Federal Vehicle Standards


  • Twenty-nine percent of U.S. greenhouse gas emissions come from the transportation sector, making it the largest source of total U.S. greenhouse gas emissions.
  • Federal and state vehicle emissions and fuel economy standards are set by three agencies: the Environmental Protection Agency (EPA), the National Highway Traffic Safety Administration (NHTSA), and the California Air Resources Board (CARB).
  • In August 2021, EPA issued proposed greenhouse gas vehicle emission standards for model year 2023–2026 light-duty vehicles (i.e., passenger cars and light-duty trucks) and NHTSA issued proposed fuel economy standards for model year 2024–2026 light-duty vehicles.
  • President Biden signed an executive order on Strengthening American Leadership in Clean Cars and Trucks, which sets a nonbinding target of making 50 percent of passenger cars and light-duty trucks zero emission vehicles by 2030. The executive order also directs EPA and NHTSA to develop standards for fuel economy and greenhouse gas emissions for medium- and heavy-duty vehicles as well as passenger cars for model years 2027–2030, to be finalized by December 2022.

The transportation sector is the largest direct source of U.S. greenhouse gas emissions, surpassing the power sector in 2015. Cars and light-duty trucks (including pickups and SUVs) are responsible for about 59 percent of transportation emissions. Medium- and heavy-duty vehicles, which include tractor-trailers, large pickups and vans, delivery trucks, buses, and garbage trucks, produce about 24 percent of transportation emissions.

U.S. Transportation Sector Emissions, 2019


In April 2010, the federal government finalized the first harmonized set of standards for light-duty vehicles with the cooperation of major automakers and the state of California. The Environmental Protection Agency (EPA) established greenhouse gas emission standards and the National Highway Traffic Safety Administration (NHTSA) established corporate average fuel economy (CAFE) standards. The first CAFE standards were adopted in 1975, and the first greenhouse gas vehicle standards were adopted in 2010.

The 1975 Energy Policy and Conservation Act directed the U.S. Secretary of Transportation to establish Corporate Average Fuel Economy (CAFE) standards for new passenger cars. CAFE is the sales-weighted average fuel economy in miles per gallon (mpg) of the vehicles in a manufacturer’s fleet. This law was updated in 2007, when Congress increased the fuel economy standards for passenger vehicles and also established efficiency standards for medium- and heavy-duty vehicles.

California is the only state allowed to set its own air emissions standards for motor vehicles. California was granted an exception under the Clean Air Act because the state had already implemented standards in 1966 to address its critical smog problem and had established an Air Resources Board (CARB) to oversee them. The Clean Air Act states EPA shall grant a waiver if California’s standards are necessary to meet compelling circumstances and are at least as stringent as federal standards. Other states may choose to adopt California’s vehicle emissions standards without EPA approval. Thirteen states and the District of Columbia, making up about 30 percent of U.S. auto sales, currently follow at least some of California’s vehicle emissions standards.

In August 2021, President Biden signed Executive Order 14037, Strengthening American Leadership in Clean Cars and Trucks. The order sets a non-binding target of making 50 percent of all new passenger car and light truck sales zero emission vehicles in 2030. Under the order, zero emission vehicles include battery electric, plug-in hybrid electric, and hydrogen fuel cell electric vehicles. The order was supported by leading U.S. automakers, including General Motors, Stellantis, and Ford, who have voluntary targets to make 40–50 percent of all sales electric by 2030. Labor groups including the United Auto Workers union supported the order as well.

In addition to setting the target, the executive order directs EPA and NHTSA to begin the rulemaking process to set emissions and fuel economy standards for passenger cars and light trucks that extend through model year 2030. It also directs the agencies to issue standards for medium- and heavy-duty trucks for model years 2027 through 2030, to be finalized no later than December 2022.


Fleet-wide carbon dioxide compliance targets compared to previous rules

Passenger Cars/Light-Duty Trucks

Proposed 2023–2026 standards

In August 2021, the Environmental Protection Agency (EPA) proposed new greenhouse gas emission standards for new passenger cars and light-duty trucks. The proposed rule requires automakers to improve average fuel efficiency by 10 percent from model years 2022 to 2023, followed by 5 percent annual increase from model years 2024 to 2026. Additionally, President Biden issued Executive Order 14037, Strengthening American Leadership in Clean Cars and Trucks, which set a target of making 50 percent of all new passenger car and light truck sales battery electric, hydrogen fuel cell, or plug-in hybrid by 2030. This is a nonbinding target that major automakers such as Ford, General Motors, and Stellantis have made voluntary commitments to meet.

In addition to the proposed vehicle greenhouse gas emission standards, the National Highway Traffic Safety Administration (NHTSA) proposed new fuel economy standards for new passenger cars and light trucks for model years 2024–2026. The standards would increase in stringency by about 8 percent each year, reaching a fleetwide average of 48 miles per gallon (mpg) by 2026. While NHTSA and EPA often coordinate fuel economy and greenhouse gas standards, NHTSA is required to provide more lead time than EPA. The agencies proposed standards with different effective dates to reflect this.


Projected 2023–2026 Fleet-wide carbon dioxide (CO2) and fuel economy standards

Vehicle Standard 2023 2024 2025 2026
Passenger Cars CO2 (g/mi) 165 157 149 142
CO2 equiv. mpg 55 59 60 63
CAFE (mpg) 49.2 53.4 58.1
Light Trucks CO2 (g/mi) 232 221 210 199
CO2 equiv. mpg 38 39 41 44
CAFE (mpg) 35.1 38.2 41.5
Combined Cars & Light Trucks CO2 (g/mi) 198 189 180 171
CO2 equiv. mpg 45 47 49 52
CAFE (mpg) 40.7 44.2 48.1

Note: EPA’s proposed greenhouse gas emissions standards is expressed in carbon dioxide grams per mile (g/mi) while NHTSA’s proposed fuel economy standard is expressed in miles per gallon (mpg). EPA’s proposed rule also includes an estimated impact on fuel economy, which is shown as CO2 equivalent mpg.

EPA’s proposed rule would retain and reinstate several flexibilities and incentives from previous rules, including maintaining the existing program for credit-based averaging, banking, and trading of greenhouse emissions first established in 2010. The rule would restore the advanced technology vehicle multiplier credits established under the Obama administration but removed by the Trump administration, which allowed zero- and near-zero-emission vehicles to be weighted stronger toward meeting standards than conventional vehicles, although this multiplier would phase out after 2026. Additionally, it would maintain the off-cycle credits allowing automakers to count non-exhaust energy efficiency improvements that reduce hydrofluorocarbon (HFC) or other emissions towards overall greenhouse gas emissions reductions. Finally, the rule would restore full-size pickup truck incentives for hybrids which were removed by the SAFE rule.

Both EPA and NHTSA cited significant manufacturer commitments to ramp up production of electric vehicles and to improve fleetwide efficiency in the coming years as justification that manufacturers will be able to meet the more stringent standards in the proposals. Additionally, both agencies cited the voluntary agreement five automakers (Ford, Honda, Volkswagen, BMW, and Volvo) made with the state of California to meet significantly more stringent emissions standards than those set by the SAFE rule, demonstrating their existing commitments to significantly exceed those standards.

2021–2026 Standards

In 2020, EPA and NHTSA issued the Safer Affordable Fuel Efficient (SAFE) Vehicles Rule, which required automakers to improve fuel efficiency 1.5 percent annually from model years 2021 through 2026. The SAFE rule was less stringent than the Obama-era rule it replaced. That rule would have required automakers to improve fuel efficiency 5 percent annually for model year 2020–2025 vehicles, reaching 46.7 miles per gallon (mpg) by 2025.

The SAFE rule justification projected that increased fuel efficiency standards have a “rebound effect” that encourages more driving and therefore more exposure to the risk of traffic accidents; that higher vehicle costs from increased fuel efficiency standards discourage consumers from purchasing new vehicles and encourage them to keep driving older, less safe vehicles; and that manufacturer “lightweighting” of vehicles to achieve fuel efficiency makes vehicles less safe. EPA and NHTSA projected the SAFE rule would reduce vehicle costs by more than $1,000, but consumers will spend between $1,125 and $1,425 dollars more on fuel costs over the life of the vehicle. The SAFE rule was also projected to slow electrification rates by 2029 to 7.9 percent compared to 19.6 percent under the Obama-era rules.

The SAFE rule also upended state emission programs. In September 2019, EPA and NHTSA issued a final action that enabled federal vehicle standards to preempt state action and withdrew the waiver for California’s Advanced Clean Cars Program, Zero Emission Vehicle Program (ZEV), and Low-Emission Vehicle Program (LEV). In response, California and other states sued in federal court to challenge the final action on preemption of state vehicle standards. In 2021, the Biden administration EPA and Department of Transportation began the process of dropping the limitations on California’s waiver.

History of Light-Duty Vehicle Standards

In October 2012, EPA and NHTSA finalized the second set of national program standards for model year 2017–2025 light-duty vehicles with the cooperation of major automakers and the state of California. Now replaced by the Trump Administration’s 2021–2026 standards, these standards aimed to raise the combined average fleet fuel efficiency to 46.7 mpg for model year 2025, nearly double the 27.5 mpg required for model year 2010 (before the first set of national program standards were adopted). Canada also adopted standards aligned with the second set of national program standards through model year 2025.

These standards included features aimed at improving flexibility, making compliance more cost-effective and encouraging technological innovation. Features for greater flexibility included:

  • A credit trading system;
  • Possibility of compliance for air conditioning improvements;
  • Qualifying off-cycle credits (like solar panels on hybrid vehicles, active aerodynamics, or adaptive cruise control) for compliance;
  • Alternative vehicle incentives; and
  • Inclusion of truck hybridization for compliance.

In January 2017, following a mid-term review of these standards and draft Technical Assessment, the Obama administration issued a determination that maintained the standards through 2025. EPA cited the success of automakers in meeting early standard requirements and a seven-year growth in U.S. auto sales as reasons to expect that automakers could affordably continue to meet the standards. The California Air Resources Board (CARB) concurred with the EPA’s determination in its own midterm review of California’s vehicle standards. California found that automakers were successfully and affordably deploying advanced technologies to meet fuel economy requirements and the state’s zero-emission vehicle program.

In April 2018, the Trump administration issued a reconsideration of the midterm evaluation for greenhouse gas emission standards for model year 2022–2025 light-duty vehicles. EPA concluded that the standards were based on outdated information and that more recent information suggested that the current standards may be too stringent, making vehicles less affordable. EPA concluded that since the 2012 rulemaking finalizing the initial standards, expectations about gas prices and consumer adoption of advanced technology vehicles had changed.

In response, a California-led group of 23 states and the District of Columbia sued in federal court to challenge EPA’s reconsideration. The group included California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Maine, Maryland, Massachusetts, Michigan, Minnesota, Nevada, New Jersey, New Mexico, New York, North Carolina, Oregon, Pennsylvania, Rhode Island, Vermont, Virginia, Washington, Wisconsin, and the District of Columbia. The lawsuit alleged that EPA’s decision lacked scientific justification.

In 2021, the Biden Administration dropped the EPA and Department of Transportation’s defenses against the lawsuit, began the process of restoring California’s waiver under the Clean Air Act, and issued new near-term standards for light-duty and passenger vehicles.

Medium- and Heavy-Duty Vehicles

Medium- and heavy-duty trucks make up only 5 percent of vehicles on the road but account for about 24 percent of U.S. transportation emissions. This category includes tractor-trailers, large pickups and vans, delivery trucks, buses, and garbage trucks.

Phase 2 standards developed by EPA and NHTSA currently apply to semi-trucks, large pickup trucks, vans, and all buses and work trucks of model years 2021–2027. Phase 2 standards for box trailers that would have gone into effect in 2018 have been stayed by court order. EPA has proposed to repeal Phase 2 emissions standards for heavy-duty glider vehicles, glider engines, and glider kits.

In August 2021, President Biden’s Executive Order 14037, Strengthening American Leadership in Clean Cars and Trucks, directed EPA to begin work on establishing new emissions standards for heavy-duty vehicles for model years 2027 through 2030 or later. The order called for EPA to finalize this rulemaking by December 2022.

History of Medium- and Heavy-Duty Standards

In 2007, Congress directed the Department of Transportation to establish efficiency standards for medium- and heavy-duty vehicles after consultation with the Department of Energy and EPA. In 2011, EPA and NHTSA established the heavy-duty national program (known as the Phase 1 standards), the world’s first harmonized greenhouse gas emissions standards and fuel economy standards for on-road heavy-duty vehicles of model years 2014-2018. The Phase 1 standards applied to combination tractors, heavy-duty pickup trucks and vans, and vocational vehicles. Some of the standards are exclusively within EPA’s jurisdiction, such as hydrofluorocarbon standards limiting leakage from vehicle air conditioning systems from certain heavy-duty vehicles, and nitrous oxide and methane emissions standards for pickup trucks and vans and heavy-duty engines. The Phase 1 standards did not apply to commercial trailers.

In August 2016, EPA and NHTSA finalized the Phase 2 standards for medium and heavy-duty vehicles. The Phase 2 standards were designed to apply to certain trailers of model years 2018 – 2027 and to semi-trucks, large pickup trucks, vans, and all buses and work trucks of model years 2021-2027.

The Phase 2 standards are divided into five segments and were designed to help provide manufacturers with flexibility.

  1. Combination Tractors: Class 7 and 8 combination tractors and their engines should reduce fuel consumption by 25 percent from Phase 1 standard levels by model year 2027.
  2. Trailers: Trailers should reduce fuel consumption by 9 percent by model year 2027, including by improving aerodynamics, reducing weight, and addressing tire pressure and resistance.
  3. Heavy-Duty Pickup Trucks and Vans: These vehicles should reduce fuel consumption by 16 percent by model year 2027.
  4. Vocational Vehicles: Delivery trucks, buses, garbage trucks should reduce fuel consumption by 24 percent by model year 2027.
  5. Engine Standards: Tractor engines should reduce carbon dioxide emissions by 5 percent, and vocational diesel and gasoline engines should reduce carbon dioxide by 4 percent from Phase 1 standard levels by improving air handling, reducing engine friction, or improving emissions after-treatment technologies and waste heat recovery.

To provide manufacturers flexibilities, the program allows averaging, banking, and trading among regulated parties in order to speed up implementation of new technologies and reduce the cost of compliance.

Penalties for Failing to Meet CAFE Standards

If the average fuel economy of a manufacturer’s fleet does not meet the standard set under the NHTSA rules, the manufacturer must pay a penalty. Automakers cannot opt out of reporting their fuel economies by choosing to pay a fine instead. The penalty for failing to meet the CAFE standards is based on the difference between the manufacturer’s fleet average fuel economy and the annual standard, and costs $14 per tenth of a mile per gallon, multiplied by the number of vehicles in the manufacturer’s fleet.

The penalty was originally set in 1975 at $5.50 per tenth of a mile per gallon. In 2015, Congress directed agencies to adjust civil monetary penalties to reflect inflation, and in 2016 NHTSA published an interim final rule raising the civil penalty rate from $5.50 to $14. However, in the final rule, NHTSA stated that it would not apply the adjusted rate until model year 2019 to allow sufficient lead time for manufacturers to make any necessary product changes.

In January 2017, NHTSA announced a rule delaying the effective date of the new $14 penalty indefinitely, effectively maintaining the $5.50 rate. [Something about who sued and why.] The Second US Circuit Court of Appeals vacated the decision in 2018, declaring that the rule was in force.  In July 2019, NHTSA finalized a rule determining that the CAFE civil penalty rate was not affected by the 2015 Act as it was not a civil monetary penalty. In 2020, the Second US Circuit Court of Appeals again reinstated the $14 penalty, unanimously ruling that the CAFE penalty is indeed a civil monetary penalty since it meets the legal definitions under the Improvements Act and NHTSA had previously treated the CAFE penalty as a civil monetary penalty.

In January 2021, NHTSA published an interim final rule delaying the effective date of the increase to model year 2022. However, in August 2021, the agency announced it would review its earlier decision, and proposed reinstating the effective date of 2019 in keeping with the two decisions by the Second US Circuit Court of Appeals and numerous comments received in response to the 2021 interim final rule.