Rule2026-17756
Resetting NHTSA's Fuel Economy Program: Commercial Medium- and Heavy-Duty On-Highway Vehicles and Work Trucks
Primary source
Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.
Published
August 31, 2026
Issuing agencies
Transportation DepartmentNational Highway Traffic Safety Administration
Abstract
The National Highway Traffic Safety Administration is issuing this interpretive rule regarding the scope of its authority to set fuel economy standards for commercial medium- and heavy-duty on-highway vehicles and work trucks. This rule describes NHTSA's authority to set vehicle standards, which does not include the authority to set separate standards for engines. NHTSA will review its existing standards applicable to commercial medium- and heavy-duty on-highway vehicles and work trucks for consistency with this interpretation in a separate rulemaking. Pending the rulemaking process, NHTSA will exercise its enforcement authority with regard to affected standards in accordance with the interpretation set forth in this rule.
Full Text
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<title>Federal Register, Volume 91 Issue 167 (Monday, August 31, 2026)</title>
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[Federal Register Volume 91, Number 167 (Monday, August 31, 2026)]
[Rules and Regulations]
[Pages 55788-55793]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-17756]
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DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration
49 CFR Parts 523, 534, and 535
[Docket No. NHTSA-2026-1948]
Resetting NHTSA's Fuel Economy Program: Commercial Medium- and
Heavy-Duty On-Highway Vehicles and Work Trucks
AGENCY: National Highway Traffic Safety Administration (NHTSA),
Department of Transportation (DOT).
ACTION: Interpretive rule.
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SUMMARY: The National Highway Traffic Safety Administration is issuing
this interpretive rule regarding the scope of its authority to set fuel
economy standards for commercial medium- and heavy-duty on-highway
vehicles and work trucks. This rule describes NHTSA's authority to set
vehicle standards, which does not include the authority to set separate
standards for engines. NHTSA will review its existing standards
applicable to commercial medium- and heavy-duty on-highway vehicles and
work trucks for consistency with this interpretation in a separate
rulemaking. Pending the rulemaking process, NHTSA will exercise its
enforcement authority with regard to affected standards in accordance
with the interpretation set forth in this rule.
DATES: This interpretive rule is applicable as of August 31, 2026.
FOR FURTHER INFORMATION CONTACT: Kerry Kolodziej, NHTSA Office of the
Chief Counsel, National Highway Traffic Safety Administration, 1200 New
Jersey Avenue SE, W44-308, Washington, DC 20590; email:
<a href="/cdn-cgi/l/email-protection#dd96b8afafa4f396b2b1b2b9a7b4b8b79db9b2a9f3bab2ab"><span class="__cf_email__" data-cfemail="4d06283f3f34630622212229372428270d292239632a223b">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION: The National Highway Traffic Safety
Administration (NHTSA) issues this interpretive rule as part of its
comprehensive effort to reset its fuel economy program to comply with
the law.\1\ NHTSA has reconsidered the scope of its authority to set
fuel economy standards for commercial medium- and heavy-duty on-highway
vehicles and work trucks. As NHTSA sets forth in this interpretation,
the Energy Independence and Security Act of 2007 (EISA) requires NHTSA
to set fuel economy standards for medium- and heavy-duty on-highway
vehicles and work trucks but did not authorize NHTSA to set standards
for engines on a standalone basis. In contrast to the Clean Air Act
(CAA), which specifically authorizes EPA to set separate standards for
engines, EISA specifically requires NHTSA set standards for vehicles,
and authorized separate standards for different classes of vehicles,
but did not authorize standalone engine standards. A related decision
of the United States Court of Appeals for the District of Columbia
Circuit further confirms that NHTSA's authority was limited to setting
vehicle standards.\2\
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\1\ See, e.g., Interpretive Rule, Resetting the Corporate
Average Fuel Economy Program, 90 FR 24518 (June 11, 2025).
\2\ This interpretation is not applicable to light-duty
vehicles. NHTSA has not established engine standards for light-duty
vehicles separate from the CAFE standards, and NHTSA confirms that
it does not have statutory authority to do so.
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This interpretation will help ensure the efficient functioning of
the market for these commercial vehicles by limiting regulation to its
legally authorized scope. This interpretation will also help ensure
that manufacturers have flexibility in how best to meet the standards
and needs of their sophisticated commercial customers, who make
business decisions that account for their own fuel economy needs. NHTSA
will review its regulations for consistency with this interpretation in
a separate rulemaking.
I. Statutory Background and Regulatory History
EISA established a statutory requirement for the Secretary of
Transportation to implement a commercial medium- and heavy-duty on-
highway vehicle and work truck fuel efficiency improvement program,
commonly known as the MDHD program.\3\ EISA requires NHTSA, by
delegation from the Secretary of Transportation,\4\ to prescribe
``average fuel economy standards for . . . work trucks and commercial
medium-duty
[[Page 55789]]
and heavy-duty on-highway vehicles in accordance with subsection (k).''
\5\ Subsection (k) requires NHTSA to establish ``a commercial medium-
and heavy-duty on-highway vehicle and work truck fuel efficiency
improvement program.'' \6\ EISA defines ``commercial medium- and heavy-
duty on-highway vehicle'' as ``an on-highway vehicle with a gross
vehicle weight rating of 10,000 pounds or more,'' and ``work truck'' as
``a vehicle that--(A) is rated at between 8,500 and 10,000 pounds gross
vehicle weight; and (B) is not a medium-duty passenger vehicle . . .
.'' \7\ Pursuant to these definitions, medium- and heavy-duty on-
highway vehicles and work trucks are all ``vehicles'' with certain
specified characteristics.
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\3\ The MDHD program encompasses both commercial medium- and
heavy-duty on-highway vehicles and work trucks, as defined in EISA.
See 49 U.S.C. 32901(a)(7) and (19).
\4\ 49 CFR 1.95(j).
\5\ EISA, Public Law 110-140 Sec. 102 (2007), 121 Stat. 1492,
1498-99; see 49 U.S.C. 32902(b)(1)(C).
\6\ 49 U.S.C. 32902(k).
\7\ 49 U.S.C. 32901(a)(7), (19).
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To inform the fuel efficiency improvement program for these
vehicles, EISA instructed the National Academy of Sciences (NAS) to
publish a study ``evaluating medium-duty and heavy-duty truck fuel
economy standards,'' including elements such as ``an assessment of
technologies and costs to evaluate fuel economy for medium-duty and
heavy-duty trucks.'' \8\ After NAS completed its study, the EISA
directed NHTSA to ``examine the fuel efficiency of commercial medium-
and heavy-duty on-highway vehicles and work trucks.'' \9\ Among other
things, EISA required NHTSA to determine ``the appropriate test
procedures and methodologies for measuring the fuel efficiency of such
vehicles and work trucks'' and ``the appropriate metric for measuring
and expressing commercial medium- and heavy-duty on-highway vehicle and
work truck fuel efficiency performance.'' \10\
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\8\ EISA, Public Law 110-140 Sec. 108 (2007), 121 Stat. 1492,
1505.
\9\ 49 U.S.C. 32902(k)(1).
\10\ Id.
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EISA then required NHTSA to ``determine in a rulemaking proceeding
how to implement a commercial medium- and heavy-duty on-highway vehicle
and work truck fuel efficiency improvement program designed to achieve
the maximum feasible improvement.'' \11\ As part of that program, NHTSA
``shall adopt and implement appropriate test methods, measurement
metrics, fuel economy standards, and compliance and enforcement
protocols that are appropriate, cost-effective, and technologically
feasible for commercial medium- and heavy-duty on-highway vehicles and
work trucks.'' \12\ The statute specifies that NHTSA ``may prescribe
separate standards for different classes of vehicles under this
subsection.'' \13\ The statute also requires that ``the commercial
medium- and heavy-duty on-highway vehicle and work truck fuel economy
standard adopted pursuant to this subsection shall provide not less
than--(A) 4 full model years of regulatory lead-time; and (B) 3 full
model years of regulatory stability.'' \14\
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\11\ Id. Sec. 32902(k)(2).
\12\ Id.
\13\ Id.
\14\ Id. Sec. 32902(k)(3).
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NHTSA first established the MDHD program through a September 2011
final rule, known as Phase 1, issued jointly with the Environmental
Protection Agency (EPA).\15\ NHTSA and EPA generally set standards for
the same vehicles and engines in the Phase 1 rule.\16\ Relying on its
EISA authority, NHTSA adopted standards for different classes of
commercial medium- and heavy-duty on-highway vehicles and work trucks
and separate standards for engines used for certain of those vehicles
(combination tractors and vocational vehicles).\17\ NHTSA's standards
generally were mandatory for Model Years 2016 and later.\18\ EPA also
set separate emissions standards for vehicles and engines. EPA relied
on its CAA authority to set air pollutant standards for ``any class or
classes of new motor vehicles or new motor vehicle engines.'' \19\
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\15\ Final Rules, Greenhouse Gas Emissions Standards and Fuel
Efficiency Standards for Medium- and Heavy-Duty Engines and
Vehicles, 76 FR 57106 (Sept. 15, 2011).
\16\ EPA set standards for recreational on-highway vehicles in
Phase 1, while NHTSA did not. Id. at 57134.
\17\ E.g., id. at 57106.
\18\ See id.
\19\ See 42 U.S.C. 7521(a)(1); see Phase 1 Final Rules, 76 FR
57114 (``The Clean Air act, of course, mandates standards for both
`new motor vehicles' and `new motor vehicle engines', so there is no
issue of authority for separate engine standards under the EPA GHG
program.''). EPA has since ``rescind[ed] the Administrator's 2009
findings of contribution and endangerment and repealing all
greenhouse gas (GHG) emission standards for light-duty, medium-duty,
and heavy-duty vehicles and engines to effectuate the best reading
of Clean Air Act (CAA) section 202(a)(1).'' Final Rule, Rescission
of the Greenhouse Gas Endangerment Finding and Motor Vehicle
Greenhouse Gas Emission Standards Under the Clean Air Act, 91 FR
7686 (Feb. 18, 2026).
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NHTSA offered several explanations for its authority to set engine
standards during the Phase 1 rulemaking despite the absence of the word
``engine'' in NHTSA's standards-setting authority. In both the proposed
and final rules, NHTSA asserted that its express authority to set
``separate standards for different classes of vehicles'' also allowed
it to set standards for engines.\20\ NHTSA recognized that it was
interpreting the statutory language ``broadly.'' \21\ In a footnote in
the proposal, NHTSA also cited the statutory requirement to set maximum
feasible standards as a basis for its authority to set engine
standards.\22\ After several industry commenters argued that NHTSA
lacked this claimed authority, the agency asserted that the statute
``grants NHTSA broad authority to regulate this sector'' and ``does not
. . . preclude[ ] the regulation of engines, but rather explicitly
leaves the regulatory approach to the agency's expertise and
discretion.'' \23\
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\20\ Phase 1 Final Rules, 76 FR 57112; Proposed Rules,
Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for
Medium- and Heavy-Duty Engines and Vehicles, 75 FR 74152, 74158
(Nov. 30, 2010).
\21\ Phase 1 Final Rules, 76 FR 57112 (``Congress also stated
that NHTSA may set separate standards for different classes of HD
vehicles, which the agency interprets broadly to allow regulation of
HD engines in addition to HD vehicles . . . .''); Phase 1 Proposed
Rules, 75 FR 74158 (``Congress also stated that NHTSA may set
separate standards for different classes of HD vehicles, which the
agency interprets broadly to allow regulation of HD engines in
addition to HD vehicles . . . .'').
\22\ Phase 1 Proposed Rules, 75 FR 74173 n.36 (``NHTSA
interprets 49 U.S.C. 32902(k)(2) to include a grant of authority to
establish engines standards pursuant to the broader statement of
authority to establish standards that achieve the maximum feasible
improvement in fuel efficiency.'').
\23\ Phase 1 Final Rules, 76 FR 57114 (``Volvo and Daimler
argued that EISA limited NHTSA's authority to the regulation of
completed vehicles and did not give NHTSA authority to regulate
engines. 49 U.S.C. 32902(k)(2) grants NHTSA broad authority to
regulate this sector . . . . NHTSA does not believe that this
language precludes the regulation of engines, but rather explicitly
leaves the regulatory approach to the agency's expertise and
discretion. See 75 FR 74173 n. 36 . . . . NHTSA continues to believe
that the separate regulation of engines and vehicles is [ ]
consistent with the agency's statutory mandate to determine how to
implement a regulatory program designed to achieve the maximum
feasible improvement and facilitates coordination with EPA's efforts
to reduce greenhouse gas emissions.'').
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NHTSA and EPA issued a second, Phase 2, joint final rule for the
MDHD program in October 2016.\24\ In the Phase 2 rule, both agencies
increased the stringency of the standards applicable to the vehicles
and engines addressed by the Phase 1 rule and set separate standards
for trailers designed to be
[[Page 55790]]
drawn by a motorized tractor.\25\ NHTSA's Phase 2 standards generally
applied to Model Years 2021 and later.\26\ In a legal challenge to the
agencies' trailer standards, the D.C. Circuit ruled the agencies
exceeded their authorities under their respective enabling statutes to
establish fuel economy or emissions standards for various categories of
``vehicles.'' \27\
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\24\ Final Rule, Greenhouse Gas Emissions and Fuel Efficiency
Standards for Medium- and Heavy-Duty Engines and Vehicles--Phase 2,
81 FR 73478 (Oct. 25, 2016). In the Phase 2 proposed and final
rules, NHTSA referred back to the explanation from the Phase 1 final
rule for the assertion that EISA ``includes authority to establish
separate engine standards.'' Phase 2 Final Rule, 81 FR 73491 n.51;
Proposed Rule, Greenhouse Gas Emissions and Fuel Efficiency
Standards for Medium- and Heavy-Duty Engines and Vehicles--Phase 2,
80 FR 40138, 40152 n.43 (July 13, 2015).
\25\ See generally Phase 2 Final Rule, 81 FR 73478. NHTSA also
added standards for recreational vehicles in the Phase 2 rule and
EPA added standards for gliders. See id. at 73521, 73584.
\26\ See id. at 73493, 73504.
\27\ Truck Trailer Mfrs. Ass'n, Inc. (``TTMA'') v. Envtl. Prot.
Agency, 17 F.4th 1198 (D.C. Cir. 2021).
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II. EISA Required NHTSA To Set Vehicle Standards and Did Not Permit
Engine Standards
``Start[ing] with the statutory text,'' \28\ NHTSA's standards-
setting authority speaks only of setting fuel economy standards for
vehicles and not their component parts. As part of NHTSA's ``commercial
medium- and heavy-duty on-highway vehicle and work truck fuel
efficiency improvement program,'' EISA instructs NHTSA to ``prescribe
separate average fuel economy standards for . . . work trucks and
commercial medium-duty or heavy-duty on-highway vehicles.'' \29\ A
``work truck'' is ``a vehicle that--(A) is rated at between 8,500 and
10,000 pounds gross vehicle weight; and (B) is not a medium-duty
passenger vehicle . . . .'' \30\ In setting these vehicle standards,
NHTSA must evaluate these vehicles as a whole. NHTSA must determine:
``the appropriate test procedures and methodologies for measuring the
fuel efficiency of such vehicles and work trucks''; ``the appropriate
metric for measuring and expressing commercial medium- and heavy-duty
on-highway vehicle and work truck fuel efficiency performance''; and
factors and conditions that may affect vehicle and work truck fuel
efficiency.\31\ And NHTSA must establish ``compliance and enforcement
protocols for commercial medium- and heavy-duty on-highway vehicles and
work trucks,'' \32\ not for various sub-components of those vehicles.
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\28\ Garland v. Cargill, 602 U.S. 406, 415 (2024).
\29\ 49 U.S.C. 32902(b)(1)(C) (emphasis added).
\30\ Id. Sec. 32901(a)(7), (19) (emphasis added).
\31\ Id. Sec. 32902(k)(1).
\32\ Id. Sec. 32902(k)(2).
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Indeed, nowhere in NHTSA's standards-setting authority does
Congress instruct NHTSA to set fuel economy standards for component
parts. In addition to setting standards for commercial medium- and
heavy-duty on-highway vehicles and work trucks, NHTSA is also
instructed to prescribe separate average fuel economy standards for
``passenger automobiles'' and ``non-passenger automobiles,'' \33\ but
not their component parts. And, unlike commercial medium- and heavy-
duty on-highway vehicles and work trucks, NHTSA has never asserted
authority to set standards for component parts of passenger and non-
passenger automobiles when establishing fuel economy standards for
those automobiles.
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\33\ Id. Sec. 32902(b)(1)(A)-(B) (emphases added).
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Congress has demonstrated that it understands the difference
between vehicles and engines, and that when it wants an agency to have
authority to regulate one or both, it says so.\34\ For example, EISA
mentioned engines in several unrelated statutory provisions.\35\ The
absence of any reference to engines in NHTSA's standards-setting
authority confirms that NHTSA's authority was limited to setting
standards for the types of vehicles referenced: work trucks and
commercial medium-duty or heavy-duty on-highway vehicles. The Supreme
Court has explained that when ``Congress includes particular language
in one section of a statute but omits it in another section of the same
Act, it is generally presumed that Congress acts intentionally and
purposely in the disparate inclusion or exclusion.'' \36\ NHTSA must
give meaning to the fact that Congress did not mention engines in its
standard-setting authority at the same time it enacted other engine-
related provisions.
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\34\ See, e.g., Bittner v. United States, 598 U.S. 85, 94 (2023)
(``When Congress includes particular language in one section of a
statute but omits it from a neighbor, we normally understand that
difference in language to convey a difference in meaning [].'').
\35\ See, e.g., EISA, Public Law 110-140 Sec. 209 (requiring
study of whether changes in vehicle and engine emissions of air
pollutants adversely impact air quality); id. Sec. 226 (``Study of
Engine Durability and Performance Associated with the Use of
Biodiesel''); id. Sec. 251 (providing for waiver related to vehicle
or engine emission standards).
\36\ Nken v. Holder, 556 U.S. 418, 430 (2009) (quoting INS v.
Cardoza-Fonseca, 480 U.S. 421, 432 (1987)).
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NHTSA must also give weight to the fact that Congress expressly
granted authority to set engine standards to another Federal agency:
the EPA. In the CAA, Congress expressly authorized EPA to set air
pollutant standards for ``any class or classes of new motor vehicles or
new motor vehicle engines.'' \37\ The differences in authority granted
to the two agencies are not arbitrary. The CAA was designed to provide
EPA with broad authority to address harmful air pollutants, which
originate from vehicle engines as well as tailpipes. The EISA
provisions described above were designed to provide the Department of
Transportation, through NHTSA, with different tools to achieve feasible
petroleum conservation from motor vehicles, which is a function of a
vehicle's entire design and construction. The CAA was not designed to
require energy conservation, and EISA was not designed to mandate
environmental improvements.\38\ EPA is not a fuel economy regulator,
and NHTSA is not an environmental regulator. The CAA and EISA granted
EPA and NHTSA specific statutory authority appropriate to accomplish
their respective goals. A desire by the agencies to achieve regulatory
harmonization does not empower NHTSA to expand its statutory authority.
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\37\ 42 U.S.C. 7521 (emphasis added). EPA has since rescinded
its standards not because it found it lacked authority to regulate
engines, but because it rescinded the endangerment finding for
greenhouse gas emissions. See Final Rule, Rescission of the
Greenhouse Gas Endangerment Finding and Motor Vehicle Greenhouse Gas
Emission Standards Under the Clean Air Act, 91 FR 7686 (Feb. 18,
2026).
\38\ See 42 U.S.C. 7521(a)(1); 49 U.S.C. 32902(f).
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In Loper Bright Enterprises v. Raimondo,\39\ the United States
Supreme Court explained that ``statutes . . . do--in fact, must--have a
single, best meaning.'' \40\ Interpreting a statute requires
``determin[ing] the best reading of the statute,'' and not a so-called
``permissible'' interpretation.\41\
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\39\ 603 U.S. 369 (2024).
\40\ Id. at 400.
\41\ Id. (``In the business of statutory interpretation, if it
is not the best, it is not permissible.'').
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Consistent with Loper Bright, NHTSA asserts the best reading of the
statute is that it lacks the authority to set fuel economy standards
for engines of work trucks and commercial medium-duty or heavy-duty on-
highway vehicles on a standalone basis. EISA commands NHTSA to set fuel
economy standards for commercial medium- and heavy-duty on-highway
vehicles and work trucks (which are defined as ``vehicles'' \42\). The
statute permits ``separate standards for different classes of
vehicles.'' \43\ The statute did not, however, authorize separate
standards for components of a vehicle, including a vehicle's engine. In
contrast, Congress expressly granted authority to set engine standards
to EPA.
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\42\ 49 U.S.C. 32901(a)(7), (19).
\43\ Id. Sec. 32902(b)(1), (k)(2).
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NHTSA's interpretation is also supported by recent case law. As
noted above, the D.C. Circuit found NHTSA's attempt to set fuel economy
standards for trailers as a type of vehicle unlawful.\44\ The court
found that trailers
[[Page 55791]]
are not vehicles ``when that term is used in the context of a vehicles'
fuel economy''; trailers ``have no motor,'' and ``motorless vehicles
use no fuel.'' \45\ Therefore, NHTSA's delegation of authority to set
fuel economy standards for vehicles did not include trailers.
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\44\ TTMA, 17 F.4th at 1208.
\45\ See e.g., id. at 1200.
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Nor does it include engines. An engine is not a vehicle. To be
sure, a vehicle's engine necessarily impacts its fuel economy. So do
tires, transmissions, and tailpipes. However, that does not grant NHTSA
authority to set fuel economy standards for those components
individually or separately from the entirety of a vehicle of which they
comprise a part.\46\ If that were the case, like NHTSA's theory in TTMA
that was rejected, ``there is no principled limit to NHTSA's theory.''
\47\ If NHTSA could set fuel economy standards for engines, NHTSA could
also set standards for any component of a vehicle that impacts fuel
economy, including tires, transmissions, and tailpipes.\48\
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\46\ While one reason the D.C. Circuit rejected the argument
that trailers are ``vehicles'' was because ``Congress put the term
`vehicle' in a context limited to machines that use fuel,'' see
TTMA, 17 F.4th at 1205, engines are plainly not vehicles despite
their use of fuel.
\47\ Id. at 1207-08 (finding that if a trailer is a vehicle
there would be no principled limit; NHTSA could regulate bike racks,
rooftop cargo carriers, or anything similar that would impact the
fuel efficiency of a vehicle).
\48\ Id.
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The D.C. Circuit similarly rejected EPA's argument that it could
regulate significant components of a vehicle: ``Perhaps sensing that it
needs to offer a limiting principle, the EPA claims that it can
regulate only `significant' vehicle components. But that limit is
atextual. . . . [W]e cannot endorse a hazy line mentioned nowhere in a
statutory provision that allows the EPA to regulate `motor vehicles,'
not motor-vehicle components.'' \49\ The same argument applies to
NHTSA's claim of authority to set separate engine standards.
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\49\ Id. at 1202.
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The D.C. Circuit set forth several other reasons why NHTSA could
not set fuel economy standards for trailers as vehicles that inform
NHTSA's interpretation here. For example, the court stated that because
the term ``vehicles'' in NHTSA's standard setting authority is preceded
by three other types of vehicles, all of which have engines and burn
fuel--``passenger automobiles, non-passenger automobiles,'' and ``work
trucks''--the term ``vehicles'' should be given a meaning similar to
those other words with which it is associated. A vehicle trailer, the
court explained, did not have any meaningful similarity to passenger
and non-passenger automobiles because trailers are not propelled by
fuel, and trailers are not like work trucks that both ``have an engine
and burn fuel.'' \50\ Here, engines have no meaningful similarity to
vehicles or passenger and non-passenger automobiles. They are not a
type of vehicle or automobile.\51\
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\50\ Id. at 1205-06.
\51\ The court also reasoned in a footnote that while a trailer
affects fuel economy, so do other ``attachments'' to vehicles like
bike racks that do not have a gross vehicle weight rating (GVWR) of
10,000 pounds or more as required by the statutory definition of
``commercial medium- and heavy-duty on highway vehicle'' at 49
U.S.C. 32901(a)(7). Id. at n.10. The same is true of the engine
(which also does not have a GVWR of between 8,500 and 10,000 pounds
as required by the statutory definition of ``work truck'' at 49
U.S.C. 32901(a)(19)). The court also noted that NHTSA regulations
separately refer to the gross combined weight rating, defined as the
``maximum load that the vehicle can haul, including the weight of a
loaded trailer and the vehicle itself.'' Id. at n.15.
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Because engines are not vehicles, NHTSA's justification for
regulating them separately has relied on the assertion that the agency
is vested with broad discretion by EISA. NHTSA's argument during its
Phase 1 rulemaking--that its mandate to ``set separate standards for
different classes of HD vehicles'' should be ``interpret[ed] broadly to
allow regulation of HD engines in addition to HD vehicles''--pushes the
text beyond its natural reading.\52\ The ability to set standards for a
vehicle does not logically include the authority to set standards for
parts of a vehicle.\53\
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\52\ See Phase 1 Final Rules, 76 FR 57112 (``Congress also
stated that NHTSA may set separate standards for different classes
of HD vehicles, which the agency interprets broadly to allow
regulation of HD engines in addition to HD vehicles . . . .'');
Phase 1 Proposed Rules, 75 FR 74158 (``Congress also stated that
NHTSA may set separate standards for different classes of HD
vehicles, which the agency interprets broadly to allow regulation of
HD engines in addition to HD vehicles . . . .'').
\53\ See, e.g., TTMA, 17 F.4th at 1207-08 (``[T]here is no
principled limit to NHTSA's theory.'').
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In the Phase 1 and Phase 2 rulemakings, NHTSA also identified other
aspects of its standard setting authority, including the requirement to
set maximum feasible standards and parts of the rulemaking mandate, to
argue that the statute conferred broad discretion on the agency.\54\
While NHTSA has the ability to exercise discretion in setting standards
and other aspects of the MDHD program, NHTSA did not explain how
standalone engine standards were consistent with its mandate to
``prescribe separate fuel economy standards for . . . work trucks and
commercial medium-duty or heavy-duty on-highway vehicles.'' \55\ The
general authority to establish various aspects of ``a commercial
medium- and heavy-duty on-highway vehicle and work truck fuel
efficiency program'' is insufficient to confer standard-setting
authority on NHTSA beyond the plain text of the statute. EISA did not
direct NHTSA to establish a MDHD vehicle and engines fuel efficiency
program, and NHTSA cannot simply assume that authority through
regulation.\56\
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\54\ See Phase 1 Final Rules, 76 FR 57114; Phase 1 Proposed
Rules, 75 FR 74173 n.36; see also Phase 2 Final Rule, 81 FR 73491
n.51 (citing to explanation of authority in Phase 1 final rule);
Phase 2 Proposed Rule, 80 FR 40138, 40152 n.43 (same).
\55\ See 49 U.S.C. 32902(b)(1)(C); see also Phase 2 Final Rule,
81 FR 73491 n.51; Phase 2 Proposed Rule, 80 FR 40138, 40152 n.43
(same); Phase 1 Final Rules, 76 FR 57114; Phase 1 Proposed Rules, 75
FR 74173 n.36.
\56\ Cf. Nat'l Fed'n of Indep. Bus. v. Dep't of Labor, 595 U.S.
109, 117 (2022) (``Administrative agencies are creatures of statute.
They accordingly possess only the authority that Congress has
provided.''); Louisiana Pub. Serv. Comm'n v. F.C.C., 476 U.S. 355
(1986) (``[A]n agency literally has no power to act . . . unless and
until Congress confers power upon it.'').
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Upon further consideration, NHTSA has determined that the statute
did not authorize it to set separate standards for engines. Unlike EPA,
NHTSA lacked express authority to set engine standards. The desire to
have harmonized requirements is insufficient for NHTSA to exercise
regulatory authority not given by statute.\57\ It is insufficient to
assert, as NHTSA has, that EISA did not ``preclude[] the regulation of
engines,'' given that the statute refers expressly and repeatedly to
NHTSA's authority to establish fuel economy standards for specific
categories of ``vehicles.''
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\57\ See, e.g., Phase 1 Proposed Rules, 75 FR 74157 (``EPA's and
NHTSA's proposed standards for the heavy-duty sector are largely
harmonized with one another due to the close and direct relationship
between improving the fuel efficiency of these vehicles and reducing
their CO<INF>2</INF> tailpipe emissions.''); id. at 74177 (``NHTSA's
fuel consumption standards . . . [include] mandatory engine
standards starting in 2017 model year, harmonized with EPA's 2017
model year standards.'').
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EISA requires NHTSA to set standards for vehicles, authorized
separate standards for different classes of vehicles, set lead time and
regulatory stability limits for those vehicle standards, and otherwise
addressed the parameters of a regulatory program for improving the fuel
efficiency of vehicles. For the reasons stated above, NHTSA does not
have authority to set fuel efficiency standards for engines separately
from vehicles.
III. Next Steps for MDHD Program Reset and Enforcement Considerations
As NHTSA explained in its June 2025 interpretive rule, Resetting
the
[[Page 55792]]
Corporate Average Fuel Economy Program, a reset of the MDHD program is
necessary to ensure the regulations are consistent with law. NHTSA will
reconsider the engine standards consistent with this interpretive rule
as part of its reset of that program and ensure that vehicle
manufacturers have practicable means to comply in the absence of
separate engine standards.\58\
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\58\ See 90 FR 24518 (June 11, 2025). NHTSA addressed other
aspects of its MDHD program in this interpretive rule. Specifically,
NHTSA stated that: (1) EISA requires NHTSA to consider the factors
in 49 U.S.C. 32902(f) in determining the maximum feasible standards;
(2) NHTSA lacked authority to assess civil penalties for violations
of MDHD standards; (3) NHTSA improperly established a credit trading
program for MDHD vehicles, and (4) NHTSA considered credits and
electric vehicles in setting the MDHD standards without express
authority to do so.
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Resetting the MDHD program in compliance with law will help prevent
market distortions. Commercial vehicle purchasers make business
decisions that account for their own fuel economy needs. Focusing the
MDHD program on vehicle standards, as the law requires, will help
ensure that manufacturers have flexibility in how best to meet the
standards and the needs of their customers.
The interpretation set forth in this rule clarifies the appropriate
scope of NHTSA's authority to set fuel economy standards for the MDHD
program. This interpretation does not change existing standards or any
rights or obligations under the MDHD program. Instead, this
interpretation lays the groundwork for notice-and-comment rulemaking to
reset the agency's regulatory program as determined necessary to bring
it into compliance with applicable substantive statutory requirements
as codified in Chapter 329 of title 49 of the United States Code and
Administration policy. NHTSA will also consider other issues as
appropriate in resetting the MDHD program, including whether any
adjustments to the vehicle standards are warranted. Among the matters
under review is the relationship between potential NO<INF>X</INF>
emission reductions arising from EPA's 2023 NO<INF>X</INF> emission
standards (taking effect in model year 2027) \59\ and fuel
consumption.\60\
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\59\ Environmental Protection Agency, Final rule, Control of Air
Pollution from New Motor Vehicles: Heavy-Duty Engine and Vehicle
Standards, 88 FR 4296 (Jan. 24, 2023).
\60\ EPA has proposed to amend the 2023 rule. Environmental
Protection Agency, Proposed rule, Amendments and Nonconformance
Penalties for Model Year 2027 and Later Heavy-Duty Highway Engines
and Amendments to Inducement Provisions for SCR-Equipped Diesel
Engines, 91 FR 43154 (July 14, 2026).
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In light of the legal interpretation set forth in this interpretive
rule, NHTSA will reset the MDHD program consistent with the law.
Pending the rulemaking process, NHTSA will exercise its enforcement
authority with regard to affected standards in accordance with the
interpretation set forth in this rule.
Regulatory Analyses
A. Administrative Procedure Act
NHTSA issues this interpretive rule to explain the statute the
agency administers and how the agency will apply its interpretation to
subsequent substantive rules. This interpretive rule does not amend or
alter the meaning of any regulations, and any costs and benefits of any
subsequent proposed changes to regulations will be analyzed in a future
rulemaking. As such, notice and comment under the Administrative
Procedure Act is not required for this interpretive rule,\61\ and the
rule similarly is not subject to a 30-day delay in effective date.\62\
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\61\ See 5 U.S.C. 553(b)(A).
\62\ See 5 U.S.C. 553(d)(2).
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B. Executive Order 12866, Regulatory Planning and Review; Executive
Order 14192, Unleashing Prosperity Through Deregulation; and Executive
Order 14219, Ensuring Lawful Governance and Implementing the
President's ``Department of Government Efficiency'' Deregulatory
Initiative
Executive Order (E.O.) 12866, ``Regulatory Planning and Review''
(58 FR 51735, Oct. 4, 1993), provides for determining whether a
regulatory action is ``significant'' and therefore subject to the
Office of Management and Budget (OMB) review process and to the
requirements of the E.O. This is a ``significant regulatory action''
under E.O. 12866. Accordingly, NHTSA submitted this action to OMB for
review. However, there are no costs or benefits associated with this
interpretive rule. Any costs and benefits of rules implementing the
interpretation will be analyzed in those subsequent rulemakings.
E.O. 14192, ``Unleashing Prosperity Through Deregulation'' (90 FR
9065, Feb. 6, 2025), requires an agency, unless prohibited by law, to
identify at least ten existing regulations to be repealed when the
agency publicly proposes for notice and comment or otherwise
promulgates a new regulation. In furtherance of this requirement,
section 3(c) of Executive Order 14192 requires that the new incremental
costs associated with new regulations shall, to the extent permitted by
law, be offset by the elimination of existing costs associated with at
least ten prior regulations. As discussed above, there are no costs or
benefits associated with this interpretive rule. However, this
interpretive rule, which sets forth NHTSA's interpretation of its
statutory authority for the MDHD program ensures that, going forward,
NHTSA will not regulate beyond its statutory authority. The costs and
benefits of future MDHD rules will be analyzed in those rulemakings.
E.O. 14219, ``Ensuring Lawful Governance and Implementing the
President's `Department of Government Efficiency' Deregulatory
Initiative,'' requires agency heads to review their regulations and
identify regulations that, among other things, are based on anything
other than the best reading of the underlying statutory authority or
prohibition, or that implicate matters of social, political, or
economic significance that are not authorized by clear statutory
authority. NHTSA has identified its MDHD engine standards as falling
within an enumerated category or categories of E.O. 14219. NHTSA is
issuing this interpretive rule to set forth the agency's interpretation
that it lacks the authority to regulate engines. This rule describes
NHTSA's interpretation of its authority to establish the necessary
legal foundation for bringing the MDHD program into compliance with
relevant statutory requirements.
C. Executive Order 13132, Federalism
A rule has implications for federalism under section 1(a) of E.O.
13132 if it has ``substantial direct effects on the States, on the
relationship between the national government and the States, or on the
distribution of power and responsibilities among the various levels of
government.'' NHTSA has determined that this interpretive rule will not
have substantial direct costs on or for States, nor would it limit the
policymaking discretion of States. Nothing in this document preempts
any State law or regulation. Therefore, this interpretive rule does not
have sufficient federalism implications to warrant the preparation of a
Federalism Impact Statement.
D. Executive Order 12988, Civil Justice Reform
E.O. 12988, ``Civil Justice Reform'' (61 FR 4729, Feb. 7, 1996),
requires that agencies promulgating new regulations or reviewing
existing regulations take steps to minimize litigation, eliminate
ambiguity, and to reduce burdens on the regulated public. NHTSA has
reviewed this interpretive rule and determined that this action
conforms to the applicable standards in sections 3(a) and 3(b)(2) of
E.O. 12988, Civil Justice Reform.
[[Page 55793]]
E. Executive Order 13175, Consultation and Coordination With Indian
Tribal Governments
This interpretive rule does not have Tribal implications under E.O.
13175, Consultation and Coordination with Indian Tribal Governments,
because it does not have a substantial direct effect on one or more
Indian Tribes, on the relationship between the Federal Government and
Indian Tribes, or on the distribution of power and responsibilities
between the Federal Government and Indian Tribes.
F. Unfunded Mandates Reform Act of 1995
The Unfunded Mandates Reform Act of 1995 (2 U.S.C. 1531-1538)
(UMRA) requires Federal agencies to assess the effects of their
discretionary regulatory actions. UMRA addresses actions that may
result in the expenditure by a State, local, or Tribal government, in
the aggregate, or by the private sector of $206 million (which is the
value equivalent of $100 million in 1995, adjusted for inflation to
2025) or more in any 1 year. As discussed above, this interpretive rule
by itself results in no expenditures and therefore the analytical
requirements of UMRA do not apply. Any costs and benefits will be
analyzed in future rules subject to the principles laid out in this
notice.
G. Regulatory Flexibility Act of 1980
The Regulatory Flexibility Act, 5 U.S.C. 601 et seq., requires
agencies to prepare a regulatory flexibility analysis for any rule
where the agency is required by law to publish a general notice of
proposed rulemaking.\63\ NHTSA is not required to complete a regulatory
flexibility analysis because, as discussed previously, this action is
not subject to notice and public comment under the Administrative
Procedure Act (APA) \64\ or any other law.
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\63\ See 5 U.S.C. 603.
\64\ See 5 U.S.C. 553(b)(A).
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H. Paperwork Reduction Act
This interpretive rule contains no new information collection
requirements under the Paperwork Reduction Act of 1995 (44 U.S.C. 3501-
3520).
I. National Environmental Policy Act of 1969
In accordance with 42 U.S.C. 4336, ``[a]n agency is not required to
prepare an environmental document with respect to a proposed agency
action if the proposed agency action is not a final agency action
within the meaning of such term in chapter 5 of title 5 [of the United
States Code].'' As discussed above, this action is not a final agency
action within the meaning of 5 U.S.C. Chapter 5. Any environmental
effects will be analyzed in a future rulemaking resetting the MDHD
program subject to the principles laid out in this notice.
J. Privacy
The Consolidated Appropriations Act, 2005 (Pub. L. 108-447, 118
Stat. 2809, 3268, Dec. 8, 2004 (5 U.S.C. 552a note)), requires certain
parties (Federal agencies and any non-Federal entity that receives
records contained in a system of records from a Federal agency for use
in a matching program) to conduct a privacy impact assessment of a
regulation that will affect the privacy of individuals. Because this
interpretive rule does not require the collection of personally
identifiable information, NHTSA is not required to conduct a privacy
impact assessment.
The E-Government Act of 2002 (Pub. L. 107-347, sec. 208, 116 Stat.
2899, 2921, Dec. 17, 2002), requires Federal agencies to conduct a
privacy impact assessment for new or substantially changed technology
that collects, maintains, or disseminates information in an
identifiable form. No new or substantially changed technology will
collect, maintain, or disseminate information as a result of this
interpretive rule. Accordingly, NHTSA has not conducted a privacy
impact assessment.
K. Congressional Review Act
Pursuant to the Congressional Review Act (CRA) (5 U.S.C. 801 et
seq.), the Office of Information and Regulatory Affairs designated this
rule as not a ``major rule,'' as defined by 5 U.S.C. 804(2). NHTSA will
submit this rule to Congress and the Government Accountability Office
as required by the CRA.
Issued on August 27, 2026 in Washington, DC, under authority
delegated in 49 CFR 1.95.
Jonathan Morrison,
Administrator.
[FR Doc. 2026-17756 Filed 8-28-26; 8:45 am]
BILLING CODE 4910-59-P
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This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.