will ensure scheduled maintenance has a reasonable likelihood of being
performed and allow manufacturers to demonstrate they meet adjustable
parameter requirements at the time of certification while addressing
operator frustration with false inducements and severe inducement speed
restrictions that may potentially lead to in-use tampering of the SCR
system. We are concerned that engine designs that may have been
intended to be responsive to the existing SCR guidance may have
resulted in high levels of false inducement and overly restrictive
speed limitations and may have increased in-use tampering.\621\ For
example, there are many technical support bulletins that have been
released by manufacturers that detail inducements occurring for reasons
outside of operator control, such as minor corrosion on electrical
connectors.\622\ In addition, we received comments on the ANPR
regarding false inducements leading to emissions tampering.\623\ EPA is
aware there are products available in the marketplace to facilitate
tampering through the removal of SCR systems, which might be being
unlawfully used by vehicle owners who are adversely affected by false
inducements. After a decade of experience with SCR-equipped engines and
existing EPA guidance, several of the initial concerns with the use of
SCR that formed the basis of some elements of the existing guidance
have been resolved. DEF is widely available and the cost of DEF at the
pump is not that different from the cost of distilled water. A less
restrictive approach could be equally effective at encouraging
operators to maintain a supply of DEF, without causing problems that
may be leading to increased in-use tampering. A less restrictive
inducement schedule would allow operators more flexibility for on-time
delivery, reduce operator costs by allowing vehicles to be driven to
repair shops thereby avoiding towing fees, and allow more time for
proper diagnosis and repair to reduce the need for repeat visits to
repair shops.
---------------------------------------------------------------------------

    \621\ See section IV.D.1. for further discussion on existing
inducement guidance documents including: CISD-07-07 and CISD-09-04
REVISED.
    \622\ Miller, Neil; Kopin, Amy. Memorandum to docket EPA-HQ-OAR-
2019-0055. ``TSB Aftertreatment Faults.'' September 9, 2021.
    \623\ See comments from NADA, Docket ID EPA-HQ-OAR-2019-0055-
0369.
---------------------------------------------------------------------------

    These seven principles, which include improved diagnostic fault
communication, NOX override checks, and revised inducement
speeds and schedules that reflect more realistic vehicle operations,
would result in a program that more effectively maintains in-use
emission reductions. We believe the proposed provisions described in
the following section would provide a net benefit to fleet operators,
small businesses, and the environment.
4. Proposed Inducement Provisions
    Consistent with the seven principles described in Section IV.D.3.
EPA is proposing to specify in 40 CFR 1036.125(a)(1) that manufacturers
must meet the specifications in 40 CFR 1036.111 to demonstrate that DEF
replenishment is reasonably likely to occur at the recommended
intervals on in-use engines and that adjustable parameter requirements
will be met. We are proposing to exclude the alternative option in 40
CFR 86.004-25(b)(6)(ii)(F) to demonstrate DEF replenishment is
reasonably likely to be performed in use and are seeking comment on
whether manufacturers should be allowed to ask for approval to use an
alternative method of compliance to meet these requirements. Consistent
with the existing guidance, the proposed requirements would codify that
SCR-equipped engines must meet critical emission-related scheduled
maintenance requirements and limit the

physically adjustable range under the adjustable parameter requirements
by triggering inducements. EPA is proposing to adopt requirements that
inducements be triggered for fault conditions including: (1) DEF supply
is low, (2) DEF quality does not meet manufacturer specifications, or
(3) tampering with the SCR system. EPA is also proposing separate
inducement schedules for low- and high-speed vehicles. The proposed
inducement requirements would include a NOX override to
prevent false inducements. EPA is proposing to require manufacturers to
improve information provided to operators regarding inducements. The
proposal also includes a provision to allow operators to remove
inducement conditions after repairing the engine either through the use
of a generic scan tool or through a drive cycle to ensure that repairs
have been properly made. EPA is proposing that if multiple repeat fault
conditions are detected that the inducement schedule would not restart
with each new fault.
    The proposed inducement provisions include several aspects. The
first three described here relate to proposed inducement triggers in 40
CFR 1036.111. First, EPA is proposing to require inducements related to
DEF quantity to ensure that high-quality DEF is used, similar to the
approach described in our existing guidance. Specifically, we propose
that SCR-equipped engines must trigger the start of an inducement when
the amount of DEF in the tank has been reduced to a level corresponding
to three hours of engine operation.
    Second, EPA proposes to require inducements related to DEF quality
to ensure that high-quality DEF is used, similar to the approach
described in our existing guidance. There was a concern when SCR was
first introduced into the market a decade ago that DEF availability may
be limited and some operators may choose to use poor quality DEF, or,
for example, dilute DEF with water to reduce operating costs. DEF
quickly became widely available and today is conveniently available
even in pump form (e.g., next to diesel pumps at refueling stations) to
refill DEF tanks while refilling diesel tanks. Modern engines are
designed with feedback controls to increase or decrease DEF flow as the
system detects that a greater or lesser quantity of DEF is needed to
supply the amount of urea needed to keep the SCR catalyst working
properly or trigger an inducement. This DEF dosing feedback removes any
practical incentive for diluting DEF, as any such attempt would result
in more volume of DEF being consumed and trigger an inducement when
emissions control is no longer possible. Further, OEMs have made clear
to operators that using water without urea would cause extensive engine
damage and void the warranty. Today, the per-gallon price of DEF at the
pump is closer to the price of a gallon of distilled water. Given an
operator's ability to physically adjust DEF quality and the increase in
NOX emissions that would result if they do so, EPA maintains
that DEF quality is an adjustable parameter and is proposing to require
inducements when DEF quality fails to meet manufacturer concentration
specifications. Due to widespread DEF availability and familiarity with
operators, EPA believes operators would readily find and use high-
quality DEF to avoid inducements. As discussed in Section IV.D.1.ii,
CD-13-13 provides guidance on DEF quality as an adjustable parameter.
The guidance states that EPA generally considers the range of
adjustment for emission testing to span the change in urea
concentration from 32.5 percent (unadulterated DEF) to the point at
which poor DEF quality can be detected. This point represents the limit
for DEF quality adjustment because it is the first point at which a
manufacturer is able to implement inducements to prevent sustained
engine or vehicle operation with poor quality DEF. EPA is not proposing
changes to this guidance.
    Third, EPA is proposing to require inducements to ensure that SCR
systems are designed to be tamper-resistant to reduce the likelihood
that the SCR system would be circumvented, similar to the approach
described in our existing guidance. CISD-09-04R discusses tamper-
resistant design with respect to a list of engine components in the SCR
system and suggests that manufacturers could design these components to
be physically difficult to access in addition to using warnings and
inducements if they are disconnected. We are proposing to require
monitoring for and triggering of an inducement for tampering with the
components listed in CISD-09-04R, as well as for a limited number of
other components. Specifically, we are proposing that open-circuit
fault conditions for the following components trigger inducements if
detected, to prevent disconnection through tampering: (1) DEF tank
level sensor, (2) DEF pump, (3) DEF quality sensor, (4) SCR wiring
harness, (5) NOX sensors, (6) DEF dosing valve, (7) DEF tank
heater, and (8) aftertreatment control module (ACM). Monitoring the DEF
tank heater is important to ensure AECD requirements are met. We are
not proposing to include the language from CISD-09-04R that such
components should be designed to be physically difficult to access
because an inducement condition would be triggered upon the unplugging
of a component (i.e., an open-circuit condition).\624\ Similar to the
approach described in CISD-09-04R which specified that disconnection of
the SCR wiring harness could trigger inducements as a tamper-resistant
design strategy, we are proposing to specify that the ACM also be
monitored for disconnection. In addition to proposing to require
detection of open-circuit conditions for certain components to prevent
tampering, EPA is also proposing to require that manufacturers trigger
an inducement for blocked DEF lines or dosing valves similar to the
approach described in CISD-09-04R.\625\ EPA is proposing that all
inducement-related diagnostic data parameters be made available with
generic scan tools (see section IV.C.1.iii.b. for further information).
Finally, EPA is proposing to require that manufacturers monitor for a
missing catalyst (see OBD requirements for this monitor in 13 CCR
1971.1(i)(3.1.6)) and trigger an inducement if this condition is found.
---------------------------------------------------------------------------

    \624\ An Open-Circuit is a fault where the resistance of a
circuit has increased to the point where electrical current will no
longer flow through it, and is typically caused by a blown fuse,
broken wire, or removal of circuit components.
    \625\ We are proposing in 40 CFR 1036.110(b)(8)(i) that
manufacturers notify operators of problems before blockages actually
occur to allow operators an opportunity to perform repairs and avoid
an inducement.
---------------------------------------------------------------------------

    As indicated in ANPR comments summarized in Section IV.D.2, many
operators report experiencing false inducements from faulty hardware
that are not a result of tampering. These experiences may indicate that
the existing triggers for inducements in engines may be too aggressive,
or that OEMs may not be able to clearly distinguish between tampering
and faulty hardware. EPA reviewed various manufacturer's inducement
strategies in their certification documents and compared those to our
existing guidance. Some manufacturers have certified engines with
nearly 200 different reasons for an engine to go into a derate
condition, including nearly 50 reasons for an SCR-related inducement.
Many of the derates are for engine protection, and we are not proposing
to make any changes to these types of derates. However, we are adopting
a list of SCR system inducement triggers for

meeting critical emissions-scheduled maintenance and adjustable
parameter requirements that focus on specific emission control
components and conditions that owners can control such as disconnecting
a DEF pump or other SCR-related emission control hardware. The proposed
list includes the tamper-resistance inducement triggers included in
CISD-09-04R as well as additional components. We believe that
standardizing the list of tampering inducement triggers would aid
owners, operators, and fleets in the repair of their vehicles by
reducing the cost and time required to diagnose the reason for
inducement.
    Fourth, we are proposing separate four-step derate schedules and
final inducement speeds for vehicles that operate at low and high
speeds as shown in Table IV-13. We are proposing that the application
of low-speed inducements (LSI) and high-speed inducements (HSI) be
based on an individual vehicle's operating profile. In particular,
vehicles that have a stored average vehicle speed below 20 mph during
the previous 30 hours of engine operation (not including idle time)
would be considered low-speed vehicles and be subject to an LSI.
Excluding idle from the calculation of vehicle speed allows us to more
effectively evaluate each vehicle's speed profile, not time spent
idling, which does not impact the effectiveness of a final inducement
speed. EPA chose this speed based on an analysis of real-world vehicle
speed activity data from the FleetDNA database maintained by the
National Renewable Energy Laboratory (NREL).\626\ Our analysis provided
us with insight into the optimum way to characterize high-speed and
low-speed vehicles in a way to ensure these categories received
appropriate inducements that would not be ineffective or overly
restrictive.
---------------------------------------------------------------------------

    \626\ Miller, Neil; Kopin, Amy. Memorandum to docket EPA-HQ-OAR-
2019-0055. ``Review and analysis of vehicle speed activity data from
the FleetDNA database.'' October 1, 2021.
---------------------------------------------------------------------------

    EPA is proposing to require specific inducement schedules for low-
speed and high-speed vehicles. We are proposing to codify progressively
increasing inducement derate schedules that allow the owner to
efficiently address conditions that trigger inducements. Table IV-13
shows the proposed default four-step inducement schedules in cumulative
hours. The time spent in each stage of inducement would include time
spent idling. The initial inducement of either 50 mph or 65 mph would
apply immediately when the OBD system detects: (1) There is
approximately three hours-worth of DEF remaining in the tank, (2) DEF
quality fails to meet manufacturers' concentration specifications, or
(3) when certain SCR system tampering events have occurred. The
inducement schedule would then step down over time to result in a final
inducement speed of either 35 mph or 50 mph depending on individual
vehicle operating profiles. In determining the appropriate final
inducement speeds for this proposal, EPA also relied in part on
analysis of data in the NREL FleetDNA database. Analyzing potential
impacts of final inducement speeds based on vehicle applications
involves a number of different considerations, beyond how much time a
particular application spent at different speeds. For example, the
ability to achieve higher speeds may be critical to many different duty
cycles and logistics necessary for commercial activities. Inducements
are intended to reduce/eliminate the ability to perform work such that
operators will replenish the tank with high-quality DEF and not tamper
with the SCR system. For example, our data show that combination long-
haul vehicles spend nearly almost 40 percent of their driving time over
65 mph. Based on this operation, an inducement speed of 65 mph will
cause a significant impact on the ability of the vehicle to be used for
commercial purposes, which means that any speed restriction below this
threshold is less likely to further incentivize operators to keep
emissions systems compliant. In addition, there were other segments
that may operate at lower average speeds, but when looking at their
duty cycle, it is clear that they depend on being able to complete
their work by achieving high rates of speed frequently, although not
for sustained periods (e.g., delivery vehicles that return to a
warehouse multiple times throughout the day to reload). These vehicles
may travel at lower speeds with frequent stop and go operation during
delivery but may need to travel on the highway to return to the
warehouse in order to complete a certain number of operations in a day.
Many vehicle segments in our sample exhibited this type of duty cycle
with frequent higher speeds, for example, some single short-haul
vehicles that had average speeds under 20 mph had duty cycles that
reached 60-70 mph briefly every hour.
    We are proposing that the inducement schedules for low- and high-
speed vehicles include four stages that ramp down speeds to the final
LSI and HSI. The first stepped decrease in speed would apply six hours
after the initial inducement, which allows time for operators to fill
the DEF tank and resume operation in a way that allows the engine to
confirm a proper DEF supply without starting the next stage of
inducement. If the fault code is not resolved, the schedule continues
to reduce the vehicle speed by 5 mph increments in two additional
stages. One of the considerations in choosing the stepped speed
decreases is allowing drivers time to safely adjust to operation at a
lower speed while also adequately incentivizing action by vehicle
owners and operators, and we are proposing that 5 mph increments
achieve this balance. Commenters noted that even small changes in
allowable speeds are sufficient incentive to use high quality DEF.
Further, we believe the first step of our proposed inducement policy
would result in the use of high-quality DEF. The proposed additional
time would also allow for the diagnosis and repair of more extensive
problems and intermittent conditions.
    The low-speed vehicle schedule and the final LSI speed of 35 mph is
designed for vehicles such as urban buses, school buses, and refuse
haulers that have sustained operation at low speeds, but frequently
travel at high speeds. Further, the final LSI speed would also apply to
concrete trucks, street sweepers, or other utility vehicles that have
low average speeds, but depend on higher speed operation to get to a
job site. In part, because of this high-speed operation, the final LSI
speed will be effective for compelling operators to properly maintain
their aftertreatment systems. The high-speed vehicle schedule and the
final HSI speed of 50 mph is designed for vehicles such as long-haul
freight trucks that have sustained operation at high speeds. The final
restricted speed of 50 mph prevents the vehicle from travel on most
interstate highways with state laws regarding impeding traffic and may
require the operator to use flashers to warn other vehicles of the
reduced speed.
    We expect that the proposed derate schedules would be no less
effective than the current approach under existing guidance for
ensuring operators properly maintain aftertreatment systems and that it
would result in lower costs and impacts to operators and ultimately
result in lower tampering rates. EPA recognizes that the fleet is very
diverse, and believes that applying two inducement schedules and speeds
is an effective and reasonable approach that is not too aggressive or
too inconsequential to ensure operators maintain compliance. Our
analysis and proposed LSI and HSI schedules are intended to achieve the
proper balance

and limit unintended consequences such as increased tampering.

               Table IV-13--Proposed Inducement Schedules
------------------------------------------------------------------------
                                                  Maximum speed (mi/hr)
                                               -------------------------
               Engine hours \a\                  Low-speed    All other
                                                  vehicles     vehicles
------------------------------------------------------------------------
0.............................................           50           65
6.............................................           45           60
12............................................           40           55
60............................................           35           50
------------------------------------------------------------------------
\a\ Hours start counting with the onset of the triggering condition
  specified in paragraph (b) of this section. For DEF supply, you may
  program the engine to reset the timer to three hours when the engine
  detects zero DEF flow.

    Sixth, to reduce occurrences of false inducements, the proposed
inducement approach would require a warning to be displayed to the
operator to indicate a fault, but utilize a NOX override
feature to prevent false inducement. We are proposing that an
inducement would not be triggered if average data from the
NOX sensor show that the catalyst is reducing NOX
emissions consistent with stored OBD REAL Bin data within an estimated
10 percent margin of error due to limitations of in-use detection and
measurement. A 10 percent reduction in NOX conversion
efficiency has been selected because the accuracy of the NOX
measurement can have errors as much as 10-20 percent based on a study
conducted by SwRI.\627\ This NOX sensor error increases as
the NOX concentration is reduced. Using a 10 percent error
is a reasonable threshold based on the work completed by SwRI and
considering continuing advances in technology of on-board
NOX sensors.
---------------------------------------------------------------------------

    \627\ ``Heavy-Duty Engine Low-Load Emission Control Calibration,
Low Load Test Cycle Development, and Evaluation of Engine Broadcast
Torque and Fueling Accuracy During Low-Load Operation,'' Low
NOX Demonstration Program--Stage 2, Christopher A. Sharp,
Southwest Research Institute, SwRI Project No. 03.22496, Final
Report, May 6, 2020.
---------------------------------------------------------------------------

    For vehicles subject to a HSI, this data would come from Bin 14
which holds data taken during operation at vehicle speeds greater than
40 mph and when the engine power output is greater than 50 percent of
rated power. For vehicles subject to a Low Speed Inducement (LSI), this
data would come from Bin 13 which holds data taken during operation at
vehicle speeds greater than 25 mph and less than or equal to 40 mph and
when the engine power output is greater than 50 percent of rated power.
This data would indicate whether DEF is present in the system as zero
NOX reductions would occur without DEF, and data showing
reductions consistent with operation prior to the condition would
indicate that the operator is adding high-quality DEF. We propose that
the NOX sensor data used to evaluate the need for inducement
would come from the 100-hour active array, which would be reset at the
time an initial inducement trigger occurred. Resetting the array at
that time would ensure that the data used to evaluate whether
sufficient high-quality DEF is present in the system would be taken
after the initial inducement was triggered and not rely on historical
data to make the assessment. The OBD system would continue to monitor
the fault condition and provide a warning to the operator that an issue
should be addressed, but an inducement would not be triggered unless
NOX performance fell below the threshold of a 10 percent
reduction in NOX conversion efficiency (e.g., indicating
that the operator has not added DEF).
    Seventh, as discussed in section IV.D.3, EPA is proposing in 40 CFR
1036.111(f) that manufacturers must display the condition that
triggered the pending or active derate and a countdown timer to
estimate the time or distance remaining before the next stage of
derating. This display requirement would apply even if the engine
overrides a detected fault condition based on NOX
measurements, and the display should indicate that the derates will not
apply as long as NOX sensors continue to show that emission
controls are functioning properly. It is critical that operators have
clear and ready access to information regarding inducements to reduce
potential anxiety over progressive engine derates (which can lead to
motivations to tamper) as well as to allow operators to make informed
decisions.
    Eighth, we are proposing that the system would remove the
inducement and resume unrestricted engine operation once the OBD system
detects the condition has been remedied. EPA would also expect
manufacturers to enable the system to reset once the problem was
repaired. EPA is proposing to require that generic scan tools be able
to remove an inducement condition. This would allow owners who repair
vehicles outside of commercial facilities to complete the repair
without delay (e.g., flushing and refilling a DEF tank where
contaminated DEF was discovered). However, if the same fault condition
repeats within 80 hours of engine operation (e.g., in response to a DEF
quantity fault an owner adds a small but insufficient quantity of DEF),
we are proposing that the system would treat the reoccurring fault
condition as the same triggering condition and immediately resume the
derate at the same point in the derate schedule where it was last
deactivated. In addition, we are proposing that the Active 100 Hour
Array would not be reset if an additional fault occurs before the first
code is resolved. The 80 hour window should be long enough to prevent
operators from applying temporary remedies, but not so long that
operators are unfairly held to the schedule for a past fault condition
when a new fault occurs. This repeat fault provision would prevent
operators from circumventing requirements by not properly addressing
the problem.
    As discussed in Section IV.C, EPA is seeking comment on whether
improvements could be made to OBD to monitor inducement conditions to
ensure a false inducement did not occur and to track such inducements
and the conditions that trigger them. Having access to additional OBD
data for inducement-related conditions can help operators and repair
technicians pinpoint and respond to conditions that currently are often
leading to reports of `no trouble found' or false inducements.
    As noted in ANPR comments, vehicle operators have experienced
inducements that do not seem to be keyed to detected fault conditions,
and inducements have occurred on a different schedule than
anticipated.\628\ These problems may be caused by wear conditions,
malfunctioning components, or inadequate system logic. Successful
implementation of the proposed inducement provisions depends on
production of engines that operate according to the engine
manufacturers' designs over a lifetime of in-use operation.
---------------------------------------------------------------------------

    \628\ See the comments of the American Trucking Associations on
the CARB Omnibus rulemaking, ``Proposed Heavy-Duty Engine and
Vehicle Omnibus Regulation and Associated Amendments.'' Available
here: https://www.arb.ca.gov/lists/com-attach/45-hdomnibus2020-U2EHMQQ3AGNSegZl.pdf.
---------------------------------------------------------------------------

    We believe this proposed approach minimizes potential adverse
impacts on operators while meeting the fundamental objective that
manufacturers design engines to ensure that operators maintain an
adequate supply of DEF to keep the SCR emission control system
functioning properly.
5. Requests for Comment
    We are open to considering a wide range of adjustments to the
proposed inducement provisions and request comment on all aspects of
the proposal described in this section. We ask that commenters
suggesting alternative approaches or specifications consider the
principles identified in Section IV.D.3 to inform our development of
the

proposed provisions. We are interested in any alternative regulatory
provisions and any different principles recommended by commenters, as
well as commenters' views on how EPA applied the identified principles
in developing the proposed inducement provisions.
    We are also interested in whether commenters support adoption of
inducement provisions that closely follow existing inducement
strategies in-use, for example derating to 5 miles per hour within four
hours of detecting certain fault conditions and, if so, whether such an
approach would meet the principles we described or whether there are
other principles that support such an approach.
    While we believe the proposed derate schedule would effectively
lead every vehicle owner to address certain detected fault conditions
within the duration of the specified schedule, we invite comment and
relevant information that would help to assess how vehicle operators in
a wide variety of vehicle applications would respond to a derate at any
specific level of operating speed restriction. Toward that end, we ask
for comments in response to the following questions:
     Is the proposed initial speed restriction of 50 (for low-
speed vehicles) and 65 miles per hour (for high-speed vehicles)
immediately upon detecting a fault condition meaningful? For example,
we may consider alternative initial speed restrictions of 40 and 55 mph
to focus the operator's attention on addressing the fault condition
since the remedy could be as simple as adding DEF or as extensive as
making substantial repairs after a thorough diagnosis.
     Is the proposed final speed restriction of 35 (for low-
speed vehicles) and 50 miles per hour (for high-speed vehicles)
meaningful? For example, we may consider alternative final speed
restrictions of 25 and 40 mph.
     Is it appropriate to create a fault condition that
triggers inducement three hours before the DEF supply will be depleted?
The engine could alternatively be designed to warn the operator when
DEF supply is running low and start the inducement when the DEF supply
is depleted.
     Is the proposed six hours of non-idle operation the right
amount of time for the first stage of inducement to take effect at 50
or 65 miles per hour before progressing to the next stage of derating?
A shorter time may be appropriate for simply refilling DEF, but in
other situations that may frequently occur, the fault condition causing
the inducement requires diagnosing and repairing a defective component.
     Is the proposed schedule for successive derates after 12
and 60 hours appropriate? We may consider additional steps. As an
example, we may also consider a longer schedule involving more time
between stages such as 20 and 120 hours. Similarly, we may consider a
shorter schedule reducing the time between stages such as 8 and 40
hours.
     Is the proposed 80 hours of operation without repeating a
fault condition the appropriate length of time to distinguish between a
new fault condition that restarts the inducement schedule at the
initial derate speed and a repeated fault condition that resumes the
previous inducement at the same point that the system deactivated the
derate?
     Is the proposed schedule of derating speeds over time for
high-speed vehicles from 65 to 50 miles per hour and from 50 to 35
miles per hour both reasonable and effective? Would a more or less
aggressive schedule work to prevent operators from being content with
restricted operation to avoid the cost or inconvenience of maintaining
SCR systems? We request that commenters also explain whether any
information provided would support an adjusted schedule consistent with
the principles described in Section IV.D.3.
     Is the proposed average speed of 20 miles per hour over
the preceding 30 hours of operation the appropriate threshold speed for
a more restrictive derate schedule for low-speed vehicles? Is it
appropriate to exclude idle from the low-speed vehicle determination?
     Should a high-speed vehicle that continues to operate at
the final inducement speed eventually be treated like a low-speed
vehicle if its average speed eventually falls to that level (20 miles
per hour) based on its slower operation during inducement? Using the
proposed values, this would cause a vehicle to eventually shift from a
final inducement speed of 50 miles per hour down to a final inducement
speed of 35 miles per hour. This question is fundamentally about
whether there are any applications or scenarios for high-speed vehicles
for which an inducement at 50 miles per hour (or another final
inducement speed for high-speed vehicles in the final rule) is
insufficient to compel corrective action.
     Monitoring for tampering due to a blocked DEF line or
injector is intended to ensure that the line itself is not crimped or
the injector plugged intentionally. However, EPA is aware that urea
crystallization can mimic this type of tampering. OEMs can monitor DEF
line and injector pressures and know at what point they consider
pressure changes to be indicative of tampering. They should be able to
use these pressure readings to indicate that the system is plugging
over time and warn operators well in advance of an inducement (see
section IV.C.1.iii.2. for more information on this proposal). If
practical, should we specify the amount of time that manufacturers
should provide operators with advance notice of a blocked DEF line or
dosing valve prior to an inducement occurring for those cases where the
blockage is caused by plugging due to DEF crystallization as opposed to
direct tampering?
    We request comment on the proposed set of fault conditions for
triggering inducements intended to address the unique aspect of SCR
systems that depend on cooperation from vehicle operators. Toward that
end, we raise the following questions:
     Is it necessary and appropriate to include DEF
concentration as a fault condition, as proposed? There is an
established practice of using DEF and engines now have built-in
features to prevent diluting DEF or filling DEF tanks with water. Also,
with the proposed warranty provisions, owners may be more likely to
properly maintain their engines over longer periods, including use of
DEF that meets the owner's manual specifications. We request comment on
whether this concern about DEF quality continues to justify the
additional complexity and the associated risk of false inducements.
     Are the proposed fault conditions of DEF fill level, DEF
quality, and tampering associated with the SCR system the proper way to
ensure an adequate supply of quality DEF in-use?
     Does the proposal properly define tampering conditions for
inducement by identifying conditions that owners can control, such as
open-circuit faults for disconnected DEF pump, SCR wiring harness, DEF
dosing valve, DEF quality sensors, DEF tank heaters, DEF level sensors,
aftertreatment control module, and NOX sensors?
     Is there a risk that the engine will incorrectly detect a
tampering fault condition based on the specified open-circuit faults?
For example, how likely is it that maintenance steps that require
disconnecting or disassembling certain components as part of a repair
will be identified as tampering? Or, how likely is it that a failing
sensor will give an incorrect signal indicating that one of the
specified components has been disconnected? The proposal addresses
this, at least in part, by including an override feature based on
measured

NOX emissions before and after the SCR catalyst.
     Should we allow or require additional fault conditions to
ensure that SCR systems are working properly? We could identify
numerous additional fault conditions based on OBD system monitoring
that detects any number of SCR-related components that need to be
adjusted or replaced. We have focused the proposal on things that
owners can actually control consistent with the original focus of the
existing guidance on ensuring an adequate supply of high-quality DEF
paired with tamper-resistant SCR systems that focus on open-circuit
conditions. We request comment on any additional OBD fault conditions
that would be needed to ensure the functionality of the SCR system.
     Should EPA codify the DEF freeze protection guidance that
describes how to meet EPA AECD requirements currently described in CD-
13-13?
     Should EPA establish an acceptable range of DEF
concentration for defining the limits of the inducement fault
condition? Inducements for DEF quality are based on the change in urea
concentration from 32.5 percent (unadulterated DEF) to the point at
which poor DEF quality can be detected and inducements are triggered.
Manufacturers design some tolerance into their SCR systems to adapt to
and compensate for in-use DEF quality variances instead of triggering
an inducement for minor concentration differences. For example, if a
vehicle with DEF in the tank has not been driven for some time, some of
the water in the DEF can evaporate, leaving a slightly higher
concentration of urea in the DEF. We seek comment on the need to
clarify in the regulations appropriate DEF quality inducement triggers
to ensure that an acceptable tolerance is being designed into SCR
systems consistently across manufacturers and that reflects real-world
conditions. Further we seek comment on what an acceptable tolerance
would be.
    The proposed approach for overriding inducements based on
NOX sensors showing that the SCR catalyst is working
properly is an important feature to reduce the risk of false
inducements. Operators would see a warning for a fault condition even
if the override prevents a speed restriction, which should allow the
operator to take the time necessary to address the fault condition. The
override should be set at a level of NOX conversion
efficiency to reliably indicate that an override is appropriate because
the detected fault condition in fact does not prevent the SCR catalyst
from working according to design. We request comment on the proposed
approach that allows for overriding inducement if the average data from
the NOX sensor show that the catalyst is reducing
NOX emissions consistent with stored OBD REAL Bin data
within an estimated 10 percent margin of error due to limitations of
in-use detection and measurement. Toward that end, we raise the
following questions:
     Should the margin of error be more or less than 10
percent? NOX conversion efficiency is more stable at higher
speed and load conditions and is generally greater than 90 percent, so
overriding based on a greater margin of error should still be
effective. Fault conditions such as depleted DEF or disconnected
aftertreatment would cause NOX conversion efficiency to be
at or near zero and would quickly impact the NOX conversion
efficiency value due to the stored data array being reset at the time a
trigger is detected. In such cases a less rigorous or stringent
threshold value would be sufficient to evaluate the validity of the
detected fault condition. Note however that some system defects may
allow for partial NOX conversion.
     Are the (reset) Active 100 Hour Array and the specified
Real Bins 13 and 14 the appropriate data to assess the NOX
override, as proposed? The selected operating conditions are intended
to be most favorable for a stable and repeatable current assessment of
NOX conversion efficiency. Would the NOX override
need to account for a wider range of vehicle operation to work properly
for the full range of vehicle applications?
     Does the proposed final inducement speed in combination
with the provision for NOX overrides provide a proper self-
healing path for deactivating derates after correcting a fault
condition? There are likely times when this may be a preferrable option
for operators for resolving an inducement instead of relying on scan
tools.
    EPA is seeking comment on provisions to accommodate equivalent
engine families that are identical except for the diagnostic system
adjustments needed to meet the different inducement protocols. If
finalized, we would count two equivalent engine families as one for the
purposes of determining the number of engine families that are subject
to OBD demonstration testing requirements for certification. This would
be analogous to the way we are proposing to treat engine families that
have a California-only federal certificate because of differences such
as warranty provisions (see Section IV.C.2.i.a. for further discussion
on this provision).
    As described in Section IV.D.1, engine manufacturers have been
producing engines for many years with inducement strategies that align
with the potential approaches described in EPA guidance. If we replace
the guidance documents with regulatory provisions that include new
derating specifications, those specifications could be understood to
represent an alternative design strategy for meeting the objectives
described in guidance relative to requirements for maintenance
specifications and adjustable parameters. It may accordingly be
appropriate to allow engine manufacturers to modify earlier model year
engines to align with the new regulatory specifications. We are not
proposing to change the regulation to address this concern. We are
seeking comment on whether and how manufacturers might use field-fix
practices under EPA's field fix guidance to modify in-use engines with
algorithms that incorporate some or all of the inducement provisions we
include in the final rule.\629\ For example, this approach could
potentially allow engine manufacturers to change the final inducement
speed from 5 miles per hour to 50 miles per hour over a 60-hour period.
---------------------------------------------------------------------------

    \629\ ``Field Fixes Related to Emission Control-Related
Components,'' EPA Advisory Circular, March 17, 1975.
---------------------------------------------------------------------------

    Engine manufacturers may similarly be interested in modifying
engines from the current model year by amending the application for
certification. See Section XII.B.3 for additional discussion related to
amending applications for certification.
    Finally, EPA is seeking comment on whether existing manufacturer
inducement strategies are causing certain vocational segments to
transition from diesel to gasoline powertrains. For example, one school
bus manufacturer introduced gasoline-powered buses in late 2016, which
appear to have quickly come to represent nearly 25 percent of
sales.\630\ Another school bus manufacturer has indicated growing
interest in alternative fuel powertrains such as gasoline or propane in
response to SCR-related maintenance issues and downtime.\631\
---------------------------------------------------------------------------

    \630\ ``Blue Bird delivers its 5,000th gasoline-powered school
bus'' March 13, 2019. Available here: https://blue-bird.com/about-us/press-releases/146-blue-bird-delivers-its-5-000th-gasoline-powered-school-bus.
    \631\ ``Fleet Managers Rethinking Fuel Choice: Many Choosing New
Engines That Reduce Budget Pressure and Maintenance Headaches''
February 1, 2019. Available here: https://thomasbuiltbuses.com/bus-advisor/articles/fleet-managers-rethinking-fuel-choice/.

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

E. Certification Updates

    In an effort to better serve the regulated community, EPA has taken
a number of important steps to streamline the data collection processes
that manufacturers use to apply for annual certificates of conformity
from the agency. These streamlining efforts include numerous
modifications and enhancements to improve the user experience, minimize
manual data submission processes, and eliminate duplication of effort
for manufacturers. Beginning with the overall process, EPA has made
user-centered design a central theme when developing systems for
manufacturers. Engaging manufacturers before and throughout the
development process helps reduce incorrect assumptions about their
business needs and ensures that systems are end-user tested for
viability. We recently transitioned our compliance information system
from the Verify System to a new Engines and Vehicles Compliance
Information System (EV-CIS). This new platform incorporates
manufacturer feedback and includes updates that help manufacturers work
more efficiently while minimizing the need for costly fixes which can
lead to rework. Although we have made significant progress to improve
the certification process, we welcome comments suggesting additional
improvements EPA could consider.

F. Durability Testing

    EPA regulations require that a heavy-duty engine manufacturer's
application for certification include a demonstration that the engines
will meet applicable emission standards throughout their regulatory
useful life. This is often called the durability demonstration.
Manufacturers typically complete this demonstration by following
regulatory procedures to calculate a deterioration factor (DF).
Deterioration factors are additive or multiplicative adjustments
applied to the results from manufacturer testing to quantify the
emissions deterioration over useful life.\632\
---------------------------------------------------------------------------

    \632\ See proposed 40 CFR 1036.240(c) and the definition of
``deterioration factor'' in 40 CFR 1036.801, which are proposed to
be migrated and updated from 40 CFR 86.004-26 and 86.004-28.
---------------------------------------------------------------------------

    Currently, a DF is determined directly by aging an engine and
exhaust aftertreatment system to useful life on an engine dynamometer.
This time-consuming service accumulation process requires manufacturers
to commit to product configurations well ahead of their pre-production
certification testing to complete the durability testing so EPA can
review the test results before issuing the certificate of conformity.
Some manufacturers run multiple, staggered durability tests in parallel
in case a component failure occurs that may require a complete restart
of the aging process.\633\
---------------------------------------------------------------------------

    \633\ See 40 CFR 1065.415.
---------------------------------------------------------------------------

    EPA recognizes that durability testing over a regulatory useful
life is a significant undertaking, which can involve more than a full
year of continuous engine operation for Heavy HDE to test to the
equivalent of the current useful life of 435,000 miles. Manufacturers
have been approved, on a case-by-case basis, to age their systems to
between 35 and 50 percent of full useful life on an engine dynamometer,
and then extrapolate the test results to full useful life.\634\ This
extrapolation reduces the time to complete the aging process, but data
from a test program shared with EPA show that while engine out
emissions for SCR-equipped engines were predictable and consistent,
actual tailpipe emission levels were higher by the end of useful life
when compared to emission levels extrapolated to useful life from
service accumulation of 75 or lower percent useful
life.635 636 In response to the new data indicating DFs
generated by manufacturers using service accumulation less than useful
life may not be fully representative of useful life deterioration, EPA
worked with manufacturers and CARB to address this concern through
guidance for MY 2020 and later engines.
---------------------------------------------------------------------------

    \634\ See 40 CFR 86.004-26.
    \635\ U.S. EPA. ``Guidance on Deterioration Factor Validation
Methods for Heavy-Duty Diesel Highway Engines and Nonroad Diesel
Engines equipped with SCR.'' CD-2020-19 (HD Highway and Nonroad).
November 17, 2020.
    \636\ Truck and Engine Manufacturers Association. ``EMA DF Test
Program.'' August 1, 2017.
---------------------------------------------------------------------------

    In this section, we describe our proposal to migrate and update the
DF provisions for heavy-duty highway engines from their current
location in 40 CFR 86.004-26(c) and (d) and 86.004-28(c) and (d) to 40
CFR 1036.245 and 1036.246. While the current DF guidance is specific to
SCR-equipped engines, we are proposing to update our DF provisions to
apply certain aspects of the current DF guidance to all engine families
starting in model year 2027.\637\ We also propose that manufacturers
could optionally use these provisions to determine and verify their
deterioration factors for earlier model years. As noted in the
following section, we propose to continue the option for Spark-ignition
HDE manufacturers to request approval of an accelerated aging DF
determination, as is allowed in our current regulations (see 40 CFR
86.004-26(c)(2)), though our proposed provision would extend this
option to all primary intended service classes. We are not proposing
changes to the existing compliance demonstration provision in 40 CFR
1037.103(c) for evaporative and refueling emission standards. As
introduced in Section III.E, our proposal would apply refueling
emission standards to incomplete vehicles above 14,000 lb GVWR.
Incomplete vehicle manufacturers certifying to the refueling emission
standards for the first time under this proposal would have the option
to use engineering analyses to demonstrate durability using the same
procedures that apply for the evaporative systems on their vehicles
today.
---------------------------------------------------------------------------

    \637\ As noted in Section III.A, the proposed update to the
definition of ``engine configuration'' in 40 CFR 1036.801 would
clarify that hybrid engines and powertrains would be part of a
certified configuration and subject to all of the criteria pollutant
emission standards and other requirements; thus the DF provisions
for heavy-duty engines discussed in this subsection would apply to
configurations that include hybrid components.
---------------------------------------------------------------------------

    In Section IV.F.1, we propose two methods for determining DFs in a
new 40 CFR 1036.245, including a new option to bench-age the
aftertreatment system to limit the burden of generating a DF over the
lengthened useful life periods proposed in Section IV.A.3. We also
propose to codify the three DF verification options available to
manufacturers in the recent DF guidance. As described in Section
IV.F.2, the verification options in a new 40 CFR 1036.246 would confirm
the accuracy of the DF values submitted by manufacturers for
certification. In Section IV.F.3, we introduce a test program to
evaluate a rapid-aging protocol for diesel catalysts that we may
consider as an option for CI engine manufacturers to use in their
durability demonstration.
    We request comment on the proposed options for DF determination and
verification, including other options we should consider. We further
request comment on whether DF testing of the engine is sufficient for
hybrid engines and powertrains, or if we should consider additional
testing requirements for manufacturers to demonstrate durability of
other key components included in a hybrid configuration (e.g., battery
durability testing).
    As described in Section XII.A.8, we are also proposing to allow
manufacturers of nonroad engines to use the procedures described in
this section to establish deterioration factors based on bench-aged
aftertreatment, along with in-use verification testing.

1. Proposed Options for Determining Deterioration Factor
    Accurate methods to demonstrate emission durability are key to
ensuring certified emission levels represent real world emissions, and
the efficiency of those methods is especially important in light of our
proposal to lengthen useful life periods. To address these needs, we
are proposing to migrate our existing regulatory options and include a
new option for heavy-duty highway engine manufacturers to determine DFs
for certification. We note that manufacturers apply these deterioration
factors to determine whether their engines meet the duty cycle
standards. For MY 2031 and later Heavy HDE, we are proposing separate
duty cycle standards at an intermediate useful life, and are further
proposing that a separate deterioration factor would apply for the
intermediate useful life as well.
    Consistent with existing regulations, proposed 40 CFR 1036.245
would allow manufacturers to continue the current practice of
determining DFs based on engine dynamometer-based aging of the complete
engine and aftertreatment system out to regulatory useful life. In
addition, under our proposed new DF determination option, manufacturers
would be able to perform dynamometer testing of an engine and
aftertreatment system to a mileage that is less than regulatory useful
life. Manufacturers would then bench age the aftertreatment system to
regulatory useful life and combine the aftertreatment system with an
engine that represents the engine family. Manufacturers would run the
combined engine and bench-aged aftertreatment for at least 100 hours
before collecting emission data for determination of the deterioration
factor. Under this option, the manufacturer would propose a bench aging
procedure and obtain prior approval from the Agency, which could be a
bench aging procedure that is established today (e.g., procedures that
apply for light-duty vehicles under 40 CFR part 86, subpart S).
    We request comment on the options proposed for DF determination.
Specifically, we ask commenters to consider if the proposed new bench-
aged aftertreatment option accurately evaluates the durability of the
emission-related components in a certified configuration. We are
proposing to allow manufacturers to define and seek approval for a
less-than-useful life mileage for the dynamometer portion of the bench-
aging option. We request comment on the need to define a minimum number
of engine hours of dynamometer testing beyond what is required to
stabilize the engine before bench-aging the aftertreatment.\638\ We
note that EPA's bench-aging proposal focuses on deterioration of
emission control components. We request comment on including a more
comprehensive durability demonstration of the whole engine, such as the
recent diesel test procedures from CARB's Omnibus regulation that
includes dynamometer-based service accumulation of 2,100 hours or more
based on engine class and other factors.\639\ We also request comment
on whether EPA should prescribe a standardized aging cycle for the
dynamometer portion, as was done by CARB in the Omnibus rule.\640\ We
also request cost and time data corresponding to the current DF
procedures, and projections of cost and time for the options proposed
in this section at the proposed useful life mileages. As discussed in
Section IV.F.3, EPA is currently validating an accelerated aging
protocol for heavy-duty diesel engine aftertreatment systems. We expect
that if the protocol is validated, manufacturers could choose to use
that protocol in lieu of developing their own for approval by EPA.
---------------------------------------------------------------------------

    \638\ We are proposing to update the definition of ``low-hour''
in 40 CFR 1036.801 to include 300 hours of operation for engines
with NOX aftertreatment to be considered stabilized.
    \639\ California Air Resources Board, ``Appendix B-1 Proposed
30-Day Modifications to the Diesel Test Procedures'', May 5, 2021,
Available online: https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2020/hdomnibuslownox/30dayappb1.pdf, page 54.
    \640\ California Air Resources Board, ``Staff Report: Initial
Statement of Reasons for Proposed Rulemaking, Public Hearing to
Consider the Proposed Heavy-duty Engine and Vehicle Omnibus
Regulation and Associated Amendments,'' June 23, 2020. Available
online: https://ww3.arb.ca.gov/regact/2020/hdomnibuslownox/isor.pdf,
page III-80.
---------------------------------------------------------------------------

2. Proposed Options for Verifying Deterioration Factors
    In proposed new 40 CFR 1036.246, manufacturers would annually
verify an engine family's deterioration factor for each duty cycle
until all DFs are verified at 85 percent of useful life. We propose
that a manufacturer could request to apply an approved DF to a future
model year for that engine family, using the proposed updates to
carryover engine data provisions in 40 CFR 1036.235(d), as long as the
carryover data includes DF verification results for the production year
of that new model year as specified in proposed 40 CFR 1036.246(b).
Since emission performance is expected to be stable early in the life
of the engine, we are proposing not to require DF verification in the
first two calendar years following a DF determination for an engine
family. Starting in the third year, manufacturers would verify the DFs
using an in-use engine with a mileage at or greater than 35 percent of
the useful life for the original model year of that DF determination.
Subsequent years after production would increase minimum mileages in 10
percent increments each year. Table IV-14 presents the minimum age we
are proposing for each year after a DF is applied. We note that these
are minimum values and manufacturers could complete the testing earlier
if they recruit higher-mileage vehicles for verification testing. If a
manufacturer is unable to find enough test vehicles that meet the
mileage specifications, we propose that they would perform the testing
using vehicles with the highest available mileage and describe how they
would attempt to test properly qualified vehicles for later years. If
this occurs in the eighth year, they would continue testing in future
years until all tested vehicles have mileage that is at least 85
percent of the engine's useful life.

      Table IV-14--Minimum Age for Obtaining In-Use Engines for DF
                          Verification Testing
------------------------------------------------------------------------
                                                         Minimum engine
                                                            service
 Year of production following the initial model year      accumulation
       that relied on the deterioration factors           (percent of
                                                          useful life)
------------------------------------------------------------------------
1....................................................               None
2....................................................               None
3....................................................                 35
4....................................................                 45
5....................................................                 55
6....................................................                 65
7....................................................                 75
8 or later...........................................                 85
------------------------------------------------------------------------

    We include three testing options in our proposed DF verification
provisions. For each option, manufacturers would select in-use engines
meeting the criteria proposed in 40 CFR 1036.246(c), including the
appropriate minimum mileage corresponding to the production year of the
engine family. We request comment on the proposed number of engines to
test under each of these three DF verification options, as well as the
corresponding pass threshold.
    In the first verification option, proposed in new 40 CFR
1036.246(d)(1), manufacturers would test at least two in-use engines
over all duty cycles with brake-specific emission standards in 40 CFR
1036.104(a) by removing each engine from the vehicle to install it on
an engine dynamometer and measure emissions. Manufacturers would

determine compliance with the emission standards after applying
regeneration adjustment factors to their measured results. We propose
that the engine family passes the DF verification if 70 percent or more
of the engines tested meet the standards for each pollutant over all
duty cycles. If a manufacturer chooses to test two engines under this
option, both engines would have to meet the standards. We are proposing
that the aftertreatment system, including all the associated wiring,
sensors, and related hardware or software be installed on the test
engine. We request comment on whether EPA should require approval for
hardware or software used in testing that differs from those used for
production engines and criteria EPA should consider for that approval.
    Under our second proposed verification option in new 40 CFR
1036.246(d)(2), manufacturers would perform the testing on-board the
vehicle using a PEMS. Manufacturers would bin and report the emissions
following the in-use testing provisions in 40 CFR part 1036, subpart E.
Compliance would be determined by comparing emission results to the
off-cycle standards for each pollutant for each bin after adjusting for
regeneration.\641\ We propose the PEMS-based verification would require
testing of at least five in-use engines to account for the increased
variability of vehicle-level measurement. We also propose that the same
70 percent threshold be used to determine a passing result for this
option, which is at least four engines if the manufacturer tests the
minimum of five engines. In the event that a DF verification fails
under the PEMS option, we propose that a manufacturer could reverse a
fail determination and verify the DF using the engine dynamometer
option in 40 CFR 1036.246(d)(1).
---------------------------------------------------------------------------

    \641\ For Spark-ignition HDE, we are not proposing off-cycle
standards; however, for the in-use DF verification options,
manufacturers would compare to the duty cycle standards applying a
2.0 multiplier for model years 2027 through 2030, and a 1.5
multiplier for model years 2031 and later, or multipliers consistent
with the corresponding medium/high load bin off-cycle standards for
CI.
---------------------------------------------------------------------------

    Our third proposed option to verify DF is to measure NOX
emissions using the vehicle's on-board NOX measurement
system (i.e., a NOX sensor) according to 40 CFR
1036.246(d)(3). We expect manufacturers would only choose this option
if they have a well-established infrastructure to access on-board data
from a large number of vehicles (e.g., telematics). Manufacturers
choosing this option would verify their NOX measurement
system meets 40 CFR 1065.920(b), is functional within 100 seconds of
engine starting, and maintains functionality over the entire shift-day.
Due to further uncertainty in measurement accuracy, and the fact that
fewer pollutants would be monitored with a NOX sensor, we
propose the on-board NOX measurement system option would
require testing 50 percent of the production for that engine family
with a 70 percent threshold to pass. Similar to the PEMS option, we
propose that a manufacturer could reverse a fail determination and
verify the DF using the engine dynamometer option in 40 CFR
1036.246(d)(1).
    In the case of a failed result from any of these verification
options, we proposed that manufacturers could request approval for a
revised DF or retest to determine a new DF, but the affected engine
families would not be able to generate emission credits using a DF that
failed to pass verification. We propose to allow the manufacturer to
continue to certify the engine family for one additional model year
using the original deterioration factor to provide time for the
manufacturer to change the engine and generate new DFs. We may require
manufacturers to certify with revised family emission limits and apply
revised DFs to retroactively adjust the family emission limits and
recalculate emission credits from previous model years that used the
invalidated DF. We note that a DF verification failure may result in an
expanded discovery process that could eventually lead to recall under
our existing provisions in 40 CFR part 1068, subpart F.
    As part of the proposed new DF verification provisions, we include
a new 40 CFR 1036.246(c) specifying how to select and prepare engines
for testing. We are proposing to allow manufacturers to exclude
selected engines from testing if they have not been properly maintained
or used and require that the engine must be in a certified
configuration, including its original aftertreatment components.
Recognizing that manufacturers may schedule maintenance for emission-
related components, we request comment on whether restricting engines
to those with original components would considerably limit the number
of candidate engines for testing.
3. Diesel Aftertreatment Rapid Aging Protocol
    As discussed in Section IV.F.1, we are proposing that manufacturers
could use engine dynamometer testing for less than full useful life in
combination with an accelerated catalyst aging protocol in their
demonstration of heavy-duty diesel engine aftertreatment durability
through full useful life. EPA has approved accelerated aging protocols
for spark-ignition engine manufacturers to apply in their durability
demonstrations for many years. While CI engine manufacturers could also
propose an accelerated aging protocol for EPA approval, CI engine
manufacturers have largely opted to seek EPA approval to use a service
accumulation test with reduce mileage and extrapolate to determine
their DF.
    Other regulatory agencies have promulgated accelerated aging
protocols,642 643 and we are evaluating how these protocols
could apply to our heavy-duty highway engine compliance program. EPA is
in the process of validating a protocol that CI engine manufacturers
could potentially choose to use in lieu of developing their own
protocol as proposed in 40 CFR 1036.245. This validation program for a
diesel aftertreatment rapid-aging protocol (DARAP) builds on existing
rapid-aging protocols designed for light-duty gasoline vehicles (64 FR
23906, May 4, 1999) and heavy-duty engines.\644\
---------------------------------------------------------------------------

    \642\ California Air Resources Board. California Evaluation
Procedure For New Aftermarket Diesel Particulate Filters Intended As
Modified Parts For 2007 Through 2009 Model Year On-Road Heavy-Duty
Diesel Engines, March 1, 2017. Available online: https://ww3.arb.ca.gov/regact/2016/aftermarket2016/amprcert.pdf.
    \643\ European Commission. Amending Regulation (EU) No 583/2011,
20 September 2016. Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32016R1718&from=HU.
    \644\ Eakle, S and Bartley, G (2014), ``The DAAAC Protocol for
Diesel Aftertreatment System Accelerated Aging''.
---------------------------------------------------------------------------

    The objective of this validation program is to artificially
recreate the three primary catalytic deterioration processes observed
in field-aged aftertreatment components: Thermal aging based on time at
high temperature, chemical aging that accounts for poisoning due to
fuel and oil contamination, and deposits. The validation program has
access to three baseline engines that were field-aged to the current
useful life of 435,000 miles. For comparison, we are aging engines and
their corresponding aftertreatment systems using our current, engine
dynamometer-based durability test procedure. We are also aging the
catalyst-based aftertreatment systems using a burner \645\ in place of
an engine. The validation test plan compares emissions at the following
approximate intervals: 0 percent, 25 percent, 50 percent, 75 percent,
and 100 percent of the current useful life of 435,000 miles.

We include more details of our DARAP test program in a memo to the
docket.\646\
---------------------------------------------------------------------------

    \645\ A burner is a computer controlled multi-fuel reactor
designed to simulate engine aging conditions.
    \646\ Memorandum to Docket EPA-HQ-OAR-2019-0055: ``Diesel
Aftertreatment Rapid Aging Program''. George Mitchell. May 5, 2021.
---------------------------------------------------------------------------

    The DARAP validation program is currently underway, and we have
completed testing of one engine through the current useful life. Our
memo to the docket includes a summary of the preliminary validation
results from this engine. We will docket complete results from our
validation program in a final report for the final rule. If the
validation is successful, we would likely include an option for
manufacturers to reference this protocol for DF determination and
streamline approval under proposed 40 CFR 1036.245(b)(2). We request
comment on improvements we should consider for the protocol outlined in
our memo to the docket, including whether EPA should prescribe a
standardized aging cycle, as was done by CARB in the Omnibus rule, for
input to the DARAP.\647\ We also request comment on the current
proposal to require approval to use DARAP or if EPA should codify this
protocol as a test procedure.
---------------------------------------------------------------------------

    \647\ California Air Resources Board, Staff Report: Initial
Statement of Reasons for Proposed Rulemaking, ``Public Hearing to
Consider the Proposed Heavy-duty Engine and Vehicle Omnibus
Regulation and Associated Amendments,'' June 23, 2020. https://ww3.arb.ca.gov/regact/2020/hdomnibuslownox/isor.pdf, page III-80.
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G. Averaging, Banking, and Trading

    EPA established an averaging, banking, and trading (ABT) program
for heavy-duty engines in 1990 (55 FR 30584, July 26, 1990). By
offering the opportunity to use ABT credits and additional
flexibilities we can design progressively more stringent standards that
help meet our emission reduction goals at a faster and more cost-
effective pace.\648\ In Section III, we show that the proposed
standards are feasible without the use of credits. However, we see
value in maintaining an ABT program to provide flexibility for
manufacturers to spread out their investment and prioritize technology
adoption in the applications that make the most sense for their
businesses during the transition to meeting new standards. An ABT
program is also an important foundation for targeted incentives that we
are proposing to encourage manufacturers to adopt advanced technology
in advance of required compliance dates.\649\
---------------------------------------------------------------------------

    \648\ See NRDC v. Thomas, 805 F. 2d 410, 425 (D.C. Cir. 1986)
that upheld emissions averaging after concluding that ``EPA's
argument that averaging will allow manufacturers more flexibility in
cost allocation while ensuring that a manufacturer's overall fleet
still meets the emissions reduction standards makes sense''.
    \649\ See Section IV.H for our proposed early adoption
incentives.
---------------------------------------------------------------------------

    In Section IV.G.1, we introduce our proposal to continue allowing
averaging, banking, and trading of NOX credits generated
against applicable heavy-duty engine NOX standards. We also
propose targeted revisions to the current ABT approach to account for
specific aspects of the broader proposed program, which include
discontinuing a credit program for HC and PM and new provisions to
clarify how FELs apply for additional duty cycles. We recognize that
ABT allows manufacturers to use generated emission credits (from
engines produced with emission levels below the standards) to produce
engines with emission levels above the standards. To limit the
production of new engines with higher emissions than the standards, we
are proposing restrictions for using emission credits generated in
model years 2027 and later that include averaging sets (Section
IV.G.2), FEL caps (Section IV.G.3), and limited credit life (Section
IV.G.4). We are also proposing that credits generated as early as MY
2024 against current criteria pollutant standards could only be used in
MY 2027 and later if they meet proposed requirements for the generation
of transitional credits (Sections IV.G.5 and IV.G.6).
    The existing ABT provisions that apply for GHG standards in 40 CFR
part 1036, subpart H, were adapted for the Phase 1 GHG rulemaking from
earlier ABT provisions for HD engines (i.e., 40 CFR 86.007-15).\650\ In
this rulemaking and described in this section, we are proposing to
revise 40 CFR part 1036, subpart H, to also apply for criteria
pollutant standards.\651\ We are also proposing a new paragraph at 40
CFR 1036.104(c) to specify how the ABT provisions would apply for MY
2027 and later heavy-duty engines subject to the proposed criteria
pollutant standards in 40 CFR 1036.104(a). The proposed interim
provision in 40 CFR 1036.150(a)(1) describes how manufacturers could
generate credits in MY 2024 through 2026 that could be applied in MY
2027 and later.
---------------------------------------------------------------------------

    \650\ 76 FR 57127 and 57238, September 15, 2011.
    \651\ Our proposal does not include substantive revisions to the
existing GHG provisions in 40 CFR 1036, subpart H; our proposed
revisions clarify whether paragraphs apply for criteria pollutant
standards or GHG standards.
---------------------------------------------------------------------------

    We request comment on our proposed revisions to the ABT program. As
discussed further below, we are particularly interested in stakeholder
feedback on alternative approaches to accounting for multiple standards
and duty cycles, as well as our proposed approaches for restricting the
use of credits that are generated for use in MY 2027 and later.
1. Multiple Standards and Duty Cycles
    Heavy-duty compression-ignition engine manufacturers currently must
certify to FTP, SET, and off-cycle standards.\652\ Based on FTP and SET
test results, CI engine manufacturers participating in the ABT program
declare FELs in their application for certification. Spark-ignition
engine manufacturers that are only subject to FTP standards may also
declare FELs based on the FTP duty cycle testing. An FEL replaces the
standard and the manufacturer agrees to meet that FEL whenever the
engine is tested over the FTP or SET duty cycle--whether for
certification or a selective enforcement audit. The current NTE
standards apply in-use whenever a CI engine is operating within the NTE
applicability limits and are equal to 1.5 times the FTP and SET
standards. The same 1.5 adjustment factor applies to the declared FEL
for CI engine manufacturers participating in ABT.
---------------------------------------------------------------------------

    \652\ As discussed in Section III, the current standards use the
same numeric value for the FTP and SET cycles. The Not to Exceed
(NTE) standard is an off-cycle standard that applies when an engine
is not on a defined laboratory test cycle.
---------------------------------------------------------------------------

    We are not proposing changes to the following aspects of the ABT
program currently specified in 40 CFR 86.007-15:
     Allow ABT credits for NOX
     Calculate NOX credits based on a single
NOX Family Emission Limit (FEL) for an engine family
     Specify FELs to the same number of decimal places as the
applicable standards
     Apply FEL caps for NOX to constrain maximum
values for FELs
     Calculate credits based on the work and miles of the FTP
cycle
     Limit credits to four averaging sets corresponding to the
four primary intended service classes (detailed in Section IV.G.2)
    As discussed in Section III, we are proposing to revise HC and PM
standards for heavy-duty engines to levels that are feasible without
the use of credits. We are proposing not to allow averaging, banking,
or trading for HC (including NOX+NMHC) or PM for MY 2027 and
later engines. This includes not allowing HC and PM emissions credits
from prior model years to be used for MY 2027 and later engines. For
engines certified to MY 2027 or later standards, manufacturers must
demonstrate in their application for certification that they meet the
proposed

PM, HC, and CO emission standards in 40 CFR 1036.104(a) without using
emission credits.
    While we continue to consider the FTP duty cycle the appropriate
reference cycle for generating NOX emission credits, we are
proposing new provisions to ensure the NOX emission
performance over the FTP is proportionally reflected in the range of
cycles that we are proposing for these heavy-duty engines.
Specifically, we propose that manufacturers would declare an FEL to
apply for the FTP standards and then they would calculate a
NOX FEL for the other applicable cycles by applying an
adjustment factor based on their declared FELFTP.\653\ We
propose the adjustment factor be a ratio of the declared NOX
FELFTP to the FTP NOX standard to scale the
NOX FEL of the other duty cycle or off-cycle standards.\654\
For example, if a manufacturer declares an FELFTP of 30 mg
NOX/hp-hr in MY 2031 for a Heavy HDE, where the proposed
NOX standard is 40 mg/hp-hr, a ratio of 30/40 or 0.75 would
be applied to calculate a FEL to replace each NOX standard
that applies for these engines in the proposed 40 CFR 1036.104(a).
Specifically, for this example, a Heavy HDE manufacturer would replace
the intermediate and full useful life standards for SET, LLC, and the
three off-cycle bins with values that are three-quarters of the
proposed standards. For an SI engine manufacturer that declares an
FELFTP of 15 mg NOX/hp-hr compared to the
proposed MY 2031 of 20 mg/hp-hr, a ratio of 15/20 or 0.75 would be
applied to the SET duty cycle standard to calculate an
FELSET. Note that an FELFTP can also be higher
than the NOX standard in an ABT program if it is offset by
lower-emitting engines in an engine family that generates equivalent or
more credits in the averaging set. For an FEL higher than the
NOX standard, the adjustment factor would proportionally
increase the emission levels allowed when manufacturers demonstrate
compliance over the other applicable cycles.\655\
---------------------------------------------------------------------------

    \653\ Our proposed approach for calculating a NOX FEL
is similar to the current approach for NTE standards; see Section
III.C.1 for more description of the current NTE standards.
    \654\ We are proposing to require manufacturers to declare the
NOX FEL for the FTP duty cycle in their application for
certification. Manufacturers and EPA will calculate FELs for the
other applicable cycles using the procedures specified in 40 CFR
1036.104(c)(3) to evaluate compliance with the other cycles;
manufacturers would not be required to report the calculated FELs
for the other applicable cycles. As noted previously, manufacturers
would demonstrate they meet the standards for PM, CO, and HC and
would not calculate or report FELs for those pollutants.
    \655\ We are proposing in 40 CFR 1036.104(c) that manufacturers
meet the PM, HC, and CO emission standards without generating or
using credits; they would not be required to calculate PM, HC, and
CO FELs as is proposed for NOX.
---------------------------------------------------------------------------

    Under the current and proposed ABT provisions, FELs serve as the
emission standards for the engine family for the respective testing. In
our proposal, manufacturers would include test results to demonstrate
their engines meet the declared and calculated FEL values for all
applicable cycles (see proposed 40 CFR 1036.240(a)). CI engine
manufacturers participating in ABT would use the FELs calculated for
the off-cycle bins to replace the standards in the in-use testing
provisions proposed in 1036, subpart E and PEMS-based DF verifications
in the proposed 40 CFR 1036.246(2).\656\ We expect manufacturers would
base their final FELFTP for credit generation on their
engine family's emission performance on the most challenging cycle. For
instance, if a CI engine manufacturer demonstrates NOX
emissions on the FTP that is 25 percent lower than the standard but can
only achieve 10 percent lower NOX emissions for the low load
cycle, the declared FELFTP would be based on that 10 percent
improvement to ensure the proportional FELLLC would be met.
For the duty cycle standards at intermediate useful life, we are
proposing that the DF determination data at the equivalent intermediate
useful life mileage serve as a demonstration of emission control
performance for certification. For off-cycle standards, we are
proposing that manufacturers may attest, rather than demonstrate, that
all the engines in the engine family comply with the proposed off-cycle
emission standards for all normal operation and use (see the proposed
40 CFR 1036.205(p)) in their application for certification.
---------------------------------------------------------------------------

    \656\ We are not proposing off-cycle standards for SI engines;
SI engine manufacturers opting for PEMS-based DF verification in the
proposed 40 CFR 1036.246(2) would use their FEL to calculate the
effective in-use standard for those procedures.
---------------------------------------------------------------------------

    Once FEL values are established, credits are calculated based on
the FTP duty cycle. We are not proposing substantive revisions to the
equation that applies for calculating emission credits in 40 CFR
1036.705, but we are proposing to update the variable names and
descriptions to apply for both GHG and criteria pollutant
calculations.\657\ In Equation IV-1, we reproduce the equation of 40
CFR 1036.705 to emphasize how the FTP duty cycle applies for
NOX credits. Credits are calculated as megagrams (i.e.,
metric tons) based on the emission rate over the FTP cycle. The
emission credit calculation represents the emission impact that would
occur if an engine operated over the FTP cycle for its full useful
life. The difference between the FTP standard and the family limit
(i.e., FEL for criteria pollutants) is multiplied by a conversion
factor that represents the average work performed over the FTP duty
cycle to get the per-engine emission rate over the cycle. This value is
then multiplied by the production volume of engines in the engine
family and the applicable useful life mileage. Credits are calculated
at the end of the model year using actual production volumes for the
engine family. The credit calculations are submitted to EPA as part of
a manufacturer's ABT report (see 40 CFR 1036.730).
---------------------------------------------------------------------------

    \657\ The emission credits equations in the proposed 40 CFR
1036.705 and the current 40 CFR 86.007-15(c)(1)(i) are functionally
the same.
[GRAPHIC] [TIFF OMITTED] TP28MR22.001

Where:
StdFTP = the FTP duty cycle NOX emission
standard, in mg/hp-hr, that applies for engines not participating in
the ABT program
FEL = the engine family's FEL for NOX, in mg/hp-hr.
WorkFTP = the total integrated horsepower-hour over the
FTP duty cycle.
MilesFTP = the miles of the FTP duty cycle. For Spark-
ignition HDE, use 6.3 miles. For Light HDE, Medium HDE, and Heavy
HDE, use 6.5 miles.
Volume = the number of engine eligible to participate in the ABT
program within the given engine family during the model year, as
described in 40 CFR 1036.705(c).
UL = the useful life for the standard that applies for a given
engine family, in miles.
2. Averaging Sets
    EPA has historically allowed averaging, banking, and trading only

within specified ``averaging sets'' for its heavy-duty engine emission
standards. This restriction is in place to avoid creating unfair
competitive advantages or environmental risks due to credit
inconsistency.\658\ We propose to continue this approach, using engine
averaging sets that correspond to the four primary intended service
classes,\659\ namely:
---------------------------------------------------------------------------

    \658\ 66 FR 5002 January 18, 2001 and 81 FR 73478 October 25,
2016.
    \659\ Primary intended service class is defined in 40 CFR
1036.140, which is referenced in the current 40 CFR 86.004-2.

 Spark-ignition HDE
 Light HDE
 Medium HDE
 Heavy HDE

    As discussed in Section IV.I, we are proposing that manufacturers
could certify battery-electric and fuel cell electric vehicles to
generate NOX emission credits. Manufacturers would include
battery-electric and fuel cell electric vehicles in an averaging set
based on a manufacturer-declared primary intended service class
considering the GVWR of the vehicle.\660\
---------------------------------------------------------------------------

    \660\ As specified in the proposed 40 CFR 1037.102(b)(1),
battery-electric and fuel cell electric vehicles would certify to
standards in the following engine categories: Light HDE, Medium HDE
and Heavy HDE, and as such would only generate NOX
emission credits in these averaging sets. The same restrictions
would apply to averaging, banking, or trading these credits only
within the averaging set in which they are generated (see the
proposed 40 CFR 1036.741)
---------------------------------------------------------------------------

3. FEL Caps
    EPA has historically capped FELs for a new criteria pollutant
standard at the level of the previous emission standard to avoid engine
technologies backsliding. FEL caps limit the amount that an individual
engine can emit above the level of emission standard when manufacturers
choose to use emission credits to comply with the standard. Without a
FEL cap, manufacturers could choose to use emission credits to produce
engines that emit at any numeric level for which they had sufficient
credits, whereas, with a FEL cap in place, EPA can constrain the level
of emissions from engines that are certified with the use of credits.
By setting the FEL cap at the level of the previous emission standard
EPA can ensure that all engines must at least maintain the current
level of emission control performance.
    In this section, we are proposing a new approach to setting FEL
caps. We believe FEL caps continue to be critical to avoid backsliding
through use of emission credits. Considering our proposal to allow
manufacturers to include BEVs or FCEVs in the NOX ABT
program, we believe FEL cap levels below the previous standard are
appropriate. The zero-tailpipe emissions performance of BEVs and FCEVs
inherently provides the opportunity for manufacturers to generate more
credits from these vehicles relative to conventional engines that
produce emissions between zero and the level the standard. We believe
that lower FEL caps would provide a necessary constraint on allowable
emission levels from CI and SI engines that would use NOX
credits generated from BEVs or FCEVs. See Section IV.I for more
discussion on our proposal to allow manufacturers to generate
NOX emission credits from BEVs and FCEVs.
    As specified in the proposed 40 CFR 1036.104(c)(2), the maximum
NOX FELFTP values for model year 2027 through
2030 under proposed Option 1, or model year 2027 and later under
proposed Option 2, would be 150 mg/hp-hr, which is consistent with the
average NOX emission levels achieved by recently certified
CI engines (see Chapter 3.1.2 of the draft RIA). We believe a cap based
on the average NOX emission levels of recent engines is more
appropriate than a cap at the current standard of 0.2 g/hp-hr (200 mg/
hp-hr) when considering the potential for manufacturers to apply
NOX credits generated from electric vehicles for the first
time. For MY 2031 and later under Option 1, we propose a consistent 30
mg/hp-hr allowance for each primary intended service class applied to
each full useful life standard. For Spark-ignition HDE, Light HDE, and
Medium HDE, this proposed allowance would equate to a NOX
FELFTP cap of 50 mg/hp-hr compared to the proposed full
useful life standard of 20 mg/hp-hr. Heavy HDE would have a separate
NOX FELFTP cap of 70 mg/hp-hr compared to the
proposed 40 mg/hp-hr full useful life standard. For MY 2031 and later
FEL caps under Option 1, we are proposing a 30 mg/hp-hr allowance in
lieu of the proposed Option 1 MY 2027 standard of 35 mg/hp-hr for two
reasons. First, we do not believe a 15 mg/hp-hr differential between
the MY 2031 and MY 2027 standards would provide an appropriate
incentive for Spark-ignition HDE, Light HDE, and Medium HDE
manufacturers to develop advanced technologies in early model years.
Second, the MY 2031 standard for Heavy HDE is higher than the MY 2027
standard to reflect deterioration over the longer useful life.
    We request comment on our proposed FEL caps, including our approach
to base the cap for MY 2027 through 2030 under Option 1, or MY 2027 and
later under Option 2, on the recent average NOX emission
levels. We request comment on whether the NOX
FELFTP cap in MY 2027 should be set at a different value,
ranging from the current federal NOX standard of 205 mg/hp-
hr to the 50 mg/hp-hr standard that will be in place for engines
subject to CARB's HD Omnibus rule starting in MY
2024.661 662 663 We also request comment on the proposal to
set the proposed Option 1 MY 2031 NOX FEL caps at 30 mg/hp-
hr above the full useful life standards. We request comment on whether
different FEL caps should be considered if we finalize standards other
than those proposed (i.e., within the range between the standards of
proposed Options 1 and 2 as described  in the feasibility analysis of
Section III).
---------------------------------------------------------------------------

    \661\ California Air Resources Board, Staff Report: Initial
Statement of Reasons for Proposed Rulemaking, ``Public Hearing to
Consider the Proposed Heavy-duty Engine and Vehicle Omnibus
Regulation and Associated Amendments,'' June 23, 2020. https://ww3.arb.ca.gov/regact/2020/hdomnibuslownox/isor.pdf, page III-4.
    \662\ Note that the current g/hp-hr emission standards are
rounded to two decimal places, which allow emission levels to be
rounded down by as much as 5 mg/hp-hr.
    \663\ As noted in Section I.D, EPA is reviewing a waiver request
under CAA section 209(b) from California for the Omnibus rule; we
may include consideration of engines meeting the Omnibus
requirements as one of the factors in our determination of an
appropriate FEL cap level for the final EPA rule.
    \664\ This includes credits generated by BEVs or FCEVs for use
in MYs 2027 and later, as discussed in Section IV.I.
---------------------------------------------------------------------------

4. Credit Life for Credits Generated for Use in MY 2027 and Later
    In the original heavy-duty criteria pollutant ABT program (55 FR
30584, July 26, 1990), the recent Phase 2 heavy-duty GHG rulemaking (81
FR 73638, October 25, 2016), and the current CARB HD Omnibus
rulemaking, a limited credit life was adopted to help encourage
continued technology development to meet the proposed standards. We are
proposing to update the existing credit life provisions in 40 CFR
1036.740(d) to apply for both CO2 and NOX
credits. As specified in the proposed 40 CFR 1036.740(d),
NOX emission credits generated for use in MY 2027 and later
could be used for five model years after the year in which they are
generated.\664\ For example, credits generated in model year 2025 could
be used to demonstrate compliance with emission standards through model
year 2030.

    We are not proposing an expiration date for the ABT program, and
manufacturers could continue to generate credits by adopting
increasingly advanced technologies. However, we do not see a need for
manufacturers to bank credits generated in a given model year
indefinitely. We recognize the need to allow enough time for
manufacturers to apply credits generated early to cover the transition
to the more stringent standards of proposed Option 1 for MY 2031. We
believe a five-year credit life adequately covers a transition period
for that option, while continuing to encourage technology development
in later years. We are not proposing to migrate 40 CFR 86.004-
15(c)(1)(ii) that specifies a discount for credits that are banked or
traded. Discounted credits were originally included to incentivize
manufacturers to adopt new technology instead of relying on the use of
older credits (62 FR 54703, October 21, 1997). We believe the proposed
five-year credit life would provide the same incentive as a credit
discount. We request comment on our proposed five-year credit life.
5. Existing Credit Balances
    Under the current HDE criteria pollutant ABT program, manufacturers
have generated NOX emission credits with an unlimited credit
life but have not used the credits in recent years. While emission
credits generated prior to MY 2027 could continue to be used to meet
the existing emission standards through MY 2026 under 40 CFR part 86,
subpart A, we are proposing that these banked credits could not be used
to meet the proposed MY 2027 and later standards for two reasons.
    First, the credits were generated without demonstrating emissions
control under all test conditions of the proposed program, and thus are
not equivalent to credits that would be generated under the proposed
program. Specifically, the existing credits were generated without
demonstrating emission control on the proposed SET duty-cycle standard
for SI engines, or the proposed low-load duty-cycle standard and
proposed off-cycle standards and test procedures for CI engines.
Second, EPA did not rely on the use of existing credit balances to
demonstrate feasibility of the proposed standards (see Section III).
    Taken together, these two factors lead us to believe that it would
not be appropriate to allow the unlimited use in the proposed new
NOX compliance program of credits generated under the
existing program. We are proposing a new interim provision in 40 CFR
1036.150(a) that includes the options for manufacturers to bank credits
for use in MY 2027 and later. In paragraph (a)(1), we are proposing
provisions to allow manufacturers to generate transitional
NOX credits prior to MY 2027 that could be applied for MY
2027 and later based on an approach that combines the current
NOX standards and the proposed test procedures (see Section
IV.G.6). Paragraph (a)(2) includes our proposal to allow manufacturers
to generate early adoption incentive credits by complying with the
proposed MY 2027 standards (or MY 2031 standards, if applicable) before
the required compliance date (see Section IV.H).\665\ Paragraph (a)(3)
would clarify that manufacturers must use one of these two options for
generating credits prior to MY 2027 for use in MY 2027 and later.
---------------------------------------------------------------------------

    \665\ Also see Section IV.I and the corresponding proposed
provisions in 40 CFR 1037 for a description of how these options
apply for manufacturers certifying electric vehicles.
---------------------------------------------------------------------------

6. Transitional Credits Generated in MYs 2024 Through 2026
    We are proposing an option for manufacturers to generate
transitional credits in MYs 2024 through 2026 that could be applied in
MYs 2027 and later. We propose these transitional credits as a
flexibility that accounts for key differences between the current and
proposed compliance programs, and incentivizes manufacturers to adopt
the proposed test procedures earlier than required in MY 2027. As
described below, the proposed approach bases the transitional credit
calculation on the current NOX standards and useful life
periods; therefore, manufacturers may not need to adopt new
technologies or demonstrate durability over longer useful life periods,
which would otherwise be needed to comply with the proposed more
stringent emission standards and longer useful life periods.\666\
---------------------------------------------------------------------------

    \666\ In Section IV.H, we propose early adoption incentives with
credit multipliers for manufacturers who achieve the full proposed
emission standards and compliance measures for engine families
before MY 2027.
---------------------------------------------------------------------------

    Specifically, we are proposing a new interim provision in 40 CFR
1036.150(a)(1) that manufacturers could use to generate transitional
credits in model years 2024 through 2026. The transitional credits rely
on the same structure as the general ABT provisions proposed in 40 CFR
1036.104(c) and subpart H, with differences noted in this section.
Manufacturers would similarly declare a NOX FEL for
operation over the FTP duty cycle. The FELFTP would then be
used to calculate FELs for operation over the other applicable duty
cycles and off-cycle bins for which there are no current standards.
Manufacturers would calculate an FEL for each other applicable cycle by
multiplying the corresponding MY 2027 standard for that cycle by the
ratio of their declared FELFTP to the MY 2027 FTP standard.
    For an example model year 2025 Light HDE engine family, the
proposed Option 1 MY 2027 NOX standards are 35 mg/hp-hr for
FTP and SET, and 90 mg/hp-hr for LLC. If a Light HDE manufacturer
declares an FELFTP of 0.10 g/hp-hr, then the calculated MY
2025 FEL for LLC (FELLLC) would equal 0.090 g/hp-hr
multiplied by the ratio 0.10/0.035, i.e., 0.26 g/hp-hr. The
manufacturer would have to demonstrate that they can meet an LLC
NOX emission level of 260 mg/hp-hr for certification.
Similar to the general ABT program, the FELs calculated for these
cycles would serve as the emission standards for the engine family for
the respective testing, and manufacturers would demonstrate that they
meet those FELs in their application for certification. Compared to the
current ABT program, CI engine manufacturers opting to generate
transitional credits under this proposal would have to show that they
meet a calculated FELLLC on the proposed LLC test procedure
in 40 CFR 1036.512. SI engine manufacturers would have to show that
they meet a calculated FELSET on the proposed SET test
procedure in 40 CFR 1036.505.
    To calculate transitional credits, we propose that manufacturers
would apply the declared FELFTP in the emission credits
equation in 40 CFR 1036.705(b)(1) (see Equation IV-1). We propose that
the credits be calculated relative to the current FTP standard of 0.20
g/hp-hr and the current useful life that applies for the engine family
as defined in 40 CFR 86.004-2.
    Since transitional credits would be used in MYs 2027 or later, we
are proposing that transitional credits would have the same five-year
credit life as proposed for other credits generated for use in MYs 2027
and later. See proposed 40 CFR 1036.740(d). Similarly, to generate
transitional NOX emission credits, manufacturers would be
required to meet the applicable current PM, HC, and CO emission
standards in 40 CFR 86.007-11 or 86.008-10 without generating or using
emission credits. We propose that manufacturers would record the PM,
HC, and CO emission levels during testing over the proposed new duty
cycles, but they would not scale PM, HC, and CO as proposed for
NOX over the other cycles.
    We request comment on our proposed approach to offer transitional
NOX

emission credits that incentivize manufacturers to adopt the proposed
test procedures earlier than required in MY 2027. We request comment on
if CI engines should be subject to off-cycle standards as proposed in
40 CFR part 1036, subpart E, to qualify for the transitional credits.
We are specifically interested in comments on other approaches to
calculating transitional credits before MY 2027 that would account for
the differences in our current and proposed compliance programs. We
also request comment on our proposal to apply a five-year credit life
for transitional NOX emission credits.

H. Early Adoption Incentives

    We are proposing an early adoption incentive program as an interim
provision in 40 CFR 1036.150(a)(2). Manufacturers have four or more
model years of lead time to meet the proposed criteria pollutant
standards that would begin to apply in MYs 2027 and 2031 for proposed
Option 1 or MY 2027 for proposed Option 2. However, we recognize that
manufacturers have opportunities to introduce some technologies earlier
than required and that public health and the environment would benefit
from early introduction. Specifically, early introduction of new
emission control technologies can accelerate the entrance of lower-
emitting engines and vehicles into the heavy-duty vehicle fleet,
thereby reducing NOX emissions from the heavy-duty sector
and lowering its contributions to ozone and PM formation.
    Early introduction of engines capable of meeting all of the
proposed standards and requirements for MY 2027, or MY 2031 if
applicable, would reduce emissions from heavy-duty trucks across
operating modes and maintain that degree of emission control throughout
a longer portion of the engine operational life. For example, our
analysis shows that without the proposed standards, low-load emissions
would account for 28 percent of the heavy-duty NOX emission
inventory in calendar year 2045, which suggests that early introduction
of technologies capable of reducing low-load emissions could help
accelerate important reductions of this portion of the inventory.
Similarly, our analysis shows that emissions attributable to
deterioration of emission controls after the existing useful life
periods would account for 25 percent of the heavy-duty emission
inventory in calendar year 2045, which again suggests that early
adoption of technologies capable of reducing emissions for longer
periods of time could have important impacts on this part of the heavy-
duty emission inventory (see Section I.E for more details on Engine
Operation and Processes Contributing to Heavy-Duty NOX
Emission Inventory in 2045). As discussed in Section II, many state and
local agencies have asked the EPA to further reduce NOX
emissions, specifically from heavy-duty engines, because such
reductions will be a critical part of many areas' strategies to attain
and maintain the ozone and PM2.5 NAAQS. Several of these
areas are working to attain or maintain NAAQS in timeframes leading up
to and immediately following the required compliance dates of the
proposed standards, which underscores the importance of the early
introduction of lower-emitting vehicles.
    We are proposing an early adoption incentive program that would
recognize the environmental benefits of lower-emitting engines and
vehicles entering the fleet ahead of required compliance dates for the
proposed standards. Under the proposed new interim provision in 40 CFR
1036.150(a)(2), this optional program would allow manufacturers who
demonstrate early compliance with the proposed MY 2027, or MY 2031 if
applicable, standards to generate more NOX credits for the
relevant early compliance model years than under the proposed ABT
program for the model years for which the standards are applicable
(described in Section IV.G).
1. Eligibility for Early Adoption Incentives
    In MYs 2024 through 2026, manufacturers may choose to participate
in the proposed early adoption incentive program by demonstrating
compliance with all of the proposed MY 2027 (or, alternatively, MY
2031) standards and other requirements specified in proposed 40 CFR
1036.205.\667\ Similarly, under proposed Option 1, manufacturers may
participate in the proposed early adoption incentive program in MYs
2027 through 2030 by demonstrating compliance with all of the proposed
Option 1 MY 2031 standards and other requirements. Early adoption
credits generated under proposed 40 CFR 1036.150(a)(2) could be used to
comply with the proposed NOX emission standards starting as
early as MY 2027 as further specified in proposed 40 CFR part 1036,
subpart H.
---------------------------------------------------------------------------

    \667\ See Section IV.G.1 for discussion on the relationship of
the FELFTP and demonstrating compliance with all duty-cycle
standards.
---------------------------------------------------------------------------

2. Calculating Credits Under the Early Adoption Incentive Program
    Our proposed early credit provisions in 40 CFR 1036.150(a)(2)
recognize the benefits of early adoption of low-NOX
technologies in two ways. First, we propose to reduce the declared FEL,
for purpose of calculating credits, to provide appropriate credit for
the additional years of emissions assurance that come with certifying
to a longer useful life. Second, we proposed to apply a traditional
credit multiplier to further incentivize early adoption of technologies
that will meet our standards. Our proposed multipliers would be based
on the current model year relative to the model year of the standards
to which the engine is being certified, with a larger multiplier for
meeting the MY 2031 requirements before MY 2027.
    To calculate credits under the early adoption incentive program, we
are proposing a manufacturer would multiply the engine family's
declared FEL by a ratio of useful life period of the current model year
relative to the longer useful life period of the model year to which
the engine family is certified.\668\ For example, a manufacturer
certifying a MY 2027 Heavy HDE to proposed Option 1 MY 2031 standards
would multiply the declared FELFTP by the ratio of 600,000 miles to
800,000 miles (i.e., MY 2027 UL to MY 2031 UL for Heavy HDE under
proposed Option 1). The manufacturer would then apply a multiplier to
calculate the total early adoption credit for the engine family.
Equation IV-2 illustrates how the Eq. 1036.705-1 would be updated to
calculate early credits as proposed in 40 CFR 1036.150(a)(2). The
proposed Early Adoption Multiplier (ECM) values are shown in Table IV-
15.
---------------------------------------------------------------------------

    \668\ This approach is similar to the early compliance approach
adopted by CARB in the 30-Day Modifications to the HD Omnibus
regulation. See Appendix B-1 and Appendix B-2 available online:
https://ww2.arb.ca.gov/rulemaking/2020/hdomnibuslownox.

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

[GRAPHIC] [TIFF OMITTED] TP28MR22.002

Where:
StdFTP = the FTP duty cycle NOX emission
standard, in mg/hp-hr, that applies for engines not participating in
the ABT program
FEL = the engine family's FEL for NOX, in mg/hp-hr.
ULMY = the useful life, in miles, that applies for
engines not participating in the ABT program in that model year.
UL = the useful life, in miles, for the standard that applies for
the applicable primary intended service class.
WorkFTP = the total integrated horsepower-hour over the
FTP duty cycle.
MilesFTP = the miles of the FTP duty cycle. For Spark-
ignition HDE, use 6.3 miles. For Light HDE, Medium HDE, and Heavy
HDE, use 6.5 miles.
Volume = the number of engines eligible to participate in the ABT
program within the given engine family during the model year, as
described in the existing 40 CFR 1036.705(c).
EAM = early adoption multiplier based on model year of the engine
family and the model year of the standard to which the engine family
is being certified. See Table IV-15.

                                Table IV-15--Proposed Early Adoption Multipliers
----------------------------------------------------------------------------------------------------------------
                                                                 Meet all  requirements       Early adoption
                 Engine family model year \a\                        for model year             multiplier
----------------------------------------------------------------------------------------------------------------
2024 through 2026.............................................                     2027                      1.5
2024 through 2026 \b\.........................................                     2031                      2.0
2027 through 2030 \b\.........................................                     2031                      1.5
----------------------------------------------------------------------------------------------------------------
\a\ BEV and FCEV could generate NOX emission credits as described in Section IV.I.2.ii, but would not be
  eligible for early adoption multipliers.
\b\ Early adoption multipliers for meeting MY 2031 standards would only apply under the two-step proposed Option
  1.

    Our proposal to reduce a manufacturer's declared FELFTP in the
early credit calculation would increase the number of credits relative
to the general ABT credit calculation in proposed 40 CFR 1036.705. We
believe it is appropriate to scale down the FEL using the useful life
ratio for all primary intended service classes to reflect the
durability improvements needed to meet the standards when the useful
life mileages differ. This adjustment is particularly important to
avoid negative credit values when calculating early credits for Heavy
HDE in model years 2027 through 2030 under the two-step approach of
proposed Option 1 when the proposed numeric value of the standard at
full useful life is lower than the MY 2031 standard.\669\
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    \669\ For example, without an FEL adjustment, the difference
between the proposed NOX standard of 35 mg/hp-hr in MY
2027 through 2030 and an otherwise credit-generating FEL in the
range of 36 to 40 mg/hp-hr would be negative (i.e., 35 mg/hp-hr - 40
mg/hp-hr = - 5 mg/hp-hr).
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    We believe that the proposed 1.5 to 2.0 multipliers in the early
adoption incentive program appropriately balance providing an incentive
for manufacturers to develop and introduce lower-emitting technologies
earlier than required while also considering that the credits could be
used to produce higher-emitting engines in later model years. Our
proposed multipliers would encourage early introduction to augment
manufacturers' longer-term flexibility in product planning to meet the
proposed standards. As discussed in Section IV.G, we are proposing
credit life limits and FEL caps to ensure that NOX emission
credits generated through the early adoption incentive program do not
compromise the environmental benefits expected from the proposal.
Specifically, our proposed NOX FEL caps would ensure
significant emission reductions from all heavy-duty highway engines
compared to today's products.
    We have aligned both the compliance requirements and numeric value
of our proposed early adoption multipliers with the Early Compliance
Credit Multipliers included in the Omnibus for MY 2024 and later. We
believe that aligning our approach with the CARB program provides
manufacturers with a common set of requirements and incentives for the
early introduction of lower emitting vehicles.\670\
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    \670\ We believe that aligning the proposed EPA early adoption
incentive program and the CARB Early Compliance Credit Multipliers
is useful for manufacturers even inf the standards and other
requirement of the EPA final rule do not fully align with the CARB
Omnibus provisions.
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3. Requests for Comment on Early Adoption Incentive Program
    Our proposed approach would incentivize manufacturers to produce
lower emitting vehicles prior to required compliance dates by offering
more emission credits for early introduction of these cleaner
technologies. EPA requests comment on all aspects of our proposed early
adoption incentive program. Specifically, we are interested in
stakeholder feedback on our approach that engine families meet all
proposed MY 2027, or MY 2031 if applicable, requirements in order to
participate in the early adoption incentive program. The proposed
eligibility criteria would ensure that products participating in the
early adoption incentive program not only meet lower numeric levels of
the standards, but also maintain emission control across a broad range
of engine operations and over a longer duration of operational life,
consistent with the proposed requirements. Nevertheless, we are aware
that there may be aspects of the proposed requirements that are
challenging to meet ahead of the required compliance dates, and thus
EPA requests comment on any needed flexibilities that we should include
in the early adoption incentive program in the final rule.
    We are also interested in stakeholder feedback on the proposed
numeric values of the credit multipliers in the early adoption
incentive program; commenters recommending alternative numeric values
for credit multipliers are encouraged to include data supporting why
those values are appropriate. In addition, we are interested in whether
EPA should further restrict the use of NOX credits generated
under the early adoption incentive program. For instance, we could
consider finalizing a shorter credit life for NOX emission
credits generated under the early adoption incentive program. We could
also consider finalizing a cap on the

number of engines with which a manufacturer could generate early
adoption incentive credits, or a cap on the number of credits per model
year that a manufacturer could generate.
    Finally, we request comment on our approach to align the
requirements and numeric values of the multipliers with the Early
Compliance Credit Multipliers included in the Omnibus. In addition, we
are interested in stakeholder input on whether EPA should adopt
specific provisions that incentivize manufacturers to certify engine
families that meet the MY 2024 Omnibus requirements.\671\ As described
in Section IV.G.6, we are proposing a transitional credit option for MY
2024 through 2026 that is calculated relative to the current standards.
We may consider a multiplier or other incentive that reflects the CARB
MY 2024 requirements being a step more stringent than the current
standards, but less comprehensive than the proposed MY 2027
requirements. For instance, in MYs 2024 through 2026, EPA could offer
an early adoption multiplier of 1.25 for manufacturers certifying 50-
state engine families that meet all of the requirements of the MY 2024
Omnibus program. We request comment on incentivizing adoption of the MY
2024 Omnibus requirements, including suggested multipliers or other
approaches we should consider.
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    \671\ As noted in Section I.D, EPA is reviewing a waiver request
under CAA section 209(b) from California for the Omnibus rule; if we
were to grant the waiver request for the CA Omnibus, then we may
consider in the final EPA rule ways to incentivize manufacturers to
produce engines that meet the Omnibus requirements and are available
for sale outside of CA or other states that may adopt the Omnibus.
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I. Compliance Options for Generating NOX Emission Credits
From Electric Vehicles

    The number of heavy-duty electric vehicles (EVs) in the form of
hybrid electric vehicles (HEVs), battery electric vehicles (BEVs), and
fuel cell electric vehicles (FCEVs) in the heavy-duty market today is a
small percentage of the total heavy-duty fleet based on estimates from
several sources.672 673 674 675 However, growing numbers of
these EV technologies are in production, in demonstration projects, or
planned for production in the early 2020s (see Chapter 1.4 of the draft
RIA for more discussion). Forecasting models and studies generally
agree that HEV, BEV, and FCEV production volumes will grow, yet the
predicted rate of growth ranges widely across various forecasts and
partly depend on the specific market segments and time periods being
evaluated, study methodologies, as well as underlying
assumptions.676 677 678 Many ANPR commenters asserted that
EV technologies would continue to grow as part of the heavy-duty fleet;
commenters generally focused on projected growth of BEVs based on their
own production plans and/or customer orders for their products,
although no specific data was provided by commenters.\679\
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    \672\ North American Council for Freight Efficiency ``Guidance
Report: Viable Class \7/8\ Electric, Hybrid and Alternative Fuel
Tractors``, available online at: https://nacfe.org/downloads/viable-class-7-8-alternative-vehicles/.
    \673\ UCS (2019) ``Ready for Work: Now Is the Time for Heavy-
Duty Electric Vehicles``; www.ucsusa.org/resources/ready-work.
    \674\ Nadel, S. and Junga, E. (2020) ``Electrifying Trucks: From
Delivery Vans to Buses to 18-Wheelers''. American Council for an
Energy-Efficient Economy White Paper, available online at: https://aceee.org/white-paper/electrifying-trucks-delivery-vans-buses-18.
    \675\ Smith, D. et al. (2019) ``Medium- and Heavy-Duty
Electrification An Assessment of Technology and Knowledge Gaps''.
Oak Ridge National Laboratory and National Renewable Energy
Laboratory. ORNL/SPR-2020/7
    \676\ Energy Information Association (2018) ``Annual Energy
Outlook; Table 50: Freight Transportation Energy Use'', available
at: https://www.eia.gov/outlooks/aeo/data/browser/#/?id=58-
AEO2018®ion=0-
0&cases=ref2018&start=2016&end=2050&f=A&linechart=ref2018-
d121317a.6-58-AEO2018~ref2018-d121317a.11-58-AEO2018~ref2018-
d121317a.17-58-AEO2018~ref2018-d121317a.22-58-AEO2018~ref2018-
d121317a.28-58-AEO2018~ref2018-d121317a.33-58-
AEO2018&ctype=linechart&sid=ref2018-d121317a.22-58-AEO2018~ref2018-
d121317a.11-58-AEO2018~ref2018-d121317a.33-58-AEO2018&sourcekey=0.
    \677\ Jadun, et al. (2017) ``Electrification Futures Study: End-
Use Electric Technology Cost and Performance Projections through
2050''. Golden, CO: National Renewable Energy Laboratory. NREL/TP-
6A20-70485. https://www.nrel.gov/docs/fy18osti/70485.pdf.
    \678\ Brooker et al. (2021) ``Vehicle Technologies and Hydrogen
and Fuel Cell Technologies Research and Development Programs
Benefits Assessment Report for 2020''. Golden, CO: National
Renewable Energy Laboratory. NREL/TP-5400-79617. https://www.nrel.gov/docs/fy21osti/79617.pdf.
    \679\ For example, see Comments of Tesla Inc. ``Control of Air
Pollution from New Motor Vehicles: Heavy-Duty Engine Standards,
Docket No. EPA-HQ-OAR-2019-0055, 85 Fed. Reg. 3306 (Jan. 21,
2020).'' Docket EPA-HQ-OAR-2019-0055-0268.; Comments of Rivian.
``Comments on the Control of Air Pollution From New Motor Vehicles:
Heavy-Duty Engine Standards Advanced Notice of Proposed Rulemaking
(EPA-HQ-OAR-2019-0055; FRL-10004-16- OAR).'' Docket EPA-HQ-OAR-2019-
0055-0272.; Comments of Volvo Group. ``Comments of the Volvo Group;
U.S. EPA Cleaner Trucks Initiative Advanced Notice of Proposed
Rulemaking.'' Docket EPA-HQ-OAR-2019-0055-0463.
---------------------------------------------------------------------------

    In the ANPR for this action we requested comment on any barriers or
incentives that EPA should consider to better encourage emission
reductions from HEVs, BEVs, and FCEVs.\680\ Most but not all ANPR
commenters were generally supportive of EPA following approaches used
in the past of offering emission credits and credit multipliers for EV
technologies.\681\ Commenters also noted that making credits in an ABT
program available for EV technologies, particularly credits available
prior to MY 2027, would provide manufacturers with flexibility by
providing additional time to develop the technologies to comply with
the proposed emission standards.\682\ However, under the current
criteria pollutant program, manufacturers do not have a pathway to
generate NOX emission credits for HEVs, BEVs, or FCEVs. For
BEVs and FCEVs, current 40 CFR 86.016-1(d)(4) stipulates that these
technologies may not generate NOX emission credits, and for
HEVs, there has historically not been a test procedure available to
demonstrate NOX emission performance of the technologies
(see Sections III.A and III.B for discussion on the current regulatory
provisions specific to heavy-duty electric vehicles, and test
procedures for HEVs, respectively).\683\ We outline in the subsections
that follow how we propose to address these barriers to generating
NOX emission credits for HEVs, and, separately, BEVs or
FCEVs.
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    \680\ 85 FR 3306, January 21, 2020.
    \681\ For example, see Comments of Tesla Inc. ``Control of Air
Pollution from New Motor Vehicles: Heavy-Duty Engine Standards,
Docket No. EPA-HQ-OAR-2019-0055, 85 Fed. Reg. 3306 (Jan. 21,
2020).'' Docket EPA-HQ-OAR-2019-0055-0268.; Comments of Rivian.
``Comments on the Control of Air Pollution From New Motor Vehicles:
Heavy-Duty Engine Standards Advanced Notice of Proposed Rulemaking
(EPA-HQ-OAR-2019-0055; FRL-10004-16- OAR).'' Docket EPA-HQ-OAR-2019-
0055-0272.; Comments of Volvo Group. '' Comments of the Volvo Group;
U.S. EPA Cleaner Trucks Initiative Advanced Notice of Proposed
Rulemaking.'' Docket EPA-HQ-OAR-2019-0055-0463.; Comments of Edison
Electric Institute. ``Comments of the Edison Electric Institute on
the U.S. Environmental Protection Agency's Advanced Notice of
Proposed Rulemaking Control of Air Pollution from New Motor
Vehicles: Heavy-Duty Engine Standards.'' Docket EPA-HQ-OAR-2019-
0055-0293.; Note that one commenter did not support credit
multipliers, see Comments of Eaton. ``Eaton Comments to EPA Control
of Air Pollution from New Motor Vehicles: Heavy-Duty Engine
Standards Docket No. EPA-HQ-OAR-2019-0055.'' Docket EPA-HQ-OAR-2019-
0055-0452.
    \682\ Tesla Inc. ``Control of Air Pollution from New Motor
Vehicles: Heavy-Duty Engine Standards, Docket No. EPA-HQ-OAR-2019-
0055, 85 Fed. Reg. 3306 (Jan. 21, 2020).'' Docket EPA-HQ-OAR-2019-
0055-0268.; Rivian. ``Comments on the Control of Air Pollution From
New Motor Vehicles: Heavy-Duty Engine Standards Advanced Notice of
Proposed Rulemaking (EPA-HQ-OAR-2019-0055; FRL-10004-16- OAR).''
Docket EPA-HQ-OAR-2019-0055-0272.; Volvo Group. ``Comments of the
Volvo Group; U.S. EPA Cleaner Trucks Initiative Advanced Notice of
Proposed Rulemaking.'' Docket EPA-HQ-OAR-2019-0055-0463.
    \683\ 40 CFR 86.016-1(d)(4) states: ``Electric heavy-duty
vehicles may not generate NOX or PM emission credits.
Heavy-duty vehicles powered solely by electricity are deemed to have
zero emissions of regulated pollutants.''
---------------------------------------------------------------------------

    EPA is proposing to allow HEVs to generate NOX emission
credits based on

their near-zero tailpipe emissions and because they provide an
opportunity for manufacturers to develop and refine transferable
technologies to BEVs and FCEVs (e.g., batteries, electric motors). We
are proposing to allow BEVs and FCEVs to generate NOX
emission credits because of the zero-tailpipe emissions performance of
these technologies and after consideration of ANPR comments.\684\ We
are further proposing to allow manufacturers to generate BEV and FCEV
NOX emission credits starting in MY 2024 in response to ANPR
comments concerning the importance of such credits in providing
manufacturers with flexibility in their product planning. Some ANPR
comments also supported emission credit multipliers for HEVs, BEVs, and
FCEVs.\685\ In developing our proposal, we considered whether to
provide credit multipliers for these technologies in the early years of
the proposed program; however, we are choosing not to propose
NOX emission credit multipliers for HEVs, BEVs, or FCEVs due
to the potential emission impacts of the use of credit multipliers and
the current state of technology development and implementation (see
Section IV.I.4 for more details on this topic).\686\ The subsections
that follow discuss: (1) How manufacturers can certify HEV, BEVs, and
FCEVs to the proposed criteria pollutant standards, (2) proposed
requirements for generating NOX emission credits for these
technologies, (3) potential options for how EPA could approach
NOX emission credits from BEVs and FCEVs in the long-term
(e.g., post-MY 2031), and (4) our reasoning for not proposing credit
multipliers for NOX emission credits generated from HEVs,
BEVs, or FCEVs.
---------------------------------------------------------------------------

    \684\ As noted in Section III.A, our proposal for how
manufacturers could generate NOX emissions credits from
BEVs and FCEVs would be available under any of the regulatory
options that we are considering for revised NOX
standards.
    \685\ Rivian. ``Comments on the Control of Air Pollution From
New Motor Vehicles: Heavy-Duty Engine Standards Advanced Notice of
Proposed Rulemaking (EPA-HQ-OAR-2019-0055; FRL-10004-16- OAR).''
Docket EPA-HQ-OAR-2019-0055-0272.; Volvo Group. ``Comments of the
Volvo Group; U.S. EPA Cleaner Trucks Initiative Advanced Notice of
Proposed Rulemaking.'' Docket EPA-HQ-OAR-2019-0055-0463.
    \686\ As noted in Section IV.I.4, BEVs and FCEVs would not be
eligible for Early Adoption Incentive credit multipliers (see
Section IV.H for details of Early Adoption Incentives).
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1. Certification Provisions for Generating NOX Emission
Credits From Electric Vehicles
    As outlined in Section III.A, we are proposing to clarify in
proposed 40 CFR 1036.101(b) that manufacturers may optionally test the
hybrid engine and powertrain together, rather than testing the engine
alone; this option would allow manufacturers to demonstrate emission
performance of the hybrid technology that are not apparent when testing
the engine alone.\687\ To generate NOX emission credits with
a hybrid engine or hybrid powertrain, manufacturers would conduct the
emission testing described in Section IV.I.2.i and apply the results as
specified for the proposed engine ABT program discussed in Section
IV.G.
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    \687\ We are also proposing to update the definition of ``engine