adopted at the projected rates for these proposed standards within the
lead time provided, as discussed in Section II.F.6 and in DRIA Chapter
2.
    EPA also gave appropriate consideration of cost of compliance in
the selection of the proposed standards as described in this Section
II.G, and as further discussed in Section II.F and DRIA Chapter 2. The
MY 2027 through MY 2031 emission standards were developed using less
aggressive application rates and, therefore, are projected to have
lower technology package costs than the proposed MY 2032 standards.
Additionally, as described in this Section II.G and as further
discussed in Section II.F and DRIA Chapter 2, we considered impacts on
vehicle purchasers and willingness to purchase (including
practicability, payback, and costs to vehicle purchasers) in applying
constraints in our analysis and selecting the proposed standards.\545\
For example, in MY 2032, we estimated that the incremental cost to
purchase a ZEV would be recovered in the form of operational savings
during the first one to three years of ownership, on average by
regulatory group, for the vocational vehicles; approximately three
years, on average by regulatory group, for short-haul tractors; and
seven years, on average by regulatory group, for long-haul tractors, as
shown in the payback analysis included in Section II.F.4. The length of
ownership of new tractors varies. One study found that first ownership
is customarily four to seven years for For-Hire companies and seven to
12 years for Private fleets.\546\ Another survey

found that the average trade-in cycle for tractors was 8.7 years.\547\
Therefore, we find that these tractor technologies on average by
regulatory group pay for themselves within the customary ownership
timeframe for the initial owner. As we discussed in the HD GHG Phase 2
rulemaking, vocational vehicles generally accumulate far fewer annual
miles than tractors and would lead owners of these vehicles to keep
them for longer periods of time.\548\ To the extent vocational vehicle
owners may be similar to owners of tractors in terms of business
profiles, they are more likely to resemble private fleets or owner-
operators than for-hire fleets. Regardless, the technologies would also
pay for themselves on average by regulatory group within the ownership
timeframe for vocational vehicles as well.
---------------------------------------------------------------------------

    \545\ Although EPA sometimes describes purchaser response
(including purchaser costs) as part of our analysis of feasibility,
we emphasize that purchaser response is not a statutorily enumerated
factor under section 202(a)(1)-(2). Rather EPA has considered
purchaser response in exercising our discretion under the statute,
and based on the record before us, the agency views purchaser
response as a material aspect of the real-world feasibility of the
proposed standards.
    \546\ Roeth, Mike, et al. ``Barriers to Increased Adoption of
Fuel Efficiency Technologies in Freight Trucking,'' Page 24. July
2013. International Council for Clean Transportation. Available at
https://theicct.org/sites/default/files/publications/ICCT-NACFE-CSS_Barriers_Report_Final_20130722.pdf.
    \547\ American Transportation Research Institute. ``An Analysis
of the Operational Costs of Trucking: 2021 Update.'' November 2021.
Page 14.
    \548\ 81 FR 73719 (October 25, 2016).
---------------------------------------------------------------------------

    Moreover, the additional flexibilities beyond averaging already
available under EPA's existing regulations, including banking and
trading provisions in the ABT program--which, for example, in effect
enable manufacturers to spread the compliance requirement for any
particular model year across multiple model years--further support
EPA's conclusion that the proposed standards provide sufficient time
for the development and application of technology, giving appropriate
consideration to cost.
    The Administrator has significant discretion to weigh various
factors under CAA section 202, and, as with the HD GHG Phase 1 and
Phase 2 rules, the Administrator notes that the purpose of adopting
standards under that provision of the Clean Air Act is to address air
pollution that may reasonably be anticipated to endanger public health
and welfare and that reducing air pollution has traditionally been the
focus of such standards. Taking into consideration the importance of
reducing GHG emissions and the primary purpose of CAA section 202 to
reduce the threat posed to human health and the environment by air
pollution, the Administrator finds it is appropriate to propose
standards that, when implemented, would result in meaningful reductions
of HD vehicle GHG emissions both near term and over the longer term,
and to select such standards taking into consideration the enumerated
statutory factors of technological feasibility and cost of compliance
within the available lead time, as well as the discretionary factor of
impacts on purchasers and willingness to purchase. In identifying the
proposed standards, EPA's goal was to maximize emissions reductions
given our assessment of technological feasibility and accounting for
cost of compliance, lead time, and impacts on purchasers and
willingness to purchase. The Administrator concludes that this approach
is consistent with the text and purpose of CAA section 202.
    There have been very significant developments in the adoption of
ZEVs since EPA promulgated the HD GHG Phase 2 rule. One of the most
significant developments for U.S. heavy-duty manufacturers and
purchasers is the adoption of the IRA, which takes a comprehensive
approach to addressing many of the potential barriers to wider adoption
of heavy-duty ZEVs in the United States. As noted in Section I, the IRA
provides tens of billions of dollars in tax credits and direct Federal
funding to reduce the upfront cost of purchasing ZEVs, to increase the
number of charging stations across the country, to reduce the cost of
manufacturing batteries, and to promote domestic source of critical
minerals and other important elements of the ZEV supply chain. By
addressing all of these potential obstacles to wider ZEV adoption in a
coordinated, well-financed, strategy, Congress significantly advanced
the potential for ZEV adoption in the near term.
    In developing this estimate, EPA considered a variety of
constraints which have to date limited ZEV adoption and/or could limit
it in the future, including: cost to manufacturers and purchasers;
availability of raw materials, batteries, and other necessary supply
chain elements; adequate electricity supply and distribution; and
availability of hydrogen. EPA has consulted with analysts from other
agencies, including the Federal Energy Regulatory Commission, DOE, DOT,
and the Joint Office for Energy and Transportation, extensively
reviewed published literature and other data, and, as discussed
thoroughly in this preamble and the accompanying DRIA, has incorporated
limitations into our modeling to address these potential constraints,
as appropriate.
    As discussed in Section II.G.4, there are additional considerations
that support, but were not used to select, the proposed standards.
These include the non-GHG emission and energy impacts, energy security,
safety, and net benefits. EPA estimates that the present value of
monetized net benefits to society would be approximately $320 billion
through the year 2055 (annualized net benefits of $17 billion through
2055),\549\ more than five times the cost in vehicle technology and
associated electric vehicle supply equipment (EVSE) combined (see
preamble Section VII and Chapter 8 of the DRIA). We recognize the these
estimates do not reflect unquantified benefits, and the Administrator
has not relied on these estimates in identifying the appropriate
standards under CAA section 202. Nonetheless, our conclusion that the
estimated benefits considerably exceed the estimated costs of the
proposed program reinforces our view that the proposed standards
represent an appropriate weighing of the statutory factors and other
relevant considerations.
---------------------------------------------------------------------------

    \549\ Using 3 percent discount rate and climate benefits
calculated with the average SC-GHGs at a 3 percent discount rate.
---------------------------------------------------------------------------

    In addition to our proposed standards, we also considered and are
seeking comment on a range of alternatives above and below the proposed
standards, as specified and discussed in Section II.H and Section IX.
Our approach and goal in selecting standards were generally the same
for the range of alternative standards as they were for the proposed
standards, while also recognizing that there are uncertainties in our
projections and aiming to identify where additional information that
may become available during the course of the rulemaking may support
standards within that range as feasible and reasonable. EPA anticipates
that the appropriate choice of final standards within this range will
reflect the Administrator's judgments about the uncertainties in EPA's
analyses as well as consideration of public comment and updated
information where available. We considered an alternative with a slower
phase-in with less stringent CO2 emission standards;
however, we did not select this level for the proposed standards
because our assessment in this proposal is that feasible and
appropriate standards are available that provide for greater GHG
emission reductions than would be provided by this slower phase-in
alternative. We also considered a more stringent alternative with
emission standards similar to those required by the CA ACT program. At
this time, we consider the proposed standards as the appropriate
balancing of the factors. However, if our analysis for the final rule
of relevant existing information, public comments, or new information
that becomes available between the proposal and the final rule supports
a set of standards within the range of alternatives we are requesting
comment on, we may promulgate final CO2 emission standards
different from

those proposed if we determine that those emission standards are
feasible and appropriate. For example, we could finalize different
standards based on different ZEV adoption rates than described for the
proposed standards based on different considerations within the inputs
of HD TRUCS or other approaches that we have requested comment on in
this proposal (e.g. payback schedules, consideration of technology
development lead time, ZEV refueling infrastructure growth,
consideration of the need for and level of emissions reductions which
can be achieved through the standards to protect public health, etc.).
    In summary, after consideration of the very significant reductions
in GHG emissions, given the technical feasibility of the proposed
standards and the moderate costs per vehicle in the available lead
time, and taking into account a number of other factors such as the
savings to purchasers in operating costs over the lifetime of the
vehicle, safety, the benefits for energy security, and the
significantly greater quantified benefits compared to quantified costs,
EPA believes that the proposed standards are appropriate under EPA's
section 202(a) authority.

H. Potential Alternatives

    EPA developed and considered an alternative level of proposed
stringency for this rule which we are seeking comment on. The results
of the analysis of this alternative are included in Section IX of the
preamble. We also request comment, including supporting data and
analysis, if there are certain market segments, such as heavy-haul
vocational trucks or long-haul tractors which may require significant
energy content for their intended use, that it may be appropriate to
set standards less stringent than the alternative for the specific
corresponding regulatory subcategories in order to provide additional
lead time to develop and introduce ZEV or other low emissions
technology for those specific vehicle applications. As described in
more detail throughout this preamble, we also are seeking comment on
setting GHG standards that would reflect values less stringent than the
lower stringency alternative for certain market segments, values in
between the proposed standards and the alternative standards, values in
between the proposed standards and those that would reflect ZEV
adoption levels used in California's ACT, values that would reflect the
level of ZEV adoption in the ACT program, and values beyond those that
would reflect ZEV adoption levels in ACT such as the 50- to 60-percent
ZEV adoption range represented by the publicly stated goals of several
major OEMs for 2030.550 551 552 553 554 For all of these
scenarios we are requesting comment on, EPA anticipates that the same
approach explained in Section II and DRIA Chapter 2 would generally be
followed, including for estimating costs, though the rationale for the
different ZEV adoption rates may be based on different considerations
within the inputs of HD TRUCS or other approaches that we have
requested comment on in this proposal (e.g. payback schedules,
consideration of technology development lead time, ZEV refueling
infrastructure growth, etc.). As explained in this Section I.D of the
preamble, EPA has significant discretion in choosing an appropriate
balance among factors in setting standards under CAA section 202(a)(1)-
(2). If our analysis for the final rule of relevant existing
information, public comments, or new information that becomes available
between the proposal and final rule supports a slower or a more
accelerated implementation of the proposed standards, we may promulgate
final CO2 emission standards different from those proposed
(within the range between the less stringent alternative and the most
stringent standards we request comment on in this section) if we
determine that those emission standards are feasible and appropriate.
---------------------------------------------------------------------------

    \550\ California Air Resources Board, Final Regulation Order--
Advanced Clean Trucks Regulation. Filed March 15, 2021. Available
at: https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2019/act2019/fro2.pdf.
    \551\ Scania, `Scania's Electrification Roadmap,' Scania Group,
November 24, 2021, https://www.scania.com/group/en/home/newsroom/news/2021/Scanias-electrification-roadmap.html.
    \552\ AB Volvo, `Volvo Trucks Launches Electric Truck with
Longer Range,' Volvo Group, January 14, 2022, https://www.volvogroup.com/en/news-and-media/news/2022/jan/news-4158927.html.
    \553\ Deborah Lockridge, `What Does Daimler Truck Spin-off Mean
for North America?,' Trucking Info (November 11, 2021). https://www.truckinginfo.com/10155922/what-does-daimler-truck-spin-off-mean-for-north-america.
    \554\ Navistar presentation at the Advanced Clean Transportation
(ACT) Expo, Long Beach, CA (May 9-11, 2022).
---------------------------------------------------------------------------

    While our assessment in this proposal is that the proposed
standards provide adequate lead time, in order to ensure fulsome
comment on all of dynamics involved in the market responding to the
proposed standards, we also considered an alternative with less
stringent standards and a more gradual phase-in. As discussed in
Section II.F.6, we considered while developing the proposed standards
that manufacturers would need time to ramp up ZEV production from the
numbers of ZEVs produced today to the higher adoption rates we project
in the proposed standards that begin between four and eight years from
now. Manufacturers would need to conduct research and develop
electrified configurations for a diverse set of applications. They
would also need time to conduct durability assessments because downtime
is very critical in the heavy-duty market. Furthermore, manufacturers
would require time to make new capital investments for the
manufacturing of heavy-duty battery cells and packs, motors, and other
EV components, along with changing over the vehicle assembly lines to
incorporate an electrified powertrain. In addition, the purchasers of
HD BEVs would need time to design and install charging infrastructure
at their facilities or determine their hydrogen refueling logistics for
FCEVs. Therefore, we developed and considered an alternative that
reflects a more gradual phase-in of ZEV adoption rates to account for
this uncertainty. The ZEV adoption rates associated with level of
stringency of the proposed CO2 emission standards shown in
Section II.F.4 and the alternative CO2 emission standards
shown in Section IX.A.1 are shown in Table II-34. We are not proposing
this alternative set of standards because, as already described, our
assessment is that feasible and appropriate standards are available
that provide for greater emission reductions than provided under this
alternative. We request comment on whether our assessment that there is
adequate lead time provided in the proposed standards is correct or if
a more gradual phase in like the one described in this alternative
would be more appropriate.

  Table II-34--Comparison of ZEV Technology Adoption Rates in the Technology Packages Considered for the Proposed Standards and Alternative Considered
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                MY 2032 and
                                                            MY 2027 (%)     MY 2028 (%)     MY 2029 (%)     MY 2030 (%)     MY 2031 (%)      later (%)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                        Proposal
--------------------------------------------------------------------------------------------------------------------------------------------------------
Vocational..............................................              20              25              30              35              40              50
Short-Haul Tractors.....................................              10              12              15              20              30              35
Long-Haul Tractors......................................               0               0               0              10              20              25
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                       Alternative
--------------------------------------------------------------------------------------------------------------------------------------------------------
Vocational..............................................              14              20              25              30              35              40
Short-Haul Tractors.....................................               5               8              10              15              20              25
Long-Haul Tractors......................................               0               0               0              10              15              20
--------------------------------------------------------------------------------------------------------------------------------------------------------

    In consideration of the environmental impacts of HD vehicles and
the need for significant emission reductions, as well as the views
expressed by stakeholders in comments on the HD2027 NPRM such as
environmental justice communities, environmental nonprofit
organizations, and state and local organizations for rapid and
aggressive reductions in GHG emissions,555 556 557 558 we
are also requesting comment on a more stringent set of GHG standards
starting in MYs 2027 through 2032 than the proposed standards and
requesting that commenters provide supporting information regarding
whether such standards are feasible, appropriate, and consistent with
our CAA section 202 authority for a national program. We specifically
are seeking comment on values that would reflect the level of ZEV
adoption used in California's ACT program (as shown in Table II-35),
values in between the proposed standards and those that would reflect
ZEV adoption levels in ACT, and values beyond those that would reflect
ZEV adoption levels in ACT, such as the 50-60 percent ZEV adoption
range represented by the publicly stated goals of several major OEMs
for 2030.559 560 561 562 563 Under any of these more
stringent set of standards that we are requesting comment on, we
estimate that the individual per-vehicle ZEV technology and operating
costs reflecting these higher level of ZEV technology adoption rates
would be the same as the individual per-vehicle ZEV costs of the
proposed standards, as described in DRIA Chapter 2.8.2 because the
costs were calculated as the incremental cost between a ZEV and a
comparable ICE vehicle. Also under a scenario with more stringent
standards, the total costs across the fleet would be higher but the
total emission reductions would be greater. The MYs 2027 through 2032
and beyond emission standards reflecting the ZEV adoptions levels in
California's ACT that we are requesting comment on can be found in a
memo to the docket.\564\
---------------------------------------------------------------------------

    \555\ ACEEE Comments to the HD2027 NPRM. See Docket Entry EPA-
HQ-OAR-2019-0055-2852-A1. Referencing Catherine Ledna et al.,
`Decarbonizing Medium-& Heavy-Duty On-Road Vehicles: Zero-Emission
Vehicles Cost Analysis' (NREL, March 2022), https://www.nrel.gov/docs/fy22osti/82081.pdf.
    \556\ EDF Comments to the HD2027 NPRM. See Docket Entry EPA-HQ-
OAR-2019-0055-1265-A1, pp.16-17.
    \557\ ICCT Comments to the HD2027 NPRM. See Docket Entry EPA-HQ-
OAR-2019-0055-1211-A1, p. 6.
    \558\ Moving Forward Network Comments to the HD2027 NPRM. See
Docket Entry EPA-HQ-OAR-2019-0055-1277-A1, pp. 19-20.
    \559\ California Air Resources Board, Final Regulation Order--
Advanced Clean Trucks Regulation. Filed March 15, 2021. Available
at: https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2019/act2019/fro2.pdf.
    \560\ Scania, `Scania's Electrification Roadmap,' Scania Group,
November 24, 2021, https://www.scania.com/group/en/home/newsroom/news/2021/Scanias-electrification-roadmap.html.
    \561\ AB Volvo, `Volvo Trucks Launches Electric Truck with
Longer Range,' Volvo Group, January 14, 2022, https://www.volvogroup.com/en/news-and-media/news/2022/jan/news-4158927.html.
    \562\ Deborah Lockridge, `What Does Daimler Truck Spin-off Mean
for North America?,' Trucking Info (November 11, 2021). https://www.truckinginfo.com/10155922/what-does-daimler-truck-spin-off-mean-for-north-america.
    \563\ Navistar presentation at the Advanced Clean Transportation
(ACT) Expo, Long Beach, CA (May 9-11, 2022).
    \564\ U.S. EPA. ``Memo to Docket: Potential Federal Heavy-Duty
GHG Emission Standards Reflecting Technology Packages Including
California's ACT Levels of ZEV Adoption.'' March 2023. Docket EPA-
HQ-OAR-2022-0985.

                       Table II-35--Comparison of ZEV Technology Adoption Rates Between the Proposed Standards and California ACT
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                MY 2032 and
                                                            MY 2027 (%)     MY 2028 (%)     MY 2029 (%)     MY 2030 (%)     MY 2031 (%)      later (%)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                        Proposed
--------------------------------------------------------------------------------------------------------------------------------------------------------
Vocational..............................................              20              25              30              35              40              50
Short-Haul Tractors.....................................              10              12              15              20              30              35
Long-Haul Tractors......................................               0               0               0              10              20              25
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                        CARB ACT
--------------------------------------------------------------------------------------------------------------------------------------------------------
Vocational..............................................              20              30              40              50              55              60
Tractors................................................              15              20              25              30              35              40
--------------------------------------------------------------------------------------------------------------------------------------------------------

I. Small Businesses

    EPA is proposing to make no changes to (i.e., maintain the
existing) MY 2027 and later GHG vehicle emission standards for any
heavy-duty manufacturers that meet the ``small business'' size criteria
set by the Small Business Administration.\565\ In other words, these
manufacturers would not be subject to the proposed revised MY 2027 and
new MYs 2028 through 2032 and later HD vehicle CO2 emission
standards but would remain subject to the HD vehicle CO2
emission standards previous set in HD GHG Phase 2.\566\ Additionally,
we are proposing that qualifying small business manufacturers could
continue to average within their averaging sets for each 2027 and later
model year to achieve the applicable standards; however, we are
proposing to restrict banking, trading, and the use of advanced
technology credit multipliers for credits generated against the Phase 2
standards for qualifying manufacturers that utilize this small business
interim provision.
---------------------------------------------------------------------------

    \565\ See our proposed updates to the definition of ``small
business'' in 40 CFR 1037.801.
    \566\ See Section XI.C for our regulatory flexibility assessment
of the potential burden on small businesses. See also Section
III.C.2 for a description of the proposed revisions to 40 CFR
1037.150(c) that clarify the standards and proposed restrictions on
participation in the ABT program for MYs 2027 and later that we are
proposing would apply for qualifying small business vehicle
manufacturers that utilize the proposed interim provision.
---------------------------------------------------------------------------

    We are also proposing that vehicle manufacturers that qualify as a
small business may choose not to utilized the proposed interim
provision and voluntarily certify their vehicles to the Phase 3
standards without ABT participation restrictions if they certify all
their vehicle families within a given averaging set to the Phase 3
standards for the given MY. In other words, small businesses that opt
into the Phase 3 program for a given MY for all their vehicle families
within a given averaging set would be eligible for the full ABT program
for those vehicle families for that MY, including advanced technology
credit multipliers. While we are proposing not to apply the proposed
new standards for vehicles produced by small businesses, we propose
that some small business manufacturers would be subject to some other
new requirements we are proposing in this rule related to ZEVs, such as
the battery durability monitor and warranty provisions proposed in 40
CFR 1037.115(f) and described in Section III.B.
    EPA may consider new GHG emission standards to apply for vehicles
produced by small business vehicle manufacturers as part of a future
regulatory action. At this time, we believe the proposed new standards,
which were developed based on technology packages using increasing
adoption of ZEVs, may create a disproportionate burden on small
business vehicle manufacturers. As described in DRIA Chapter 9, we have
identified a small number of manufacturers that would appear to qualify
as small businesses under the heavy-duty vehicle manufacturer category.
The majority of these small businesses currently only produce ZEVs,
while one company currently produces ICE vehicles.
    Since there would only be a small emissions benefit from applying
the proposed standards to the relatively low production volume of ICE
vehicles produced by small businesses, we believe that maintaining the
existing HD vehicle CO2 standards for these companies at
this time would have a negligible impact on the overall GHG emission
reductions that the program would otherwise achieve. We request comment
on our assessment that the emission impact of this approach for small
businesses would be small considering the number and type of vehicle
manufacturers described in DRIA Chapter 9.

III. Compliance Provisions, Flexibilities, and Test Procedures

    In this proposed rule, we are retaining the general compliance
structure of existing 40 CFR part 1037 with some revisions described in
this section. Vehicle manufacturers would continue to demonstrate that
they meet emission standards using emission modeling and EPA's
Greenhouse gas Emissions Model (GEM) and would use fuel-mapping or
powertrain test information from procedures established and revised in
previous rulemakings.\567\
---------------------------------------------------------------------------

    \567\ See the HD GHG Phase 2 rule (81 FR 73478, October 25,
2016), the Heavy-Duty Engine and Vehicle Technical Amendment rule
(86 FR 34308, June 29, 2021), and the HD2027 rule (88 FR 4296,
January 24, 2023). In this rulemaking, EPA is not reopening any
portion of our heavy-duty compliance provisions, flexibilities, and
testing procedures, including those in 40 CFR parts 1037, 1036, and
1065, other than those specifically identified in this document as
the subject of our proposal or a solicitation for comment. For
example, while EPA is proposing to revise discrete elements of the
HD ABT program, EPA is not reopening the general availability of
ABT.
---------------------------------------------------------------------------

    The existing HD GHG Phase 2 program provides flexibilities,
primarily through the HD GHG ABT program, that facilitate compliance
with the emission standards. In addition to the general ABT provisions,
the current HD GHG Phase 2 program also includes advanced technology
credit (including for BEVs and FCEVs) and innovative technology credit
provisions. As described in Section II of this preamble, the proposed
revisions to the existing MY 2027 Phase 2 GHG emission standards and
new proposed standards for MYs 2028 through 2032 are premised on
utilization of a variety of technologies, including technologies that
are considered advanced technologies in the existing HD GHG Phase 2 ABT
program. As also explained in Section II, we consider averaging in
supporting the feasibility of the proposed Phase 3 GHG standards in
this rule. Averaging and other aspects of the ABT program would also
continue to help provide additional flexibility for manufacturers to
make necessary technological improvements and reduce the overall cost
of the program, without compromising overall environmental objectives.
    We are not proposing any changes to and are not reopening the use
of credits from MY 2027 and earlier in MY 2027 and later. In other
words, credits earned in HD GHG Phase 2 would be allowed to carry over
into Phase 3, subject to the existing credit life limitation of five
years, as described in 40 CFR 1037.740(c). Similarly, we are not
proposing any revisions to and are not reopening the allowance that
provides manufacturers three years to resolve credit deficits, as
detailed in 40 CFR 1037.745.
    In Section III.A, we describe the general ABT program and how we
expect manufacturers to apply ABT to meet the proposed standards. In
Section III.A, we propose a revision to the definition of ``U.S.-
directed production volume'' to clarify consideration in this
rulemaking of nationwide production volumes, including those that may
in the future be certified to different state emission standards.\568\
This proposed revision is intended to address a potential interaction
between the existing definition of U.S.-directed production volume and
the ACT regulation for HD vehicles.\569\ Section III.A.2 includes
proposed updates to advanced technology credit provisions after
considering comments received on the HD2027 NPRM (87 FR 17592, March
28, 2022). In Section III.A.3, we request comment on other
flexibilities, including how credits could be used across averaging
sets. In Section III.B,

we propose durability monitoring requirements for BEVs and PHEVs,
clarify existing warranty requirements for PHEVs, and propose warranty
requirements for BEVs and FCEVs. Finally, in Section III.C, we propose
additional clarifying and editorial amendments to the HD highway engine
provisions of 40 CFR part 1036, the HD vehicle provisions of 40 CFR
part 1037 and the test procedures for HD engines in 40 CFR part 1065.
---------------------------------------------------------------------------

    \568\ The proposed definition update includes corresponding
proposed clarifications throughout the HD engine and vehicle
regulations of 40 CFR parts 1036 and 1037, respectively.
    \569\ EPA granted the ACT rule waiver requested by California
under CAA section 209(b) on March 30, 2023.
---------------------------------------------------------------------------

A. Proposed Revisions to the ABT Program

    As noted in the introduction to this section, we are generally
retaining the HD GHG Phase 2 ABT program that allows for emission
credits to be averaged, banked, or traded within each of the averaging
sets specified in 40 CFR 1037.740(a). To generate credits, a vehicle
manufacturer must reduce CO2 emission levels below the level
of the standard for one or more vehicle families. The manufacturer can
use those credits to offset higher emission levels from vehicles in the
same averaging set such that the averaging set meets the standards on
``average'', ``bank'' the credits for later use, or ``trade'' the
credits to another manufacturer. The credits are calculated based on
the production volume of the vehicles in the averaging set and their
respective emission levels relative to the standard. To incentivize the
research and development of the new technologies, the current HD
vehicle ABT program also includes credit multipliers for certain
advanced technologies. In this Section III.A, we describe proposed
changes to two aspects of the ABT program: the applicable production
volume for use in calculating ABT credits and credit multipliers for
advanced technologies. We also request comment on other potential
flexibilities we could consider adopting in this rule.
1. U.S-Directed Production Volume
    As described in Section II, the proposed Phase 3 GHG vehicle
standards include consideration of nationwide production volumes.
Correspondingly, we are proposing that the GHG ABT program for
compliance with those standards would be applicable to the same
production volumes considered in setting the standards. In Section II,
we also request comment on how to account for ZEV adoption rates that
would result from compliance with the California ACT program in setting
the proposed GHG standards.\570\ The existing HD GHG Phase 2 vehicle
program has certain provisions (based off the regulatory definition of
``U.S.-directed production volume'') that would exclude production
volumes that are certified to different state emission standards,
including exclusion from participation in ABT. To address this
potential interaction between the existing definition of U.S.-directed
production volume and the ACT regulation for HD vehicles, we propose a
revision to the definition of ``U.S.-directed production volume.'' The
proposed revision would clarify that in this rulemaking we consider
nationwide production volumes, including those that may in the future
be certified to different state emission standards, within the proposed
Phase 3 standards described in Section II and within the ABT GHG
vehicle program.
---------------------------------------------------------------------------

    \570\ EPA granted the ACT rule waiver requested by California
under CAA section 209(b) on March 30, 2023.
---------------------------------------------------------------------------

    The exclusion of engines and vehicles certified to different state
standards in the existing definitions have not impacted the HD GHG
program under parts 1036 and 1037 to-date because California has
adopted GHG emission standards for HD engines and vehicles that align
with the Federal HD GHG Phase 1 and Phase 2
standards.571 572 As discussed in Section I, the ACT
regulation requires manufacturers to produce and sell increasing
numbers of zero-emission medium- and heavy-duty highway vehicles. Given
the distinct difference between what is required under the ACT compared
to the existing Phase 2 vehicle program and the HD vehicle GHG
standards proposed under this rulemaking, we are considering the impact
of the ACT on the HD GHG vehicle program. To that end, we are proposing
that the revision to this definition revision apply starting with MY
2024 to provide consistent treatment of any production volumes
certified to ACT. We request comment on the MY 2024 start and whether
other options should be considered for transitioning to this new
definition.
---------------------------------------------------------------------------

    \571\ California Air Resources Board. ``Final Regulation Order
for Phase 1 Greenhouse Gas Regulations.'' December 5, 2014,
available at https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2013/hdghg2013/hdghgfrot13.pdf.
    \572\ California Air Resources Board. ``Final Regulation Order
for Phase 2 Greenhouse Gas Regulations and Tractor-Trailer GHG
Regulations.'' April 1, 2019, available at https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2018/phase2/finalatta.pdf?_ga=2.122416523.1825165293.1663635303-1124543041.1635770745.
---------------------------------------------------------------------------

    The existing definition of ``U.S.-directed production volume'' for
HD vehicles explicitly does not include vehicles certified to state
emission standards that are different than the emission standards in 40
CFR part 1037.\573\ The term U.S.-directed production volume is key in
how the existing regulations direct manufacturers to calculate credits
in the HD vehicle ABT GHG program, in 40 CFR part 1037, subpart H. In
the existing regulations, vehicle production volumes that are excluded
from that term's definition cannot generate credits. EPA first excluded
such production volumes from participation in HD ABT in a 1990
rulemaking on NOX emissions from HD engines. In the preamble
to that rulemaking, which established NOX and PM banking and
trading and expanded the averaging program for HD engines, EPA
explained that HDEs certified under the California emission control
program are excluded from this program.\574\ We further explained that
HDEs certified under the California emission control program may not
generate credits for use by Federal engines (49-state) or use credits
generated by Federal engines.\575\ In addition, we explained that while
fifty-state engines participating in the Federal banking, trading or
averaging programs may be sold in California if their FELs are lower
than the applicable emission standard, California engines may not
generate credits for the Federal program.\576\
---------------------------------------------------------------------------

    \573\ An equivalent definition of ``U.S-directed production
volume'' can be found at 40 CFR 1036.801 for HD engines.
    \574\ 55 FR 30592, July 26, 1990.
    \575\ 55 FR 30592, July 26, 1990.
    \576\ 55 FR 30592, July 26, 1990.
---------------------------------------------------------------------------

    In 2001, in a rulemaking that established criteria pollutant
emission standards phasing in to MY 2010 and later for HD engines and
vehicles, EPA adopted a definition for ``U.S.-directed production.''
The adopted definition included similar regulatory language to our
existing part 1037 definition.\577\ Regarding compliance with the MY
2007-2009 emission standards phase-in requirements, which were based on
percentage of production volumes meeting the MY 2010 and later
standards, EPA again noted our intent to exclude production volumes
certified to different state standards. We explained that we were
clarifying that this phase-in excludes California complete heavy-

duty vehicles, which are already required to be certified to the
California emission standards.\578\ We further explained that the
phase-in also excludes vehicles sold in any state that has adopted
California emission standards for complete heavy-duty vehicles.\579\ We
also explained that it would be inappropriate to allow manufacturers to
``double-count'' the vehicles by allowing them to count those vehicles
both as part of their compliance with this phase-in and for compliance
with California requirements.\580\ In addition, we noted that we would
handle HD engines similarly if California were to adopt different
emission standards than those being established by this rule.\581\
---------------------------------------------------------------------------

    \577\ 66 FR 5002, 5159, January 18, 2001 (amending 40 CFR
86.004-2 to add a definition for ``U.S.-directed production'' where
``U.S.-directed production means the engines and/or vehicles (as
applicable) produced by a manufacturer for which the manufacturer
has reasonable assurance that sale was or will be made to ultimate
purchasers in the United States, excluding engines and/or vehicles
that are certified to state emission standards different than the
emission standards in [40 CFR part 86].'').
    \578\ 66 FR at 5043, January 18, 2001.
    \579\ 66 FR at 5043, January 18, 2001.
    \580\ 66 FR at 5043, January 18, 2001.
    \581\ 66 FR at 5043, January 18, 2001.
---------------------------------------------------------------------------

    In the HD GHG Phase 1 rule, EPA adopted the existing definitions of
U.S.-directed production volume in 40 CFR 1036.801 and 1037.801, which
were unchanged in HD GHG Phase 2 and currently apply for HD engines and
vehicles.\582\
---------------------------------------------------------------------------

    \582\ 76 FR 57397 and 57431, September 15, 2011; 81 FR 74043 and
74123, October 25, 2016.
---------------------------------------------------------------------------

    We are proposing a revision to the definition of ``U.S.-directed
production volume'' in 40 CFR 1037.801 such that it represents the
total nationwide production volumes, including vehicles certified to
state emission standards that are different than the emission standards
of 40 CFR part 1037. As described in Section II, the proposed standards
are feasible and appropriate based on nationwide adoption rates of
technology packages that include adoption of ZEV technologies.
Manufacturers may be motivated to produce ZEVs by this rule and in
response to other initiatives and we want to support any U.S. adoption
of these technologies by allowing manufacturers to account for their
nationwide production volumes to comply with the proposed standards. We
recognize that the existing definition of ``U.S.-directed production
volume'' may cause challenges to manufacturer plans, including long-
term compliance planning, due to the uncertainty surrounding whether
additional states may adopt more stringent standards in the future.
    Given that EPA granted the ACT rule waiver requested by California
under CAA section 209(b) on March 30, 2023, the existing definition of
U.S.-directed production volume excludes all vehicles (ICE vehicles and
ZEVs) certified to meet the ACT program in California and any other
states that adopt the ACT.\583\ In this scenario, the ZEV production
volumes destined for California and other states would correspond to a
large portion of the nationwide production on which the proposed EPA
standards are based, and it would be challenging for vehicle
manufacturers to comply with the proposed standards if they could not
account for those ZEVs. As described in Section II, we request comment
on how to account for ZEV adoption rates that would result from
compliance with the California ACT program in setting the proposed GHG
standards. If we were to finalize standards that account for the ACT
program, we expect to similarly base the final standards on nationwide
production volumes that would continue to rely on our proposal to
revise the current definition of U.S.-directed production volume to
include nationwide production.
---------------------------------------------------------------------------

    \583\ As of September 2022, the following states have adopted
California's ACT program: Massachusetts, New York, New Jersey,
Washington, and Oregon.
---------------------------------------------------------------------------

    We are proposing this revision consistent with our intended
approach of considering such production volumes in setting the
stringency of the Phase 3 standards in this rulemaking, as well as
allowing inclusion of such production volumes in demonstrating
compliance with the standards through participation in the HD vehicle
ABT GHG program. We believe this approach would address both the
potential ``double counting'' issue EPA previously articulated in past
HD rulemakings and the potential difficulties surrounding
manufacturers' long-term compliance planning (due to the uncertainty
surrounding whether additional states may adopt the California ACT
program in the future) we recognize in the context of this rulemaking.
Our proposed revision would also align with the approach in the LD GHG
program.
    In addition to this proposed revision to the definition of ``U.S.-
directed production volume'', we are proposing additional conforming
amendments throughout 40 CFR part 1037 to streamline references to the
revised definition; see Section III.E.3 for further discussion on one
of those proposed revisions.\584\
---------------------------------------------------------------------------

    \584\ As discussed in Section III.C.3, we are also proposing a
similar update to the heavy-duty highway engine definition of
``U.S.-directed production volume'' in 40 CFR 1036.801, with
additional proposed updates where it is necessary to continue to
exclude production volumes certified to different standards (i.e.,
the ABT program for highway heavy-duty engines).
---------------------------------------------------------------------------

2. Advanced Technology Credits for CO2 Emissions
    In HD GHG Phase 1, we provided advanced technology credits for
hybrid powertrains, Rankine cycle waste heat recovery systems on
engines, all-electric vehicles, and fuel cell electric vehicles to
promote the implementation of advanced technologies that were not
included in our technical basis of the feasibility of the Phase 1
emission standards (see 40 CFR 86.1819-14(k)(7), 1036.150(h), and
1037.150(p)). The HD GHG Phase 2 CO2 emission standards that
followed Phase 1 were premised on the use of mild hybrid powertrains in
vocational vehicles and waste heat recovery systems in a subset of the
engines and tractors, and we removed mild hybrid powertrains and waste
heat recovery systems as options for advanced technology credits. At
the time of the HD GHG Phase 2 final rule, we believed the HD GHG Phase
2 standards themselves provided sufficient incentive to develop those
specific technologies. However, none of the HD GHG Phase 2 standards
were based on projected utilization of the other even more-advanced
Phase 1 advanced credit technologies (e.g., plug-in hybrid electric
vehicles, all-electric vehicles, and fuel cell electric vehicles). For
HD GHG Phase 2, EPA promulgated advanced technology credit multipliers
through MY 2027, as shown in Table III-1 (see also 40 CFR 1037.150(p)).

 Table III-1--Advanced Technology Multipliers in Existing HD GHG Phase 2
                        for MYs 2021 Through 2027
------------------------------------------------------------------------
                       Technology                           Multiplier
------------------------------------------------------------------------
Plug-in hybrid electric vehicles........................             3.5
All-electric vehicles...................................             4.5
Fuel cell electric vehicles.............................             5.5
------------------------------------------------------------------------

    As stated in the HD GHG Phase 2 rulemaking, our intention with
these multipliers was to create a meaningful incentive for those
manufacturers considering developing and applying these qualifying
advanced technologies into their vehicles. The multipliers under the
existing program are consistent with values recommended by CARB in
their HD GHG Phase 2 comments.\585\ CARB's values were based on a cost
analysis that compared the costs of these advanced technologies to
costs of other GHG-reducing

technologies. CARB's cost analysis showed that multipliers in the range
we ultimately promulgated as part of the HD GHG Phase 2 final rule
would make these advanced technologies more competitive with the other
GHG-reducing technologies and could allow manufacturers to more easily
generate a viable business case to develop these advanced technologies
for HD vehicles and bring them to market at a competitive price.
---------------------------------------------------------------------------

    \585\ Letter from Michael Carter, CARB, to Gina McCarthy,
Administrator, EPA and Mark Rosekind, Administrator, NHTSA, June 16,
2016. EPA Docket ID EPA-HQ-OAR-2014-0827_attachment 2.
---------------------------------------------------------------------------

    In establishing the multipliers in the HD GHG Phase 2 final rule,
we also considered the tendency of the HD sector to lag behind the
light-duty sector in the adoption of a number of advanced technologies.
There are many possible reasons for this, such as:
     HD vehicles are more expensive than light-duty vehicles,
which makes it a greater monetary risk for purchasers to invest in new
technologies.
     These vehicles are primarily work vehicles, which makes
predictable reliability and versatility important.
     Sales volumes are much lower for HD vehicles, especially
for specialized vehicles.
    At the time of the HD GHG Phase 2 rulemaking, we concluded that as
a result of factors such as these, and the fact that adoption rates for
the aforementioned advanced technologies in HD vehicles were
essentially non-existent in 2016, it seemed unlikely that market
adoption of these advanced technologies would grow significantly within
the next decade without additional incentives.
    As we stated in the HD GHG Phase 2 final rule preamble, our
determination that it was appropriate to provide large multipliers for
these advanced technologies, at least in the short term, was because
these advanced technologies have the potential to lead to very large
reductions in GHG emissions and fuel consumption, and advance
technology development substantially in the long term. However, because
the credit multipliers are so large, we also stated that they should
not necessarily be made available indefinitely. Therefore, they were
included in the HD GHG Phase 2 final rule as an interim program
continuing only through MY 2027.
    The HD GHG Phase 2 CO2 emission credits for HD vehicles
are calculated according to the existing regulations at 40 CFR
1037.705. For BEVs and FCEVs, the family emission level (FEL) value for
CO2 emissions is deemed to be 0 grams per ton-mile.\586\
Under those existing regulations, the CO2 emission credits
for HD BEVs built between MY 2021 and MY 2027 would be multiplied by
4.5 (or the values shown in Table III-1 for the other technologies)
and, for discussion purposes, can be visualized as split into two
shares.\587\ The first share of credits would come from the reduction
in CO2 emissions realized by the environment from a BEV that
is not emitting from the tailpipe, represented by the first 1.0 portion
of the multiplier. Therefore, each BEV or FCEV produced receives
emission credits equivalent to the level of the standard, even before
taking into account the effect of a multiplier. The second share of
credits does not represent CO2 emission reductions realized
in the real world but rather, as just explained, was established by EPA
to help incentivize a nascent market: in this example, the emission
credits for BEVs built between MY 2021 and 2027 receive an advanced
technology credit multiplier of 4.5, i.e., an additional 3.5 multiple
of the standard.
---------------------------------------------------------------------------

    \586\ 40 CFR 1037.150(f).
    \587\ 40 CFR 1037.705.
---------------------------------------------------------------------------

    The HD GHG Phase 2 advanced technology credit multipliers represent
a tradeoff between incentivizing new advanced technologies that could
have significant benefits well beyond what is required under the
standards and providing credits that do not reflect real world
reductions in emissions, which could allow higher emissions from
credit-using engines and vehicles. At low adoption levels, we believe
the balance between the benefits of encouraging additional
electrification as compared to any negative emissions impacts of
multipliers would be appropriate and would justify maintaining the
current advanced technology multipliers. At the time we finalized the
HD GHG Phase 2 program in 2016, we balanced these factors based on our
estimate that there would be very little market penetration of ZEVs in
the heavy-duty market in the MY 2021 to MY 2027 timeframe, during which
the advanced technology credit multipliers would be in effect.
Additionally, the primary technology packages in our technical basis of
the feasibility of the HD GHG Phase 2 standards did not include any
ZEVs.
    In our assessment conducted during the development of HD GHG Phase
2, we found only one manufacturer had certified HD BEVs through MY
2016, and we projected ``limited adoption of all-electric vehicles into
the market'' for MYs 2021 through 2027.\588\ However, as discussed in
Section II, we are now in a transitional period where manufacturers are
actively increasing their PHEV, BEV, and FCEV HD vehicle offerings and
are being further supported through the IRA tax credits, and we expect
this growth to continue through the remaining timeframe for the HD GHG
Phase 2 program and into the proposed Phase 3 program timeframe.
---------------------------------------------------------------------------

    \588\ 81 FR 75300 (October 25, 2016).
---------------------------------------------------------------------------

i. Advanced Technology Credits in the HD2027 NPRM
    We requested comment in the HD2027 NPRM on three approaches that
would reduce the number of incentive credits produced by battery
electric vehicles in the MY 2024 through MY 2027 timeframe. The three
approaches considered in the HD2027 NPRM (87 FR 17605-17606) are
summarized as follows:
     Approach 1: The MY 2024 through MY 2027 ZEVs certified in
California to meet the ACT program would not receive the advanced
technology credit multipliers that currently exist.
     Approach 2: The advanced technology credits generated by a
manufacturer would be capped on an annual basis. Advanced technology
credits generated for EVs on an annual basis that are under a cap would
remain unchanged. Above the cap, the multipliers would effectively be a
value of 1.0; in other words, after a manufacturer reaches their cap in
any model year, the multipliers would no longer be available and would
have no additional effect on credit calculations. This advanced
technology credit cap approach would limit the credits generated by a
manufacturer's use of the advanced technology credit multipliers for
battery electric vehicles to the following levels of CO2 per
manufacturer per model year beginning in MY 2024 and extending through
MY 2027:
    [cir] Light Heavy-Duty Vehicle Averaging Set: 42,000 Mg
CO2.
    [cir] Medium Heavy-Duty Vehicle Averaging Set: 75,000 Mg
CO2.
    [cir] Heavy Heavy-Duty Vehicle Averaging Set: 325,000 Mg
CO2.
     Approach 3: Phase-out the magnitude of the credit
multipliers from MY 2024 through MY 2027.
    EPA received a number of comments on the HD2027 NPRM in response to
our request for comment on potential approaches to modify the existing
Advanced Technology Credit multipliers. The entire set of comments may
be found in Section 28 of EPA's Response to Comments Document for the
HD2027 final rule.\589\
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    \589\ U.S. EPA, ``Control of Air Pollution from New Motor
Vehicles: Heavy-Duty Engine and Vehicle Standards--Response to
Comments.'' Section 28. Docket EPA-HQ-OAR-2019-0055.
---------------------------------------------------------------------------

    Several commenters supported Approach 1, sometimes along with

Approach 3. A common theme in these comments was that the incentive
provided by the credit multipliers is not warranted for ZEVs that will
already be produced due to state requirements. Some commenters also
stated that the credit multipliers should not apply to any state that
adopts ACT and should not be limited to California. Another commenter
suggested an alternate approach whereby credit multipliers would not be
provided for the vehicle segments targeted in the HD2027 NPRM for early
adoption, such as some vocational vehicles and short-haul tractors, but
remain available for other vehicle segments.
    Other commenters raised concerns with Approach 1. For example, some
commenters stated that the states' adoption of the ACT rule is
unpredictable and may have a negative impact on manufacturer and
supplier development plans. Another commenter raised a concern that
eliminating the credit multipliers for ZEVs sold in California could
impact manufacturers unequally and have a greater negative impact on
manufacturers with more ZEV sales in California. One commenter
suggested that this approach would create a disincentive for additional
states to adopt ACT. Another commenter recommended that if EPA selects
this approach, then EPA should consider allowing credit multipliers for
ZEVs sold in California that exceed the ACT sales requirements.
Finally, another commenter raised concerns about the implementation of
this approach because it is difficult for manufacturers to account for
sales by state in the heavy-duty market.
    No commenters expressed support for Approach 2, and some commenters
raised potential concerns with this approach. For example, a commenter
stated this approach creates a disincentive to produce ZEVs above the
annual cap and would negatively impact manufacturers that sell a
greater number of ZEVs by making a smaller percentage of their fleet
eligible for the credit multipliers. One commenter questioned whether a
cap approach, while an incentive to small manufacturers and low volume
ZEV producers, would incentivize additional sales beyond what is
required by the states that adopt ACT under CAA section 177.
    Many commenters supported a phase out or elimination of the credit
multipliers, similar to Approach 3. A theme among many of the
commenters was to phase out the credit multiplier as soon as
practicable, with some commenters suggesting the phase out begin as
early as MY 2024. On the other hand, two commenters suggested an annual
decrease in the value of the credit multipliers to prevent a potential
pre-buy situation. Common themes expressed by the commenters supporting
an elimination of phase-out of the credit multipliers included stating
that the credit multipliers are no longer necessary because of state
requirements and that the credit multipliers reduce the overall
effectiveness of the HD GHG regulatory program. One concern raised by a
commenter is that the existing credit multipliers would slow the
progression of CO2-reducing technologies for HD vehicles
that are powered by ICE. Some commenters suggested removing the credit
multipliers for all of the existing technologies qualifying for
advanced technology credits, including PHEVs, BEVs, and FCEVs.
    Some of the commenters opposed any changes to the existing credit
multipliers. Some commenters indicated that the credit multipliers are
necessary to justify the research and development of these new and
higher-cost technologies into new markets. They also noted that the
credit multipliers provide a role in the overall suite of incentives
for ZEVs and infrastructure in the HD market. Two commenters suggested
extending the credit multipliers beyond MY 2027 to allow the HD ZEV
market to further mature.
ii. Proposed Changes to the Advanced Technology Credit Multipliers
    While we did anticipate some growth in electrification would occur
due to the credit incentives in the HD GHG Phase 2 final rule when we
finalized the rule, we did not expect the level of innovation since
observed, the IRA or BIL incentives, or that California would adopt the
ACT rule at the same time these advanced technology multipliers were in
effect. Based on this new information, we believe the existing advanced
technology multiplier credit levels may no longer be appropriate for
maintaining the balance between encouraging manufacturers to continue
to invest in new advanced technologies over the long term and potential
emissions increases in the short term. We believe that, if left as is,
the multiplier credits could allow for backsliding of emission
reductions expected from ICE vehicles for some manufacturers in the
near term (i.e., the generation of excess credits which could delay the
introduction of technology in the near or mid-term) as sales of
advanced technology vehicles which can generate the incentive credit
continue to increase.
    After considering the comments received on the HD2027 NPRM and the
proposed HD vehicle Phase 3 GHG standards and program described in
Section II and this Section III, we propose to phase-out the advanced
technology credit multipliers for HD plug-in hybrid and battery
electric vehicles after MY 2026, one year earlier than what is
currently in the regulations. We weighed several considerations in
proposing this one year earlier phase-out. We do not foresee a need for
any advanced technology credits for these technologies to extend past
MY 2026. We recognize the need to continue to incentivize the
development of BEVs in the near-term model years, prior to MY 2027.
However, our analysis of the feasibility of PHEVs and BEVs described in
Section II indicates there is sufficient incentive for those
technologies for the model years we are proposing HD vehicle Phase 3
GHG emission standards (MYs 2027 through 2032). We note that we did not
rely on credits generated from credit multipliers in developing the
proposed HD vehicle Phase 3 emission standards, however this
flexibility further supports the feasibility of the proposed Phase 3
emission standards.
    As explained earlier in this subsection, we recognize that a
portion of the credits that result from an advanced technology
multiplier do not represent CO2 emission reductions realized
in the real world and thus should be carefully balanced amongst the
other considerations. We considered that we are proposing to revise the
existing regulatory definition of ``U.S.-directed production volume,''
as discussed in Section II, such that vehicle production volumes sold
in California or Section 177 states that adopt ACT would be included in
the ABT credit calculations and continuing to allow these multipliers
could create a large bank of credits with the potential to delay the
real world benefits of the proposed program. We also took into
consideration that the IRA and other new incentives are available that
could help reduce the role of the multipliers. Finally, we recognize
that some manufacturers' long-term product plans for PHEV or BEV
technologies may have extended to model years closer to MY 2027 when
the HD GHG Phase 2 standards were at their most stringent levels. We
are proposing a MY 2026 phase-out for PHEV and BEV credit multipliers,
in part, because it is expected to have a lesser impact on current
manufacturer product plans. We request comment on our proposed MY

2026 phase-out date or whether we should consider other approaches to
account for ACT or incentive programs.
    We propose to revise existing 40 CFR 1037.150(p) to reflect the
proposed phase-out of advanced technology credit multipliers for BEVs
and PHEVs and clarify the applicable standards for calculating credits.
We propose parallel edits to existing 40 CFR 1037.615(a) to clarify
when the advanced technology credit calculations described in that
section would apply. We are not proposing any changes to the existing
advanced technology multipliers for fuel cell electric vehicles, which
continue to apply through MY 2027. We believe it is still appropriate
to incentivize fuel cell technology, because it has been slower to
develop in the HD market, as discussed in Section II.D, but request
comment on this approach for FCEVs. Additionally, we are retaining and
are not reopening the existing off-cycle provisions of 40 CFR 1037.610
that allow manufacturers to request approval for other ``innovative''
technologies not reflected in GEM.
3. Other Potential HD CO2 Emission Credit Flexibilities
    We recognize that the proposed HD GHG Phase 3 standards would
require significant investments from manufacturers to reduce GHG
emissions from HD vehicles. We request comment on the potential need
for additional flexibilities to assist manufacturers in the
implementation of Phase 3.
    Specifically, we request comment on providing the flexibility for
manufacturers to use advanced technology credits across averaging sets,
subject to a cap. In HD GHG Phase 1, the advanced technology credits
earned a multiplier of 1.5 and they could be applied to any heavy-duty
engine or vehicle averaging set.\590\ To prevent market distortions, we
capped the amount of advanced credits that could be brought into any
service class in any model year of the Phase 1 program at 60,000 Mg. In
HD GHG Phase 2, we adopted larger advanced technology multipliers, and
we discontinued the allowance for advanced technology credits to be
used across averaging sets. The primary reason for the averaging set
restriction was to reduce the risk of market distortions if we allowed
the use of the credits across averaging sets combined with the larger
credit multipliers.\591\ As discussed in Section III.A.2, we are
proposing to phase-out the advanced technology credit multipliers for
HD plug-in hybrid and battery electric vehicles after MY 2026, one year
earlier than what is currently in the regulations, and under the
existing regulations the fuel cell electric vehicle advanced technology
multipliers end after MY 2027.
---------------------------------------------------------------------------

    \590\ 40 CFR 1036.740(c) and 1037.740(b).
    \591\ 81 FR 73498 (October 25, 2016).
---------------------------------------------------------------------------

    We recognize the proposed Phase 3 standards would require the
increasing use of CO2 emission reducing technologies. During
this proposed Phase 3 standards transition, we are considering whether
additional flexibilities in the Phase 3 program emissions credit ABT
program design may be warranted, similar to the Phase 1 provision which
allowed credits generated from advanced technologies to be transferred
across averaging sets. We request comment on including a similar
flexibility for the Phase 3 program. For example, we may consider an
interim provision that would allow vehicle CO2 credits
generated by PHEVs, BEVs, and FCEVs to be used across vehicle averaging
sets or possibly across engine averaging sets as specified in 40 CFR
part 1036. If we were to adopt such an allowance, we would expect this
flexibility to begin with MY 2027 and end after the last year the new
Phase 3 standards phase-in, which as proposed is after MY 2032. We also
would expect to restrict the number of credits (i.e., the quantity of
CO2 megagrams) that could be transferred from one averaging
set to another in a given model year, considering the level of the
standards and our goal to prevent market distortions, and we request
comment on what an appropriate restriction should be. We also may set
different credits transfer cap values per averaging set that vary
across the various averaging sets. We request comment on the model
years and credit volume limitations we should consider for such an
allowance for PHEV, BEV, and FCEV generated CO2 credits. We
also request comment on extending this flexibility with some
restrictions to the PHEV, BEV, and FCEV generated CO2
credits from chassis-certified Class 2b and Class 3 vehicles. More
specifically, we request comment on allowing PHEV, BEV, and FCEV
generated CO2 credits in the chassis-certified Class 2b and
Class 3 vehicle category (under the part 86, subpart S ABT program for
MYs 2027-2032) to be used in the HD Phase 3 light heavy-duty and medium
heavy-duty vehicle averaging sets (under the part 1037 ABT program for
MYs 2027-2032) in a single direction of movement (i.e., not into the
heavy heavy-duty averaging set, and not allowing HD Phase 3 credits
from light heavy-duty and medium heavy-duty averaging sets to be
transferred into the chassis-certified Class 2b and Class 3 vehicle
category), and similarly request comment on what appropriate
restrictions to MYs and credit volume limitations should be included if
adopted.
    We also request comment on considerations of a program similar to
CARB's credit program included in their ACT rule. As briefly described
in DRIA Chapter 1.3.3, CARB would apply vehicle class-specific ``weight
class modifiers'' (i.e., credit multipliers) for credits generated by
ZEVs and near zero-emission vehicles to further incentivize adoption
electrification of the larger vehicle classes.\592\
---------------------------------------------------------------------------

    \592\ California Air Resources Board, Final Regulation Order--
Advanced Clean Trucks Regulation. Section 1963.2. Filed March 15,
2021. Available at: https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2019/act2019/fro2.pdf.
---------------------------------------------------------------------------

B. Battery Durability Monitoring and Warranty Requirements

    This section describes our proposal to adopt battery durability
monitoring requirements for BEVs and PHEVs and to clarify how warranty
applies for several advanced technologies. Our proposal is motivated by
three factors: BEV, PHEV, and FCEV are playing an increasing role in
vehicle manufacturers' compliance strategies to control GHG emissions
from HD vehicles; BEV, PHEV, and FCEV durability and reliability are
important to achieving the GHG emissions reductions projected by this
proposed program; and that GHG emissions credit calculations are based
on mileage over a vehicle's full useful life.
1. Battery and Plug-In Hybrid Electric Vehicle Durability Monitoring
Requirements
    EPA's HD vehicle GHG emission standards apply for the regulatory
useful life of the HD vehicle, consistent with CAA section 202(a)(1)
(``Such standards shall be applicable to such vehicles and engines for
their useful life''). Accordingly, EPA has historically required
manufacturers to demonstrate the durability of their emission control
systems on vehicles, including under our CAA section 206 authority.
Without durability demonstration requirements, EPA would not be able to
assess whether vehicles originally manufactured in compliance with
relevant emissions standards would remain compliant over the course of
their useful life. Recognizing that BEVs, PHEVs, and FCEVs are playing
an increasing role in manufacturers' compliance strategies, and that
emission credit calculations are based on mileage over a vehicle's
useful life, the same logic applies to BEV, PHEV, and FCEV

durability. Under 40 CFR part 1037, subpart H, credits are calculated
by determining the family emission limit (FEL) each vehicle achieves
beyond the standard and multiplying that by the production volume and a
useful life mileage attributed to each vehicle subfamily.\593\ Having a
useful life mileage figure for each vehicle subfamily is integral to
calculating the credits attributable to that vehicle, whether those
credits are used for calculating compliance through averaging, or for
banking or trading. Compliance with standards through averaging depends
on all vehicles in the regulatory subcategory, or averaging set,
achieving their certified level of emission performance throughout
their useful life. As explained in Section II and this Section III, EPA
also anticipates most if not all manufacturers would include the
averaging of credits generated by BEVs and FCEVs as part of their
compliance strategies for the proposed standards, thus this is a
particular concern given that the calculation of credits for averaging
(as well as banking and trading) depend on the battery and emission
performance being maintained for the full useful life of the vehicle.
Thus, without durability requirements applicable to such vehicles
guaranteeing certain performance over the entire useful life of the
vehicles, EPA is mindful that there would not be a guarantee that a
manufacturer's overall compliance with emission standards would
continue throughout that useful life. Similarly, EPA is concerned that
we would not have assurance that the proposed standards would achieve
the emission reductions projected by this proposed program. Therefore,
EPA is proposing new battery durability monitoring for HD BEVs and
PHEVs as a first key step towards this end, beginning with MY 2027.
---------------------------------------------------------------------------

    \593\ The useful life values for the HD vehicle standards are
located in 40 CFR 1037.105(e) and 1037.106(e).
---------------------------------------------------------------------------

    As implemented by light-duty vehicle manufacturers in current BEVs
and PHEVs, lithium-ion battery technology has been shown to be
effective and durable for use and we expect that this will also be the
case for HD BEVs and PHEVs. It is also well known that the energy
capacity of a battery will naturally degrade to some degree with time
and usage, resulting in a reduction in driving range as the vehicle
ages. The degree of this energy capacity and range reduction
effectively becomes an issue of durability if it negatively affects how
the vehicle can be used, or how many miles it is likely to be driven
during its useful life.
    Vehicle and engine manufacturers are currently required to account
for potential battery degradation in both hybrid and plug-in hybrid
vehicles that could result in an increase in CO2 emissions
(see, e.g., existing 40 CFR 1037.241(c) and 1036.241(c)).\594\ In
addition, engine manufacturers are required to demonstrate compliance
with criteria pollutant standards using fully aged emission control
components that represent expected degradation during useful life (see,
e.g., 40 CFR 1036.235(a)(2) and 1036.240). EPA is applying this well-
established approach to the durability of BEV and PHEV batteries by
proposing to require battery durability monitoring.
---------------------------------------------------------------------------

    \594\ As discussed in Section III.C.3.vi, we are proposing to
remove 40 CFR 1037.241(b), which if finalized, 40 CFR 1037.241(c)
will be moved to 40 CFR 1037.241(b).
---------------------------------------------------------------------------

    The proposed requirements are similar to the battery durability
monitor regulation framework developed by the United Nations Economic
Commission for Europe (UN ECE) and adopted in 2022 as Global Technical
Regulation (GTR) No. 22. The proposed durability monitoring regulations
would require manufacturers of BEVs and PHEVs to develop and implement
an on-board state-of-certified-energy (SOCE) monitor that can be read
by the vehicle user. We are not proposing durability monitoring
requirements for FCEVs at this time because the technology is currently
still emerging in heavy-duty vehicle applications and we are still
learning what the appropriate metric might be for quantifying FCEV
performance.
    The importance of battery durability in the context of zero-
emission and hybrid vehicles, such as BEVs and PHEVs, is well
documented and has been cited by several authorities in recent years.
In their 2021 report, the National Academies of Science (NAS)
identified battery durability as an important issue with the rise of
electrification. Among the findings outlined in that report, NAS noted
that: ``battery capacity degradation is considered a barrier for market
penetration of BEVs,'' and that ``[knowledge of] real-world battery
lifetime could have implications on R&D priorities, warranty provision,
consumer confidence and acceptance, and role of electrification in fuel
economy policy.'' NAS also noted that ``life prediction guides battery
sizing, warranty, and resale value [and repurposing and recycling]'',
and discussed at length the complexities of state of health (SOH)
estimation, life-cycle prediction, and testing for battery
degradation.\595\
---------------------------------------------------------------------------

    \595\ National Academies of Sciences, Engineering, and Medicine
2021. ``Assessment of Technologies for Improving Light-Duty Vehicle
Fuel Economy 2025-2035''. Washington, DC: The National Academies
Press. https://doi.org/10.17226/26092, p. 5-113 to 5-115.
---------------------------------------------------------------------------

    Several rulemaking bodies have also recognized the importance of
battery durability in a world with rapidly increasing numbers of zero-
emission vehicles. In 2015, the United Nations Economic Commission for
Europe began studying the need for a GTR governing battery durability
in light-duty vehicles. In 2021, it finalized United Nations GTR No.
22, ``In-Vehicle Battery Durability for Electrified Vehicles,'' \596\
which provides a regulatory structure for contracting parties to set
standards for battery durability in light-duty BEVs and PHEVs. In 2022,
the United Nations Economic Commission for Europe began studying the
need for a GTR governing battery durability in heavy-duty vehicles. EPA
representatives chaired the informal working group that developed the
GTR and worked closely with global regulatory agencies and industry
partners to complete its development in a form that could be adopted in
various regions of the world, including potentially the United States.
The European Commission and other contracting parties have also
recognized the importance of durability provisions and are working to
adopt the GTR standards in their local regulatory structures. In
addition, the California Air Resources Board, as part of the Zero-
Emission Powertrains (ZEP) Certification program, has also included
battery durability and warranty requirements as part of a suite of
customer assurance provisions designed to ensure that zero-emission
vehicles maintain similar standards for usability, useful life, and
maintenance as for ICE vehicles.\597\
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    \596\ United Nations Economic Commission for Europe, Addendum
22: United Nations Global Technical Regulation No. 22, United
Nations Global Technical Regulation on In-vehicle Battery Durability
for Electrified Vehicles, April 14, 2022. Available at: https://unece.org/sites/default/files/2022-04/ECE_TRANS_180a22e.pdf.
    \597\ California Air Resources Board. ``Attachment C: California
Standards and Test Procedures for New 2021 and Subsequent Model
Heavy-Duty Zero-Emissions Powertrains'', available at: https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2019/zepcert/froattc.pdf (last accessed September 20, 2021) (see Section D for
details of CARB rated energy capacity test procedure requirements).
---------------------------------------------------------------------------

    EPA concurs with the emerging consensus that battery durability is
an important issue. The ability of a zero-emission vehicle to achieve
the expected emission reductions during its lifetime depends in part on
the ability of the battery to maintain sufficient

driving range, capacity, power, and general operability for a period of
use comparable to that expected of a comparable ICE vehicle. Durable
and reliable electrified vehicles are therefore critical to ensuring
that projected emissions reductions are achieved by this proposed
program.
    Because vehicle manufacturers can use electrification as an
emissions control technology to comply with EPA standards as well as
generate credits for use in averaging, and also banking and trading,
EPA believes that it is appropriate to set requirements to ensure that
electrified vehicles certifying to EPA standards are durable and
capable of providing the anticipated emissions reductions, including
those that they are credited under our provisions. For example, in
order for the environmental emission reductions that are credited to
BEVs and PHEVs to be fully realized under this proposed rule's
structure, it is important that their potential to achieve a similar
mileage during their lifetime be comparable to that assumed for ICE
vehicles in the same vehicle service class. In addition, under the EPA
GHG program, BEVs and PHEVs generate credits that can be traded among
manufacturers and used to offset debits generated by vehicles using
other technologies that do not themselves meet the proposed standards.
In either case, if credits generated by zero-emission vehicles are to
offset debits created by other vehicles on an equivalent basis, it is
thus important that they should be capable of achieving a similar
mileage, and this depends, in part, on the life of the battery.
Further, if BEVs and PHEVs were less durable than comparable ICE
vehicles, this could result in increased use of ICE vehicles. In
particular, and especially for vehicles with shorter driving ranges,
loss of a large portion of the original driving range capability as the
vehicle ages could reduce the ability for zero-emission miles to
displace greater-than-zero-emission miles traveled, as well as
undermine purchaser confidence in this emerging but highly effective
technology.
    We proposed a specific durability testing requirement in the HD2027
NPRM and received comment on that proposal, including comment stating
that the requirements could result in increases in the battery capacity
beyond what was needed to meet the job of the customer. Due to these
concerns and because we are still evaluating the range of durability
metrics that could be used for quantifying HD BEV performance, EPA is
not proposing specific durability testing requirements in this rule.
However, EPA is including in this proposal a requirement for a battery
durability monitor that would be applicable to HD BEVs and PHEVs. The
battery durability monitor proposal would require manufacturers to
provide a customer-facing battery state-of-health (SOH) monitor for all
heavy-duty BEVs and PHEVs. We are proposing a new 40 CFR 1037.115(f)
that would require manufacturers to install a customer-accessible SOH
monitor which estimates, monitors, and communicates the vehicle's state
of certified energy (SOCE) as it is defined in GTR No. 22.\598\
Specifically, manufacturers would implement onboard algorithms to
estimate the current state of health of the battery, in terms of the
state of its usable battery energy (UBE) expressed as a percentage of
the original UBE when the vehicle was new.
---------------------------------------------------------------------------

    \598\ We are proposing to incorporate by reference the UN
Economic Commission for Europe document as described in Section
XI.I.
---------------------------------------------------------------------------

    For HD PHEVs, we are proposing that manufacturers would use the
existing powertrain test procedures defined in 40 CFR 1036.545 to
determine UBE.\599\ The powertrain test procedures requires that PHEVs
be tested in charge depleting and charge sustaining modes using a range
of vehicle configurations. For the determination of UBE, we are
proposing that the PHEV manufacturer would select the most
representative vehicle configuration.
---------------------------------------------------------------------------

    \599\ We are proposing to move the existing powertrain procedure
from its current location in 40 CFR 1037.550 to the heavy-duty
highway engine provisions as a new 40 CFR 1036.545. See Section
III.C.3 for more information.
---------------------------------------------------------------------------

    For HD BEVs, we are proposing that manufacturers develop their own
test procedures for determining UBE. This is due to the range of HD BEV
architectures, and the limited test facilities for conducting
powertrain testing of BEVs with e-axles. With the SOCE being a relative
measure of battery health and not absolute UBE, we believe that leaving
the test procedure up to the manufacturer will still provide a
meaningful measure of the health of the battery. We also believe that
requiring the SOH to be customer-accessible will provide assurance that
the SOH monitor is relatively accurate while also providing more time
for EPA to work with manufacturers to develop a standardized test
procedure for determining UBE for HD BEVs.
    We proposed a specified test procedure to determine UBE in the
HD2027 NPRM and received comment on that proposal, including comment
requesting changes to the proposed test procedure, which EPA considered
in developing this proposal's approach. EPA requests comment both on
this rule's proposed approach and on an alternative approach of EPA
defining a test procedure to determine UBE, such as the test procedure
EPA proposed in the HD2027 NPRM, CARB zero-emission powertrain
certification, and the test procedures being considered by the UN ECE
EVE IWG.\600\ Regarding our request for comment on the HD2027 NPRM test
procedure, we note that one of the main concerns with the test
procedure in submitted comments on the HD2027 NPRM was that commenters
stated the powertrain test cell required for powertrains with e-axles
were not widely available, and we believe there has been some
indication that this is changing; we request comment on this issue.
Regarding our request for comment on the test procedures being
considered by the UN ECE EVE IWG, we note that some of these test
procedures don't rely on chassis or powertrain dynamometers, like the
charge-discharge test procedure, and request comment on this issue.
---------------------------------------------------------------------------

    \600\ Memorandum to Docket EPA-HQ-OAR-2022-0985: ``Draft Test
Procedures for Determining UBE''. James Sanchez. February 1, 2023.
---------------------------------------------------------------------------

    Many of the organizations and authorities that have examined the
issue of battery durability, including the UN Economic Commission for
Europe, the European Commission, and the California Air Resources
Board, have recognized that monitoring driving range as an indicator of
battery durability performance (instead of or in addition to UBE) may
be an attractive option because driving range is a metric that is more
directly experienced and understood by the consumer. While we are not
proposing to require that heavy-duty BEVs and PHEVs implement a state-
of-certified-range (SOCR) monitor, we are requesting comment on whether
we should require the SOCR monitor defined in GTR No. 22.
2. Battery and Fuel Cell Electric Vehicle Component Warranty
    EPA is proposing new warranty requirements for BEV and FCEV
batteries and associated emission-related electric powertrain
components (e.g., fuel-cell stack, electric motors, and inverters) and
is proposing to clarify how existing warranty requirements apply for
PHEVs.\601\ The proposed warranty requirements build on existing
emissions control warranty provisions by establishing specific new
requirements tailored to the emission control-related role of the high-
voltage

battery and fuel-cell stack in durability and performance of BEVs and
FCEVs.
---------------------------------------------------------------------------

    \601\ Note, EPA is not reopening the existing emission-related
warranty periods for HD engines and vehicles in parts 1036 and 1037.
---------------------------------------------------------------------------

    As described in the previous section, the National Academies of
Science (NAS) in their 2021 report \602\ identified battery warranty
along with battery durability as an important issue with the rise of
electrification. The proposed vehicle warranty requirements for battery
and other emission-related electric powertrain components of HD BEVs
and FCEVs would be similar to those that EPA has the authority to
require and has historically applied to emission control-related
components for HD vehicles, including HD ICE vehicles, under EPA's HD
vehicle regulations, and would similarly implement and be under the
authority of CAA section 207.\603\ EPA believes that this practice of
ensuring a minimum level of warranty protection should be extended to
the high-voltage battery and other emission-related electric powertrain
components of HD BEV, PHEV, and FCEV for multiple reasons. Recognizing
that BEVs, PHEVs, and FCEVs are playing an increasing role in
manufacturers' compliance strategies, the high-voltage battery and the
powertrain components that depend on it are emission control devices
critical to the operation and emission performance of HD vehicles, as
they play a critical role in reducing the vehicles' emissions and
allowing BEVs and FCEVs to have zero tailpipe emissions. As explained
in Section II and this Section III, EPA also anticipates most if not
all manufacturers would include the averaging of credits generated by
BEVs and FCEVs as part of their compliance strategies for the proposed
standards, thus this is a particular concern given that the calculation
of credits for averaging (as well as banking and trading) depend on the
battery and emission performance being maintained for the full useful
life of the vehicle. Additionally, warranty provisions are a strong
complement to the proposed battery durability monitoring requirements.
We believe a component under warranty is more likely to be properly
maintained and repaired or replaced if it fails, which could help
ensure that credits granted for BEV and FCEV production volumes
represent real emission reductions achieved over the life of the
vehicle. Finally, we expect manufacturers provide warranties at the
existing 40 CFR 1037.120 levels for the BEVs they currently produce,
and the proposed requirements to certify to offering those warranty
periods and document them in the owner's manual would provide
additional assurance for owners that all BEVs have the same minimum
warranty period.\604\
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    \602\ National Academies of Sciences, Engineering, and Medicine
2021. ``Assessment of Technologies for Improving Light-Duty Vehicle
Fuel Economy 2025-2035''. Washington, DC: The National Academies
Press. https://doi.org/10.17226/26092.
    \603\ See Section I.D. of this preamble for further discussion
of EPA's authority under CAA section 207.
    \604\ The Freightliner eCascadia includes a powertrain warranty
of 5 yr/150K or 300K miles (depending on battery pack size). DDCTEC
16046--eCascadia Spec Sheet_6.0.pdf.
---------------------------------------------------------------------------

    For heavy-duty vehicles, EPA is proposing that manufacturers
identify BEV and FCEV batteries and associated electric powertrain
components as component(s) covered under emission-related warranty in
the vehicle's application for certification. We propose those
components would be covered by the existing regulations' emissions
warranty periods \605\ of 5 years or 50,000 miles for Light HDV and 5
years or 100,000 miles for Medium HDV and Heavy HDV (see proposed
revisions to 40 CFR 1037.120).
---------------------------------------------------------------------------

    \605\ EPA promulgated the existing HD vehicle warranty periods
in 40 CFR part 1037 under our CAA section 207 authority.
---------------------------------------------------------------------------

    We are not proposing new battery warranty requirements for PHEVs as
``hybrid system components'' are covered under the existing regulations
in 40 CFR part 1036 and 40 CFR part 1037. In the HD2027 rule, we
finalized as proposed that when a manufacturer's certified
configuration includes hybrid system components (e.g., batteries,
electric motors, and inverters), those components are considered
emission-related components, which would be covered under the warranty
requirements (see, e.g., 88 FR 4363, January 24, 2023). We are
proposing revisions to 40 CFR 1036.120(c) to clarify that the warranty
requirements of 40 CFR part 1036 apply to hybrid system components for
any hybrid manufacturers certifying to the part 1036 engine standards.
In 40 CFR 1037.120(c), we are also proposing a clarifying revision to
remove the sentence stating that the emission-related warranty does not
need to cover components whose failure would not increase a vehicle's
emissions of any regulated pollutant while extending the existing
statement that warranty covers other emission-related components in a
manufacturer's application for certification to specifically include
any other components whose failure would increase a vehicle's
CO2 emissions.

C. Additional Proposed Revisions to the Regulations

    In this subsection, we discuss proposed revisions to 40 CFR parts
1036, 1037, 1065.
1. Updates for Cross-Sector Issues
    This section includes proposed updates that would make the same or
similar changes in related portions of the CFR or across multiple
standard-setting parts for individual industry sectors.
i. LLC Cycle Smoothing and Accessory Load
    EPA finalized a new LLC duty-cycle in the HD2027 rule that included
a procedure for smoothing the nonidle nonmotoring points immediately
before and after idle segments within the duty-cycle.\606\ It was
brought to our attention that the smoothing procedure in 40 CFR
1036.514(c)(3) allows smoothing based on the idle accessory torque but
says nothing about how to address the contribution of curb idle
transmission torque (CITT), while 40 CFR 1065.610(d)(3)(v) through
(viii) requires smoothing based on CITT and says nothing about how to
address idle accessory torque. This could create confusion and
difficulties for common cases where CITT is required in addition to the
40 CFR 1036.514 idle accessory torques. 40 CFR 1036.514(c)(3), as
currently written, would only apply if the transmission was in neutral,
because it only allows you to account for the accessory load and not
CITT, which was not EPA's intent. To illustrate the concern, for
example, a MHD engine could have an LLC idle accessory load of 23.5
foot-pounds, which is 19 percent of a typical automatic transmission
CITT of 124 foot-pounds. To resolve this potential issue, we are
proposing to remove the smoothing instructions in 40 CFR 1036.514 and
incorporate them into 40 CFR 1065.610.
---------------------------------------------------------------------------

    \606\ 88 FR 4296 (January 24, 2023).
---------------------------------------------------------------------------

    The original intent of the 40 CFR 1065.610 duty-cycle generation
procedure was to avoid discontinuities in the reference torque values.
It was written with the assumption that idle load in neutral was zero,
meaning the vehicle or machine idle accessory load was zero. When we
introduced the required LLC idle accessory load in 40 CFR 1036.514, we
failed to realize that amendments would be needed to 40 CFR
1065.610(d)(3) to clarify how to handle the accessory load in the
denormalization process. The engine mapping section 40 CFR 1065.510 is
another area of concern as it does not address the possibility of droop
in the idle governor, which would result in different idle speeds when
the transmission is in drive versus neutral. This results in an
additional

complication as the required idle accessory torque will be different in
drive versus neutral to keep the accessory power at the level specified
in Table 1 to 40 CFR 1036.514(c)(4).
    40 CFR 1065.610(d)(4) is a related paragraph that allows a
different deviation for an optional declared minimum torque that
applies to variable- and constant-speed engines and both idle and
nonidle nonmotoring points in the cycle. Its scope of application is
wider than 40 CFR 1065.610(d)(3). 40 CFR 1065.610(d)(4) applies to all
nonidle nonmotoring points in the cycle, not just the ones immediately
preceding or following an idle segment and using it instead of (d)(3)
would not get the intended constant idle accessory power loads or the
intended smoothing.
    There is also an existing historical conflict between 40 CFR
1065.510(f)(4) and 1065.610(d)(4). 40 CFR 1065.510(f)(4) requires that
manufacturers declare non-zero idle, or minimum torques, but 40 CFR
1065.610(d)(4), permissible deviations, make their use in cycle
generation optional. This results in an inconsistency between the two
sections as 40 CFR 1065.510(f)(4) requires these parameters to be
declared, but 40 CFR 1065.610(d)(4) does not require them to be used.
    Additionally, there is a historical conflict in 40 CFR
1065.610(d)(3)(v). This paragraph, as written, includes zero percent
speed and, if the paragraph is executed in the order listed, it would
include idle points that were changed to neutral in the previous step
for neutral while stationary transmissions. This conflict would change
the torque values of those idle-in-neutral points back to the warm-
idle-in-drive torque and the speed would be left unaltered at the idle-
in-neutral speed. This was clearly not the intent of this paragraph,
yet we note that this conflict spans back all the way to when these
procedures were located in 40 CFR 86.1333-90.
    The smoothing of idle points also raises the need for smoothing of
the few occurances of non-idle points in the duty-cycles where the
vehicle may be moving, the torque converter may not be stalled, and the
warm-idle-in-drive torque may not be appropriate. This would result in
the smoothing of consecutive points around nonidle nonmotoring points
with normalized speed at or below zero percent and reference torque
from zero to the warm-idle-in-drive torque value where the reference
torque is set to the warm-idle-in-drive torque value.
    To address all of these concerns, we are proposing to make changes
to 40 CFR 1065.510, 1065.512, and 1065.610. Note, other proposed
changes to these subsections not specifically mentioned here are edits
to fix citations to relocated or new paragraphs and to improve the
clarity of the test procedures. The proposed changes to 40 CFR 1065.610
include basing the smoothing of points preceding an idle segment and
following an idle segment on the warm-idle-in-drive torque value (sum
of CITT and idle accessory torque). Exceptions to this are for manual
transmissions and for the first 24 seconds of initial idle segments for
automatic transmissions. Here the warm-idle-in-neutral torque value
(idle accessory torque) is used. We are proposing to include manual
transmissions in the required deviations for reference torque
determination for variable-speed engines in 40 CFR 1065.610(d)(3) for
completeness. The proposed amendments to 40 CFR 1065.610(d)(3) include
the option to skip these deviations for a manual transmission where
optional declared idle torque and the optional declared power are not
declared (idle torque is zero). This provides labs that have not yet
implemented these required deviations the option to not implement them
if they only need to run tests with manual transmissions with zero idle
torque. We also proposed the addition of manual transmissions to 40 CFR
1065.512(b)(2) where these required deviations in 40 CFR 1065.610 are
cited.
    We are also proposing changes to 40 CFR 1065.510(b) and (f) to
address the effect of droop in the idle governor and how to determine
idle speed when idle torque is a function of idle speed (where a
component is specified as power or CITT is specified as a function of
speed and the idle speeds need to be determined for each setpoint of
the idle governor). We are also proposing the addition of an option to
declare the warm idle speed(s) equal to the idle speed setpoint for
electronically governed variable-speed engines with an isochronous low-
speed governor. Recent updates to the mapping test procedure in 40 CFR
1065.510 regarding running the map at the minimum user-adjustable idle
speed setpoint and using the map for any test assumed that one could
declare the warm idle speed(s) equal to the idle speed setpoint for
electronically governed variable-speed engines.\607\ We are proposing
changes to make it clear that this option is allowed, which would help
simplify the mapping process.
---------------------------------------------------------------------------

    \607\ 88 FR 4296 (January 24, 2023).
---------------------------------------------------------------------------

    To resolve the conflict between 40 CFR 1065.510(f)(4) and
1065.610(d)(4), we are proposing to move the requirement to declare
torques to 40 CFR 1065.510(f)(5), which would make it optional and
consistent with 40 CFR 1065.610(d)(4).
    To resolve the conflict in 40 CFR 1065.610(c)(3)(v), which we are
proposing to reorganize as 40 CFR 1065.610(c)(3)(vii), we are proposing
to restrict the applicability of the paragraph from ``all points'' to
``all nonidle nonmotoring points.'' To address the smoothing of
consecutive nonidle nonmotoring points that immediately follow and
precede any smoothed idle points we are proposing to change their
reference torques to the warm-idle-in-drive torque value by adding a
new 40 CFR 1065.610(c)(3)(xi).
    We are also proposing revisions to 40 CFR 1036.514 to reorganize
and clarify the process for cycle denormalization of speed and torque
where accessory load is included and to add more specific transmission
shift points for greater than 200 seconds idle segments for LLC engine
and hybrid powertrain testing. Shifting the transmission to neutral
during very long idle segments is more representative of in-use
operation than leaving it in drive, so we are proposing more specific
shift points instead of a range to reduce lab-to-lab variability. The
proposal would require setting the reference speed and torque values to
the warm-idle-in-drive values for the first three seconds and the last
three seconds of the idle segment for an engine test, requiring keeping
the transmission in drive for the first 3 seconds of the idle segment,
shifting the transmission from drive to park or neutral immediately
after the third second in the idle segment, and shifting the
transmission into drive again three seconds before the end of the idle
segment.
ii. Calculating Greenhouse Gas Emission Rates
    We are proposing to revise 40 CFR 1036.550(b)(2) and 40 CFR
1054.501(b)(7) to clarify that when determining the test fuel's carbon
mass fraction, WC, the fuel properties that must be measured
are [alpha] (hydrogen) and [beta] (oxygen). These paragraphs, as
currently written, imply that you cannot use the default fuel
properties in 40 CFR 1065.655 for [alpha], [beta], [gamma] (sulfur),
and [delta] (nitrogen). The fuel property determination in 40 CFR
1065.655(e) makes it clear that if you measure fuel properties and the
default [gamma] and [delta] values for your fuel type are zero in Table
2 to 40 CFR 1065.655, you do not need to measure those properties. The
sulfur ([gamma]) and nitrogen ([delta]) content of these highly refined
gasoline and diesel fuels are not enough to affect the WC
determination

and the original intent was to not require their measurement. We are
proposing this change to ensure there is no confusion on the
requirement. We are also proposing to update 40 CFR 1036.550(b)(2) and
40 CFR 1054.501(b)(7) so that they reference 40 CFR 1065.655(e), which
includes the default fuel property table whose number had been
previously changed and we did not make the corresponding update in 40
CFR 1036.550(b)(2) and 40 CFR 1054.501(b)(7).
iii. ABT Reporting
    We are proposing to allow manufacturers to correct previously
submitted vehicle and engine GHG ABT reports, where a mathematical or
other error in the GEM-based or fleet calculations used for compliance
was discovered after the 270-day final report submission deadline. In
the Phase 1 program, EPA chose the 270-day deadline for submitting a
final GHG ABT report to coincide with existing criteria pollutant
report requirements that manufacturers follow for heavy-duty
engines.\608\ The 270-day deadline was based on our interest in
manufacturers maintaining good quality assurance/quality control (QA/
QC) processes in generating ABT reports. We continue to believe that
aligning the ABT report deadlines for criteria and GHG pollutants can
provide consistency within a manufacturer's certification and
compliance processes, but further consideration of the inherent
differences and complexities in how credits are calculated and
accounted for in the two programs led us to consider a time window
beyond 270 days for allowing corrections to the GHG report. Certifying
an engine or vehicle fleet with attribute-based features (Phase 1) or
GEM (Phase 2) involves a greater risk of error compared to EPA's engine
or vehicle test-based programs for criteria pollutants, where direct
measurement of criteria pollutant emissions at time of certification is
well established. Whether an indirect, physics-based model for
quantifying GHG emissions such as GEM, or a unique technology-,
attribute-, or engine production volume-based credit accounting system,
unintentional errors, if not detected prior to submitting the final GHG
ABT report and not realized until the accounting process for the
following model year was initiated, could negatively affect a
manufacturer's credit balance. For example, the loss of these credits
could result in a manufacturer purchasing credits or making unplanned
investments in additional technologies to make up for the credits lost
due to the report error.
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    \608\ See the HD GHG Phase 1 rule (76 FR 57284, September 15,
2011).
---------------------------------------------------------------------------

    Under the proposed revisions to 40 CFR 1036.730(f) and 1037.730(f),
EPA would consider requests to correct previously submitted MY 2021 or
later ABT reports only when notified of the error within a time period
of 24 months from the September 30 final report deadline. For requests
to correct reports for MY 2020 or earlier, we are proposing an interim
deadline of October 1, 2024 (see proposed new 40 CFR 1036.150(aa) and
1037.150(y)). We believe that corrections to ABT reports, where
justified, will have no impact on emissions compliance as the actual
performance of a manufacturer's fleet was better than what was reported
in error, and correcting the report simply adjusts the credit balance
for the model year in question to the appropriate value, such that
those credits can then be used in future model years.
    This proposed narrowly focused allowance for correcting accounting,
typographical, or GEM-based errors after a manufacturer submits the
270-day final report (see proposed revisions in 40 CFR 1037.730) is
intended to address the disproportionate financial impact of an
unintentional error in the complex modeling and accounting processes
that manufacturers use to determine compliance and credit balances for
a given model year. We are proposing a 10 percent discount to these
credit corrections to the final report, which will reduce the value of
the credits that are restored upon approval of the request. The 10
percent discount is intended to balance the goal of encouraging
accuracy in ABT reports and use of robust QA/QC processes against the
considerations for allowing manufacturers the ability to correct
unforeseen errors.
iv. Migration of 40 CFR 1037.550 to 40 CFR 1036.545
    We are proposing to migrate the powertrain test procedure in 40 CFR
1037.550 to 40 CFR 1036.545. Over the course of the development of this
test procedure, its use expanded to include certification of engines to
the criteria pollutant standards in 40 CFR part 1036 (including test
procedures in 40 CFR 1036.510, 1036.512, and 1036.514) and the
procedure can be used in place of the engine GHG testing procedures (40
CFR 1036.535 and 1036.540) for hybrid engines and hybrid powertrains.
We are proposing to migrate the test procedure to 40 CFR 1036.545 as-
is, with the following exceptions. We are proposing to add a new figure
that provides an overview of the steps involved in carrying out testing
under this section. We are proposing to clarify that if the test setup
has multiple locations where torque is measured and speed is
controlled, the manufacturer would be required to sum the measured
torque and validate that the speed control meets the requirements
defined in the proposed 40 CFR 1036.545(m). Positive cycle work,
W[cycle], would then be determined by integrating the sum of
the power measured at each location in the proposed 40 CFR
1036.545(o)(7). We are also proposing to clarify that manufacturers may
test the powertrain with a chassis dynamometer as long as they measure
speed and torque at the powertrain's output shaft or wheel hubs. We are
also proposing to replace all references to 40 CFR 1037.550 throughout
40 CFR part 1036 and part 1037 with new references to 40 CFR 1036.545.
For test setups where speed and torque are measured at multiple
locations, determine W[cycle] by integrating the sum of the power
measured at each location.
v. Median Calculation for Test Fuel Properties in 40 CFR 1036.550
    40 CFR 1036.550 currently requires the use of the median value of
measurements from multiple labs for the emission test fuel's carbon-
mass-specific net energy content and carbon mass fraction for
manufacturers to determine the corrected CO2 emission rate
using equation 40 CFR 1036.550-1. The current procedure does not
provide a method for determining the median value. We are proposing to
add a new calculation for the median value in the statistics
calculation procedures of 40 CFR 1065.602 as a new paragraph (m). We
also propose to reference the new paragraph (m) in 40 CFR
1036.550(a)(1)(i) and (a)(2)(i) for carbon-mass-specific net energy
content and carbon mass fraction, respectively. This proposed new
calculation procedure would ensure that labs are using the same method
to calculate the median value. This proposed calculation is a standard
statistical method for determining median and it would require order
ranking the data in increasing order from smallest value to largest.
    Determining the median from data sets containing an even number of
data points would require dividing the number of data points by two to
determine the rank of one of the data points whose value would be used
to determine the median. This data point would then be added to the
next highest ranked data point and the sum would be divided by two to
determine the median.

    Determining the median from data sets containing an odd number of
data points would be determined by adding one to the number of data
points and dividing the sum by two to determine the rank of the data
point whose value would be the median.
2. Updates to 40 CFR Part 1036 Heavy-Duty Highway Engine Provisions
i. Manufacturer Run Heavy Duty In-Use Testing
    We are proposing a clarification to 40 CFR 1036.405(d) regarding
the starting point for the 18-month window manufacturers have to
complete an in-use test order. Under the current provision, the clock
for the 18-month window starts after EPA has received the
manufacturer's proposed plan for recruiting, screening, and selecting
vehicles. There is concern that manufacturers could delay testing by
unnecessarily prolonging the selection process. To alleviate this
concern and keep the testing timeline within the originally intended
18-month window, we are proposing to start the clock on the 18-month
window when EPA issues the order for the manufacturer to test a
particular engine family.
    In the HD2027 final rule, we adopted a new 40 CFR 1036.420 that
includes the pass criteria for individual engines tested under the
manufacturer run in-use testing program. Table 1 to 40 CFR 1036.420
contains the accuracy margins for each criteria pollutant. We are
proposing to correct an inadvertent error in the final rule's
amendatory text for the regulations that effects the accuracy margin
for carbon monoxide (CO), which is listed in Table 1 as 0.025 g/hp-hr.
The HD2027 preamble is clear that the CO accuracy margin that we
finalized was intended to be 0.25 g/hp-hr and we are proposing to
correct Table 1 to reflect the value in the preamble.\609\
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    \609\ See HD2027 final rule preamble (88 FR 4353, January 24,
2023) (``PEMS measurement allowance values in 40 CFR 86.1912 are
0.01 g/hp-hr for HC, 0.25 g/hp-hr for CO, 0.15 g/hp-hr for
NOX, and 0.006 g/hp-hr for PM. We are maintaining the
same values for HC, CO, and PM in this rulemaking.'').
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ii. Low Load Cycle (LLC)--Cycle Statistics
    We are proposing to update 40 CFR 1036.514 to address the ability
of gaseous fueled non-hybrid engines with single point fuel injection
to pass cycle statistics to validate the LLC duty cycle. We referenced,
in error in 40 CFR 1036.514(e), the alternate cycle statistics for
gaseous fueled engines with single point fuel injection in the cycle
average fuel map section in 40 CFR 1036.540(d)(3) instead of adding LLC
specific cycle statistics in 40 CFR 1036.514(e). We are proposing the
addition of a new Table 1 in 40 CFR 1036.514(b) to provide cycle
statistics that are identical to those used by the California Air
Resources Board for the LLC and to remove the reference to 40 CFR
1036.540(d)(3) in 40 CFR 1036.514(e).
iii. Low Load Cycle (LLC)--Background Sampling
    We are proposing to remove the provision in 40 CFR 1036.514(d) that
allows periodic background sampling into the bag over the course of
multiple test intervals during the LLC because the allowance to do this
is convered in 40 CFR 1065.140(b)(2). The LLC consists of a very long
test interval and the intent of the provision was to address emission
bag sampling systems that do not have enough dynamic range to sample
background constantly over the entire duration of the LLC. 40 CFR
1065.140(b)(2) affords many flexibilities regarding the measurement of
background concentrations, including sampling over multiple test
intervals as long as it does not affect your ability to demonstrate
compliance with the applicable emission standards.
iv. U.S.-Directed Production Volume
    In the recent HD2027 rule, we amended the heavy-duty highway engine
provision in 40 CFR 1036.205 and several other sections to replace
``U.S.-directed production volume'' with the more general term
``nationwide'' where we intended manufacturers report total nationwide
production volumes, including production volumes that meet different
state standards.
    In this rule, for the reasons explained in Section III.A.1, we are
proposing a broader change to the definition of ``U.S.-directed
production volume'' for vehicles in 40 CFR 1037.801 to include
production volumes for vehicles certified to different standards. We
are proposing to adopt the same updated definition of ``U.S.-directed
production volume'' in 40 CFR 1036.801 to maintain consistency between
the engine and vehicle regulations' definitions, and are proposing to
reinstate the term ``U.S.-directed production volume'' where we
currently use ``nationwide'' in 40 CFR part 1036 to avoid having two
terms with the same meaning.\610\
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    \610\ See proposed revisions in 40 CFR 1036.205(v), 1036.250(a),
1036.405(a), 1036.605(e), 1036.725(b), and 1036.730(b).
---------------------------------------------------------------------------

    Since certain existing part 1036 requirements use the existing term
and definition to exclude production volumes certified to different
state standards (i.e., the NOX ABT program for HD engines),
we are proposing corresponding clarifying updates throughout 40 CFR
part 1036 to ensure no change to those existing exclusions in tandem
with the proposed change to the definition of the term ``U.S.-directed
production volume.'' For example, we are also proposing to update 40
CFR 1036.705(c) to establish this paragraph as the reference for
specifying the engines that are excluded from the production volume
used to calculate emission credits for HD highway engines, and we
propose that a new 40 CFR 1036.705(c)(4) be the location where we
exclude engines certified to different state emission standards for the
HD engine program.\611\ The proposed changes also include replacing
several instances of ``U.S.-directed production volume'' with a more
general ``production volume'' where the text clearly is connected to
ABT or a more specific reference to the production volume specified in
40 CFR 1036.705(c).\612\
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    \611\ The proposed revision would also move the statement to
keep records relating to those production volumes from its current
location in 40 CFR 1036.705(c) to 40 CFR 1036.735 with the other ABT
recordkeeping requirements.
    \612\ See proposed revisions in 40 CFR 1036.150(d) and (k),
1036.725(b), and 1036.730(b).
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v. Correction to NOX ABT FEL Cap
    We are proposing to amend 40 CFR 1036.104(c)(2) to remove paragraph
(iii) which corresponds to a FEL cap of 70 mg/hp-hr for MY 2031 and
later Heavy HDE that we proposed in HD2027 but did not intend to
include in the final amendatory text. In the final rule for the HD2027
rule, we did not intend to include in the final amendatory text
paragraph (iii) alongside the final FEL cap of 50 mg/hp-hr for MY 2031
and later which applies to all HD engine service classes including
Heavy HDE in paragraph (ii) described by EPA in the preamble and
supporting rule record. We are proposing to correct this error and
remove paragraph (iii). This correction will not impact the stringency
of the final NOX standards because even without correction
paragraph (ii) controls.\613\
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    \613\ EPA is not reopening the final HD2027 standards or any
other portion of that rule besides those specifically identified in
this document as subject to new proposed revisions.
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vi. Rated Power and Continuous Rated Power Coefficient of Variance in
40 CFR 1036.520
    We are proposing to correct an error and include a revision to a
provision we intended to include in HD2027, regarding determining power
and vehicle speed values for powertrain

testing. In 40 CFR 1036.520, paragraphs (h) and (i) describe how to
determine rated power and continuous rated power, respectively, from
the 5 Hz data in paragraph (g) averaged from the 100 Hz data collected
during the test. We inadvertently left out the coefficient of variance
(COV) limits of 2 percent that are needed for making the rated and
continuous rated power determinations in the HD2027 final 40 CFR
1036.520(h) and (i), which were intended to be based on the COVs
calculated in 40 CFR 1036.520(g) and we correctly included in the
HD2027 final 40 CFR 1036.520(g). We are proposing to add the 2 percent
COV limit into 40 CFR 1036.520(h) and (i). We are also proposing to
correct a paragraph reference error in 40 CFR 1036.520(h). The
paragraph references the data collected in paragraph (f)(2) of the
section. The data collection takes place in paragraph (d)(2) of the
section.
vii. Selection of Drive Axle Ratio and Tire Radius for Hybrid Engine
and Hybrid Powertrain Testing
    We are proposing to combine and modify the drive axle ratio and
tire radius selection paragraphs in 40 CFR 1036.510(b)(2)(vii) and
(viii). When testing hybrid engines and hybrid powertrains a series of
vehicle parameters must be selected. The paragraphs for selecting drive
axle ratio and tire radius are separate from each other, however the
selection of the drive axle ratio must be done in conjunction with the
tire radius as not all tire sizes are offered with a given drive axle
ratio. We are proposing to combine these paragraphs into one to
eliminate any possible confusion on the selection of these two
parameters.
    The maximum vehicle speed for SET testing of hybrid engines and
powertrains is determined based on the vehicle parameters and maximum
achievable speed for the configuration in 40 CFR 1036.510. This is not
the case for the FTP vehicle speed which reaches a maximum of 60 miles
per hour. It has been brought to our attention that there are some
vehicle configurations that cannot achieve the FTP maximum speed of 60
mile per hour. To resolve this, we are proposing changes to 40 CFR
1036.510(b)(2)(vii) instructing the manufacturer to select a
representative combination of drive axle ratio and tire size that
ensure a vehicle speed of no less than 60 miles per hour. We are also
proposing to include, as a reminder, that manufacturers may request
approval for selected drive axle ratio and tire radius consistent with
the provisions of 40 CFR 1036.210. We are also proposing to add a
provision for manufacturers to follow the provisions of 40 CFR
1066.425(b)(5) if the hybrid powertrain or hybrid engine is used
exclusively in vehicles which are not capable of reaching 60 mi/hr.
This would allow the manufacturer to seek approval of an alternate test
cycle and cycle-validation criteria for powertrains where the
representative tire radius and axle ratio do not allow the vehicle to
achieve the maximum speeds of the specified test cycle.
viii. Determining Power and Vehicle Speed Values for Powertrain Testing
    We are proposing to revise 40 CFR 1036.520(d)(2) to address the
possibility of clutch slip when performing the full load acceleration
with maximum driver demand at 6.0 percent road grade where the initial
vehicle speed is 0 mi/hr. The proposed revision would allow hybrid
engines and hybrid powertrains to modify the road grade in the first 30
seconds or increase the initial speed from 0 miles per hour to 5 miles
per hour to mitigate clutch slip. This road grade alteration or change
in initial speed should reduce the extreme force on the clutch when
accelerating at 6.0 percent grade.
    We are proposing to revise 40 CFR 1036.520(d)(3) to address
situations where the powertrain does not reach maximum power in the
highest gear 30 seconds after the grade setpoint has reached 0.0
percent. To address this we are proposing to replace the 30 second time
limit with a speed change stability limit of 0.02 m/s\2\ which would
trigger the end of the test.
ix. Request for Comment on Determining Vehicle Mass in 40 CFR 1036.510
    As engines and powertrains evolve with time, changes to vehicle
mass may be needed to maintain equivalent cycle work between the
powertrain and engine test procedures. We request comment on updating
equation 40 CFR 1036.510-1 to better reflect the relationship of
vehicle mass and rated power. With the increase in rated power of
heavy-duty engines, at least one manufacturer has raised to EPA that
there is some concern that equation 40 CFR 1036.510-1 might need
updating to better reflect the relationship of vehicle mass and rated
power. If you provide comment that the equation should be updated, we
request that you provide data to justify the change and show that the
change would provide comparable values of cycle work and power versus
time, for both the engine and powertrain versions of the duty cycles.
For the engine duty cycles (e.g., FTP and SET), the cycle work of the
duty cycle is a function of the engine torque curve. For the powertrain
duty cycles (e.g., vehicle FTP and vehicle SET), the cycle work of the
duty cycle is a function of the rated power of the powertrain.