[Federal Register Volume 86, Number 122 (Tuesday, June 29, 2021)]
[Rules and Regulations]
[Pages 34308-34590]
[FR Doc No: 2021-05306]

Vol. 86

Tuesday,

No. 122

June 29, 2021

Part II

Environmental Protection Agency

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40 CFR Parts 9, 59, 60, et al.

 Improvements for Heavy-Duty Engine and Vehicle Test Procedures, and
Other Technical Amendments; Final Rule

Federal Register / Vol. 86, No. 122 / Tuesday, June 29, 2021 / Rules
and Regulations

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 9, 59, 60, 85, 86, 88, 89, 90, 91, 92, 94, 1027, 1033,
1036, 1037, 1039, 1042, 1043, 1045, 1048, 1051, 1054, 1060, 1065,
1066, 1068, and 1074

[EPA-HQ-OAR-2019-0307; FRL-10018-52-OAR]
RIN 2060-AU62

Improvements for Heavy-Duty Engine and Vehicle Test Procedures,
and Other Technical Amendments

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is amending the test
procedures for heavy-duty engines and vehicles to improve accuracy and
reduce testing burden. EPA is also making other regulatory amendments
concerning light-duty vehicles, heavy-duty vehicles, highway
motorcycles, locomotives, marine engines, other nonroad engines and
vehicles, and stationary engines. These amendments affect the
certification procedures for exhaust emission standards and related
requirements. EPA is finalizing similar amendments for evaporative
emission standards for nonroad equipment and portable fuel containers.
The amendments increase compliance flexibility, harmonize with other
requirements, add clarity, correct errors, and streamline the
regulations. Given the nature of the amendments, they will have neither
significant environmental impacts nor significant economic impacts for
any sector.

DATES: This final rule is effective on July 29, 2021. The incorporation
by reference of certain publications listed in this regulation is
approved by the Director of the Federal Register as of July 29, 2021.

ADDRESSES: The EPA has established a docket for this action under
Docket ID No. EPA-HQ-OAR-2019-0307. All documents in the docket are
listed on the www.regulations.gov website. Although listed in the
index, some information is not publicly available, e.g., confidential
business information (CBI) or other information whose disclosure is
restricted by statute. Certain other material, such as copyrighted
material, is not placed on the internet and will be publicly available
only in hard copy form. Publicly available docket materials are
available either electronically in www.regulations.gov or in hard copy
at Air and Radiation Docket and Information Center, EPA Docket Center,
EPA/DC, EPA WJC West Building, 1301 Constitution Ave. NW, Room 3334,
Washington, DC. Note that the EPA Docket Center and Reading Room were
closed to public visitors on March 31, 2020, to reduce the risk of
transmitting COVID-19. The Docket Center staff will continue to provide
remote customer service via email, phone, and webform. The telephone
number for the Public Reading Room is<PHONE_NUMBER>, and the telephone
number for the Air Docket is<PHONE_NUMBER>. For further information on
EPA Docket Center services and the current status, go to https://www.epa.gov/dockets.

FOR FURTHER INFORMATION CONTACT: Alan Stout, Office of Transportation
and Air Quality, Assessment and Standards Division, Environmental
Protection Agency, 2000 Traverwood Drive, Ann Arbor, MI 48105;
telephone number:<PHONE_NUMBER>; email address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

Table of Contents

I. General Information
II. Heavy-Duty Highway Amendments
    A. Test Procedures and Compliance Model Changes
    B. Heavy-Duty Engine GHG Emission Standards and Flexibility
    C. Heavy-Duty Vehicle GHG Emission Standards and Flexibility
    D. Onboard Diagnostics (``OBD'')
III. Other Amendments
    A. Ethanol-Blend Test Fuels for Nonroad Spark-Ignition Engines
and Vehicles, Highway Motorcycles, and Portable Fuel Containers
    B. Removing Obsolete CFR Content
    C. Certification Fees (40 CFR Part 1027)
    D. Additional Amendments for Motor Vehicles and Motor Vehicle
Engines (40 CFR Parts 85 and 86)
    E. Additional Amendments for Locomotives (40 CFR Part 1033)
    F. Additional Amendments for Land-Based Nonroad Diesel Engines
(40 CFR Part 1039)
    G. Additional Amendments for Marine Diesel Engines (40 CFR Parts
1042 and 1043)
    H. Portable Fuel Containers (40 CFR Part 59)
    I. Evaporative Emission Standards for Nonroad Spark-Ignition
Engines and Equipment (40 CFR Part 1060)
    J. Additional Amendments for Nonroad Spark-Ignition Engines at
or Below 19 kW (40 CFR Part 1054)
    K. Amendments for General Compliance Provisions (40 CFR Part
1068)
    L. Other Requests for Comment
IV. Statutory Authority and Executive Order Reviews

I. General Information

Does this action apply to me?

    This action relates to companies that manufacture, sell, or import
into the United States new heavy-duty engines or Class 2b through 8
trucks, including combination tractors, vocational vehicles, and all
types of buses.\1\ Vocational vehicles include municipal, commercial,
and recreational vehicles. Additional amendments apply for different
manufacturers of light-duty vehicles, light-duty trucks, highway
motorcycles, stationary engines, and various types of nonroad engines,
vehicles, and equipment.\2\ Regulated categories and entities include
the following:
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    \1\ ``Heavy-duty engine'' and ``heavy-duty vehicle,'' are
defined in 40 CFR 1037.801.
    \2\ ``Light-duty vehicle'' and ``light-duty truck'' are defined
in 40 CFR 86.1803-01.

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                                                          Examples of
                                                          potentially
          NAICS codes a              NAICS titles          regulated
                                                           entities
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333618, 336111, 336112, 336120,   Other Engine        Motor vehicle
 336211, 336212, 336611, 336999.   Equipment           manufacturers and
                                   Manufacturing,      engine
                                   Automobile          manufacturers.
                                   Manufacturing,
                                   Light Truck and
                                   Utility Vehicle
                                   Manufacturing,
                                   Heavy Duty Truck
                                   Manufacturing,
                                   Motor Vehicle
                                   Body
                                   Manufacturing,
                                   Truck Trailer
                                   Manufacturing,
                                   Ship Building and
                                   Repairing, All
                                   Other
                                   Transportation
                                   Equipment
                                   Manufacturing.
811111, 811112, 811198, 423110..  General Automotive  Commercial
                                   Repair,             importers of
                                   Automotive          vehicles and
                                   Exhaust System      vehicle
                                   Repair, All Other   components.
                                   Automotive Repair
                                   and Maintenance,
                                   Automobile and
                                   Other Motor
                                   Vehicle Merchant
                                   Wholesalers.
335312, 811198..................  Motor and           Alternative fuel
                                   Generator           vehicle
                                   Manufacturing,      converters.
                                   All Other
                                   Automotive Repair
                                   and Maintenance.

326199, 332431..................  All Other Plastics  Portable fuel
                                   Product             container
                                   Manufacturing,      manufacturers.
                                   Metal Can
                                   Manufacturing.
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a North American Industry Classification System (NAICS).

    This list is not intended to be exhaustive, but rather provides a
guide for readers regarding entities likely to be regulated by this
action. If you have questions regarding the applicability of this
action to a particular entity, consult the person listed in the FOR
FURTHER INFORMATION CONTACT section.

What action is the Agency taking?

    This action amends the regulations that implement our air pollutant
emission standards for engines, vehicles and mobile equipment. The
amendments include corrections, clarifications, and flexibilities for
multiple types of vehicles, engines and equipment.
    The majority of these amendments modify existing test procedures
for heavy-duty highway engines and vehicles. These test procedure
changes improve accuracy, and in some cases, reduce test burden. They
mainly apply for measurement of greenhouse gas (GHG) pollutants
(primarily CO2), though some apply for criteria pollutants (such as
NOX), as well. See Section II.A.
    Additional heavy-duty highway amendments update EPA regulations to
enhance implementation of existing emission standards. For example,
some changes reduce the likelihood that manufacturers would need to
duplicate certification efforts to comply with EPA, Canadian, and
Californian standards. Some amendments make it easier for manufacturers
to more fully account for the emission benefits of advanced emission
control technology, which could provide them the opportunity to
generate additional emission credits. These heavy-duty highway
amendments are described in Section II.B.
    This rule includes other amendments that are generally
administrative or technical in nature and include amendments for
nonroad engines and vehicles, stationary engines, and portable fuel
containers. These amendments are described in Section III. Perhaps the
most visible administrative amendment is the elimination of hundreds of
pages of obsolete regulations, which is described in Section III.B.
    EPA published a proposed rule on May 12, 2020 (85 FR 28140). This
final rule follows from that proposal, with several adjustments that
reflect EPA's consideration of comments received. Most of the proposed
revisions from that document are addressed in this final rule. EPA is
also issuing a new notice of proposed rulemaking to supplement the
earlier proposed rule, published in the Proposed Rules section of this
issue of the Federal Register, titled ``Improvements for Heavy-Duty
Engine and Vehicle Test Procedures,'' docket number EPA-HQ-OAR-2019-
0307; FRL-10018-51-OAR. In the supplemental proposal, EPA proposes
further amendments concerning only certain specific aspects of the
Greenhouse gas Emissions Model (GEM) (see Section II of the preamble to
the supplemental proposal).
    The proposed rule included requests for comment on a wide range of
issues, including some broad areas where we were interested only in
gathering information for potential future rulemaking(s). This preamble
does not include a discussion of those comment areas where we are not
taking any action in this final rule. The ``Improvements for Heavy-Duty
Engine and Vehicle Test Procedures, and other Technical Amendments
Response to Comments'' document (``Response to Comments'') in the
docket for this rulemaking includes a summary of the input received
from commenters and EPA's responses.\3\
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    \3\ EPA, ``Improvements for Heavy-Duty Engine and Vehicle Test
Procedures, and other Technical Amendments Response to Comments,''
December 2020, Docket EPA-HQ-OAR-2019-0307, Publication Number: EPA-
420-R-20-026.
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    In addition, we have prepared a docket memo with redline text to
highlight all the changes to the regulations in the proposed rule.\4\
This is especially helpful for reviewing provisions that we are
removing from the Code of Federal Regulations. For obsolete provisions
we are removing, see especially 40 CFR 1027.105, 1033.150, 1042.145,
1045.145, 1048.145, 1051.145, 1054.145, and 1054.625. We prepared
additional docket memos to show regulatory changes after the proposed
rule.\5\
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    \4\ ``Redline Document Showing Proposed Changes to Regulatory
Text in the Heavy-Duty Greenhouse Gas Amendments'', EPA memorandum
from Alan Stout to Docket EPA-HQ-OAR-2019-0307, March 2020.
    \5\ ``Redline Version of EPA's Final Regulatory Amendments for
Heavy-Duty Greenhouse Gas Standards and other Programs'', EPA
memorandum from Alan Stout to Docket EPA-HQ-OAR-2019-0307, December
9, 2020.
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What are the incremental costs and benefits of this action?

    This action is limited in scope and does not include amendments
that have significant economic or environmental impacts. EPA has
therefore not estimated the potential costs or benefits of this final
rule (and we did not for the proposal).

II. Heavy-Duty Highway Amendments

A. Test Procedures and Compliance Model Changes

    Since the promulgation of the Phase 2 regulations, manufacturers
have been revising their internal test procedures to ensure they will
be able to comply with the new requirements that begin in model year
2021. In doing so, they have identified several areas in which the test
procedure regulations could be improved (in terms of overall accuracy,
repeatability and clarity) without changing the effective stringency of
the standards.
    EPA is making numerous changes to the test procedure regulations to
address manufacturers' concerns and other issues we have identified.
These changes are described below. The list includes numerous editorial
changes that simply correct typographical/formatting errors or revise
the text to improve clarity. Although these amendments are being made
primarily in the context of heavy-duty engines and vehicles, the
amendments to part 1065 will also apply to nonroad engines, and the
amendments to part 1066 will also apply to light-duty vehicles. Since
these amendments are mostly editorial or adding flexibility, they will
not adversely impact these other sectors.
1. 40 CFR Part 1036 Test Procedures
    EPA proposed several updates to the testing and measurement
provisions of part 1036, subpart F, and appendices of part 1036 related
to how to measure emissions from heavy-duty engines and requested
comment on general improvements to the engine test procedures and
compliance provisions (85 FR 28141). This section presents the changes
we are adopting to engine test procedures after consideration of
comments received. Additional details on some of these and other engine
testing and measurement amendments or clarifications requested by

commenters and our responses are available in Chapter 2 of our Response
to Comments. Amendments to other subparts of part 1036 (i.e.,
amendments not directly related to test procedures) are discussed in
Section II.B.
    These updates are primarily for the purposes of adding flexibility
and reducing variability in test results. Additional information that
led to and supports these changes arose from a test program at
Southwest Research Institute (SwRI) that was jointly funded by EPA and
the Truck and Engine Manufacturers Association (EMA).\6\
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    \6\ Sharp, Christopher A., et al., ``Measurement Variability
Assessment of the GHG Phase 2 Fuel Mapping Procedure'', Final
Report, Southwest Research Institute, December 2019.
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    We are generally finalizing revisions as proposed; however, some
revisions include further changes and clarifications after
consideration of public comments to better ensure clarity, accuracy and
consistency with the intent of the proposed rule.
     Section 1036.501(g)--Providing a new paragraph (g) to
specify duty cycles for testing model year (MY) 2016-2020 engines,
including additional clarifications to the proposed amendment to refer
to the steady-state duty cycle as the Supplemental Emission Test
(``SET'') rather than the Ramped Modal Cycle (``RMC'') to avoid
confusion as steady-state cycles are run as RMCs in many standard
setting parts, and to change a reference for the Federal Test Procedure
(``FTP'') duty cycle from appendix B of 40 CFR part 1036 to 40 CFR
1036.510 because 40 CFR 1036.510 gives an overview of the duty cycle
and provides the reference to appendix B of 40 CFR part 1036.
     Section 1036.501(h)--Renumbering existing paragraph (g)
concerning testing of MY 2021 and later engines as new paragraph (h),
modifying paragraph (h)(1) to address restarting the engine during
dynamometer testing for engines with stop-start technologies, and
adding paragraph (h)(3) (shown as (h)(2) in the proposed rule) to
cross-reference transient test cycle specifications, including
additional clarifications in final paragraph (h)(2) to refer to the
Supplemental Emission Test cycle to avoid confusion as steady-state
cycles are run as RMCs in many standard setting parts and in paragraph
(h)(2)(ii) that weighting factors for the Supplemental Emission Test
are to be applied to CO2 to calculate the composite emission result.
     Section 1036.503--Migrating Sec.  1036.510 to new Sec.
1036.503, renumbering existing paragraph (d) as new paragraph (c),
updating paragraphs (b) and (c)(1) through (3) and adding paragraphs
(c)(4) and (5) and (d), including provisions to specify that the engine
manufacturer must provide idle speed and torque to the vehicle
manufacturer and to provide additional direction on handling data
points for a low speed governor where the governor is active. We
further modified proposed paragraph (b) to denote that there are four
methods to generate fuel maps with the addition of the hybrid
powertrain and hybrid engine testing procedures and to more clearly
explain which method(s) apply to which application, paragraphs (b)(1)
and (2) to add more specificity to which referenced paragraphs in Sec.
1036.535 are applicable, paragraph (b)(3) to clarify that the option in
Sec.  1037.520(d)(2) is only allowed for hybrid powertrain testing and
not powertrain testing in general, and added paragraph (b)(4) to
include a method to perform hybrid engine testing. We also further
updated paragraph (c)(1) to clarify how to measure torque curve for
engines that have a rechargeable energy storage system (RESS) and for
those that don't.
     Section 1036.505--Adding paragraph (b) to give direction
on both engine and powertrain testing and modifying Table 1 to include
vehicle speed and grade parameters to facilitate the hybrid powertrain
testing option. We further modified the proposed language in this
section by: Adding a new paragraph (b)(2)(v) to calculate curb mass for
hybrid powertrain testing as this calculation is needed to determine
the linear equivalent mass of rotational moment of inertias in
clarified paragraph (b)(2)(vi), adding reference speed determination
requirements for powertrain testing in paragraphs (c)(2)(i) and (ii) to
address underspeed conditions in the hybrid powertrain SET testing,
including a removal of default A, B, and C SET speeds and calculation
of the A and B speeds based on C speed, modifying Table 1 further to
include vehicle speed and grade parameters to facilitate the hybrid
powertrain testing option so the road grade equation is now vehicle
speed-dependent to address vehicle underspeed concerns corresponding to
the determination and use of vehicle C speed, and replacing ramped
modal cycle with supplemental emission test for the reason discussed in
the first bullet of this subsection of the preamble.
     Section 1036.510--Providing a new section regarding
transient testing of engines and hybrids to facilitate hybrid
certification for both GHG and criteria pollutants.
     Section 1036.525(a)--Adding a clarification in the final
rule that the hybrid engine testing procedure in this section applies
only for model year 2014 to 2020 hybrid engines since the new hybrid
powertrain and hybrid engine test procedure being adopted in this
rulemaking will apply for model year 2021 and later engines.
     Section 1036.525(d)(4)(i)--Editorial revisions to equation
and the addition of example calculations.
     Section 1036.527--Adding a section to provide a means to
determine powertrain systems rated power and continuous rated power, to
facilitate the hybrid and conventional powertrain testing options. This
test procedure is applicable for powertrain testing defined in 40 CFR
1037.550 for both the engine and vehicle standards. We further modified
the proposed language, including modifying how the test is carried out
by reducing the number of test intervals from 9 to 1, paragraph (e) to
address the determination of Psys for speed and torque measurements at
different locations, with new paragraphs (g) and (h) to provide an
improved method for determining continuous rated power and vehicle C
speed, and addressed typographical errors.
     Section 1036.530(a), (b)(1)(i) and (ii), and (b)(2)(i) and
(ii)--Updating carbon mass fraction determination to allow analysis by
a single lab only to facilitate on-line analysis from pipeline supplied
natural gas and adding the ASTM International method for determination
of test fuel mass-specific energy content for natural gas. We have
further modified the proposed language by clarifying in paragraph (a)
that the infrequent regeneration adjustment factors (IRAF) are applied
to CO2 emission results for all duty-cycles, not just cycle average
engine fuel map results, and updating paragraph (b) to require test
fuel mass-specific energy content and carbon mass fraction to be
analyzed by at least three different labs and the median of all the
results to be used in the calculation. We are also adding a
recommendation that you screen your results to determine if additional
observations are needed by performing an outlier test and provided
critical values for this check. The critical values were determined as
1.27 times the method reproducibility R. The R value used for fuel
mass-specific energy content is 0.234 which is the published R value
for ASTM D4809 and the R value used for carbon mass fraction is 1.23,
which was based on analysis of the fuel survey data for ASTM D5291 that
was used in the Fuel Mapping Variability Study at SwRI.
     Section 1036.530 Table 1--Updating footnote format in
table.

     Section 1036.535--Generally updating to improve the engine
fuel mapping test procedures based on the jointly funded EPA-EMA test
program. The overall result of these updates is to reduce the
variability of the emission test results to reduce lab-to-lab
variability. We further modified the proposed language by adding
paragraph (h) to describe how EPA will determine the official fuel
consumption rate during a confirmatory test, based on carbon balance
results, updating paragraph (b)(7)(iv) to require validation of test
intervals that were complete prior to a lab equipment or engine
malfunction, updating the variable description for wCmeas in
paragraph (b)(8) to make clear that you may not account for the
contribution to [alpha], [beta], [gamma], and [delta] of diesel exhaust
fluid or other non-fuel fluids injected into the exhaust, and
clarifying regulatory text and correcting paragraph references.
     Section 1036.540--Generally updating to improve the cycle-
average engine fuel mapping test procedure as a result of the jointly
funded EPA-EMA test program at SwRI. The overall result of these
updates is to reduce the variability of the emission test results to
reduce lab-to-lab variability. We further modified the proposed
language in a few ways by adding paragraph (b)(4) to address the
ability of gaseous fueled engines with single point fuel injection to
pass alternate cycle statistics to validate the transient duty cycle in
40 CFR part 1037, appendix I, by adding paragraph (e)(2) to describe
how EPA will determine the official fuel consumption rate during a
confirmatory test, based on carbon balance results, by deleting the
requirement for EPA to use an average of indirect measurement of fuel
flow with dilute sampling and direct sampling for fuel mapping as EPA
will now perform the carbon balance verification in 40 CFR 1065.543,
and by generally adding some clarifying text.
     Section 1036.543--Adding a section to address carbon
balance error verification. This is a result of the jointly funded EPA-
EMA test program. The overall result of these updates is to reduce the
variability of the emission test results to reduce lab-to-lab
measurement variability.
     Section 1036.801--Adding a definition for hybrid engine to
correspond with the addition of the hybrid powertrain test procedures
to part 1036. Modifying the definition from the proposed language to
provide examples of hybrid engine architecture and hybrid energy
storage systems.
     Section 1036.801--Adding definitions for ``hybrid
powertrain'' and ``mild hybrid'' in the final rule. These definitions
are needed as a result of adding hybrid powertrain test procedures to
part 1036, subpart F, including mild hybrid certification where engine
testing can use a transmission model. The definitions make clear what
hybrid architectures are covered by each of these terms.
     Section 1036.801--Updating definition of ``steady-state''
to clarify that fuel map and idle tests are steady-state tests.
     Section 1036.805(b)--Updating quantity and quantity
descriptions, including some changes to those proposed to ensure
consistency throughout the part.
     Section 1036.805(c) and (d)--Updating table introductory
sentence and column headings in the table to be consistent with format
in other parts.
     Section 1036.805(e)--Updating acronyms and abbreviations,
including some changes to those proposed to ensure that the table
contained all that were used throughout the part.
     Section 1036.805(f)--Adding gravitational constant,
including an updated value for the gravitational constant based on
consideration of comments received on the proposal.
     Part 1036, appendix A--Adding a new appendix A to provide
a historic summary of previous emission standards which EPA originally
adopted under 40 CFR part 85 or 86, that apply to compression-ignition
engines produced before model year 2007 and to spark-ignition engines
produced before model year 2008.
     Part 1036, appendix B(a)--Adding a new paragraph (a) of
appendix B to specify transient duty cycles for the engine and
powertrain testing described in Sec.  1036.510.
     Part 1036, appendix B(b)--Adding a new paragraph (b) of
appendix B to migrate over the spark-ignition FTP duty cycle from part
86, which includes no changes to the FTP duty-cycle weighting factors
or the duty-cycle speed values from the current heavy duty diesel
engine (HDDE) FTP duty cycle that applies to criteria pollutant
regulation in paragraph (f)(1) of 40 CFR part 86, appendix I, a change
to the negative torque values, and migration of the HDDE FTP drive
schedule to paragraph (b) of 40 CFR part 1036, appendix B, to add
vehicle speed and road grade to the duty-cycle to facilitate powertrain
testing for compliance with the HD Phase 2 GHG standards. The change to
negative torque values is the removal of and footnoting of the negative
normalized vehicle torque values over the HDDE FTP duty-cycle. The
footnote denotes that these torque points are controlled using closed
throttle motoring, which would then match how negative torque values
have been controlled in the HDDE FTP. This change also reflects the way
that engine manufacturers are already controlling to negative torque
from spark-ignition engines and harmonizes the methodology with the
HDDE FTP, with no effect on stringency. The spark-ignition engine
denormalization equation in 40 CFR 86.1333(a)(1)(ii) includes division
by 100 which equates it to the denormalization equation in 40 CFR
1065.610(c)(1) (Equation 1065.610-3), with no effect on stringency. We
have further modified the proposed language in this section by updating
the road-grade coefficients to reflect additional refinement of the
road-grade development process that is described in Section II.A.7 of
the preamble.
     Part 1036, appendix B(c)--Adding a new paragraph (c) of 40
CFR part 1036, appendix B, to migrate over the compression-ignition FTP
duty cycle from part 86, which includes no changes to the HDDE FTP
weighting factors or the duty-cycle torque values from the duty cycle
that currently apply to criteria pollutant regulations in paragraph
(f)(2) of 40 CFR part 86, appendix I, a change to the speed values that
does not influence the ultimate denormalized speed, and migration of
the HDDE FTP drive schedule to add vehicle speed and road grade to the
duty-cycle to facilitate powertrain testing for compliance with the
Phase 2 GHG standards. The change to speed values takes the normalized
vehicle speeds over the HDDE FTP duty-cycle and multiplies them by 100/
112 to eliminate the need to divide by 112 in the diesel engine
denormalization equation in 40 CFR 86.1333(a)(1)(i). This eliminates
the need for use of a denormalization equation and allows commonization
(between compression- and spark-ignition engines) of the use of the
denormalization equation in 40 CFR 1065.610(c)(1) (Equation 1065.610-
3), with no effect on stringency. We have further modified the proposed
language in this section by updating the road grade coefficients to
reflect additional refinement of the road grade development process
that is described in Section II.A.7 of the preamble.
2. 40 CFR Part 1037 Test Procedures
    EPA proposed several updates to the testing and measurement
provisions of 1037 subpart F related to how to measure emissions from
heavy-duty vehicles and determine certain GEM inputs and requested
comment on general improvements to the vehicle test procedures and
compliance provisions (see 85 FR 28142). This section presents

the changes we are adopting to vehicle test procedures after
consideration of comments received. Chapter 2 of our Response to
Comments includes additional details on some of these amendments, as
well as other testing and measurement amendments or clarifications
requested by commenters and our responses. Amendments for other
subparts of part 1037 (i.e., amendments not directly related to test
procedures) are discussed in Section II.C.15. We are generally
finalizing revisions as proposed; however, some revisions include
further changes and clarifications after consideration of public
comments to better ensure clarity, accuracy and consistency with the
intent of the proposed rule.
     Section 1037.501(i)--Adding paragraph (i) to note that the
declared GEM inputs for fuel maps and aerodynamic drag area typically
includes compliance margins to account for testing variability; for
other measured GEM inputs, the declared values are typically the
measured values without adjustment.
     Section 1037.510(a)(2)--Updating the powertrain testing
procedure used to generate GEM inputs to reduce the variability of the
emission test results and to improve lab-to-lab measurement variability
consistent with the results from the jointly funded EPA-EMA test
program at SwRI.
     Section 1037.510 Table 1--Updating footnote format in
table.
     Section 1037.510(d)--Clarifying the reference to
specifically refer to paragraphs ``(b) and (c)'' of Sec.  1066.425.
     Section 1037.510(e)--Clarifying to specifically state that
the use of cruise control is optional.
     Section 1037.515 Table 2--Correcting a table entry to
include the proper mathematical symbols in response to a comment by the
California Air Resources Board (CARB).
     Section 1037.515 Table 3--Updating footnote format in
table.
     Section 1037.520--Updating a reference to reflect the
updated version of the GEM model released in conjunction with this
rulemaking.
     Section 1037.520(b)(3)(i)--Adding a reference to Sec.
1037.525 to clarify how to determine a high-roof tractor's aerodynamic
test results in response to a comment request from EMA.
     Section 1037.520 Table 4--Correcting a typographical error
in a tractor aerodynamic test result CdA value for Bin III
low-roof cabs.
     Section 1037.520 Table 5--Correcting a typographical error
in a tractor input CdA value for Bin II High-Roof Sleeper
Cabs.
     Section 1037.520(c)--Adding a clarification to Sec.
1037.520(c)(6) and updating the GEM user guide to clarify that a time-
and load-weighted average be applied to calculate the rolling
resistance of tires installed on liftable axles, given that tires on
liftable axles are only in contact with the ground when the axle is in
a deployed state in response to a comment from EMA.
     Section 1037.520 Table 6--Updating footnote format in
table.
     Section 1037.520 Table 7--Clarifying that the nonwheel-
related weight reductions from alternative materials applied to
tractors for non-suspension crossmembers is for a set of three.
     Section 1037.520 Table 8--Adding two footnotes to address
how weight reduction values apply and what values to use for medium
heavy-duty vehicles (Medium HDV) with 6x4 or 6x2 axle configurations.
Also see Section II.C.3.
     Section 1037.520(f)--Updating a cross-reference.
     Section 1037.520(g)--Adding and clarifying which vehicle
characteristics need to be reported, including providing a better
description in paragraph (g)(2)(iv) of the 6x4D drive axle
configuration as well as qualifying conditions for use of this
configuration. After considering comments received by Allison and Ford,
we are further modifying this paragraph by noting in paragraph (g)(1),
and similarly in Sec.  1037.231(b)(7), that available forward gear
means the vehicle has the hardware and software to allow operation in
those gears and providing in paragraph (g)(2)(i) that the 4x2 drive
axle configuration is available to vehicles with two drive axles where
one of them is disconnectable and designed to be connected only when
used in off road or slippery road conditions and based on a qualifying
condition.
     Section 1037.520(h)--Adding provisions to determine
appropriate vehicle idle speed based on vehicle service class and
applicable engine standard, including in the final rule a clarification
that the 750 rpm value applies to Light HDV and Medium HDV vocational
vehicles and providing an idle speed value of 700 rpm for Medium HDV
tractors, corresponding to the idle speed used to set the standards for
those vehicles, in response to a comment from EMA. These final
provisions incorporated in a new table format, with an updated footnote
noting the appropriate adjustable idle speed to choose if an engine
cannot operate at the idle speed specified in the table.
     Section 1037.520(i)--Adding that a manufacturer can
characterize a torque converter, in addition to an axle and
transmission, which will improve the accuracy of GEM by replacing
default GEM values with more representative values.
     Section 1037.520(j)(2)--Removing a superfluous reference
to tractors in paragraph (j)(2)(i); clarifying paragraph (j)(2)(iii) in
response to a comment from EMA to indicate how to demonstrate the
performance of high-efficiency air conditioning compressors.
     Section 1037.520(j)(4) Table 9--Including additional
combinations of idle reduction technologies and their corresponding GEM
input values.
     Section 1037.520(j)(5)--Correcting typographical error
that transposed school and coach bus GEM inputs.
     Section 1037.525--See Section II.A.6 for a description of
comments and final revisions to this section.
     Section 1037.528--Replacing the phrase ``primary
procedures'' with ``reference method'' for tractors and ``alternate
procedures'' with ``an alternate method'' for trailers to maintain
consistency with terminology used throughout subpart F.
     Section 1037.528(c)--Clarifying that the conditions listed
in paragraph (c) apply to each run separately.
     Section 1037.528(e)--Removing requirement that the
anemometer be ``electro-mechanical'' to rely instead on the
specifications outlined in the existing reference to SAE J1263.
     Section 1037.528(g)(3)--Clarifying that the measured air
direction correction is ``from all the high-speed segments.''
     Section 1037.528(h)(3)(i)--Clarifying how to account for
measurement noise near the 2 mile/hour boundary.
     Section 1037.528(h)(6)--Adding a definition of
DFTRR to the introduction of paragraph (h)(6) to clarify the
required calculations; relocating the proposed direction to determine
the difference in rolling resistance between 65 mph and 15 mph for each
tire and to use good engineering judgment when measuring multiple
results to paragraph (v) with the corresponding DFTRR
equation.
     Section 1037.528--Updating equation 11 and the
corresponding example to include the appropriate variable to represent
inflation pressure variable with a lowercase ``p''.
     Section 1037.528--Updating equation 13 to include
appropriate units for the ambient temperature variable.
     Section 1037.528--Updating equation 14 to replace a ``+''
with a ``-'' to correct a typographical error.
     Section 1037.528(h)(12)--Updating a variable name to
provide consistency with updates made to Sec.  1037.525.

     Section 1037.532--See Section II.A.6 for a description of
comments and final revisions to this section.
     Section 1037.534--Updating equation 6 and the
corresponding example to include the appropriate variable to represent
increments by italicizing the ``i''.
     Section 1037.540--Updating equations 1, 2, and 3 to
include the appropriate variable to represent increments by italicizing
the ``i''.
     Section 1037.540 Table 1--Updating footnote format in
table; updating a parameter name.
     Section 1037.540(e) and (f)--Removing incorrect cross-
reference to Sec.  1036.540(d)(5); adding reference to definition of
standard payload.
     Section 1037.550--Updating the powertrain testing
procedure to reduce the variability of the emission test results and
improve lab-to-lab variability consistent with the results from the
jointly funded EPA-EMA test program at SwRI. We further modified this
section to include an introduction paragraph and reorganized paragraphs
with new paragraph headings to improve navigation. Additional
modifications to this section in the final rule include clarifying in
paragraph (a)(3) options available to create the models for powertrain
testing, adding clarifications in several paragraphs to address where
the torque and speed are measured based on powertrain setup, adding a
new paragraph (f)(2) to address testing of hybrid engines using the
transmission model in GEM, modifying paragraph (b) to give additional
clarification on how to set the engine idle speed, adding a new
paragraph (f)(2) for testing with torque measurement at the engine's
crankshaft and how to calculate the transmission output rotational
speed, updating paragraph (j)(2) to describe how to transition between
duty cycles if the preceding cycle ends at 0 mi/hr, adding a new
paragraph (j)(5) to describe how to warm up the powertrain, adding a
new paragraph (o)(2) to describe how EPA will determine the official
fuel consumption rate during a confirmatory test, based on carbon
balance results, and updating paragraphs (o)(3) through (5) to better
define when a vehicle is not moving, moving the text from paragraph (p)
into paragraph (o)(1), moving the text of paragraph (q) to the general
provisions as a new paragraph (a)(5). The final rule includes
additional revisions regulatory text to provide greater clarity and
more carefully describe the procedures.
     Section 1037.551(b)--Updating a reference.
     Section 1037.555--Updating equations 1 and 3 to include
the appropriate variable to represent increments by italicizing the
``i''; updating a parameter name in Table 1 for consistency in this
part.
     Section 1037.560--Clarifying that it is optional to drain
gear oil after the break in period is complete, providing the option of
an alternative temperature range to provide international harmonization
of testing, editing the Ploss (i.e., power loss) variable
description to improve the readability, and adding paragraph (h) to
describe how to derive axle power loss maps for untested configurations
in a family. We further modified this section in the final rule by
clarifying in paragraph (a) that for tandem axles that can be
disconnected, testing both single-drive and tandem axle configurations
includes 4x4 axles where one of the axles is disconnectable; adding a
new paragraph (h)(4) and modifying (h)(5) to address comments regarding
results when multiple gear ratios are tested and one of the points is
above the linear regression line, which could cause the regression
values to understate power loss, to clarify that you must add the
difference between the datapoint and the regression line to the
intercept values of the regression line to mitigate this effect; and
updating the use of the term ``axle'' to ``axle assembly'' throughout
the section to provide consistency.
     Section 1037.565--Providing an option to map additional
test points to provide international harmonization of testing,
including edits to improve the readability of the Ploss
variable description, and adding paragraph (d)(4) and clarifying
paragraphs (e)(6) and (7) regarding the gears the transmission is
tested in. After considering comments from Allison, EMA, and Eaton
Cummins Automated Transmission Technologies, we further modified this
section by: Updating the torque transducer accuracy requirements in
paragraph (c) to link it to the highest transmission input torque or
respective output torque; adding additional detail in paragraph (d)(1)
on the maximum transmission input shaft speed to test, specifically the
maximum rated input shaft speed of the transmission or the maximum test
speed of the highest speed engine paired with the transmission. and the
minimum idle speed to test, specifically 600 r/min or the minimum idle
speed of the engines paired with the transmission; modifying paragraph
(d)(2) in response to comments regarding transmission torque setpoints
to optionally allow, in higher gear ratios where output torque may
exceed dynamometer torque limits, the use of good engineering judgment
to measure loaded test points at input torque values lower than
specified (in this case GEM may need to extrapolate values outside of
the measured map, however extrapolation time may not exceed 10% for any
given cycle and you must describe in the application for certification
how you adjusted the torque setpoints); modifying paragraph (e)(9) to
allow the use of the maximum loss value achieved from all the repeats
of the test points to calculate transmission efficiency if you cannot
meet the repeatability requirements; adding a new paragraph (e)(11)
clarifying what needs to be calculated for each point in the test
matrix; modifying paragraph (g) and moving part of existing paragraph
(g) to a new paragraph (h) to avoid a potentially never-ending cycle of
repeat testing if repeatability requirements are not achieved. If the
repeatability requirement is not met after conducting three or more
tests, the maximum loss value may be used to calculate transmission
efficiency, or you can continue to test until you pass the
repeatability requirement.
     Section 1037.570--Adding new section to characterize
torque converters to allow a manufacturer to determine their own torque
converter capacity factor instead of using the default value provided
in GEM. The option to use the default value remains. The final rule
includes updated regulatory text to provide greater clarity and more
carefully describe the procedures. Final revisions do not change the
proposed procedure; instead, they include updates to revise the section
heading, reorganize paragraphs, ensure consistent terminology, and
clarify measurement points.
3. 40 CFR Part 1065 Test Procedures
    EPA proposed several updates to the testing and measurement
provisions of 40 CFR part 1065 related to how to measure emissions from
heavy-duty highway and nonroad engines and requested comment on general
improvements to the engine test procedures and compliance provisions
(see 85 FR 28142). This section presents the changes we are adopting
primarily to reduce variability associated with engine test procedures
after consideration of comments received. Chapter 2 of our Response to
Comments includes additional details on some of these amendments, as
well as other testing and measurement amendments or clarifications
requested by commenters and our responses.

    The regulations in part 1065 rely heavily on acronyms and
abbreviations (see 40 CFR 1065.1005 for a complete list). Acronyms used
here are summarized in Table II-1:

  Table II-1--Summary of Acronyms Related to 40 CFR Part 1065 That Are
                     Referenced in These Amendments
------------------------------------------------------------------------

------------------------------------------------------------------------
ASTM.............................  American Society for Testing and
                                    Materials
CVS..............................  Constant-Volume Sampler
DEF..............................  Diesel Exhaust Fluid
ECM..............................  Electronic Control Module
NIST.............................  National Institute for Standards and
                                    Technology
NMC FID..........................  Nonmethane Cutter with a Flame
                                    Ionization Detector
NMHC.............................  Nonmethane Hydrocarbon
NMNEHC...........................  Nonmethane Nonethane Hydrocarbon
RMC..............................  Ramped Modal Cycle
THC FID..........................  Flame Ionization Detector for Total
                                    Hydrocarbons
------------------------------------------------------------------------

    We are generally finalizing revisions as proposed; however, some
revisions include further changes and clarifications after
consideration of public comments to better ensure clarity, accuracy and
consistency with the intent of the proposed rule.
     Section 1065.1(g)--Updating the test procedure Uniform
Resource Locator (URL).
     Section 1065.2(c)--Correcting a typographical error by
replacing ``engines'' with ``engine''.
     Section 1065.130(e)--Revising to denote that a carbon
balance procedure should be performed to verify exhaust system
integrity in place of a chemical balance procedure.
     Section 1065.140(c)(6)(i)--Correcting a typographical
error by replacing ``dew point'' with ``dewpoint''.
     Section 1065.140(e)(2)--Clarifying how to determine the
minimum dilution ratio for discrete mode testing.
     Section 1065.145(e)(3)(i)--Removing the requirement to
heat a sample pump if it is located upstream of a NOX
converter or chiller and replacing it with a requirement to design the
sample system to prevent aqueous condensation to better address
concerns with the loss of NO2 in the sampling system where
methods other than heating the pump can be used to prevent
condensation.
     Section 1065.170--Updating to allow you to stop sampling
during hybrid tests when the engine is off and allow exclusion of the
sampling off portions of the test from the proportional sampling
verification, and adding a provision for hybrid testing to allow
supplemental dilution air to be added to the bag in the event that
sampled volumes are too low for emission analysis.
     Section 1065.205 introductory and Table 1--Revising and
adding recommended performance specifications for fuel and DEF mass
scales and flow meters to reduce fuel flow measurement error.
     Section 1065.220(a) introductory and (a)(3)--Updating the
application of fuel flow meters to more correctly reflect how and what
they are used for in part 1065.
     Section 1065.225(a) introductory and (a)(3)--Updating the
application of intake flow meters to more correctly reflect how and
what they are used for in part 1065.
     Section 1065.247--Revising to add acronym for DEF
throughout in place of ``diesel exhaust fluid'' and in paragraph (c)(2)
account for any fluid that bypasses or returns from the dosing unit to
the fluid storage tank.
     Section 1065.260(e)--Adding the word ``some'' as a
qualifier for gaseous fueled engines with respect to using the additive
method for NMHC determination.
     Section 1065.266(a) and (b)--Adding flexible fuel engines
under the allowance to use Fourier transform infrared (FTIR) and
updating the URL for EPA method 320.
     Section 1065.275--Deleting the URL and replacing with a
reference to Sec.  1065.266(b).
     Section 1065.280(a)--Updating to reflect that there is no
method in Sec.  1065.650 for determining oxygen balance and that you
may develop a method using good engineering judgment.
     Section 1065.303 Table 1--Updating the formatting and
entries in the summary table to reflect revised requirements, including
adding fuel mass scale and DEF mass scale to the linearity
verifications in Sec.  1065.307, updating the verification in Sec.
1065.341 to replace ``batch sampler'' with ``PFD'' as partial-flow
dilution (PFD) is the preferred language, updating one footnote to
include the PFD flow verification (propane check) as not being required
for measurement systems that are verified by a carbon balance error
verification as described in Sec.  1065.341(h) and adding two footnotes
excluding linearity verification for DEF flow if the ECM is used and
for intake air, dilution air, diluted exhaust, batch sampler, and raw
exhaust flow rates flow if propane checks or carbon balance is
performed. These are not new exemptions; they are simply relocated to
the footnotes.
     Section 1065.307(c)(13)--Adding a clarification that the
calculation used for arithmetic mean determination in Sec.  1065.602
uses a floating intercept.
     Section 1065.307(d)(4)--Revising to include DEF mass flow
rate and to correct or account for buoyancy effects and flow
disturbances to improve the flow measurement.
     Section 1065.307(d)(6)(i)--Revising to state that the span
gas can only contain one single constituent in balance air (or
N2 if using a gas analyzer) as the reference signal for
linearity determination.
     Section 1065.307(d)(7)--Revising to state that the span
gas can only contain one single constituent in balance air (or
N2 if using a gas analyzer) as the reference signal for
linearity determination.
     Section 1065.307(d)(9)--Expanding the paragraph to include
fuel and DEF mass scales and requirements for performing the linearity
verification on these scales.
     Section 1065.307(e)(3)(i) and (ii)--Editing to clarify the
intent of the requirements.
     Section 1065.307(e)(3)(iii) through (xi)--Defining maximum
flowrate for fuel and DEF mass scales and flow meters as well as
maximum molar flowrate for intake air and exhaust flow meters and
defining maximum for electrical power, current, and voltage
measurement.
     Section 1065.307(e)(5)--Providing additional information
surrounding requirements for using a propane check or carbon balance
verification in place of a flow meter linearity verification.
     Section 1065.307(e)(7)(i)(F) and (G)--Adding transmission
oil and axle gear oil to temperature measurements that require
linearity verification.
     Section 1065.307(f)--Adding new paragraph (f) to denote
that table 1 follows.
     Section 1065.307 Table 1--Adding DEF flow rate, fuel mass
scale, and DEF mass scale to measurement systems and updating the
footnote format.
     Section 1065.307(g)--Adding a new paragraph (g) to denote
that table 2 follows.
     Section 1065.307 Table 2--Adding a new Table 2 to provided
additional guidance on when optional verifications to the flow meter
linearity verifications can be used.
     Section 1065.309(d)(2)--Updating to allow the use of water
vapor injection for humidification of gases. After considering comments
from EMA and Auto Innovators, we further modified this section to make
language consistent where water vapor injection was added as an
alternative.
     Section 1065.320(b)--Deleting existing paragraph (b) and
marking it

``reserved'' as this is now adequately covered in Sec.  1065.307.
     Section 1065.341--Revising section heading, adding
introductory text, revising paragraph (a) to clarify which
subparagraphs apply to CVS and which apply to PFD, relocating some of
existing paragraph (a) to paragraph (f) and reordering existing
paragraphs (b) through (f) as paragraphs (a) through (e).
     Section 1065.341(g)--Revising to replace ``batch sampler''
with ``PFD'' throughout and editing to provide further clarification on
the procedure.
     Section 1065.341(h)--Adding a new paragraph to reference
Table 2 of Sec.  1065.307 regarding when alternate verifications can be
used.
     Section 1065.342(d)(2)--Updating to allow the use of water
vapor injection for humidification of gases. After considering comments
by EMA and Auto Innovators, we further modified this section to make
language consistent where water vapor injection was added as an
alternative.
     Section 1065.350(d)(2)--Updating to allow the use of water
vapor injection for humidification of gases. After considering comments
by EMA and Auto Innovators, we further modified this section to make
language consistent where water vapor injection was added as an
alternative.
     Section 1065.355(d)(2)--Updating to allow the use of water
vapor injection for humidification of gases. After considering comments
by EMA and Auto Innovators, we further modified this section to make
language consistent where water vapor injection was added as an
alternative.
     Section 1065.360(a)(4)--Adding a new option to determine
methane and ethane THC FID response factors as a function of exhaust
molar water content when measuring emissions from a gaseous fueled
engine. This is to account for the effect water has on non-methane
cutters. We received a comment regarding whether the new regulatory
text for the allowance is optional. The intent is that if you decide to
use the option to determine the methane and ethane THC FID response
factors as a function of exhaust molar water content, you must generate
and verify the humidity as described in Sec.  1065.365(d)(12).
Paragraph (a)(4) has been modified to make this clear.
     Section 1065.360(d)(12)--Adding a process to determine
methane and ethane THC FID response factors as a function of exhaust
molar water content when measuring emissions from a gaseous fueled
engine. This is to account for the effect water has on non-methane
cutters.
     Section 1065.365(a)--Removing chemical symbol for methane
in parenthetical.
     Section 1065.365(d)--Adding a requirement to determine NMC
FID methane penetration fraction and ethane response factor as a
function of exhaust molar water content when measuring emissions from a
gaseous fueled engine. This is to account for the effect water has on
non-methane cutters.
     Section 1065.365(d)(9)--Adding C2H6
before ``response factor'' and ``penetration fraction'' to clarify, as
intended, that these are the ethane response factor and ethane
penetration fraction.
     Section 1065.365(d)(10), (11), and (12)--Adding a process
to determine NMC FID methane penetration fraction and ethane response
factors as a function of exhaust molar water content when measuring
emissions from a gaseous fueled engine. This is to account for the
effect water has on non-methane cutters.
     Section 1065.365(f)(9) and (14)--Adding
C2H6 before ``response factor'' and ``penetration
fraction'' to clarify, as intended, that these are the ethane response
factor and ethane penetration fraction. Adding CH4 before
``penetration fraction'' to clarify, as intended, that this is the
methane penetration fraction.
     Section 1065.370(e)(5)--Updating to allow the use of water
vapor injection for humidification of gases. After considering comments
by EMA and Auto Innovators, we further modified this section to make
language consistent where water vapor injection was added as an
alternative.
     Section 1065.375(d)(2)--Updating to allow the use of water
vapor injection for humidification of gases. After considering comments
by EMA and Auto Innovators, we further modified this section to make
language consistent where water vapor injection was added as an
alternative.
     Section 1065.410(c)--Replacing ``bad engine'' with
``malfunctioning'' in relation to engine components after considering a
comment by Auto Innovators.
     Section 1065.410(d)--Updating to state that you may repair
a test engine if the parts are unrelated to emissions without prior
approval. If the part may affect emissions, prior approval is required.
     Section 1065.510(a), (b)(5)(i), (c)(5), and (f)(4)(i)--
Moving provision for engine stabilization during mapping from Sec.
1065.510(a) to Sec.  1065.510(b)(5)(i), which lays out the mapping
procedure, adding allowance in Sec.  1065.510(f)(4)(i) to specify curb
idle transmission torque (CITT) as a function of idle speed in cases
where an engine has an adjustable warm idle or enhanced idle. We
further modified this section in the final rule by adding a provision
in Sec.  1065.510(c)(5) for hybrid powertrain testing to map negative
torque required to motor the engine with the RESS fully charged.
     Section 1065.512(b)(1) and (2)--Updating procedures on how
to operate the engine and validate the duty-cycle when an engine
utilizes enhanced-idle speed. This also addresses denormalization of
the reference torque when enhanced-idle speed is active.
     Section 1065.514(e)--Clarifying that a floating intercept
as described in Sec.  1065.602 is used to calculate the regression
statistics to harmonize with changes made to Sec.  1065.602 and further
modifying paragraph (e)(3) in the final rule to change ``standard
estimates of errors'' to ``standard error of the estimate'' for
consistency with other parts.
     Section 1065.514 Table 1--Updating a parameter name in the
final rule for consistency with other parts.
     Section 1065.530(a)(2)(iii)--Adding instructions on how to
determine that the engine temperature has stabilized for air cooled
engines.
     Section 1065.530(g)(5)--Adding a new paragraph on carbon
balance error verification if it is performed as part of the test
sequence.
     Section 1065.543--Adding a new section on carbon balance
error verification procedure to further reduce measurement variability
for the fuel mapping test procedure in part 1036. We have further
modified this section in the final rule to make it optional to account
for the flow of other non-fuel carbon-carrying fluids into the system
as the overall contribution from any such fluids to the total carbon in
the system is negligible.
     Section 1065.545--Revising to clarify that a forcing the
intercept through zero as described in Sec.  1065.602 is used to
calculate the standard error of the estimate (SEE) to harmonize with
changes to Sec.  1065.602.
     Section 1065.602(b), (c), (d), (e), (f), (g), (h), (j),
(k)--Updating to include the appropriate variable to represent
increments by italicizing the ``i''.
     Section 1065.602 Table 1--Updating footnote format in
table.
     Section 1065.602 Table 2--Correcting a typographical error
where the Nref-1 value should be ``22'' but was mistakenly
listed as ``20''.
     Section 1065.602(h)--Defining the existing Equation
1065.602-9 as a least squares regression slope calculation where the
intercept floats, i.e., is not forced through zero, designating this

paragraph as (h)(1) and adding a new paragraph (h)(2) for Equation
1065-602-10, a least squares regression slope calculation where the
intercept is forced through zero.
     Section 1065.602(i)--Editing to state that the intercept
calculation Equation 1065.602-11 is for a floating intercept.
     Section 1065.602(j)--Defining the existing Equation
1065.602-12 (renumbered from 1065.602-11) as a SEE calculation where
the intercept floats, i.e., is not forced through zero, designating
this paragraph as (j)(1), adding a new paragraph (j)(2) for Equation
1065.602-13, a SEE calculation where the intercept is forced through
zero, and further modifying paragraph (j) in the final rule to change
``Standard estimate of error'' to ``Standard error of the estimate''
for consistency with other parts.
     Section 1065.610(a)(1)(iv)--Updating to include the
appropriate variable to represent increments by italicizing the ``i''.
     Section 1065.610(a)(2)--Clarifying that the alternate
maximum test speed determined is for all duty-cycles.
     Section 1065.610(d)(3)--Adding provision to use good
engineering judgment to develop an alternate procedure for adjusting
CITT as a function of speed.
     Section 1065.640(a), (b)(3), and (d)(1)--Deleting a comma
in paragraph (a), specifying that the least square regression
calculation in paragraph (b)(3) is with a floating intercept, providing
a conversion to kg/mol for Mmix in the example problem for
paragraph (d)(1), and correcting an error in the example problem in
applying Equation 1065.640-10 where Mmix was used with the
wrong units.
     Section 1065.640(d)(3)--Providing additional guidance on
how to calculate SEE for Cd to correspond with the changes
made to Sec.  1065.602.
     Section 1065.642(b)--Correcting a cross-reference.
     Section 1065.642(c)(1)--Defining Cf.
     Section 1065.643--Adding a new section on carbon balance
error verification calculations to support the new Sec.  1065.543.
     Section 1065.650(b)(3)--Adding DEF to clarify what is
needed for chemical balance calculations.
     Section 1065.650(c)(1)--Relocating transformation time
requirement from Sec.  1065.650(c)(2)(i) to Sec.  1065.650(c)(1).
     Section 1065.650(c)(3)--Updating the equation to include
the appropriate variable to represent increments by italicizing the
``i''.
     Section 1065.650(d)--Correcting cross-references.
     Section 1065.650(d)(7)--Updating to include the
appropriate variable to represent increments by italicizing the ``i''.
     Section 1065.650(f)(2)--Adding DEF to clarify what is
needed for chemical balance calculations.
     Section 1065.650(g)--Updating the equations to include the
appropriate variable to represent increments by italicizing the ``i''
and correcting variable name from eNOxcomposite to
eNOxcomp.
     Section 1065.655--Adding ``DEF'' to the section heading.
     Section 1065.655(a) and (c) introductory text--After
considering comments by EMA, we modified this section to clarify that
the inclusion of diesel exhaust fluid in the chemical balance is
optional.
     Section 1065.655(c)(3)--Updating the xCcombdry
variable description to include injected fluid.
     Section 1065.655(d)--After considering comments by EMA, we
modified this section to clarify that the inclusion of diesel exhaust
fluid in the wC determination is optional.
     Section 1065.655(e)(1)(i)--Clarifying the determination of
carbon and hydrogen mass fraction of fuel, specifically to S and N
content.
     Section 1065.655(e)(3)--Clarifying that nonconstant fuel
mixtures also applies to flexible fueled engines.
     Section 1065.655(e)(4)--Updating to include the
appropriate variable to represent increments by italicizing the ``i''.
     Section 1065.655(e)(5)--Adding new paragraph (e)(5) to
denote that table 1 follows.
     Section 1065.655 Table 1--Updating cross-reference.
     Section 1065.655(f)(3)--Restricting the use of Equation
1065.655-25 if the standard setting part requires carbon balance
verification and including the appropriate variable to represent
increments by italicizing the ``j''; adding in the final rule a
description of the variable for carbon mass fraction, as it was
missing.
     Section 1065.655(g)(1)--Updating cross-reference.
     Section 1065.659(c)(2) and (3)--Adding DEF to clarify what
is needed for chemical balance chemical balance calculations.
     Section 1065.660(a)(5) and (6)--Adding new paragraphs to
those proposed codifying existing practice to calculate THC based on
measurements made with FTIR for gaseous fueled engines. EPA intended in
previous updates to part 1065 to allow the determination of NMNEHC and
NMHC using FTIR from gaseous fueled engines, but the HD Phase 2
rulemaking inadvertently omitted instructional text in paragraph (a) on
calculating THC using the two FTIR additive methods.
     Section 1065.660(b)(2) and (3)--Correcting typographical
errors, including adding missing commas.
     Section 1065.660(b)(4)--Correcting a typographical error
for the chemical formula of acetaldehyde in a variable.
     Section 1065.660(c)(2)--Including NMC FID as allowable
option in NMNEHC calculation and further modifying Sec.  1065.660(c) in
the final rule adding additional information on performing the NMNEHC
calculation and to correct typos in variables.
     Section 1065.660(d)--Adding missing parentheses.
     Section 1065.665(a)--Deleting the variable and description
for C# as it is not used in any calculation in this section.
     Section 1065.667(d)--Adding DEF to clarify what is needed
for chemical balance description.
     Section 1065.675(d)--Editing variable descriptions to
refer to a humidity generator rather than a bubbler (accommodates both
a bubbler and humidity generator).
     Section 1065.695(c)(8)(v)--Adding carbon balance
verification.
     Section 1065.701(b)--Updating name of California gasoline
type.
     Section 1065.701 Table 1--Updating footnote format in
table.
     Section 1065.703 Table 1--Updating to correct units for
kinematic viscosity and updating footnote format in table.
     Section 1065.705 Table 1--Updating to correct units for
kinematic viscosity and updating footnote format in table.
     Section 1065.710 Table 1--Editing format for consistency
and updating footnote format in table.
     Section 1065.710 Table 2--Editing format for consistency,
adding allowance to use ASTM D1319 or D5769 for total aromatic content
determination and ASTM D1319 or D6550 for olefin determination because
the dye used in ASTM D1319 is becoming scarce and an alternate method
is needed, and updating a footnote format in table.
     Section 1065.715 Table 1--Updating footnote format in
table.
     Section 1065.720 Table 1--Updating footnote format in
table and revising Table 1 after considering a comment by EMA to
specify ASTM D6667 instead of ASTM D2784 as the reference procedure for
measuring sulfur in liquefied petroleum gas. We requested comment on
amending the

regulation to replace ASTM D2784, which has been withdrawn by ASTM
without replacement, received comment from EMA and agree that ASTM
D6667 is a suitable method. EPA is similarly changing other regulatory
provisions to specify ASTM D6667 as the reference procedure for fuel
manufacturers measuring sulfur in butane (see 40 CFR 1090.1350).
     Section 1065.750 Table 1--Updating footnote format in
table.
     Section 1065.790(b)--Adding a NIST traceability
requirement for calibration weights for dynamometer, fuel mass scale,
and DEF mass scale.
     Section 1065.905 Table 1--Updating footnote format in
table.
     Section 1065.910(a)(2)--Adding a revision in the final
rule to change the requirement to use 300 series stainless steel tubing
to connect the PEMS exhaust and/or intake air flow meters into a
recommendation because there are other materials that are equally
suitable for in-use testing other than stainless steel tubing.
     Section 1065.915 Table 1--Updating footnote format in
table.
     Section 1065.1001--Adding a definition for enhanced-idle.
     Section 1065.1001--Clarifying definition of test interval
as duration of time over which the mass of emissions is determined.
     Section 1065.1005(a)--Updating footnote format in table
and parameter names for consistency with other parts.
     Section 1065.1005(c), (d), and (e)--Updating to ensure
column headings use terminology consistent with NIST SP-811.
     Section 1065.1005(a) and (e)--Updating tables of symbols
and subscripts to reflect revisions to part 1065.
     Section 1065.1005(f)(2)--Adding molar mass of ethane and
updating footnote format in table.
     Section 1065.1005(g)--Updating acronyms and abbreviations
for ASTM, e.g., and i.e.
     Section 1065.1010(b)(23) and (43)--Incorporating by
reference ASTM D6667 into the regulations instead of ASTM D2784,
consistent with replacing ASTM D2784 with ASTM D6667 as the reference
procedure for measuring sulfur in liquefied petroleum gas in Sec.
1065.720, as explained above in this section. EPA is similarly
specifying ASTM D6667 as the reference procedure for fuel manufacturers
measuring sulfur in butane.
4. 40 CFR Part 1066 Test Procedures
    EPA proposed several updates to the testing and measurement
provisions of 40 CFR part 1066 related to how to measure emissions from
light- and heavy-duty vehicles and requested comment on general
improvements to the vehicle test procedures and compliance provisions
(see 85 FR 28144). This section presents the changes we are adopting to
vehicle test procedures after consideration of comments received.
Chapter 2 of our Response to Comments includes additional details on
some of these amendments, as well as other testing and measurement
amendments or clarifications requested by commenters and our responses.
    We are generally finalizing revisions as proposed; however, some
revisions include further changes and clarifications after
consideration of public comments to better ensure clarity, accuracy and
consistency with the intent of the proposed rule.
     Section 1066.1(g)--Updating the URL.
     Section 1066.135(a)(1)--Revising to widen the range for
verifications of a gas divider derived analyzer calibration curve to 10
to 60% to ease lab burden with respect to the number of gas cylinders
they must have on hand and revising to make the midspan check optional
as the part 1066 requirement for yearly linearity verification of the
gas divider has provided more certainty of the accuracy of the gas
blending device.
     Section 1066.210(d)(3)--Changing the value for
acceleration of Earth's gravity from a calculation under 40 CFR
1065.630 to a default value of 9.80665 m/s2 because the
track coastdown doesn't take place in the same location that the
dynamometer resides. Therefore, best practice is to use a default value
for gravity.
     Section 1066.255(c)--Clarifying that the torque transducer
zero and span are mathematically done prior to the start of the
procedure.
     Section 1066.260(c)(4)--Correcting an error in the example
problem result.
     Section 1066.265(d)(1)--Correcting example equation to
replace a subtraction sign that was a typographical error with a
multiplication sign.
     Section 1066.270(c)(4)--Correcting units for force in mean
force variable description and correcting example problem solution.
     Section 1066.270(d)(2)--Adding corrections in the final
rule of typographical errors on maximum allowable error where error
tolerances were indicated as ``'', but paragraph is clear
that the allowable error is a maximum value as Equation 1066.270-2
determines error as an absolute value. Therefore, the error values are
positive and not a positive and negative range.
     Section 1066.275--Extending the dynamometer readiness
verification interval from within 1 day before testing to an optional 7
days prior to testing if historic data from the test site supports an
interval of more than 1 day. Adding corrections in the final rule of
typographical errors in paragraphs (d)(1) and (2) on allowable error
where error tolerances were indicated as ``'', but
paragraph is clear that the allowable error is a maximum value as
Equation 1066.270-2 determines error as an absolute value. Therefore,
the error values are positive and not a positive and negative range.
     Section 1066.405--Updating heading to include
``maintenance''.
     Section 1066.405(a) through (c)--Designating existing text
as paragraph (a), adding new paragraphs (b) and (c) to address test
vehicle inspection, maintenance and repair, consistent with Sec.
1065.410, and, after considering a comment by Auto Innovators,
replacing ``bad engine'' with ``malfunctioning'' in relation to engine
components in paragraph (b).
     Section 1066.420 Table 1--Updating footnote format in
table and, after considering comments from Auto Innovators and VW,
clarifying that SC03 humidity tolerance is an ``average'' value
consistent with 40 CFR 86.161-00(b)(1) and inadvertently not carried
over in part 1066. All SC03 capable test cells have been designed to
meet the humidity requirement in Sec.  86.161-00 which is on an average
basis.
     Section 1066.605--Correcting a typographical error in
paragraph (c)(4) where NMHC should read NMHCE and editing Equation
1066.605-10 adding italics for format consistency.
     Section 1066.610--Editing Equation 1066.610-4 adding
italics for format consistency.
     Section 1066.710(c)--Clarifying to reflect how heating,
ventilating, and air conditioning (HVAC) control systems operate in
vehicles and how they should be operated for the test. Further
modifying paragraph (c)(1)(i)(A) in the final rule to state that for
automatic temperature control systems that allow the operator to select
a specific temperature, set the air temperature at 72 [deg]F or higher,
which the vehicle then maintains by providing air at that selected
constant temperature. Further modifying paragraph (c)(2) in the final
rule to state that for full automatic temperature control systems that
allow the operator to select a specific temperature, set the air
temperature at 72 [deg]F, which the vehicle then maintains by varying
temperature, direction and

speed of air flow. Clarifying terminology is consistent with EPA
compliance guidance CD-2020-04.
     Section 1066.801 Figure 1--Updating to reflect that the
initial vehicle soak, as outlined in the regulations, is a 6-hour
minimum and not a range of 6 to 36 hours.
     Section 1066.835(a)--Clarifying that the last drain and
fill operation is after the most recent FTP or highway fuel economy
test (HFET) measurement (with or without evaporative emission
measurements).
     Section 1066.835(f)(2)--Deleting the word
``instantaneous'' to reflect that the SC03 temperature and humidity
tolerances in paragraph (f)(1) are not all instantaneous in response to
comments received from Auto Innovators and Volkswagen. This was an
inadvertent error in part 1066.
     Section 1066.930--Adding a period to the end of the
sentence.
     Section 1066.1005(a)--Updating a parameter name to be
consistent with use in other parts.
     Section 1066.1005(c) and (d)--Updating to ensure column
headings use terminology consistent with NIST SP-811.
     Section 1066.1005(f)--Updating footnote format in table.
5. Greenhouse Gas Emissions Model (GEM)
    EPA proposed several updates to the GEM model related to how to
measure emissions from heavy-duty engines and requested comment on
whether the differences in GEM would impact the effective stringency of
the standards and, if so, whether either GEM or the regulations need to
be revised to address the changes (see 85 FR 28145, May 12, 21020).
This section presents the changes we are adopting to GEM after
consideration of comments received. Additional details on these and
other amendments or clarifications requested by commenters and our
responses are available in Chapter 2 of our Response to Comments.
    GEM is a computer application that estimates the greenhouse gas
(GHG) emissions and fuel efficiency performance of specific aspects of
heavy-duty (HD) vehicles. GEM is used to determine compliance with the
Phase 2 standards from several vehicle-specific inputs, such as engine
fuel maps, aerodynamic drag coefficients, and vehicle weight rating.
GEM simulates engine operation over two cruise cycles, one transient
cycle, and for vocational vehicles, idle operation. These results are
weighted by GEM to provide a composite GEM score that is compared to
the standard.
    EPA proposed to update GEM, in a revised version 3.5 to replace the
current version 3.0, and requested comment on whether the differences
in GEM would impact the effective stringency of the standards and, if
so, whether either GEM or the regulations need to be revised to address
the changes. We received one comment on the proposal on this topic from
the California Air Resources Board (CARB), stating the importance of
GEM results being consistent with the current program standards to
ensure stringency is maintained and recommending that EPA revise GEM to
maintain this consistency.
    After considering the comment and further evaluating the
performance of GEM 3.5 with the input files used to set the Phase 2
vehicle standards, EPA is finalizing GEM version 3.5.1 applicable for
MY 2021 vehicles that includes the changes proposed in version 3.5 as
well as changes that correct three errors in the GEM 3.5 code. The
following changes were proposed in version 3.5 and are finalized in
version 3.5.1 to allow additional compliance flexibilities and improve
the vehicle simulation:
     Corrected how idle emission rates are used in the model.
     Increased the allowable weight reduction range to 25,000
pounds.
     For powertrain input, added an input for powertrain rated
power to scale default engine power.
     Recalibrated driver over speed allowance on cruise cycles
from 3 mph to 2.5 mph.
     Revised engine cycle generation outputs with corrected
engine cycle generation torque output from model based on simulated
inertia and rate limited speed target.
     Added scaling of powertrain simulation default engine and
transmission maps based on new rated power input.
     Changed interpolation of fuel map used in post processing
to be consistent with one used in simulation.
     Corrected accessory load value on powertrain test when
coasting or decelerating.
     Added torque converter k-factor input option.
     Cycle average cycles: added flag for points that are to be
considered ``idle.''
     Improved handling of large input tables.
     Allow hybrid engine input.
    The three additional changes in GEM 3.5.1 correct the following
errors in GEM 3.5 code: (1) A typographical error, where GEM used a
weighting factor of 0.25 instead of 0.23 for the Heavy Heavy-Duty (HHD)
Multipurpose vehicle subcategory; (2) an idle map error when the cycle
average fuel mapping procedure is used for all three drive cycles; and
(3) a functional error that unnecessarily required transmission power
loss data when using the option to enter a unique (instead of default)
k-factor for the torque converter. The GEM version we are releasing
with and incorporating by reference in this final rule is identified as
``3.5.1.''
    EPA is also issuing a supplemental proposal published in the
Proposed Rules section of this issue of the Federal Register, titled
``Improvements for Heavy-Duty Engine and Vehicle Test Procedures,''
docket number EPA-HQ-OAR-2019-0307; FRL-10018-51-OAR. This supplemental
proposal provides notice and opportunity for comment on a proposed
further updated version of GEM for MY 2022 and later, proposes to allow
use of the updated model for MY 2021 for demonstrating compliance with
the Phase 2 standards, including obtaining a certificate of conformity
and submitting end-of-year reports, and requests comment on whether
this version of GEM should be required for MY2021 end-of-year reports.
This proposed revised version in the supplemental proposal includes
corrections, clarifications, additional flexibilities, and adjustment
factors to the Greenhouse gas Emissions Model (GEM) compliance tool for
heavy-duty vehicles after consideration of comments received on the
proposed rule. The supplemental proposal proposes limiting the use of
GEM 3.5.1 to MY 2021 vehicles only, except where this MY 2021 data can
be used for carryover requests for certificates of conformity for MY
2022 and future years for qualifying vehicles under Sec.  1036.235(d);
however, manufacturers would still need to use GEM 3.8 for end-of-year
reporting for MY 2022 and future years.
    EPA is finalizing GEM 3.5.1 after considering comments, further
evaluating the performance of GEM 3.5.1 with the input files used to
set the Phase 2 vehicle standards, considering the corrections and
improvements made in GEM 3.5.1, and identifying potential additional
corrections and improvements for GEM. Evaluation of GEM 3.5.1 indicated
that there was some difference in output 96results for both tractor and
vocational vehicles when compared to GEM 3.0. To assess the magnitude
of any differences between using GEM 3.0 and GEM 3.5.1, we repeated the
process used in 2016 to calculate the numerical level of the vehicle
standards, replacing GEM 3.0 with GEM 3.5.1. On average, the
differences in the resulting standards

from using GEM 3.5.1 instead of GEM 3.0 are decreases of 0.09 percent
and 0.54 percent for the tractor and vocational vehicle standards,
respectively. The tractor standards resulting from GEM 3.5.1 ranged
from 0.29 percent below to 0.15 percent above the GEM 3.0 standards.
The vocational vehicle standards resulting from GEM 3.5.1 ranged from
0.32 percent above to 1.45 percent below the GEM 3.0 standards. A
summary of the process taken to calculate the vehicle standards using
GEM and a comparison of the results generated by GEM 3.0 and GEM 3.5.1
are provided in a docket memo.\7\
---------------------------------------------------------------------------

    \7\ Sanchez, James, Memorandum to Docket EPA-HQ-OAR-2019-0307.
Process of Using GEM to Set Vehicle Standards. December 4, 2020.
---------------------------------------------------------------------------

    We are finalizing GEM 3.5.1 without adopting adjustment factors in
the related test procedures.\8\ In the same memo noted previously, we
compare the GEM 3.8 results to those from GEM 3.0. In the supplemental
proposal, EPA proposes GEM 3.8 and corresponding adjustment factors to
adjust the results to more closely match the results produced by the
original GEM 3.0 version and we intend to issue a final rule before the
start of model year 2022. If finalized as proposed, we would limit the
potential impact on effective stringency due to a change in GEM
versions to model year 2021 only, which should have a minimal impact on
the effective stringency and environmental benefits of the overall
Phase 2 program.
---------------------------------------------------------------------------

    \8\ Greenhouse gas Emissions Model (GEM) Phase 2, Version 3.5.1,
December 2020. A working version of this software is also available
for download at https://www.epa.gov/regulations-emissions-vehicles-and-engines/greenhouse-gas-emissions-model-gem-medium-and-heavy-duty.
---------------------------------------------------------------------------

6. Aerodynamic Test Procedures
    EPA proposed several updates to the testing and modeling provisions
of 1037 subpart F related to aerodynamic testing and requested comment
on general improvements to the aerodynamic test procedures and
compliance provisions (see 85 FR 28147). This section presents the
changes we are adopting to aerodynamic test procedures after
consideration of comments received. Additional details on these and
other aerodynamic amendments or clarifications requested by commenters
and our responses are available in Chapter 2 of our Response to
Comments.
a. Aerodynamic Measurements for Tractors
    The aerodynamic drag of a vehicle is determined by the vehicle's
coefficient of drag (Cd), frontal area, air density and
speed. The regulations in Sec.  1037.525 allow manufacturers to use a
range of techniques, including wind tunnel testing, computational fluid
dynamics, and constant speed tests. This broad approach is appropriate
given that no single test procedure is superior in all aspects to other
approaches. However, we also recognized the need for consistency and a
level playing field in evaluating aerodynamic performance. To address
the consistency and level playing field concerns, EPA adopted an
approach that identified coastdown testing as the reference aerodynamic
test method, and specified a procedure to align results from other
aerodynamic test procedures with the reference method by applying a
correction factor (Falt-aero) to results from alternative
methods (Sec.  1037.525(b)). We are adding a sentence to the
introductory text of Sec.  1037.525 to clarify that coastdown testing
is the ``reference method for aerodynamic measurements''.
    In the proposed rule, we proposed to separate Sec.  1037.525(b)(1)
into a paragraph (b)(1) defining Falt-aero and a new
paragraph (b)(2) allowing manufacturers to assume Falt-aero
is constant for a given alternate method. We are finalizing two
separate paragraphs and the subsequent renumbering of the remaining
paragraphs as proposed except as explained here. Our proposed update to
the definition of Falt-aero in Equation 1037.525-1 and the
related text in Sec.  1037.525(b)(1) inadvertently removed the
definition of effective yaw, ceff, which is used throughout
Sec.  1037.525 and incorrectly replaced the CdA variables
measured at [psi]eff with wind-averaged CdA
values, as noted in comment by EMA. We agree that Equation 1037.525-1
should continue to be based on the definition from HD GHG Phase 2 final
rule such that Falt-aero is a function of the coefficient of
drag areas at the effective yaw angle. We are finalizing paragraph
(b)(1) with the same Equation 1037.525-1 as the current requirement but
with the updated variable names throughout Sec.  1037.525 (and where
referenced in Sec.  1037.525(h)(12)(v)) to more clearly relate the drag
areas to the defined effective yaw variable, as recommended by EMA.\9\
We are also adding a ``Where:'' statement to Equation 1037.525-1 to
define the variables in that equation and are restoring the existing
language we proposed to remove that defines the effective yaw angle to
apply for Phase 1 and Phase 2 compliance.
---------------------------------------------------------------------------

    \9\ The variables
CdAeffective-yaw-coastdown and
CdAeffective-yaw-alt are now
CdAcoastdown(ceff) and
CdAalt(ceff), respectively.
---------------------------------------------------------------------------

    We proposed and received no adverse comments on two additional
changes in Sec.  1037.525(b). In paragraph (b)(3), we proposed and are
finalizing removal of the sentence ``Where you have test results from
multiple vehicles expected to have the same Falt-aero, you
may either average the Falt-aero values or select any
greater value.'' By removing this statement, we are allowing
manufacturers the flexibility to propose a method for calculating their
Falt-aero from multiple test vehicles that suits their
unique compliance margin targets. In paragraph (b)(5), we proposed to
add a statement that manufacturers may test earlier model years than
the 2021, 2024, and 2027 model years specified and are finalizing
additional clarifying text and a new example. We are finalizing two
additional typographical edits correcting references to our renumbered
paragraphs in the paragraph (b)(5). The reference to ``paragraph
(b)(2)'' was corrected to paragraph (b)(3) and the reference to ``this
paragraph (b)(4)'' was corrected to paragraph (b)(5). Finally, we are
adding the phrase ``drag area from your alternate method'' to describe
the previously undefined term, CdAalt.
    EPA proposed a change to Sec.  1037.525(b)(7), to clarify that the
use of good engineering judgment with respect to the specified tractor-
trailer gap dimension ``applies for all testing, including confirmatory
and SEA testing''. Both EMA and Volvo requested further clarification
through use of an example. We are finalizing three clarifying changes
to Sec.  1037.525(b)(7). First, we are adding a reference to the
tractor-trailer gap specifications in Sec.  1037.501(g)(1)(ii), as
requested. Second, we provide an example of good engineering judgment
that could be applied to correct a difference between the specified and
tested tractor-trailer gaps. Lastly, we clarify that the allowance
applies ``for certification, confirmatory testing, SEA, and all other
testing to demonstrate compliance with standards.''
    We also proposed a provision to our regulations at Sec.
1037.525(b)(8) to encourage manufacturers to proactively coordinate
with EPA to have compliance staff present when a manufacturer conducts
its coastdown testing to establish Falt-aero values. Section
208 of the Clean Air Act provides EPA broad oversight authority for
manufacturer testing. Being present for the testing would give EPA
greater confidence that the test was conducted properly, and thus,
would make it less likely that EPA would need to conduct aerodynamic
confirmatory testing on the

vehicle. Consistent with the intent of the proposed revision and EPA's
authority under section 208, we are finalizing in Sec.  1037.525(b)(8)
a provision that refers to the existing preliminary approval provisions
of Sec.  1037.210 with the note that EPA may witness the testing.
Section 1037.210 provides an established protocol for manufacturers to
coordinate with EPA for testing.
    EMA's comment requested additional modifications to the yaw sweep
correction provisions in Sec.  1037.525(c), suggesting that coastdown
results do not need to be corrected to wind-averaged and that all of
paragraph (c)(2) was ``unnecessary'' because another regulatory
provision ``serves that function''. Their request appears to be a
misunderstanding of the existing regulations. Wind-averaged drag area
(CdAwa) is a required input for GEM in Phase 2.
Paragraph (c)(1) specifies how to calculate CdAwa
when using an alternate test method and paragraph (c)(2) specifies how
to calculate it for coastdown testing. EPA may use coastdown for
confirmatory testing and manufacturers may choose to use coastdown
testing for all aerodynamic testing. Consequently, paragraph (c)(2) is
needed to properly calculate the wind-averaged input required by GEM in
these situations. To address any potential confusion on the necessity
of both paragraphs under the current regulatory text, we are finalizing
three updates to Sec.  1037.525(c) as follows:
     Clarifying the use of the yaw correction provisions by
revising paragraph (c) introductory text to add ``as specified in Sec.
1037.520'' and to remove the phrase ``differences from coastdown
testing'' that only applies to paragraph (c)(1).
     Updating the text of paragraphs (c)(1) and (2) to more
clearly communicate that they are two separate options that apply based
on which testing method is chosen.
     Adopting the updated drag area variable names from Sec.
1037.525(b).
b. Aerodynamic Measurements for Vocational Vehicles
    We did not specifically propose changes to or request comment on
our procedures for measuring aerodynamic performance of vocational
vehicles in Sec.  1037.527. EMA commented that the existing provisions
of Sec.  1037.527 to determine a DCdA value for vocational
vehicles refer to the trailer provisions in Sec.  1037.526; however,
Sec.  1037.526 does not specify how to choose an appropriate baseline
for vocational vehicles. EMA requested that manufacturers should be
able to ``choose an appropriate baseline vehicle for the technology and
applications''. We are not taking any final action on this issue at
this time. However, we are providing a summary of the current
provisions and their original intent in this preamble to assist
manufacturers.
    The current Sec.  1037.527(a) states that DCdA is
determined for vocational vehicles as follows: ``Determine
DCdA values by performing A to B testing as described for
trailers in Sec.  1037.526, with any appropriate adjustments,
consistent with good engineering judgment.'' The A to B testing
provisions for trailers are specified in Sec.  1037.526(a), where
paragraph (a)(1) describes the baseline trailer, paragraph (a)(2)
describes the general intent of the A to B test, and paragraph (a)(3)
describes how to calculate the DCdA from the test results.
    We acknowledge that the reference to a ``standard trailer'' in
Sec.  1037.526(a)(1) may cause confusion to vocational vehicle
manufacturers, since it would be a challenge to identify a single
``standard'' vehicle to represent the range of vocational applications.
However, the baseline trailer description in that paragraph equates to
a trailer without aerodynamic components, which is the key aspect of
that baseline description the regulatory cross-reference in Sec.
1037.527(a) applies to vocational vehicles. The trailer provision of
Sec.  1037.526(a)(2) states that the general intent of the A to B test
is to ``demonstrate the reduction in aerodynamic drag associated with
the improved design'', which can be directly applied to vocational
vehicles. The general process of calculating DCdA in Sec.
1037.526(a)(3) could be applied to vocational vehicles as well, but its
reference to test trailer and baseline trailer may cause confusion for
reasons similar to those discussed for Sec.  1037.526(a)(1).
    Similar to the trailer provision, a vocational vehicle's
aerodynamic performance is based on a DCdA value relative to
a baseline vehicle. Manufacturers wishing to perform aerodynamic
testing on their vocational vehicles are encouraged to coordinate with
their Designated Compliance Officer and use the existing provision in
Sec.  1037.527, including its reference to the description of how to do
so for the trailer-specific provision in Sec.  1037.526. As noted in
Sec.  1037.527(a), we expect manufacturers to make ``appropriate
adjustments'' when applying the cross-referenced provision to
vocational vehicle testing consistent with good engineering judgment.
When followed, this should result in a manufacturer choosing an
appropriate baseline vehicle, similar to the clarification requested by
the commenter. For example, a manufacturer may choose an aerodynamic
test method, determine a baseline CdA value (in m\2\) using
a vehicle that represents a production configuration without the
aerodynamic improvement, then repeat the same aerodynamic method for a
test vehicle that is a nearly equivalent configuration but includes the
aerodynamic improvement of interest. In this case, the manufacturer
would calculate DCdA by subtracting the measured drag area
for the test vehicle from the drag area for the baseline vehicle.
Calculating DCdA in this manner would generally be
consistent with the intent that the test ``accurately demonstrate the
reduction in aerodynamic drag associated with the improved design'' for
the vocational vehicle since any improvement to aerodynamic performance
would be attributable to the aerodynamic technology on the test
vehicle.
c. Computational Fluid Dynamics Procedures
    We proposed one correction to our computational fluid dynamics
(CFD) provisions of Sec.  1037.532 that replaced the incorrect ``or''
in paragraph (a)(1) with ``and'' to include yaw angles of +4.5[deg] and
-4.5[deg]. EMA requested three additional modifications related to our
CFD provisions. In Sec.  1037.532(a)(3), they requested that we clarify
our specified Reynolds number of 5.1 million is based on the 102-inch
trailer width as the characteristic length. We agree with this
suggestion and updated the language in Sec.  1037.532(a)(3) for clarity
that the Reynolds number is based on a 102-inch trailer width
consistent with our specifications for a ``standard trailer'' in Sec.
1037.501(g)(1)(i). EMA also suggested the phrase ``the General On-Road
Simulation'' in Sec.  1037.532(a)(4) be replaced with ``an open-road
simulation'' to avoid confusion with SAE International's revisions of
SAE J2966 to incorporate the impact of traffic. We agree that open-road
simulation is representative of our initial intent and are updating the
regulatory text of Sec.  1037.532(a)(4). See Chapter 2 of our Response
to Comments for additional details.
    EMA's third request was that we remove the requirement to set the
``free stream turbulence intensity to 0.0 percent'' in Sec.
1037.532(a)(5), and instead recommended we replace that requirement
with a ``uniform inlet velocity profile.'' EPA is not taking any final
action on revision to that paragraph at this time. Furthermore, EPA
disagrees with the requested change to paragraph (a)(5). Turbulence
intensity is a common parameter in CFD packages and, as described in
Chapter

<IP_ADDRESS> of the Final Regulatory Impact Analysis (Final RIA) for the HD
Phase 2 Rule, we evaluated a range of turbulence intensities and
intentionally specified a value of zero to ensure consistency, stating
that ``Turbulence intensity must be 0.0 percent.'' \10\ Manufacturers
who wish to use alternative parameters and criteria related to their
CFD models, which includes seeking to substitute the specified
turbulence intensity with a uniform inlet velocity profile, continue to
have the option to seek to do so through requesting EPA approval under
Sec.  1037.532(f).
---------------------------------------------------------------------------

    \10\ US EPA, US DOT/NHTSA. Greenhouse Gas Emissions and Fuel
Efficiency Standards for Medium- and Heavy-Duty Engines and
Vehicles--Phase 2: Regulatory Impact Analysis. EPA-420-R-16-900.
August 2016. Page 3-41.
---------------------------------------------------------------------------

    CARB requested EPA add provisions that set a requirement for a
maximum limit of computational elements to perform Computational Fluid
Dynamics (CFD) simulation, define a specific transient averaging
methodology, quantify the uncertainty in using CFD simulation, and
assess CFD simulation credibility. We are not taking any final action
on these requests, but may consider the changes suggested by the
commenter in an appropriate future rulemaking with notice and comment.
See our complete response in Chapter 2 of our Response to Comments.
7. Hybrid Powertrain Test Procedures
    As explained above in Sections II.A.1 and II.A.2, EPA proposed
several updates to the hybrid powertrain test procedures that apply to
engine and vehicle standards provisions in 40 CFR 1036.503, 1036.505,
1036.510, and 1036.527, 40 CFR part 1036, appendix B, and 40 CFR
1037.550 related to how to perform hybrid powertrain testing and
requested comment on general improvements to the hybrid powertrain test
procedure provisions (see 85 FR 28152). This section further explains,
in addition to the specific descriptions in Sections II.A.1. and
II.A.2. above, the changes we are adopting to hybrid powertrain test
procedures after consideration of comments received. Additional details
on these and other hybrid powertrain testing and measurement amendments
or clarifications requested by commenters and our responses are
available in Chapter 2 of our Response to Comments.
a. Hybrid Test Procedures for Engine Standards
    EPA worked with industry prior to proposal and also considered
input provided during this rulemaking to develop a powertrain test
procedure that includes the addition of a transmission model to GEM and
options in GEM to test without the transmission present, using the
model in its place to be used to certify a hybrid powertrain to the FTP
and SET HD GHG Phase 2 greenhouse gas engine standards. The two primary
goals of this development process were to make sure that the powertrain
version of each test cycle was equivalent to the respective engine
cycle in terms of positive power demand versus time and that the
powertrain cycle had appropriate levels of negative power demand.
    Our current regulations do not have a certification procedure for
powertrain certification of heavy-duty hybrid vehicles to any engine
standards. The powertrain certification test for certification to both
the FTP and SET is carried out by following 40 CFR 1037.550 as
described in 40 CFR 1036.505 and 1036.510 and is applicable for
powertrain systems located in the P0, P1, P2, and P3 positions.
    For this test procedure, EPA is finalizing addition of a vehicle
speed and road grade profile to the existing FTP duty cycles for
compression-ignition and spark-ignition engines in 40 CFR part 1036,
appendix B, and to the SET duty cycle in 40 CFR 1036.505. EPA also is
finalizing vehicle parameters to be used in place of those in 40 CFR
1037.550; namely vehicle test mass, vehicle frontal area, vehicle drag
area, coefficient of rolling resistance, drive axle ratio, tire radius,
vehicle curb mass, and linear equivalent mass of rotational moment of
inertias. Under the final test procedure, determination of system and
continuous rated power along with the maximum vehicle speed (C speed)
is also required using 40 CFR 1036.527. Under the final test procedure,
the combination of the generic vehicle parameters, the engine duty-
cycle vehicle speed profile, and road grade profile fully defines the
system load and this is designed to match up the powertrain load with
the compression-ignition engine vFTP, spark ignition engine vFTP, and
vSET load for an equally powered engine.
    The development of this test procedure was based on the process
contained in Global Technical Regulation No. 4.11 12
Generally speaking, the final test procedure is powertrain in the loop
using a vehicle-based cycle (vehicle speed vs. time and grade vs.
time). The final vehicle speed profiles were developed by following SAE
2012-01-0878.\13\
---------------------------------------------------------------------------

    \11\ United Nations Economic Commission for Europe. Addendum 4:
Global technical regulation No. 4. Test procedure for compression
ignition (C.I.) engines and positive-ignition (P.I.) engines fueled
with natural gas (NG) or liquefied petroleum gas (LPG) with regard
to the emission of pollutants Amendment 3., March 12, 2015.
    \12\ Six, C., Siberholz, G., Fredriksson, J., Geringer, B.,
Hausberger, S. Development of an exhaust emission and CO2
measurement test procedure for heavy-duty hybrids (HDH). October 27,
2014. Available online at: https://wiki.unece.org/download/attachments/4064802/20141027_ACEA_Report.pdf?api=v2.
    \13\ Andreae, M., Salemme, G., Kumar, M., and Sun, Z.,
``Emissions Certification Vehicle Cycles Based on Heavy Duty Engine
Test Cycles,'' SAE Int. J. Commer. Veh. 5(1):299-309, 2012, https://doi.org/10.4271/2012-01-0878.
---------------------------------------------------------------------------

    The engine operational profile for engines installed in vehicles
depends on the entire vehicle setup, including the use of hybrid
systems if applicable, thus the entire vehicle must be considered when
certifying a powertrain. Given that heavy duty vehicles can vary quite
a bit even though the powertrain configuration remains unchanged,
testing of every conceivable configuration is not possible; therefore,
a representative average vehicle, consisting of generic vehicle
parameters, is used to provide a representative configuration for
certification testing. Generic vehicle parameters were developed with
the intent of maintaining the same system load for engines installed in
conventional vehicles and hybrid systems with the same power rating to
maintain comparability in terms of emissions.\14\
---------------------------------------------------------------------------

    \14\ Six, C., Siberholz, G., Fredriksson, J., Geringer, B.,
Hausberger, S. Development of an exhaust emission and CO2
measurement test procedure for heavy-duty hybrids (HDH). October 27,
2014. Available online at: https://wiki.unece.org/download/attachments/4064802/20141027_ACEA_Report.pdf?api=v2.
---------------------------------------------------------------------------

    EPA is finalizing vehicle parameters for hybrid powertrain testing
in place of those in 40 CFR 1037.550 to be used in the vehicle model in
40 CFR 1037.550(f). These final parameters can be found in 40 CFR
1036.505 (via reference from 40 CFR 1036.510 for FTP testing) and
included vehicle test mass, M, vehicle frontal area, Afront,
vehicle drag area, CdA, coefficient of rolling resistance,
Crr, drive axle ratio, ka, tire radius, r,
transmission efficiency if the hybrid powertrain is being tested
without the transmission, axle efficiency, Effaxle, vehicle
curb mass, Mcurb, and linear equivalent mass of rotational
moment of inertias, Mrotating. The requirements for the
determination of these parameters were taken from the Global Technical
Regulation (GTR) No. 4 referenced above.
    Under the final test procedure, to align the system demands for
conventional and hybrid engines, the generic vehicle parameters are
defined as a function of the system's power

rating. 40 CFR 1036.527 provides the procedure for determining the peak
rated power, Prated, and continuous rated power of the
hybrid system, Pcontrated, that goes into the vehicle test
mass determination. These revisions also provide a procedure for the
determination of the maximum vehicle speed (C speed), vrefC. In
general, the process for determining both Prated and
Pcontrated is very similar to the GTR No. 4 hybrid system
rated power determination procedure with a few exceptions. In the final
40 CFR 1036.527 procedure, the default axle efficiency is 0.955 because
that is the default value in GEM. The determination of continuous rated
power in the final EPA process versus the system rated power in the GTR
No. 4 process is to address the lack of a steady state vehicle test
cycle in GTR No. 4. The full throttle test to determine system rated
power in GTR No. 4 lasts 50 to 150 seconds and GTR No. 4 determines
rated power as peak power during these tests. While this process is
appropriate for the FTP, the SET is 2400 seconds long and the extended
operation at some high speed and load points can lead to some hybrid
systems not being able to sustain peak power over the course of the
test due to thermal limitations on the motor generator (generally due
to material limitations) and limitations on the battery storage
capacity and available usable energy. Under these scenarios, the hybrid
system will typically derate the motor generator to thermally protect
it, resulting in a sustained peak power that is lower than that
determined using the GTR No. 4 process.
    Under the final test procedure, the powertrain system rated power
determination in 40 CFR 1036.527 includes the determination of both
peak and continuous rated power. The peak rated power
(Prated) is used in the transient FTP test procedure, while
the continuous rated power (Pcontrated) is used in the
steady-state SET test procedure. The vehicle C speed, vrefC,
is also determined as a result of this process. This is the maximum
vehicle speed at which Psys equals Pcontrated.
    The final compression-ignition vFTP duty cycle vehicle speed
profile was derived from the compression-ignition FTP vehicle duty-
cycle developed in SAE 2012-01-0878. In this work, a vehicle FTP cycle
and a vehicle SET cycle were created based on the transient diesel
engine FTP and engine SET duty cycles. The vehicle cycles are the same
duration and have similar power requirements and performance when
compared to the engine cycles. The alignment of the engine and vehicle
cycles maintain a consistency within vehicle and engine emissions
evaluations. The compression-ignition FTP vehicle speed profile is not
applicable to the spark-ignition FTP vehicle speed profile due to
differences in the engine duty-cycle lengths, speed profiles, and
torque profiles. Thus, a separate vehicle speed profile had to be
developed for the spark-ignition FTP duty cycle. Using the methodology
in SAE 2012-01-0878, a vehicle speed profile was developed for the
spark-ignition FTP duty cycle and a comparison between the two cycles
can be found in Table II-2. The vehicle speed profiles can be found in
Figure II-1 and Figure II-2.

    Table II-2--Comparison Between FTP Vehicle Duty-Cycle Metrics for
      Vehicles with Compression-Ignition and Spark-Ignition Engines
------------------------------------------------------------------------
                                      Compression-       Spark-ignition
          Cycle metric               ignition  FTP     FTP vehicle  duty
                                  vehicle  duty cycle        cycle
------------------------------------------------------------------------
Maximum acceleration (m/s2).....                 1.55               1.47
Maximum deceleration (m/s2).....                -2.26              -2.15
Average speed (mph).............                 20.1               19.2
Maximum speed (mph).............                 60.6               60.8
Stop duration (%)...............                  3.3                4.7
Distance (miles)................                  6.4                6.4
------------------------------------------------------------------------

BILLING CODE 6560-50-P

[GRAPHIC] [TIFF OMITTED] TR29JN21.003

    The road gradient profile is designed to further align the
powertrain system load for engines installed in conventional vehicles
and hybrid systems to eliminate the deviations in cumulative work done
between the engine and powertrain test. The grade profiles were
developed to align the power versus time and cycle work of the vehicle
profiles (compression-ignition vFTP, spark-ignition vFTP, and vSET) to
the compression-ignition and spark-ignition FTPs, and SET. The general
process was based on the development of the grade profile for the World
Harmonized Vehicle Cycle (WHVC).\15\ A reference normalized power curve
was generated using denormalized torque and speed curves from 50
different compression-ignition engines with multiple engine ratings for
the compression-ignition FTP, and SET. The denormalized curves were
normalized individually for each engine based on the engine's rated
power. The normalized power curves were then averaged to define the
final reference normalized power curve. Ten different spark-ignition
engine torque curves were used for the spark-ignition FTP. The duty-
cycle velocity profile over time was then divided into multiple mini-
cycles. Within each mini-cycle, a constant grade was defined in such a
way that the energy calculated from the normalized power curve was
matched for a given engine power rating. Power ratings between 100 and
500 kW were used to develop the compression-ignition vFTP, spark-
ignition vFTP, and vSET duty-cycles. The average slope was calculated
from the road grade profiles generated for the power ratings between
100 and 500 kW. The average fixed slope was calculated for every time
step along the drive cycle, and a second order polynomial was chosen
for the FTP duty-cycles to describe correlation between, and account
for the differences in, the average fixed and individual slopes based
on the rated power (Prated) of the powertrain. The equation and
coefficient descriptions follow:
---------------------------------------------------------------------------

    \15\ Six, C., Siberholz, G., Fredriksson, J., Geringer, B.,
Hausberger, S. Development of an exhaust emission and CO2
measurement test procedure for heavy-duty hybrids (HDH). October 27,
2014. Available online at: https://wiki.unece.org/download/attachments/4064802/20141027_ACEA_Report.pdf?api=v2.
[GRAPHIC] [TIFF OMITTED] TR29JN21.004

    Where a is error compensation in %/kW\2\, b is error compensation
in %/kW, and c is the average fixed slope pattern. Negative road grade
is included in the profile to ensured that a representative amount of
recuperation energy is provided by the test cycle for hybrid
applications. This enables accurate cycle power/work alignment for all
vehicles with the FTP duty cycles for both compression-ignition and
spark-ignition engines. Example vehicle road

grade profiles for a 350 kW compression-ignition and 400 kW spark-
ignition engine can be found in Figure II-3 and Figure II-4.
BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TR29JN21.005

    During additional review of the development of the road grade
profile for vSET included in the proposal, it became apparent that the
powertrain might not be able to achieve the default vehicle C speed of
75.0 mph. To provide a representative maximum vehicle speed and vehicle
A and B speeds that are scaled to the C speed in the final test
procedure, the determination of vehicle C speed was added as an
additional revision to 40 CFR 1036.527. This maximum achievable vehicle
speed is used as the vehicle C speed in Table 1 of Sec.  1036.505 and A
and B speed are calculated as described in 40 CFR 1036.505. The final
test procedure replaces the proposed maximum vehicle C speed and the
default vehicle A and B speeds in the proposed additions to Table 1 of
Sec.  1036.505 with these calculated speeds. Adding the allowance to
scale the vSET test speeds based on the vehicle maximum achievable
speed required an accounting of the effect of these lower speeds on the
road grade determination. This resulted in an expansion of the proposed
second order polynomial equation for the vFTP to include vehicle speed
in the final test procedure. The expanded equation and coefficient
descriptions follow:
[GRAPHIC] [TIFF OMITTED] TR29JN21.006

    Where a is error compensation in %/kW3, b is error compensation in
%/kW2[middot]mi/hr, c is error compensation in %/kW2, d is error
compensation in %/(mi/hr)2, e is error compensation in %/kW[middot]mi/
hr, f is error compensation in %/kW, g is error compensation in %/mi/
hr, and h is the average fixed slope pattern. Negative road grade is
included in the profile to ensure that a representative amount of
recuperation energy is provided by the test cycle for hybrid
applications. This enables accurate cycle power/work alignment for all
vehicles with the engine SET duty-cycle.
    The final test procedure also includes updates to the road grade
coefficients for the compression-ignition and spark-ignition vFTP duty
cycles from those proposed. EPA further reviewed the GTR No. 4 process
and noted that the work in mini cycles number 4 and 6 was set to zero.
This was a policy decision made during the GTR No. 4 process but is not
appropriate for the generation of EPA's duty-cycles, which should
include the actual work for these two mini cycles. While this
improvement results in only a marginal difference from that proposed,
it provides a more aligned comparison of work between the engine and
vehicle duty-cycles. The result of this was included in the final test
procedure in updated coefficients for the compression-ignition vFTP,
spark-ignition vFTP, and vSET duty cycles (vSET improvements are in
addition to the road grade coefficient updates already discussed).
Figure II-5 and Figure II-6 show a comparison of the effect on work
matching from changing the mini cycle work in mini cycles number 4 and
6 from zero to the actual work for a 300 kW engine. Note, this final
test procedure is limited to hybrid powertrains to avoid having two
different testing pathways for non-hybrid engines for the same
standards.

[GRAPHIC] [TIFF OMITTED] TR29JN21.007

BILLING CODE 6560-50-C
b. Hybrid Test Procedures for Vehicle Standards
i. Hybrid Fuel Maps
    We are finalizing an option, after consideration of comments
received, to generate fuel maps for engine hybrids using the powertrain
test procedure in 40 CFR 1037.550. This was done by updating the hybrid
engine test procedures finalized in 40 CFR 1036.503, 1036.505,
1036.527, and 1037.550 and include the addition of a transmission model
to GEM and options in GEM to test without the transmission present,
using the model in its place.
ii. Mild Hybrid Certification
    Under the Phase 2 regulations, manufacturers must conduct
powertrain testing if they wish to take credit for hybrid systems,
including mild hybrid systems. However, manufacturers have expressed
concerns about the cost of powertrain testing and that the existing
procedure may not measure improvements from certain mild hybrid
systems. EPA requested comment on alternative means of evaluating mild
hybrids noting that manufacturers have asked EPA to consider the
following options:

     Allow manufacturers to test a powertrain and apply
analytically derived scaling factors to others (e.g., scale by fraction
of battery capacity or motor capacity) under 40 CFR 1037.235(h).
     Allow manufacturers to use international test procedures
for battery capacity, motor power, and motor efficiency.
     Provide smaller credit (potentially with a volume limit
and/or only for limited time) in exchange for less testing (e.g.,
reduced benefit when using the simplified model spreadsheet that is
available under docket no. EPA-HQ-OAR-2014-0827-2109).
    Commenters generally responded with support for EPA addressing mild
hybrid certification but did not provide any concrete means to address
concerns surrounding the cost of powertrain testing. In addition,
commenters stated that the existing procedures in the proposal may not
measure improvements from certain mild hybrid systems. This section
presents the changes we are adopting to hybrid test procedures after
consideration of comments received. Additional details on these and
other hybrid test procedure amendments or clarifications requested by
commenters and our responses are available in Chapter 2 of our Response
to Comments.
    After further consideration, including the lack of additional input
on these mild-hybrid certification options, we have concluded that the
engine hybrid test procedure proposed in this rule, is the best pathway
for these hybrids. This will allow a manufacturer to test a mild hybrid
engine without having to certify the hybrid with a transmission under
the powertrain testing option. Finalizing these changes allows the test
results to better reflect the performance of mild hybrid's that are not
integrated into the transmission, without requiring that the
transmission be part of the certified configuration. Finalizing this
procedure also allows the test results to be used for additional
appropriate vehicles, since the test results will not be limited to the
transmission that was included during the test, as is required for non-
hybrid powertrains utilizing 40 CFR 1037.550. This mild hybrid engine
test procedure was finalize via additions to the hybrid powertrain test
procedure revisions in 40 CFR 1036.503, 1036.505, 1036.510, 1036.527,
and 1037.550 and includes the addition of a transmission model to GEM
and options in GEM to test without the transmission present, using the
model in its place.

B. Heavy-Duty Engine GHG Emission Standards and Flexibility

1. Revisions to Credit Provisions for Vocational Engine Emissions
Standards
    EPA proposed several updates to the credit provisions related to
credit provisions for vocational engines and requested comment on these
credit provisions (see 85 FR 28145). This section presents the changes
we are adopting to vocational engine credit provisions after
consideration of comment received. Additional details on comment on
these credit provisions and our response are available in Chapter 2.4
of our Response to Comments.
    In developing the baseline emission rates for vocational engines in
the final Phase 2 rulemaking, we considered MY 2016 FTP certification
data for diesel engines, which showed an unexpected step-change
improvement in engine fuel consumption and CO2 emissions
compared to data considered in the proposed rule. The proposed baseline
emission rates came from the Phase 1 standards, which in turn were
derived from our estimates of emission rates for 2010 engines. The
underlying reasons for this shift in the 2016 Phase 2 final rule were
mostly related to manufacturers optimizing their selective catalytic
reduction (SCR) thermal management strategy over the FTP in ways that
we (mistakenly) thought they already had in MY 2010 (i.e., the Phase 1
baseline).
    As background, the FTP includes a cold-start, a hot-start and
significant time spent at engine idle. During these portions of the
FTP, the NOX SCR system can cool down and lose
NOX reducing efficiency. To maintain SCR temperature,
manufacturers initially used a simplistic strategy of burning extra
fuel to heat the exhaust system. However, during the development of
Phase 1, EPA believed manufacturers were using more sophisticated and
efficient strategies to maintain SCR temperature. EPA's
misunderstanding of the baseline technology for Phase 1 provided engine
manufacturers the opportunity to generate windfall credits against the
FTP standards.
    For the Phase 2 final rule, EPA revised the baseline emission rate
for vocational engines to reflect the actual certified emission levels.
The Phase 2 vocational engine final CO2 baseline emissions
are shown in the table below. More detailed analyses on these Phase 2
baseline values of tractor and vocational vehicles can be found in
Chapter 2.7.4 of the Phase 2 Final RIA.\16\
---------------------------------------------------------------------------

    \16\ U.S. EPA, U.S. DOT/NHTSA. Greenhouse Gas Emissions and Fuel
Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles
-Phase 2: Regulatory Impact Analysis, August 2016, EPA-420-R-16-900.
See p. 2-76.

 Table II-3--Phase 2 Vocational Engine CO2 and Fuel Consumption Baseline
                                Emissions
------------------------------------------------------------------------
                    Units                        HHD      MHD      LHD
------------------------------------------------------------------------
g/bhp-hr.....................................      525      558      576
gal/100 bhp-hr...............................   5.1572   5.4813   5.6582
------------------------------------------------------------------------

    EPA did not allow the carryover of Phase 1 vocational engine
credits into the Phase 2 program, consistent with these adjustments to
the baselines. Since this issue does not apply for RMC emissions, the
restriction was applied only for engines certified exclusively to the
FTP standards (rather than both FTP and RMC standards). We believed
that allowing engine credits generated against the Phase 1 diesel FTP
standards to be carried over into the Phase 2 program would have
inappropriately diluted the Phase 2 engine program. However, this was
in the context of unadjusted credits.
    After further consideration, we now believe that it would not
dilute the program if the credits were appropriately adjusted to more
accurately reflect improvement over the true baseline levels.
    Allowing the portion of the credits that represent actual emission
improvements to be carried forward is consistent with our rationale
from Phase 2. Thus, we are allowing in Sec.  1036.701(j), for the
purpose of carrying Phase 1 credits into the Phase 2 program, and not
compliance with Phase 1 standards, that manufacturers may recalculate
the credits in their initial Phase 1 averaging, banking, and trading
(ABT) vocational engine averaging set relative to the Phase 2 baseline
engine values. The recalculated vocational engine credits for an ABT
averaging set will be allowed into the Phase 2 engine program to the
same extent as tractor engine credits. Cummins submitted a late comment
(see Docket ID EPA-HQ-OAR-2019-0307-0066) requesting clarification of
whether manufacturers would have the option of applying these
vocational carryover provisions to one ABT averaging set but not
another (i.e., that EPA would not require the recalculation of all
averaging sets.) This final rule affirms that recalculation of
vocational credits is to be applied to all engines within an individual
ABT averaging set and that

other averaging sets, such as tractors, are not affected by these
vocational carryover provisions. EMA commented that manufacturers
should be able to opt in to recalculating credits on an engine family
by engine family basis, as applying this adjustment to all engine
families could affect existing Phase 1 compliance for engines above the
Phase 2 baseline value. However, EPA is only allowing this
recalculation for the purpose of determining the amount of credit that
can be carried into the Phase 2 program, and adjusting the credits for
all the engine families a manufacturer chose to include in their
initial ABT averaging set for Phase 1 program properly accounts for the
net credits that can be carried forward. In the ABT program, all engine
families within an averaging set are used in the calculation of
credits, and manufacturers cannot pick and choose which engine families
are used in that calculation.
    As noted in the Phase 2 final rule, allowing additional flexibility
for compliance with engine standards does not cause any increase in
emissions because the manufacturers must still comply with the vehicle
standards (See 81 FR 73499, October 25, 2016). However, this
flexibility could allow some manufacturers to find a less expensive
compliance path.
2. Special Flexibility for Vocational Engines and Credits
    EPA requested comment on several updates to the special flexibility
provisions for vocational engines (see 85 FR 28145). This section