Regulation Database – EPA & NHTSA - Motor Vehicles

Motor vehicles emissions are regulated by the EPA in coordination with the the National Highway Traffic Safety Administration (NHTSA), an agency within the Department of Transportation, which regulates fuel economy standards.

In May 2010, together with the National Highway Traffic Safety Administration (NHTSA), EPA promulgated standards applicable to passenger cars, light-duty trucks, and medium-duty passenger vehicles, covering model years 2012 through 2016. Under the coordinated program, EPA finalized greenhouse gas emissions standards under the Clean Air Act, and NHTSA finalized Corporate Average Fuel Economy (CAFE) standards under the Energy Policy and Conservation Act. The EPA standards were the first-ever national greenhouse gas emission standards under the Clean Air Act, enabled by the endangerment and cause or contribute findings EPA made in 2009 with respect to greenhouse gas emissions from motor vehicles.

Rule documents:

In October 2012, EPA extended greenhouse gas emission standards for light-duty vehicles to model years 2017-2025, and NHTSA extended CAFE standards for these same model years. The standards are expected to result in an average industry fleetwide level of 163 grams/mile of carbon dioxide in model year 2025, equivalent to 54.5 miles per gallon. Together with the 2012-2016 standard, the program is expected to cut six billion metric tons of greenhouse gases over the lifetimes model year 2012-2025 vehicles.

The rule called for a mid-term evaluation to determine whether the standards should be revised for light duty vehicles MY 2022-2025. In January 2017, EPA issued a final determination on the appropriateness of the emission standards in which it concluded that no change was warranted for the MY 2022-2025 standards.

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Deregulatory Action: 

On March 15, 2017, EPA and NHTSA announced their intention to reconsider the GHG standards for light duty vehicles model years 2022-2025 (see Notice of Intention to Reconsider the Final Determination of the Mid-Term Evaluation of Greenhouse Gas Emissions Standards for Model Year 2022-2025 Light Duty Vehicles).

EPA and NHTSA issued the notice shortly after the Alliance of Automobile Manufacturers filed a petition for review of the Jan. 17 determination in the D.C. Circuit Court of Appeals. Prior to filing that petition, the Alliance also sent a letter to EPA Administrator Scott Pruitt urging EPA to reconsider the emission standards. The Alliance dropped the lawsuit shortly after EPA and NHTSA announced that they would reconsider the emission standards.

On July 26, 2017, NHTSA announced that it would prepare an environmental impact statement to assess the potential environmental impacts of new Corporate Average Fuel Economy (CAFE) standards it is proposing to adopt for model year 2022-2025 passenger cars and light trucks.

On August 10, 2017, NHTSA and EPA announced that they were opening a public comment period on the reconsideration of the greenhouse gas (GHG) emissions standards for cars and light trucks for model years (MY) 2022-2025. EPA stated that it would also take comment on whether the MY 2021 standards are appropriate.

On April 13, 2018, EPA published a notice stating that it had completed its mid-term evaluation of the GHG standards for light-duty vehicles, that it determined the standards were too stringent, and that it intended to initiate a new notice-and-comment rulemaking proceeding to revise the standards to make them less stringent.

On August 2, 2018, EPA and NHTSA published a proposed rule to weaken the light-duty vehicle emission and fuel economy standards. The proposal – entitled the “Safer Affordable Fuel-Efficient (SAFE) Vehicles Rule" – would freeze the light-duty vehicle standards for MY 2021-2026 at 2020 levels, rather than having the standards become more stringent over time as provided for in the original rule. It would also revoke the waiver allowing California to establish more stringent standards which other states can then adopt.

On September 19, 2019, EPA and NHTSA finalized the portion of the SAFE Rule that revokes the waiver permitting California to establish vehicle standards for greenhouse gases and zero-emission vehicles.  California and twenty-two other states - plus Washington, D.C., New York City and Los Angeles - have challenged the action in court. 

On March 31, 2020, EPA and NHTSA finalized the SAFE Rule. Under the final rule, GHG and CAFE standards will become 1.5% more stringent every year from 2020-2026.


On May 27, 2020, a coalition of states and a coalition of environmental groups challenged the SAFE Rule in the D.C. Circuit.

Reregulatory Action

On August 5, 2021, EPA proposed new greenhouse gas standards for light-duty motor vehicles for model years 2023-26. EPA proposed to increase the stringency of the standards from the average roughly 1.5 percent year-over-year stringency increase of the SAFE Rule to a nearly 10 percent proposed stringency increase in MY 2023, followed by a nearly 5 percent proposed stringency increase in each MY from 2024 through 2026.

On December 20, 2021, the Environmental Protection Agency (EPA) finalized light-duty vehicle greenhouse gas emissions standards for Model Years (MY) 2023 and later. The final rule revises current GHG standards beginning in MY 2023 and increases in stringency between 5 and 10 percent each year from 2023 through 2026. The standards are expected to result in average fuel economy label values of 40 mpg, while the previous standards would achieve only 32 mpg in MY 2026.

Furthermore, on September 3, 2021, NHTSA proposed revised CAFE standards for passenger cars and light trucks for model years 2024–2026. This proposal follows from NHTSA's conclusion that, consistent with NHTSA's statutory mandate to improve energy conservation, the 2020 SAFE standards should be revised so that they increase at a rate of 8 percent year over year for each model year from 2024 through 2026, for both passenger cars and light trucks. 

On April 1, 2022, NHTSA finalized revised corporate average fuel economy (CAFE) standards for passenger cars and light trucks for model years (MY) 2024–2026. The final rule sets fuel economy standards that increase at a rate of 8 percent per year, and increase at a rate of 10 percent per year for MY 2026 vehicles.

In August 2011, EPA and NHTSA finalized greenhouse gas emission standards and fuel economy standards for heavy-duty highway vehicles for model years 2014-2018, cutting an estimated 270 million metric tons of carbon dioxide emissions.

Rule Documents:

In August 2016, EPA and NHTSA extended GHG and CAFE standards for medium- and heavy-duty vehicles through model years 2018-2027 for certain trailers, and model years 2021-2027 for semi-trucks, large pickup trucks, vans, buses, and work trucks. These new standards are expected to cut 1.1 billion metric tons of carbon dioxide emissions.

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The provisions of the extended GHG and CAFE standards applying to trailers were challenged in Truck Trailer Manufacturers Association, Inc. v. EPA (2016). The Truck Trailer Manufacturers Association has argued that EPA and NHTSA lack authority to regulate GHG emissions from trailers under the Clean Air Act and the Energy Independence and Security Act. On September 29, 2020, the D.C. Circuit Court of Appeals stayed the compliance dates for fuel economy regulations to the extent the regulations apply to truck trailers. On November 12, 2021, the D.C. Circuit Court of Appeals vacated all portions of the rule that apply to trailers.

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On December 28, 2016, NHTSA published a final rule to increase penalties for automobile manufacturers that fail to meet fuel economy standards. The rule increased the fines from $5.50 to $14 per tenth-of-an-mpg, and allowed for adjustments for inflation between the publication date and the assessment of the violation.

Deregulatory Action:

On July 12, 2018, NHTSA announced that it would indefinitely delay the effective date of the rule. In a separate notice, NHTSA announced that it would reconsider and potentially revise the rule.


On September 8, 2017, five state attorneys general filed a lawsuit alleging that NHTSA’s indefinite delay of the rule was unlawful and should be vacated. On April 23, 2018, the 2nd U.S. Circuit Court of Appeals issued a one-page order vacating the delay, granting petitions by environmental groups and a coalition of state attorneys general.

Deregulatory Action:

On July 26, 2019, NHTSA finalized a rule to freeze civil penalties for violating fuel efficiency standards at $5.50 per ten-of-an-mpg. The rule replaced a 2016 rule that would have increased fines to $14 per ten-of-an-mpg in 2019.


On August 31, 2020, the Second Circuit Court of Appeals vacated NHTSA's rule freezing civil penalties and reinstated the 2016 rule increasing the penalty rate to $14.

Deregulatory Action:

On January 14, 2021, NHTSA published an interim rule delaying the increase in civil penalties for failing to meet fuel efficiency standards until 2022.


On January 25, 2021, the Sierra Club and NRDC challenged the interim rule in the Second Circuit Court of Appeals.


In July 2011, EPA and NHTSA finalized a rule to redesign and add information to the fuel economy label that is posted on the window sticker of all new cars and light-duty trucks sold in the U.S. The redesigned label provides new information to American consumers about fuel economy and consumption, fuel costs, and environmental impacts associated with purchasing new vehicles beginning with model year 2013 cars and trucks. The rule also develops new labels for certain advanced technology vehicles poised to enter the U.S. market, including plug-in hybrid electric vehicles and electric vehicles.

Rule Documents:

The Clean Air Act allows California to enact air pollution standards for motor vehicles more stringent than those of federal government. EPA must approve a waiver before California’s rules may go into effect. In December 2005, the California Air Resources Board (CARB) requested a waiver to regulate GHG emissions from new motor vehicles. The request was denied by EPA in March 2008. In January 2009, CARB requested that EPA reconsider its waiver denial, and in June 2009, EPA granted a waiver.

With new federal greenhouse gas standards for vehicles being developed, CARB later requested to align its vehicle-related GHG regulations with the nationwide vehicle standards. In June 2011, EPA published a notice stating that requested revisions made by CARB fall within the scope of the CAA preemption waiver granted to California in 2009.

In January 2013, EPA granted California a waiver to implement the state’s Advanced Clean Car Program. The program includes regulations to phase in stricter fleet average standards for 2015-2025 model year cars  and light-duty trucks. The regulations also set new greenhouse gas emissions limits for 2017-2025 model year cars and light duty trucks, and mandates that a certain percentage of new vehicles produce no carbon dioxide tailpipe emissions. The waiver reaffirms California’s key role under the Clean Air Act as a laboratory for setting new motor vehicle emissions standards.

In August 2014, EPA granted CARB’s request to regulate greenhouse gas emissions for certain model year 2011-2013 tractors, and dry- and refrigerated-van trailers pulled by such tractors. In December 2016, EPA then granted CARB’s request to regulate greenhouse gas emissions for 2014 and subsequent model year on-road medium- and heavy-duty engines and vehicles.

Deregulatory Action:

In September 2019, the National Highway Traffic Safety Administration (NHTSA) and Environmental Protection Agency (EPA) finalized the the Safer Affordable Fuel-Efficient (SAFE) Vehicles Rule Part One: One National Program. In the SAFE Rule Part One, EPA revoked California's preemption waiver as applied to the greenhouse gas emissions standards and zero-emission vehicle mandate. One basis for EPA's action was NHTSA's new interpretation of its authority to set fuel efficiency standards as preempting states' authority to regulate greenhouse gas emissions from cars.


On October 28, 2019, a coalition of environmental groups challenged the waiver revocation in the D.C. Circuit. California and twenty-two other states - plus Washington, D.C., New York City and Los Angeles - followed suit on November 15, 2019. On February 8, 2021, the court granted the government's motion to hold the case in abeyance while the agencies reconsider the SAFE Rule pursuant to President Biden's executive order on “Protecting Public Health and the Environment and Restoring Science to Tackle the Climate Crisis.”

Rereregulatory Action:

On April 22, 2021, NHTSA proposed repealing its preemption rule. On April 26, 2021 EPA announced that it was reconsidering the withdrawal of California's preemption waiver and requested comments.

On December 21, 2021, NHTSA published its Corporate Average Fuel Economy (CAFE) Preemption rule, which finalizes its repeal of 2019’s SAFE Vehicles Rule Part One.

On March 9, 2022, the EPA took final action to restore California’s authority to set its own vehicle emissions standards that are more climate-protective than federal requirements. The March 9 Notice of Decision rescinds the 2019 waiver withdraw, bringing the 2013 ACC program waiver back into force, and additionally rescinds the 2019 interpretation that prevented other states from adopting California’s greenhouse gas standards.


On May 13, 2022, seventeen Republican states petitioned the D.C. Circuit for review of EPA's California waiver, alleging that the waiver violates the constitutional doctrine of equal sovereignty. 

Rule Documents:

On March 7, 2022, the EPA proposed new standards for reducing air pollution from highway heavy-duty vehicles and engines, including ozone, particulate matter, and greenhouse gases. EPA’s proposal would alter many aspects of the agency’s heavy-duty emission control program, including standards, test procedures, useful life, warranty, and other requirements. EPA’s proposal would also update the agency’s Heavy-Duty Greenhouse Gas Emissions Phase 2 program by proposing additional greenhouse gas reductions in the model year 2027 timeframe.