[Federal Register Volume 88, Number 175 (Tuesday, September 12, 2023)]
[Notices]
[Pages 62567-62571]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-19116]


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ENVIRONMENTAL PROTECTION AGENCY

[FRL-11012-01-OAR]


Official Release of the MOVES4 Motor Vehicle Emissions Model for 
SIPs and Transportation Conformity

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice of availability.

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SUMMARY: The Environmental Protection Agency (EPA) is announcing the 
availability of the latest MOtor Vehicle Emission Simulator model major 
release (MOVES4) for official purposes outside of California. MOVES4 is 
the latest version of EPA's state-of-the science modeling tool for 
estimating emissions from cars, trucks, buses, and motorcycles based on 
the latest data and regulations. MOVES4 is available for use in state 
implementation plans (SIPs) and transportation conformity analyses 
outside of California. This notice starts a two-year grace period 
before MOVES4 will need to be used as the latest EPA emissions model 
for transportation conformity determinations outside of California, 
both in new regional emissions analyses and in new hot-spot analyses.

DATES: EPA's announcement of the MOVES4 emissions model for SIPs and 
transportation conformity analyses in states other than California is 
effective September 12, 2023. This announcement starts a two-year 
transportation conformity grace period that ends on September 12, 2025. 
After this date, MOVES4 will need to be used as the latest EPA 
emissions model for new transportation conformity analyses outside of 
California in both regional emissions analyses and in hot-spot 
analysis.

FOR FURTHER INFORMATION CONTACT: For technical model questions 
regarding the official release or use of MOVES4, please email EPA at 
<a href="/cdn-cgi/l/email-protection#9ff2f0fdf6f3fadffaeffeb1f8f0e9"><span class="__cf_email__" data-cfemail="45282a272c2920052035246b222a33">[email protected]</span></a>. For questions about SIPs, contact Rudy Kapichak at 
<a href="/cdn-cgi/l/email-protection#3f745e4f565c575e54116d4a5b50534f577f5a4f5e11585049"><span class="__cf_email__" data-cfemail="f7bc96879e949f969cd9a58293989b879fb7928796d9909881">[email protected]</span></a>. For transportation conformity questions, 
contact Aaron Letterly at <a href="/cdn-cgi/l/email-protection#430f26373726312f3a6d0222312c2d032633226d242c35"><span class="__cf_email__" data-cfemail="024e67767667706e7b2c4363706d6c426772632c656d74">[email protected]</span></a>.

SUPPLEMENTARY INFORMATION: The contents of this notice are as follows:

I. General Information
II. What is MOVES4?
III. SIPs and MOVES4
IV. Transportation Conformity and MOVES4

I. General Information

A. Does this action apply to me?

    Entities potentially impacted by the approval of MOVES4 are those 
that adopt, approve, or fund transportation plans, transportation 
improvement programs (TIPs), or projects as defined in 40 CFR 93.101 
under title 23 U.S.C. or title 49 U.S.C. chapter 53 and those that 
develop and submit SIPs to EPA. Regulated categories and entities 
affected by today's action include:

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           Category                  Examples of regulated entities
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Local government.............  Local air quality and transportation
                                agencies, including metropolitan
                                planning organizations (MPOs).
State government.............  State air quality and transportation
                                agencies.

[[Page 62568]]

 
Federal government...........  Department of Transportation (Federal
                                Highway Administration (FHWA) and
                                Federal Transit Administration (FTA)).
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    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be affected by the 
release of MOVES. Other entities not listed in the table could also be 
affected. To determine whether your organization is affected by this 
action, you should carefully examine the transportation conformity 
applicability requirements in 40 CFR 93.102. If you have questions 
regarding the applicability of this action to a particular entity, 
consult the persons listed in the preceding FOR FURTHER INFORMATION 
CONTACT section.

B. How can I get copies of MOVES4 and other related information?

    The official version of the MOVES4 model and supporting 
documentation are available on EPA's MOVES website: www.epa.gov/moves. 
Individuals who want to receive EPA announcements related to the MOVES4 
model can subscribe to the EPA-MOBILENEWS email listserv, which can be 
done at EPA's website at: www.epa.gov/moves/forms/epa-mobilenews-listserv.
    Available guidance on how to apply MOVES4 for SIPs and 
transportation conformity purposes can be found on EPA's transportation 
conformity website, www.epa.gov/state-and-local-transportation/policy-and-technical-guidance-state-and-local-transportation,\1\ including 
``MOVES4 Policy Guidance: Use of MOVES for State Implementation Plan 
Development, Transportation Conformity, General Conformity, and Other 
Purposes.'' (420-B-23-009, August 2023).
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    \1\ Interested parties can find these documents under the 
``Emission Models and Conformity'' and ``Project-Level Conformity'' 
topics on this website.
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    EPA will continue to update these websites as other MOVES support 
materials and guidance are developed or updated.

II. What is MOVES4?

    MOVES4 is EPA's latest motor vehicle emissions model for state and 
local agencies to estimate volatile organic compounds (VOCs), nitrogen 
oxides (NO<INF>X</INF>), particulate matter (PM<INF>2.5</INF> and 
PM<INF>10</INF>), carbon monoxide (CO), and other pollutants and 
precursors from cars, trucks, buses, and motorcycles for SIP purposes 
and conformity determinations outside of California.\2\ The model is 
based on analyses of millions of emission test results and considerable 
advances in the Agency's understanding of vehicle emissions. MOVES4 is 
a major revision to the MOVES series of models. This model is the 
fourth major MOVES release--the first three were MOVES2010, MOVES2014, 
and MOVES3.\3\
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    \2\ MOVES can also model emissions in the District of Columbia, 
Puerto Rico, and the U.S. Virgin Islands. Nonattainment and 
maintenance areas located in California use the latest approved 
version of the Emission FACtor (EMFAC) model.
    \3\ For more information, see EPA's MOVES Versions in Limited 
Current Use website.
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    MOVES4 includes new regulations, features, and significant new 
data, as detailed in the MOVES4 technical reports. Notably, MOVES4 
incorporates:
    <bullet> The emission impacts of the EPA heavy-duty low 
NO<INF>X</INF> rule for model years 2027 and later \4\ and the light-
duty greenhouse gas rule for model years 2023 and later.\5\
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    \4\ 88 FR 4296, January 24, 2023.
    \5\ 86 FR, December 30, 2021.
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    <bullet> The ability to model heavy-duty battery-electric and fuel-
cell vehicles, as well as CNG long-haul combination trucks.
    <bullet> Improved modeling of light-duty electric vehicles.
    <bullet> New tools to make the model easier to use and updates for 
compatibility with newer software.
    <bullet> Updated data and forecasts on vehicle populations 
(including electric vehicle fractions), travel activity, and emission 
rates, as well as updated fuel supply information at the county level.
    <bullet> The latest data on ammonia emission rates for light-duty 
and heavy-duty vehicles.
    <bullet> A number of limited-impact updates to specific emissions 
rates and adjustments.
    Like its predecessors, MOVES4 includes the capability to estimate 
vehicle exhaust and evaporative emissions as well as brake wear and 
tire wear emissions for criteria pollutants and precursors. However, 
like previous versions, MOVES4 does not include the capability to 
estimate emissions of re-entrained road dust. To estimate emissions 
from re-entrained road dust, practitioners should continue to use the 
latest approved methodologies.\6\
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    \6\ See EPA's notice of availability, ``Official Release of the 
January 2011 AP-42 Method for Estimating Re-Entrained Road Dust from 
Paved Roads,'' published in the Federal Register on February 4, 2011 
(76 FR 6328).
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    The structure of MOVES4 is fundamentally the same as MOVES3, 
although there are new format options for some inputs, and the model 
run time may differ depending on the type of run and user inputs and 
computer configuration. As for emissions, EPA performed a comparison of 
MOVES4 to MOVES3 using default information in MOVES4 at the national 
level, and for three sample urban counties with different local travel 
patterns and ambient conditions. In general, compared to MOVES3, MOVES4 
will produce notable decreases in NO<INF>X</INF> for future years due 
to the emissions reductions of new regulations and small decreases in 
most other pollutants. However, ammonia emissions increase 
significantly because real-world emission measurements show ammonia 
emissions from both gasoline and diesel vehicles are much higher than 
MOVES3 predicted. Similarly, nitrous oxide (N<INF>2</INF>O) emissions 
have increased due to new data for heavy-duty diesel vehicles. Note 
that results will vary based on the pollutant selected and that area's 
local inputs.

III. SIPs and MOVES4

    EPA has articulated its policy regarding the use of MOVES4 in SIP 
development in its ``MOVES4 Policy Guidance: Use of MOVES for State 
Implementation Plan Development, Transportation Conformity, General 
Conformity, and Other Purposes'' (EPA-420-B-23-009, August 2023). 
Today's notice highlights certain aspects of the guidance, but state 
and local governments should refer to the guidance for more detailed 
information on how and when to use MOVES4 in reasonable further 
progress SIPs, attainment demonstrations, maintenance plans, inventory 
updates, and other SIP submissions.
    MOVES4 should be used in ozone, CO, PM, and nitrogen dioxide 
(NO<INF>2</INF>) SIP development as expeditiously as possible, as there 
is no grace period for the use of MOVES4 in SIPs. The Clean Air Act 
requires that SIP inventories and control measures be based on the most 
current information and applicable models that are available when a SIP 
is developed.\7\ However, EPA also

[[Page 62569]]

recognizes the time and level of effort that certain states may have 
already undertaken in SIP development using a version of MOVES3. States 
should consult with their EPA Regional Office if they have questions 
about how MOVES4 affects SIPs under development in specific 
nonattainment or maintenance areas. Early consultation can facilitate 
EPA's adequacy finding for SIP motor vehicle emissions budgets for 
transportation conformity purposes or EPA's SIP approval.
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    \7\ See Clean Air Act section 172(c)(3). Also see the discussion 
of emissions inventory requirements in the ``Fine Particulate Matter 
National Ambient Air Quality Standards: State Implementation Plan 
Requirements'' rule (81 FR 58029, August 24, 2016) and in the 
``Implementation of the 2015 National Ambient Air Quality Standards 
for Ozone: Nonattainment Area State Implementation Plan 
Requirements'' rule (83 FR 63022, December 6, 2018).
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    States should use the latest version of MOVES that is available at 
the time that a SIP is developed. All states other than California 
should use MOVES4 for SIPs that will be submitted in the future so that 
they are based on the most accurate estimates of emissions possible. 
However, state and local agencies that have already completed 
significant work on a SIP with a version of MOVES3 (e.g., attainment 
modeling has already been completed with MOVES3) may continue to rely 
on this earlier version of MOVES. It would be unreasonable to require 
the states to revise these SIPs with MOVES4 since significant work has 
already occurred based on the latest information available at the time 
the SIP was developed, and EPA intends to act on these SIPs in a timely 
manner.
    The Clean Air Act does not require states that have already 
submitted SIPs or will submit SIPs shortly after the release of a new 
model to revise these SIPs simply because a new motor vehicle emissions 
model is now available.\8\ States can choose to use MOVES4 in these 
SIPs, for example, if it is determined that it is appropriate to update 
motor vehicle emissions budgets (``budgets'') with the model for future 
conformity determinations. However, as stated above, states should use 
MOVES4 where SIP development is in its initial stages or has not 
progressed far enough along that switching from a previous model 
version would create a significant adverse impact on state resources.
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    \8\ Sierra Club v. EPA, 356 F.3d. 296, 308 (D.C. Cir. 2004) 
(``To require states to revise completed plans every time a new 
model is announced would lead to significant costs and potentially 
endless delays in the approval processes.'')
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    Incorporating MOVES4 into the SIP now could assist areas in 
mitigating possible transportation conformity difficulties in the 
future after the MOVES4 conformity grace period ends. New regional 
emissions analyses using EPA's emissions model that are started after 
the grace period is over must be based on MOVES4 (40 CFR 93.111), so 
having MOVES4-based SIP budgets in place at that time could provide 
more consistency with transportation conformity determinations.

IV. Transportation Conformity and MOVES4

    In today's notice, EPA is announcing the availability of MOVES4 for 
use in transportation conformity analyses outside of California. EPA is 
also establishing a two-year grace period before MOVES4 will need to be 
used in regional emissions analysis for transportation conformity 
determinations and in hot-spot analyses for project-level 
transportation conformity determinations which use EPA's emissions 
model. The MOVES4 grace period for regional emissions and hot-spot 
analyses applies to the use of MOVES4 and any future minor revisions 
that occur during the grace period.
    Transportation conformity is a Clean Air Act requirement to ensure 
that federally supported highway and transit activities are consistent 
with (``conform to'') the SIP. Conformity to a SIP means that a 
transportation activity will not cause or contribute to new air quality 
violations; worsen existing violations; or delay timely attainment of 
national ambient air quality standards or any interim milestones. 
Transportation conformity applies in nonattainment and maintenance 
areas for transportation-related pollutants: ozone, CO, 
PM<INF>2.5</INF>, PM<INF>10</INF> and NO<INF>2</INF>. EPA's 
transportation conformity regulations (40 CFR parts 51.390 and 93 
subpart A) describe how federally funded and approved highway and 
transit projects meet these statutory requirements.
    The remainder of this section describes how the transportation 
conformity grace period was determined and summarizes how it will be 
implemented, including those circumstances when the grace period could 
be shorter than two years for regional emissions analyses. However, for 
complete explanations of how MOVES4 is to be implemented for 
transportation conformity, including details about using MOVES4 during 
the grace period, refer to ``MOVES4 Policy Guidance: Use of MOVES for 
State Implementation Plan Development, Transportation Conformity, 
General Conformity, and Other Purposes.'' (EPA-420-B-23-009).

A. Why is EPA establishing a two-year conformity grace period?

    Section 176(c)(1) of the Clean Air Act states that ``. . .[t]he 
determination of conformity shall be based on the most recent estimates 
of emissions, and such estimates shall be determined from the most 
recent population, employment, travel, and congestion estimates. . .''. 
Additionally, the transportation conformity rule (40 CFR 93.111) 
requires conformity analyses to be based on ``the latest emissions 
estimation model available,'' and further states that this requirement 
is satisfied if the most current version of EPA's motor vehicle 
emissions model is used. When EPA announces a new emissions model, such 
as MOVES4, we establish a grace period before the model needs to be 
used for transportation conformity purposes (40 CFR 93.111(b)). In 
consultation with DOT, EPA must consider the degree of change in the 
emissions model and the effects of the new model on the transportation 
planning process (40 CFR 93.111(b)(2)). The transportation conformity 
rule provides that EPA will establish a grace period for new emissions 
models of between three and 24 months (40 CFR 93.111(b)(1)).
    EPA articulated its intentions for establishing the length of a 
conformity grace period in the preamble to the 1993 transportation 
conformity rule (November 24, 1993; 58 FR 62211):
    ``EPA and DOT [the Department of Transportation] will consider 
extending the grace period if the effects of the new emissions model 
are so significant that previous SIP demonstrations of what emission 
levels are consistent with attainment would be substantially affected. 
In such cases, States should have an opportunity to revise their SIPs 
before MPOs must use the model's new emissions factors.''
    In consultation with DOT, EPA considered the degree of change in 
MOVES4 and the effects of the new model on the transportation planning 
process (40 CFR 93.111(b)(2)). EPA considered the time it will take 
state and local transportation and air quality agencies to conduct and 
provide technical support for analyses. State and local agencies will 
need to become familiar with the MOVES4 emissions model and may need to 
convert existing data for use in MOVES4. Since 1993, the fundamental 
purpose of section 93.111(b) of the transportation conformity rule has 
been to provide a sufficient amount of time for MPOs and other state 
and local agencies to learn and employ new emissions models. The 
transition to a new emissions model for conformity involves more than 
learning to use the new model and preparing input data and model 
output. After model start-up is complete, state and local agencies also 
need to consider how the model affects regional emissions analysis 
results and whether SIP and/or transportation plan/TIP changes are

[[Page 62570]]

necessary to assure future conformity determinations.
    The two-year conformity grace period also provides sufficient time 
for state and local agencies to learn and apply new technical guidance 
and training that reflect MOVES4. EPA is working to update guidance 
documents and training materials as quickly as possible. EPA will 
notify MOVES4 users when these important materials are available. 
Training materials will address different levels of state and local 
expertise.
    In addition, many agencies will be implementing the transition to 
MOVES4 for PM and CO hot-spot analyses for applicable projects in those 
nonattainment and maintenance areas, with each analysis potentially 
involving multiple state and local agencies. States with CO hot-spot 
protocols that were previously approved into the SIP (40 CFR 
93.123(a)(1)) that are based on a previous model will need time to 
revise them. Additional time is necessary to revise previously approved 
CO hot-spot protocols, and the SIP revision process and state 
requirements can vary. Finally, EPA considered the general time and 
monetary resource constraints in which state and local agencies 
currently operate. Upon considerations of all these factors, EPA is 
establishing a two-year grace period, which begins today and ends on 
September 12, 2025, before MOVES4 needs to be used for new 
transportation conformity analyses outside of California.

B. Circumstances When Grace Period Will Be Shorter Than Two Years

    The grace period for regional emissions analyses will be shorter 
than two years for a given pollutant if an area revises its SIP and 
motor vehicle emissions budgets with MOVES4 and such budgets have been 
found adequate or approved into the SIP prior to the end of the two-
year grace period. In this case, the new regional emissions analysis 
must use MOVES4 if the conformity determination is based on a MOVES4-
based budget (40 CFR 93.111).
    Areas that are designated nonattainment or maintenance for multiple 
pollutants may rely on both MOVES4 and MOVES3 to determine conformity 
for different pollutants during the grace period. For example, if an 
area revises a previously submitted (but not approved) MOVES3-based 
PM<INF>10</INF> SIP with MOVES4 and EPA finds these revised MOVES4 
budgets adequate for conformity, such budgets would apply for 
conformity on the effective date of the Federal Register notice 
announcing EPA's adequacy finding. In this example, if the area is 
nonattainment for PM<INF>10</INF> and ozone, the MOVES4 grace period 
would end for PM<INF>10</INF> regional emissions analyses once EPA 
found the new MOVES4-based SIP budgets adequate. However, MOVES3 could 
continue to be used for ozone-related regional emissions analyses begun 
before the end of the MOVES4 grace period.\9\ In addition, the length 
of the grace period for hot-spot analyses would not be affected by an 
early submission of MOVES4-based budgets. In this example, the two-year 
grace period for PM<INF>10</INF> hot-spot analyses would continue to 
apply even if the grace period is shortened for regional 
PM<INF>10</INF> conformity analyses. EPA Regional Offices should be 
consulted for questions regarding such situations in multi-pollutant 
areas.
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    \9\ In this example, such an area would use MOVES4 to develop a 
regional emissions analysis for PM<INF>10</INF> for comparison to 
the revised MOVES4-based budgets (e.g., PM<INF>10</INF> budgets). 
The regional emissions analysis for ozone could be based on MOVES3 
for the VOC and NO<INF>X</INF> budgets in the ozone SIP for the 
remainder of the conformity grace period.
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    In addition, in most cases, if the state revises previously 
approved budgets based on an earlier EPA emissions model, the revised 
MOVES4 budgets could not be used for conformity purposes until EPA 
approves them, i.e., approves the SIP revision. In general, submitted 
SIPs cannot supersede approved budgets until the submitted SIP is 
approved. See 40 CFR 93.118(e)(1).
    However, 40 CFR 93.118(e)(1) allows an approved budget to be 
replaced by an adequate budget if EPA's approval of the initial budgets 
specifies that the budgets being approved may be replaced in the future 
by new adequate budgets. This flexibility has been used in limited 
situations in the past. In such cases, the MOVES4-based budgets would 
be used for conformity purposes once they have been found adequate, if 
requested by the state in its SIP submission and specified in EPA's SIP 
approval. States should consult with their EPA Regional Office to 
determine if this flexibility applies to their situation.

C. Use of MOVES4 for Regional Emissions Analyses During the Grace 
Period

    During the conformity grace period, areas should use interagency 
consultation to examine how MOVES4 will impact their future 
transportation plan and TIP conformity determinations, including 
regional emissions analyses. Isolated rural areas should also consider 
how future regional emissions analyses will be affected when the MOVES4 
grace period ends. Areas should carefully consider whether the SIP and 
budgets should be revised with MOVES4 or if transportation plans and 
TIPs should be revised before the end of the conformity grace period, 
since doing so may be necessary to ensure conformity in the future.
    Finally, the transportation conformity rule provides flexibility 
for completing conformity determinations based on regional emissions 
analyses that use MOVES3 that are started before the end of the grace 
period. Regional emissions analyses that are started during the grace 
period can use either MOVES3 or MOVES4. The interagency consultation 
process should be used if it is unclear if a MOVES3-based analysis was 
begun before the end of the grace period. If there are questions about 
which model should be used in a conformity determination, the EPA 
Regional Office can be consulted.
    When the grace period ends on September 12, 2025, MOVES4 will 
become the only EPA motor vehicle emissions model for regional 
emissions analyses for transportation conformity in states other than 
California. In general, this means that all new transportation plan and 
TIP conformity determinations started after the end of the grace period 
must be based on MOVES4, even if the SIP is based on MOVES3 or an older 
version of the MOVES model.

D. Use of MOVES4 for Project-Level Hot-Spot Analyses During the 
Conformity Grace Period

    The MOVES4 grace period also applies to the use of MOVES4 for CO, 
PM<INF>10</INF> and PM<INF>2.5</INF> hot-spot analyses. Sections 93.116 
and 93.123 of the transportation conformity regulation contain the 
requirements for when a hot-spot analysis is required for project-level 
conformity determinations.\10\ The transportation conformity rule 
provides flexibility for analyses that are started before the end of 
the grace period. A conformity determination for a transportation 
project may be based on a previous model if the analysis was begun 
before or during the grace period, and if the final environmental 
document for the project is issued no more than three years after the 
issuance of the draft environmental document (40 CFR 93.111(c)). 
Interagency consultation should be used if it is unclear if a

[[Page 62571]]

previous analysis was begun before the end of the grace period. For CO, 
PM<INF>10</INF> and PM<INF>2.5</INF> hot-spot analyses that start 
during the grace period, project sponsors can choose to use MOVES3 or 
MOVES4.
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    \10\ In CO nonattainment and maintenance areas, a hot-spot 
analysis is required for all non-exempt projects, with quantitative 
hot-spot analyses being required for larger, congested intersections 
and other projects (40 CFR 93.123(a)(1)). In addition, in 
PM<INF>2.5</INF> and PM<INF>10</INF> nonattainment and maintenance 
areas, the transportation conformity regulation requires that a 
quantitative hot-spot analysis be completed for certain projects 
(see 40 CFR 93.123(b)(1)).
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    EPA encourages sponsors to use the consultation process to 
determine which option may be most appropriate for a given situation. 
Any new CO, PM<INF>10</INF> or PM<INF>2.5</INF> hot-spot analyses for 
conformity purposes begun after the end of the grace period must be 
based on MOVES4. EPA has guidance on how to conduct quantitative 
PM<INF>2.5</INF> and PM<INF>10</INF> hot-spot modeling for 
transportation conformity purposes, and on how to use MOVES for a CO 
hot-spot analysis. Until EPA updates these guidance documents, the 
MOVES3-based guidance still generally applies for MOVES4. See EPA's 
``Project-level Conformity'' website, www.epa.gov/state-and-local-transportation/project-level-conformity-and-hot-spot-analyses, for the 
latest information and guidance documents on how to conduct CO, 
PM<INF>10</INF> and PM<INF>2.5</INF> hot-spot modeling for 
transportation conformity purposes.
    Any new, quantitative CO, PM<INF>10</INF> or PM<INF>2.5</INF> hot-
spot analysis for conformity purposes begun after the end of the grace 
period using EPA's emissions model must use MOVES4. The interagency 
consultation process should be used if it is unclear whether these 
conditions are met. For questions about which model should be used in a 
project-level conformity determination, consult with your EPA Regional 
Office.

E. FHWA's CO Categorical Hot-Spot Finding

    FHWA released the most recent CO categorical hot-spot finding for 
intersection projects on January 31, 2023, that was based on 
MOVES3.\11\ During the MOVES4 grace period, a project sponsor outside 
of California may continue to rely on the categorical finding for 
applicable projects that are determined through interagency 
consultation to be covered by the finding's parameters. However, new CO 
hot-spot analyses for conformity purposes begun after the end of the 
MOVES4 grace period would not be able to rely on the MOVES3-based 
January 2023 CO categorical hot-spot finding.
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    \11\ See www.epa.gov/state-and-local-transportation/project-level-conformity-and-hot-spot-analyses#cohotspot.
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F. CO Hot-Spot Protocols That Were Previously Approved Into the SIP

    Section 93.123(a)(1) of the transportation conformity regulation 
allows areas to develop alternate procedures for determining localized 
CO hot-spot analyses, when developed through interagency consultation 
and approved by the EPA Regional Administrator. Some states have chosen 
in the past to develop such procedures based on previous EPA emissions 
models.
    During the MOVES4 grace period, areas with previously approved CO 
hot-spot protocols based on MOVES3 may continue to rely on these 
protocols. Once the MOVES4 two-year grace period ends, new CO hot-spot 
analyses for conformity purposes will need to be based on MOVES4. 
Previously approved SIP CO hot-spot protocols that are based on 
emissions models prior to MOVES3 can no longer be used for 
transportation conformity purposes.

Karl Simon,
Director, Transportation and Climate Division, Office of Transportation 
and Air Quality.
[FR Doc. 2023-19116 Filed 9-11-23; 8:45 am]
BILLING CODE 6560-50-P


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