EPA proposes new Heavy-Duty GHG phase 3 emission standards for model years 2028-2032

On April 12, 2023, the Environmental Protection Agency (EPA) issued a Notice of Proposed Rulemaking for “Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles – Phase 3” (the Phase 3 proposed rule or NPRM), establishing new GHG standards for model years 2028-2032 and revising certain MY2027 provisions established under EPA’s Phase 2 rule. The proposed standards are the most stringent federal standards to date for GHG emissions from heavy-duty vehicles and engines (with a GVWR over 14,000 pounds). The NPRM also includes new battery and electric powertrain warranty requirements for zero-emission vehicles (ZEVs), new battery state-of-health monitor requirements for plug-in hybrid vehicles (PHEVs) and battery electric vehicles (BEVs), and updates to the Averaging, Banking, and Trading (ABT) program. In addition, the NPRM proposes to revise EPA’s locomotive preemption regulations to align more closely with the language of section 209(e) of the Clean Air Act.

(See pre-publication version of the Phase 3 proposed rule linked here: “Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles – Phase 3.”)

Overview of EPA Proposed MY2028-2032 GHG Standards


The Phase 3 proposed rule is one of three rulemakings under EPA’s Clean Trucks Plan. EPA finalized its new criteria pollutant rule for MY2027 and later heavy-duty engines and vehicles (HD2027) on December 20, 2022, and announced its proposed rule for “Multi-Pollutant Emissions Standards for Model Years 2027 and Later Light-Duty and Medium-Duty Vehicles” on the same day as the Phase 3 proposed rule (see “EPA proposes most stringent vehicle emission standards ever for model years 2027-2032”). Unlike the heavy-duty GHG Phase 1 and Phase 2 rules, which were jointly developed by EPA and the National Highway Traffic Safety Administration, EPA is moving forward with the Phase 3 proposed rule on its own. According to EPA, EPA has coordinated with NHTSA and consulted with the California Air Resources Board during the development of the Phase 3 proposed rule. 

Proposed MY2028-2032 GHG Standards

The NPRM proposes new CO2 emission standards using the same regulatory subcategories of vehicles that were adopted in the heavy-duty GHG Phase 2 rule, including separate standards for optional custom chassis vehicles and heavy-haul tractors. While EPA has not proposed a ZEV sales mandate (like under California’s Advanced Clean Trucks Regulation), the proposed standards do project that manufacturers will produce a mix of heavy-duty vehicles that utilize both internal combustion engine (ICE) and ZEV technologies, and EPA factors into its analysis Inflation Reduction Act provisions that may impact heavy-duty vehicles and increase adoption of heavy-duty ZEV technologies, including tax credits across the supply chain and charging infrastructure funding.

See Table II-19, NPRM.

See Table II-21, NPRM.

In EPA’s analysis for the proposed standards, the representative ICE vehicles include technologies that would be present in a vehicle meeting the existing MY2027 Phase 2 GHG emission standards. EPA also includes projected ZEV adoption rates in the MY2027-2032 technology packages analyzed for the proposed standards. For example, EPA’s projected ZEV adoption rate is 57% for light heavy-duty vocational vehicles, 35% for medium heavy-duty vocational vehicles, and 40% for heavy heavy-duty vocational vehicles in MY2032. For day cab tractors, EPA’s projected ZEV adoption rate is 10% in MY2027 increasing to 34% in MY2032, while for sleeper cab tractors, EPA projects 0% ZEV adoption in MY2027-2029, 10% in MY2030, 15% in MY2031, and 25% in MY2032, as shown in the table below.

See Table ES-3, NPRM.

See Table ES-4, NPRM.

EPA is requesting comment on whether the GHG standards for MY2027-2032 should be less stringent for certain market segments or more stringent overall at various levels such as values that would reflect the level of ZEV adoption under California’s Advanced Clean Trucks Regulation or the 50-60% ZEV adoption goals announced publicly by several heavy-duty manufacturers for 2030. EPA is also requesting comment on whether it should establish additional new GHG standards with increasing stringency in MY2033 through MY2035.

Proposed PHEV/BEV Battery Durability and Warranty Requirements

Battery Durability

EPA is proposing new battery durability monitoring requirements for heavy-duty PHEVs and BEVs beginning with MY2027. Under the proposal, heavy-duty BEVs and PHEVs would be required to include an onboard battery state-of-health monitor that reports the vehicle’s state of certified energy and can be read by the vehicle user. EPA expects that manufacturers would implement onboard algorithms to estimate the state of usable battery energy (UBE) expressed as a percentage of the original UBE when the vehicle was new.  For heavy-duty PHEVs, EPA proposes that manufacturers would use the existing powertrain test procedures to determine UBE, while manufacturers would develop their own test procedures for heavy-duty BEVs, due to the range of BEV architectures and limited availability of heavy-duty BEV powertrain testing facilities. EPA is not proposing durability monitoring requirements for fuel cell electric vehicles (FCEVs) at this time because the technology is developing and EPA is still evaluating the appropriate metric for quantifying FCEV performance.

Battery Warranty

EPA is also proposing new warranty requirements for ZEV (BEV and FCEV) batteries and associated electric powertrain components (e.g., fuel-cell stack, electric motors, and inverters) and clarifying how existing warranty requirements apply to PHEVs. For heavy-duty BEVs and FCEVs, manufacturers would be required to designate the batteries and associated electric powertrain components as components covered under emission-related warranty in the vehicle’s certification application and subject to the existing GHG emissions warranty periods of 5 years or 50,000 miles for light heavy-duty vehicles and 5 years or 100,000 miles for medium and heavy heavy-duty vehicles. EPA is not proposing new battery warranty requirements for PHEVs because “hybrid system components” included in a manufacturer’s certified configuration are already addressed under the existing regulations.

Proposed Changes to the ABT Program

First, the NPRM proposes a revision to the definition of “U.S.-directed production volume” to clarify that nationwide production volumes should be considered, including vehicles certified to different state emission standards, for the ABT program, in contrast to EPA’s approach under earlier heavy-duty GHG regulations.  The definition would apply starting with MY2024 in order to provide consistent treatment of production volumes certified under the Advanced Clean Trucks Regulation in California.

Second, the NPRM proposes to phase out the advanced technology credit multipliers for heavy-duty PHEVs and BEVs after MY2026—one year earlier than under the current regulations.  No changes are proposed to the existing advanced technology credit multipliers for FCEVs, which apply through MY2027.

Preemption of State Regulation of Locomotives

The NPRM proposes to revise EPA’s locomotive preemption regulations, originally adopted in 1998, to align more closely with the language of section 209(e) of the Clean Air Act, and EPA’s directive from Congress to implement the prohibition of state regulation of new locomotives and engines while also ensuring that states can adopt programs to address air pollutant emissions from non-new locomotives and engines. EPA proposes to remove the explicit period of preemption (equal to 133 percent of the regulatory useful life of a new locomotive or engine under existing regulations) and the listed categories of state control measures that are included in the existing regulations at 40 C.F.R. § 1074.12. The preempted requirements currently include emission standards, mandatory fleet average standards, certification requirements, retrofit and aftermarket equipment requirements, and nonfederal in-use testing requirements.

EPA believes these regulatory changes are needed “to provide regulatory space for state controls that do not inappropriately affect the design and manufacture of new locomotives or new engines used in locomotives”—for example, requiring retrofitting of an auxiliary power unit to support engine shutdown for idle reduction or installation of a new load control calibration strategy that better manages load on the main engine while the locomotive is in line haul service. State authorization applications received by EPA would still need to demonstrate why the proposed state control measure would not significantly affect the design or manufacture of a new locomotive, and California regulations addressing non-new locomotives or engines would still need to go through an EPA authorization process to ensure compliance with the statutory criteria.


Next steps

EPA will hold a virtual public hearing on the NPRM on May 2 and 3, 2023. An additional session may be held on May 4, 2023, if necessary. More information is available on EPA’s Rule Summary website and Fact Sheet. Comments on the NPRM are due 60 days following publication in the Federal Register.



Authored by Katie Lannon and Christina Bassick.


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