 CCR 1956.8(a)(6)(C)--Optional NOX idling
emission standard.
---------------------------------------------------------------------------

    We received comments on the EPA's proposal to adopt California's
Clean Idle NOX standard as a voluntary emission standard for
Federal certification.\260\ All commenters provided general support for
EPA's proposal to set idle standards for heavy duty engines, with some
qualifications. Some commentors supported making idle standards
mandatory, while others commented that the idle standards should be
optional. With regard to the level of the idle standard, there was
support from many commenters that the standards should be set at the
Proposed Option 1 levels or lower, while several manufactures stated
that 10 g/hr for certification and 15 g/hr in-use would be the lowest
feasible standards for NOX. One manufacturer commented that
EPA must set standards that do not increase CO2 emissions.
EPA has considered these comments, along with the available data
including the data from the EPA Stage 3 engine,\261\ and we are
finalizing optional idle standards in 40 CFR 1036.104(b) and a new idle
test procedure in 40 CFR 1036.525. The standards are based on CARB's
test procedure with revisions to not require the measurement of PM, HC
and CO,\262\ to allow compression-ignition engine manufacturers to
voluntarily certify to an idle NOX standard of 30.0 g/hr for
MY 2024 to MY 2026, which is consistent with proposed Option 1 for MY
2023. For MY 2027 and beyond, the final NOX idle standard is
10.0 g/hr, which is the same as proposed Option 2 for those MYs.
Manufacturers certifying to the optional idle standard must comply with
the standard and related requirements as if they were mandatory.
---------------------------------------------------------------------------

    \260\ See RTC section 3.
    \261\ See RIA Chapter 3 for a summary of the data collected with
the EPA Stage 3 engine run on the Clean Idle test in three
configurations. These data show that the MY 2027 and beyond, final
NOX idle standard of 10 g/hr is feasible through useful
life with margin, and show that an additional 5 g/hr in-use margin
is not justified.
    \262\ 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.
---------------------------------------------------------------------------

    We received comments stating that the proposed PM, HC, and CO
standards are unworkable since the standards are set at the level the
engine emits at during idle over the engine SET and FTP duty cycles and
that variability in the emissions between the different tests could
cause the engine to fail the idle PM, HC, and CO standards. EPA
recognized this issue in the proposal and requested comment on if EPA
should instead set PM, HC, and CO standards that are fixed and not
based on the emissions from the engine during the SET and FTP. EPA has
considered these comments and we are not finalizing the proposed
requirement to measure brake-specific HC, CO, and PM emissions during
the Clean Idle test for comparison to emission rates from the idle
modes in the SET or the idle segments of the FTP.\263\ The measurement
of these additional pollutants would create unnecessary test burden for
the manufacturers at this time, especially with respect to measuring PM
during idle segments of the SET or FTP as it would require running
duplicate tests or adding a PM sampler. Further, setting the PM, HC and
CO standards right at the idle emissions level of the engine on the SET
and FTP could cause false failures due to test-to-test variability from
either the SET or FTP, or the Clean Idle test itself.

Idle operation is included as part of off-cycle testing and the SET,
FTP, and LLC duty cycles; standards for off-cycle and duty-cycle
testing ensure that emissions of HC, CO, and PM are well controlled as
aftertreatment temperatures are not as critical to controlling these
pollutants over extended idle periods as they are for NOX.
We are therefore not requiring the measurement of these other
pollutants to meet EPA voluntary clean idle standards.
---------------------------------------------------------------------------

    \263\ See 40 CFR 1036.104(b).
---------------------------------------------------------------------------

    We are finalizing a provision in new 40 CFR 1036.136 requiring
engine manufacturers that certify to the Federal Clean Idle
NOX standard to create stickers to identify their engines as
meeting the Federal Clean Idle NOX standard. The regulatory
provisions require that the stickers meet the same basic requirements
that apply for stickers showing that engines meet CARB's Clean Idle
NOX standard. For example, stickers must be durable and
readable throughout each vehicle's operating life, and the preferred
placement for Clean Idle stickers is on the driver's side of the hood.
Engine manufacturers must provide exactly the right number of these
stickers to vehicle manufacturers so they can apply the stickers to
vehicles with the engines that the engine manufacturer has certified to
meet the Federal Clean Idle NOX standard. If engine
manufacturers install engines in their own vehicles, they must apply
the stickers themselves to the appropriate vehicles. Engine
manufacturers must keep the following records for at least five years:
(1) Written documentation of the vehicle manufacturer's request for a
certain number of stickers, and (2) tracking information for stickers
the engine manufacturer sends and the date they sent them. 40 CFR
1036.136 also clarifies that the provisions in 40 CFR 1068.101 apply
for the Clean Idle sticker in the same way that those provisions apply
for emission control information labels. For example, manufacturing,
selling, and applying false labels are all prohibited actions subject
to civil penalties.
v. Powertrain
    EPA recently finalized a separate rulemaking that included an
option for manufacturers to certify a hybrid powertrain to the SET and
FTP greenhouse gas engine standards by using a powertrain test
procedure (86 FR 34321, June 29, 2021).\264\ In this rulemaking, we are
similarly finalizing as proposed that manufacturers may certify hybrid
powertrains to criteria pollutant emissions standards by using the
powertrain test procedure. In this section we describe how
manufacturers would apply the powertrain test procedure to certify
hybrid powertrains.
---------------------------------------------------------------------------

    \264\ 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. However, powertrain testing
requires the translation of an engine test procedure to a powertrain
test procedure. Chapter 2 of the RIA describes how we translated the
SET, FTP, and LLC engine test cycles to the powertrain test
cycles.\265\ 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.
---------------------------------------------------------------------------

    \265\ As discussed in Section III.B.1, as part of the technical
amendments rulemaking, EPA finalized that manufacturers may use the
powertrain test procedure for GHG emission standards on the FTP and
SET engine-based test cycles. In this rulemaking we are extending
this to allow the powertrain test procedure to be used for criteria
emission standards on these test cycles and the LLC. As discussed in
Section 2.ii, we are setting new weighting factors for the engine-
based SET procedure for criteria pollutant emissions, which are
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 finalizing
clarifications in 40 CFR 1036.101 that manufacturers may optionally
test the hybrid engine and hybrid powertrain to demonstrate compliance.
We are finalizing as proposed with one clarification that the
powertrain test procedures specified in 40 CFR 1036.510 and 1036.512,
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. The clarification in 40 CFR 1036.510 provides
direction that the idle points in the SET should be run as neutral or
parked idle. In addition, for GHG emission standards we are finalizing
updates to 40 CFR 1036.510 and 1036.512 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 LLC to a powertrain test
procedure, and we are finalizing that manufacturers can similarly
certify hybrid engines and hybrid powertrains to criteria pollutant
emission standards on the LLC using the test procedures defined in 40
CFR 1036.514.
    We are allowing manufacturers to use the powertrain test procedures
to certify hybrid engine and powertrain configurations to all MY 2023
and later criteria pollutant engine standards. Manufacturers can choose
to use either the SET duty-cycle in 40 CFR 86.1362 or the SET in 40 CFR
1036.510 in model years prior to 2027, and may use only the SET in 40
CFR 1036.510 for model year 2027 and beyond.\266\ \267\
---------------------------------------------------------------------------

    \266\ We are allowing 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 RIA, the criteria pollutant
emissions level of current production engines is similar between the
two cycles.
    \267\ Prior to MY 2027, only manufacturers choosing to
participate in the 2026 Service Class Pull Ahead Credits, Full
Credits, or Partial Credits pathways under the Transitional Credits
Program need to conduct LLC powertrain testing (see Section IV.G for
details on).
---------------------------------------------------------------------------

    We are allowing the use of these procedures starting in MY 2023 for
plug-in hybrids and, consistent with the requirements for light-duty
plug-in hybrids, we are finalizing that the applicable criteria
pollutant standards must be met under the worst-case conditions, 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
received comment stating that the charge-depleting and charge-
sustaining operation should be weighted together for criteria
pollutants as well as GHG pollutants, but consistent with the light-
duty test procedure we want to ensure that criteria pollutant emissions
are controlled under all conditions, which would include under
conditions where the vehicle is not charged and is only operated in
charge sustaining-operation.
    We are finalizing changes to the test procedures defined in 40 CFR
1036.510 and 1036.512 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 SET and FTP duty cycles. This weighting is done using
an application specific utility factor curve that is approved by EPA.
We are also finalizing a provision 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 finalized in 40 CFR 1036.512 include both
cold and hot start emissions by running repeat FTP cycles back-to-back.
By running back-to-back FTPs, the finalized 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 are finalizing the application of the powertrain test procedure
only for hybrid powertrains, to avoid having two different testing
pathways (engine only and powertrain) for non-hybrid engines for the
same standards. That said, we recognize there may be other technologies
where the emissions performance is not reflected on the engine test
procedures, so in such cases manufacturers may seek approval from EPA
to use the powertrain test procedure for non-hybrid engines and
powertrains consistent with 40 CFR 1065.10(c)(1).
    Finally, for all pollutants, we requested comment on if we should
remove 40 CFR 1037.551 or limit the use of it to only selective
enforcement audits (SEAs). 40 CFR 1037.551 was added as part of the HD
GHG Phase 2 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. We didn't receive any comments on this topic and, for the
reason just stated, we are limiting the use of 40 CFR 1037.551 to SEA
testing.
vi. Crankcase Emissions
    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 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 were 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. We estimate
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 proposed
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.\268\ Comments were received
regarding concerns closing the crankcase that included coking, degraded
performance and turbo efficiencies leading to increased CO2
emissions, secondary damage to components, and increased engine-out PM
(see section 3 of the Response to Comments document for further
details). After considering these comments, we are finalizing a
requirement for manufacturers to use one of two options for controlling
crankcase emissions, either: (1) As proposed, closing the crankcase, or
(2) an updated version of the current requirements for an open
crankcase that includes additional requirements for measuring and
accounting for crankcase emissions. We believe that either approach is
appropriate, so long as the total emissions are accounted for during
certification and in-use testing through useful life (including full
accounting for crankcase emission deterioration).
---------------------------------------------------------------------------

    \268\ We proposed 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.
---------------------------------------------------------------------------

a. Closed Crankcase Option
    As EPA explained at proposal, the environmental advantages to
closing the crankcase 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 significant methane
emissions. We note that in the HD GHG Phase 2 rule we set methane
standards which required natural gas engines to close the crankcase in
order to comply with the methane standard. EPA proposed to require that
all natural gas-fueled engines have closed crankcases in the HD GHG
Phase 2 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 reduced engine
wear due to improved engine component 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 currently included in the durability tests that
estimate an engine's deterioration at useful life, 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.
    After considering all of the manufacturer concerns, we still
believe, noting that one-third of current highway heavy-duty diesel
engines have closed crankcases, that improvements in the design of
engine hardware would allow manufacturers to close the crankcase, with
the potential for increased maintenance intervals on some

components. For these reasons, EPA is finalizing provisions in 40 CFR
1036.115(a) to require a closed crankcase ventilation system as one of
two options for all highway compression-ignition engines to control
crankcase emissions for MY 2027 and later engines.
b. Open Crankcase Option
    Given consideration of the concerns from commenters regarding
engine hardware durability associated with closing the crankcase, we
have decided to finalize an option that allows the crankcase to remain
open. This option requires manufacturers of compression ignition
engines that choose to leave the crankcase open to account for any
increase in the contribution of crankcase emissions (due to reduction
in performance of piston seals, etc.) to the total emissions from the
engine throughout the engine's useful life. Manufacturers that choose
to perform engine dynamometer-based testing out to useful life will
provide a deterioration factor that includes deteriorated crankcase
emissions because the engine components will be aged out to the
engine's useful life. Manufacturers that choose to use the accelerated
aging option in 40 CFR 1036.245(b), where the majority of the emission
control system aging is done, must use good engineering judgment to
determine the impact of engine deterioration on crankcase emissions and
adjust the tailpipe emissions at useful life to reflect this
deterioration. For example, manufacturers may determine deteriorated
crankcase emissions from the assessment of field-aged engines.
    Manufacturers who choose this option must also account for
crankcase criteria pollutant emissions during any manufacturer run in-
use testing to determine the overall compliance of the engine as
described in 40 CFR 1036.415(d)(2). The crankcase emissions must be
measured separately from the tailpipe emissions or be routed into the
exhaust system, downstream from the last catalyst in the aftertreatment
system, to ensure that there is proper mixing of the two streams prior
to the sample point. In lieu of these two options, manufacturers may
use the contribution of crankcase emissions over the FTP duty-cycle at
useful life from the deterioration factor determination testing in 40
CFR 1036.245, as described in 40 CFR 1036.115(a) and add them to the
binned emission results determined in 40 CFR 1036.530.
    Chapter 1.1.4 of the RIA describes EPA's recent test program to
evaluate the emissions from open crankcase systems on two modern heavy-
duty diesel engines. Results suggest HC 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 control of the crankcase emissions.
If a manufacturer chooses the option to keep the crankcase open,
overall emission control will still be achieved, but the manufacturer
will have to design and optimize the emission control system for lower
tailpipe emissions to offset the emissions from the crankcase as the
total emissions are accounted for both in-use and at useful life.
3. Feasibility of the Diesel (Compression-Ignition) Engine Standards
i. Summary of Technologies Considered
    Our finalized standards for compression-ignition engines are based
on the performance of technology packages described in Chapters 1 and 3
of the 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.\269\ 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.
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    \269\ As described in Chapter 3 of the RIA, we are evaluating 3
different aftertreatment systems that contain different catalyst
formulation.
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ii. Summary of Feasibility Analysis
a. Projected Technology Package Effectiveness and Cost
    Based upon data from EPA's and CARB's Stage 3 Heavy-duty Low
NOX Research Programs (see Chapter <IP_ADDRESS> and Chapter
<IP_ADDRESS> of the RIA), an 80 percent reduction in the Heavy HDE
NOX standard as compared to the current NOX
standard is technologically feasible when using CDA or other
valvetrain-related air control strategies in combination with dual SCR
systems, and closed crankcase. As noted in the proposal, EPA 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 RIA. In
assessing the technical feasibility of each of our final standards, we
have taken into consideration the emissions of the EPA Stage 3 engine
and other available data, the additional emissions from infrequent
regenerations, the final longer useful life, test procedure
variability, emissions performance of other child engines in an engine
family, production and engine variability, fuel and DEF quality,
sulfur, soot and ash levels on the aftertreatment, aftertreatment aging
due to severe-service operation, aftertreatment packaging and lead time
for manufacturers.
    Manufacturers are required to design engines that meet the duty
cycle and off-cycle standards throughout the engines' useful life. In
recognition that emissions performance will degrade over time,
manufacturers generally 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 in this section and in Chapter 3 of
the RIA and shown in Table III-12 and Table III-13, some manufactures
have submitted certification data with zero emissions (with rounding),
which results in a margin at 100 percent of the FEL, while other
manufacturers have margin that is less than 25 percent of the FEL.
    To assess the feasibility of the final MY 2027 standards for Light,
Medium, and Heavy HDE at the corresponding final useful lives, EPA took
into consideration and evaluated the data from the EPA Stage 3 engine
as well as other available data and comments received on the proposed
standards. See section 3 of the Response to Comment document for
further information on the comments received and EPA's detailed
response.

    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 catalyst.
These improvements lowered the emissions on the SET, FTP, and LLC below
what was measured with the CARB Stage 3 engine. The emissions for the
EPA Stage 3 engine on the SET, FTP, and LLC aged to an equivalent of
435,000, 600,000 and 800,000 miles are shown in Table III-7, Table III-
8, and Table III-9. To account for the IRAF for both particulate matter
and sulfur on the aftertreatment system, we assessed and determined it
was appropriate to rely on an analysis by SwRI that is summarized in
Chapter 3 of the RIA. In this analysis SwRI determined that IRAF
NOX emissions were at 2 mg/hp-hr for both the SET and FTP
cycles and 5 mg/hp-hr for the LLC. To account for the crankcase
emissions, we assessed and determined it was appropriate to rely on an
analysis by SwRI that is summarized in Chapter 3 of the RIA. In this
analysis, SwRI determined that the NOX emissions from the
crankcase were at 6 mg/hp-hr for the LLC, FTP, and SET cycles.
    To determine whether or how to account for the effects of test
procedure variability, emissions performance of other ratings in an
engine family, production and engine variability, fuel and DEF quality,
sulfur, soot and ash levels on the aftertreatment, aftertreatment aging
due to severe-service operation, and aftertreatment packaging--and
given the low level of the standards under consideration--EPA further
assessed two potential approaches after taking into consideration
comments received. The first approach considered was assigning standard
deviation and offsets to each of these effects and then combining them
using a mathematical method similar to what one commenter presented in
their comments to the NPRM.\270\ The second approach considered was
defining the margin as a percentage of the standards, similar to
assertions by two commenters. We considered both of these approaches,
the comments and supporting information submitted, historical
approaches by EPA to compliance margin in previous heavy-duty criteria
pollutant standards rules, and the data collected from the EPA Stage 3
engine and other available data, to determine the numeric level of each
standard over the corresponding useful life that is technically
feasible.
---------------------------------------------------------------------------

    \270\ See RIA Chapter 3 for the details on this analysis.
---------------------------------------------------------------------------

    For the first approach, we determined that a minimum of 15 mg/hp-hr
of margin between an emission standard and the NOX emissions
of the EPA Stage 3 engine for each of the duty cycles was
appropriate.\271\ For the second approach, we first assessed the
average emissions rates from the EPA Stage 3 engine at the respective
aged miles. For Light HDEs, we looked at the data at the equivalent of
435,000 miles. For the Medium and Heavy HDEs standards the interpolated
emissions performance at 650,000 miles was determined from the tests at
the equivalent of 600,000 and 800,000 miles, which is shown in Table
III-10.\272\ Second, the average emissions values were then adjusted to
account for the IRAF and crankcase emissions from the EPA Stage 3
engine. Third, we divided the adjusted emissions values by 0.55 to
calculate an emission standard that would provide 45 percent margin to
the standard. We determined it would be appropriate to apply a 45
percent margin in this case after evaluating the margin in engines that
meet the current standards as outlined in RIA chapter 3 and in CARB's
comment to the NPRM and considering the level of the standards in this
final rule. Our determination is based on our analysis that the
certification data from engines meeting today's standards shows that
more than 80 percent of engine families are certified with less than 45
percent compliance margin. For Light HDEs, we took the resulting values
from the third step of our approach and rounded them. EPA then also
checked that each of these values for each of the duty cycles
(resulting from the second approach) provided a minimum of 15 mg/hp-hr
of margin between those values and the NOX emissions of the
EPA Stage 3 engine (consistent with the first approach). For Light
HDEs, we determined those resulting values were appropriate final
numeric emission standards (as specified in Preamble Section III.B.2).
The last step of checking that the Light HDE standards provide a
minimum of 15 mg/hp-hr of NOX margin was to ensure that the
margin determined from the percent of the standard (the second approach
to margin) also provided the margin that we determined under the first
approach to margin. For Light HDEs, given the level of the final
standards and the length of the final useful life mileages, we
determined that this approach to margin was appropriate for both
certification and in-use testing of engines.
---------------------------------------------------------------------------

    \271\ See RIA Chapter 3 for the details on how the margin of 15
mg/hp-hr was defined.
    \272\ See RIA Chapter <IP_ADDRESS> for additional information on why
each aging test point was used for each primary intended service
class. We note that we received data claimed as confidential
business information from a manufacturer on August 2, 2022, and
considered that data as part of this assessment to use the EPA Stage
3 data at the equivalent of 650,000 miles for setting the Medium HDE
standards. The data were added to the docket prior to the signing of
the final rule. See also U.S. EPA. Stakeholder Meeting Log.
December, 2022.
---------------------------------------------------------------------------

    Given the very long useful life mileages for Heavy HDE and greater
amounts of certain aging mechanisms over the long useful life periods
of Medium HDE, we determined that a different application of
considering these two approaches to margin was appropriate. The in-use
standards of Medium and Heavy HDEs were determined using the second
approach for determining margin. The certification standards where then
determined by subtracting the margin from the first approach (15 mg/hp-
hr) from the in-use standards.
    Separating the standards from the level that applies for in-use
testing was appropriate because we recognize that laboratory aging of
the engine doesn't fully capture all the sources of deterioration of
the aftertreatment that can occur once the engine enters the real-world
and those uncertainties would be most difficult for these engine
classes at the level of the final standards and the final useful life
mileages. Some of these effects are SCR sulfation, fuel quality, DEF
quality, sensor variability, and field aging from severe duty cycles.
Thus, the last step in determining the standards for Medium and Heavy
HDE was to subtract the 15 mg/hp-hr from the rounded value that
provided 45 percent margin to the Stage 3 data. We determined each of
the resulting final duty cycle NOX standards for Medium and
Heavy HDE that must be demonstrated at the time of certification out to
350,000 and 750,000 miles, respectively, are feasible with enough
margin to account for test procedure variability. We determined this by
comparing the EPA Stage 3 emissions results at 800,000 miles (Table
III-9) after adjusting for IRAF and crankcase emissions to each of the
NOX standards in Section III.B.2. The EPA Stage 3
NOX emissions results at 800,000 miles adjusted for IRAF and
crankcase emissions are 26 mg/hp-hr for the SET, 33 mg/hp-hr for the
FTP, and 33 mg/hp-hr for the LLC. For any in-use testing of Medium and
Heavy HDEs, a 15 mg/hp-hr compliance allowance is added to the
applicable standard, in consideration of the other sources of
variability and deterioration of the aftertreatment that can occur once
the engine enters the real world.

    As explained in the proposal, our technology cost analysis included
an increased SCR catalyst volume from what was used on the EPA and CARB
Stage 3 engines. By increasing the SCR catalyst volume, the
NOX reduction performance of the aftertreatment system
should deteriorate slower than what was demonstrated with the EPA 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 final standards are achievable
in MY 2027, including for the final useful life of 650,000 miles for
Heavy HDEs. In addition to NOX, the final HC and CO
standards are feasible for CI engines on all three cycles. This is
shown in Table III-10, where the demonstrated HC and CO emission
results are below the final standards discussed in Section III.B.2. The
final standard for PM of 5 mg/hp-hr for the SET, FTP, and LLC continue
to be feasible with the additional technology and control strategies
needed to meet the final NOX standards, as seen by the PM
emissions results in Table III-10. As discussed in Section III.B.2,
taking into account measurement variability of the PM measurement test
procedure, we believe PM emissions from current diesel engines are at
the lowest feasible level for standards starting in MY 2027.

             Table III-7--Stage 3 Engine Emissions at 435,000 Mile Equivalent Test Point Without Adjustments for IRAF or Crankcase Emissions
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                            NOX (mg/hp-hr)                        NMHC (nonmethane                         CO2 (g/hp-hr)   N2O (g/hp-hr)
                Duty cycle                                   PM (mg/hp-hr)     hydrocarbon) (mg/hp-hr)     CO (g/hp-hr)