Technical Standards

1978-2004 CAFE standards

NHTSA regulates CAFE standards. CAFE standards began in 1978 and were significantly reformed in 2010. Mile-per-gallon standards for 1978-2004 for passenger vehicles and light-duty trucks are listed below.

2005-2007 CAFE standards for light trucks

In May 2003, NHTSA established CAFE standards for light trucks for MYs 2005-2007. CAFE standards were increased for light trucks but remained the same for passenger vehicles. 

2008-2011 CAFE reform for light trucks

In 2006, reforms to the CAFE standards for light trucks were adopted , and took effect in 2011. During a transition period from 2008-2010, manufacturers had the choice of complying either with the unreformed CAFE standards or with the reformed CAFE rules.

Under the reformed CAFE, each manufacturer’s required level of CAFE was based on target levels set according to vehicle size. The targets were assigned according to a vehicle’s footprint: the product of the average track width (the distance between the centerline of the tires) and wheelbase (the distance between the centers of the axles). Each vehicle footprint value was assigned a target specific to that footprint value. Compliance was determined by comparing a manufacturer’s fleet average fuel economy in a model year with a required fuel economy level calculated using the manufacturer’s actual production levels and the category targets. 

The target values were determined from the following continuous mathematical equation, based on the vehicle footprint and four parameters (a … d) which are adopted for each model year. 

T = [1/a + (1/b – 1/a) e^(x-c)/d/(1 + e^(x-c)/d)]^-1

where:
T – fuel economy target, mpg
a – maximum fuel economy target, mpg
b – minimum fuel economy target, mpg
c – footprint value at which the fuel economy target is midway between a and b, ft²
d – parameter defining the rate at which the value of targets decline from the largest to smallest values, ft²
e = 2.718
x – footprint of the vehicle model, ft²

The resulting CAFE target curve was an elongated S-shape, with fuel economy targets decreasing from a to b as the footprint increases. 

The reformed CAFE regulation also applied to medium-duty passenger vehicles (MDPVs) of GVWR up to 10,000 lbs as part of the MY 2011 regulated light truck fleet. Thus, the regulation captured nearly all larger size passenger vans and SUVs which were excluded from previous CAFE standards. (The weight limit for cargo vans and pickup trucks remained at 8,500 lbs.) The US Department of Transportation (DOT) estimated that the average light truck target required of manufacturers under the reformed CAFE rule in MY 2011 would be 24.0 mpg. 

2012-2016 CAFE/GHG

In May 2010, EPA and NHTSA issued a joint final rule applicable to passenger vehicles and light trucks covering model years 2012-2016. The regulation mandated a reduction in GHG emissions and a combined CAFE standard of 34.1 mpg by 2016 under the US CAFE combined driving test cycle. Combined with the improvement of vehicle A/C systems and the use of flexible-fuel vehicles, fuel economy is expected to result in improvement levels equivalent to 35.5 mpg (250 gCO₂e/mile).6 The final rule provisions are largely unchanged from the proposed rule issued on September 15, 2009. In addition, EPA granted a waiver to California to implement its GHG standard for MYs 2009-2011 vehicles. California also agreed to forgo its own 2012-2016 program and comply with the new federal program for 2012-2016 vehicles. 

Key Elements

• Applicability – EPA will regulate GHG emissions from passenger vehicles up to 8,500 lbs. GVWR (plus medium-duty SUVs and passenger vans up to 10,000 pounds).
• CO₂ Testing – The program sets standards for CO₂ emissions on the combined US federal test procedure (FTP) and highway cycles.
• Additional GHGs – There are additional provisions for the non-CO₂ GHG emissions of hydrofluorocarbons (HFCs) from vehicle air conditioning systems and per-vehicle emission caps set for nitrous oxide (N₂O) and methane (CH₄) emissions. EPA did not consider the global warming potential of other emissions (e.g., black carbon).
• Stringency – The average light duty vehicle GHG emission rate is reduced from the average MY 2009 level of 337 gCO₂e/mile to 250 gCO₂e/mile for MY 2016, a 26% reduction. The estimated improvement in fuel economy by MY 2016 is 29%, from an average MY 2009 level of 26.4 mpg to 34.1 mpg. Annually, this is a 4.2% reduction per model year in the average GHG emissions, and 3.7% increase per model year in miles-per-gallon fuel economy.
• Regulatory design – The standards use a vehicle size-based standard for two vehicle categories, following the current NHTSA fuel economy standard framework. The program sets separate numerical standards for vehicle size or “footprint” (i.e., the area defined by the wheelbase and average track width) for passenger cars and for light trucks. In contrast to previous federal regulation, which employ an S-shaped constrained logistical curve, the new system uses “piecewise linear” functions between vehicle footprint and the test-cycle GHG emission rate. This general shape allows for different-size vehicles to have different standards in the sloped portion, but constrains the largest vehicles at the upper bend and incentivizes vehicles below the lower bend. The changes in the final rule from the proposal are slight.

Because there are two categories, car and truck, and the standards are based on the footprint attributes of future year vehicle sales, the exact GHG and fuel economy outcomes are unknown and subject to the sales mix of vehicles sold from 2012 to 2016. 

The footprint-based system means that selling more small vehicles does not necessarily help manufacturers meet the standards. Smaller vehicles are subject to more stringent requirements, such that a manufacturer of smaller vehicles has a lower CO₂ standard while a manufacturer of larger vehicles has a higher CO₂ standard. Footprint systems encourage improvements in efficiency, regardless of vehicles size, and have relatively little impact on vehicle size mix. Unlike a weight-based standard, a footprint-based standard encourages use of lightweight materials while maintaining the vehicle size, without subjecting the manufacturers to a higher CO₂ requirement. Each auto manufacturer will ultimately have a different footprint-based standard for 2012 to 2016 based on its sales mix of vehicles at each vehicle size. See ICCT’s analysis for an in-depth write-up of the 2012-2016 standards. 

2017-2025 CAFE/GHG

In August 2012, EPA and NHTSA issued a joint final rulemaking for GHG emission and fuel economy standards for MYs 2017-2025 light-duty vehicles, including passenger cars, light-duty trucks, and medium-duty passenger vehicles. The adopted rule follows the proposal released in November 2011. For additional information, see the EPA’s Fact Sheet and the final rule. 

The EPA GHG standards are projected to require, on an average industry fleet-wide basis, 163 g/mile of CO₂  in MY 2025, which is equivalent to 54.5 mpg (4.3 L/100km) if this level were achieved solely through improvements in fuel efficiency. However, it is expected that a portion of the GHG emission reduction will be made through improvements in air conditioning leakage and using alternative refrigerants, which do not contribute to fuel economy. 

For more information, see the full text of ICCT’s analysis. Summary highlights are below and are contained in the EPA’s Fact Sheet of 2017-2025 Standards. 

Key Elements of the Program 

• GHG Reductions – The average light-duty vehicle GHG emission rate was reduced from the 2016 level of 250 gCO₂ e/mile to 163 gCO₂ e/mile for MY 2025, a 35% reduction. Passenger vehicle fuel economy is estimated to increase from an average MY 2016 level of 34.1 to 49.6 mpg in 2025, an increase of 45%. Annually, this is a 4.6% reduction per model year in the average GHG emissions, and 4.25% increase per model year in miles-per-gallon fuel economy. 
• Credit Provisions – Emission reduction compliance credits include air-conditioning system technology, flexible fuel vehicle deployment, off-cycle technologies, incentives for electric vehicles, and “game-changing” technologies installed on pickup trucks. Of these credits, only the air-conditioning credits and some off-cycle technology credits reflect real-world emission reductions that are not included in the compliance test cycles. The others reduce the overall stringency of the standards, without corresponding to reductions in real-world emissions. 
• Regulatory design – The rules use a vehicle size-based standard for two vehicle categories, following the current 2012–2016 standard framework. Different numerical standards for vehicle size or “footprint” are used for passenger cars and light trucks. Because there are two categories, car and truck, and the standards are based on the footprint attributes of future year vehicle sales, the exact GHG and fuel economy outcome from the program is somewhat unknown and subject to the sales mix of vehicles sold in the future. Each auto manufacturer will ultimately have a different footprint-based standard based on its sales mix of vehicles at each vehicle size and its car and light truck sales mix. 
• Consistent improvements – The 2022–2025 standards set annual improvements for all cars and light trucks, with CAFE increases of 4.7% per year and CO₂ reductions of 5.0% per year. Both EPA and NHTSA set a lower annual rate of improvement for light-trucks in the early years of the program. EPA set an annual CO₂reduction for cars of 5%, but only 3.5% for light trucks. Similarly, NHTSA set an annual fuel economy increase of 4.3% for cars, but only 2.9% for light trucks. The required reductions for light trucks are also tilted, such that the smallest light trucks have larger increases (but still less than cars), while the larger light trucks have smaller increases. The annual fuel economy increases for cars from 2016 to 2025 is almost flat and ranges from 4.4% to 4.5%. The annual fuel economy increase for light trucks starts at 4.3% for the smallest trucks, drops to 3.4% for larger SUVs, and falls off to only 2.2% for the largest pickup trucks. 

International context – The U.S. agreement for 250 gCO/mile is equivalent to about 172 gCO₂e/km when miles are converted to kilometers and adjusted to the European driving cycle. The 2025 standard of 163 gCO₂e/mile is similarly equivalent to 107 gCO₂e/km. Note that the US light-duty standard is composed of passenger cars as well as light-duty trucks. When passenger cars alone are considered, the 2025 standard is equivalent to 91 gCO₂e/km when adjusted for European driving cycle. For more information on European standards, see the European Light-duty GHG page. 

2024-2026 CAFE/2023-2026 GHG STANDARDS 

In December 2021, the EPA finalized federal GHG emissions standards for passenger cars and light trucks for Model Years (MY) 2023 through 2026. Later, in March 2022, the NHTSA issued the final rule of the CAFE standards for MY 2024-2026 passenger cars and light trucks.  

EPA establishes mechanisms to help manufacturers manage the transition toward more stringent emission standards, including flexibilities or incentives to its GHG regulations. The final MY 2023-2026 rule updates four types of flexibilities. These are a limited carry-forward extension for credits generated or banked from previous model years in MY 2017-2018, advanced technology vehicle multiplier credits for MY 2023-2024 with a cumulative cap, full-size pickup truck incentives for strong hybrids or similar performance-based credits for MY 2023-2024, and an increase in the cap for menu off-cycle credits. The air conditioning credits remain unchanged. 

For the CAFE standard, NHTSA also includes most of the flexibilities described in the EPA’s GHG standard although with some minor differences. Credit is earned from over-compliance by multiplying the number of tenths of an mpg by which a manufacturer exceeds the standards. Credits can be carried forward 5 years and back 3 years, similar to EPA regulation. However, NHTSA does not adopt EPA’s one-year credit life extension for MY 2017 and MY 2018 to MY 2023 and MY 2024. NHTSA’s program allows credit transfer of up to 2mpg per manufacturer fleet and unlimited credit trade. In addition, the regulation maintains statutory flexibility for compliance using credit banking, trading, and transferring with certain restrictions for minimum domestic passenger car standards (MDPCS). NHTSA is required by the statute to set MDPCS and they are 44.3 mpg in 2024, 48.2 mpg in 2025, and 53.5 mpg in 2026. 

1. Although the GHG and CAFE standards were issued separately, the regulatory designs are like previous standards. There are three key differences between the two regulations that ultimately lead to the differing projected emissions reductions and fuel economy improvements.
2. AC refrigerant leakage (direct emissions) credits are excluded from the CAFE standards because they do not affect fuel consumption. The projected average MY 2024-2026 AC direct emissions are approximately 13.1 to 13.6 g/mile for cars, and 15.1 to 16.1 g/mile for light trucks. 
3. Due to statutory constraints, the NHTSA’s analysis excludes advanced technology multiplier credit incentives in the final compliance calculation. This incentive is applied only for MY2023-2024 in EPA compliance calculation.  
4. The remaining difference between the programs comes from the EPA and NHTSA adoption of different estimates of future battery electric vehicle (BEV) and plug-in hybrid electric vehicle (PHEV) penetration rates. Because NHTSA’s analysis excludes the introduction of new dedicated alternative fuel vehicle models (including BEVs) during MYs 2024-2026 as a response to final fuel economy standards1, the BEV and PHEV penetration rate under NHTSA’s final rule is lower than EPA’s estimation, especially for the later years (see table below)

The tables below present the projected overall industry fleet-wide CO₂-equivalent emission and fuel economy compliance target levels, respectively, based on projected vehicle production. The italicized agency name in each table indicate who has authority over the specific regulation, while the non-italicized agency shows their equivalent estimation. NHTSA also adjusts its targets for the exclusion of AC direct emission credits, thus, not shown in the table. If the AC direct emission credit is included in NHTSA compliance calculation, these two programs would roughly align. 

The EPA’s projection for average light-duty vehicle GHG emission begins with a rate of 202 gCO₂e/mile in MY 2023 and ends with a rate of 161 gCO₂e/mile for MY 2026, a 20% reduction. The GHG standard will reduce GHG emissions from cars and light trucks on average by 5% to 10% per year in model years 2023 to 2026, specifically 5.1% in 2023–2024, 6.6% in 2024–2025, and 10.3% in 2025–2026. The combined fuel economy for passenger cars, light-duty trucks, and SUVs is estimated to increase from an average MY 2023 level of 40.6 mpg to 49.1 mpg in 2026, an increase of almost 21%. The fuel economy standards will increase fuel economy at a rate of 8% per year for both cars and light trucks for MYs 2024-2025, and at a rate of 10% for MY 2025-2026.  

Key Elements of the Program 

• GHG Reductions – Under the EPA rule, the average light-duty vehicle fleet GHG emission rate is reduced from the 2022 projection (SAFE CAFE/GHG) of 224 gCO₂e/mile to 2o2 gCO₂e/mile in 2023. The 2026 target of 161 gCO₂e/mile represents a 28% decrease in emissions from SAFE rule MY 2022. 
• Fuel Economy Improvements – Similar to changes made to GHG targets, the NHSTA raises their fleet-wide average emissions compliance target of 37.9 mpg for MY 2022 (SAFE) under the 2017-2025 regulation to 40.6 mpg in MY 2024, with an end goal of achieving 49.1 mpg in MY 2026, a 23% increase from MY 2022. 
• Regulatory design – Keeping with prior regulations, the rules use a vehicle size-based standard for two vehicle categories. Separate numerical standards for vehicle size or “footprint” are used for passenger cars and for light trucks. Because there are two categories, car and truck, and the standards are based on the footprint attributes of future year vehicle sales, the exact GHG and fuel economy outcome from the program is somewhat unknown and subject to the sales mix of vehicles sold in the future. Each auto manufacturer will ultimately have a different footprint-based standard based on its sales mix of vehicles at each vehicle size and its car and light truck sales mix.  
• Credit Provisions – Like the MY 2017-2025 standards passed in 2012, this set of standards provides compliance credits for the implementation of air-conditioning system technology, off-cycle technologies, incentives for battery electric vehicles, FCVs, and PHEVs, and better performance technologies installed on pickup trucks. The final MY 2023-2026 rule updates four types of flexibilities from the 2017-2015 standards, but the overall system remains largely the same. Changes include a limited (1-year) carry-forward extension for credits generated or banked from previous model years in MY 2017-2018, advanced technology vehicle multiplier credits for MY 2023-2024 with a cumulative cap, full-size pickup truck incentives for strong hybrids or similar performance-based credits for MY 2023-2024, and an increase in the cap for menu off-cycle credits (from 10 g/mile to 15 g/mile combined car and truck fleet average per year). The air conditioning credits remain unchanged. Like the previous set of GHG/CAFE standards, many of the credits. 
• Consistent improvements – The 2023–2026 GHG and 2024-2026 CAFE standards set consistent improvements for all cars and light trucks, with annual CO₂ reductions averaging 5% to 10% per year in model years 2023 to 2026, specifically 5.1% in 2023–2024, 6.6% in 2024–2025, and 10.3% in 2025–2026. The fuel economy standards will increase fuel economy at a rate of 8% per year for both cars and light trucks for MYs 2024-2025, and at a rate of 10% for MY 2025-2026. 

International Context – This latest round of GHG and fuel economy standards put the US back on track to keep pace with the leading governments in standard stringency until 2026, with the European Union being a possible exception. The nation’s longer-term trend in improvements will be determined by the next phase of standard making for MY 2027 and beyond. The EPA’s emissions compliance target of 161 gCO₂e/mi by MY 2026 is equivalent to 95 gCO₂e/km while the NHTSA’s target of 49.1 mpg is equivalent to 21 km/l. For more information on European standards, see the European Light-duty GHG page. 

Testing

CAFE fuel economy testing is done over the Federal Test Procedure 75 (FTP-75) weighted with the highway cycle to determine compliance. CAFE certification is typically done based on fuel economy data provided by the manufacturers. In some cases, EPA performs the testing in its laboratory in Ann Arbor, MI. The CAFE fuel economy figures can be significantly different from the vehicle fuel economy data published by EPA/Department of Energy (DOE) in the Fuel Economy Guide report and on new vehicle labels. There are two sets of fuel economy figures: 

• EPA’s unadjusted dynamometer values, which are equal to NHTSA’s CAFE values 
• EPA’s adjusted on-road values 

The unadjusted EPA values are calculated based on a carbon balance equation measured over the dynamometer test. These values are also used directly for compliance with NHTSA’s CAFE standards. In 2008, additional test cycles were included only for the calculation of EPA’s adjusted on-road values, to better reflect true driving conditions: US06 for high-speed driving and SC03 for using air conditioning while driving.7 

The CAFE values – used to determine manufacturer’s compliance with the average fuel economy standards – are significantly higher than the EPA on-road values. Furthermore, the following caveats apply to the CAFE values: 

1. The unreformed CAFE standards (before MY 2011) did not apply to vehicles above 8,500 lbs GVWR. Many pickup trucks which belong to this category were, and still are, excluded from CAFE data. Some of the largest SUVs and passenger vans (GVWR 8,500 – 10,000) are included. 
2. Credits are provided for alternative fuel vehicles. The CAFE fuel economy of an alternative fueled vehicle is calculated by dividing its real fuel economy by a factor of 0.15. For instance, a 15-mpg natural gas vehicle will be rated as a 100-mpg gasoline vehicle. For bi-fuel vehicles, this calculation is applied to the expected percentage of alternative fuel use.
3. Manufacturers who exceed the standards earn CAFE credits, which can be applied to any three consecutive model years immediately prior to or after the model year in which the credit was earned. 

Additional resources include the FTP75 Test Procedures page and the EPA Test Schedule website. 

Compliance and Enforcement

CAFE fuel economy figures achieved for the total US market fleet of cars, light trucks, and the combined cars and LDTs since 2000 are listed below (in mpg and in the metric units of liters per 100 km).

Manufacturers whose fleets fail to meet CAFE standards are liable for a civil penalty of $5.50 per tenth of an mpg under the target value times the total volume of vehicles manufactured for a given model year. From 1983 to 2004, manufacturers paid more than $618 million in civil penalties. Most European manufacturers regularly pay CAFE civil penalties ranging from less than $1 million to more than $27 million annually. Asian and US manufacturers have never paid a civil penalty. 

Data Collection and Verification

The US’ fuel economy data collection and verification system is highly developed in comparison to other countries. EPA has extensive requirements defining all aspects of testing. Additional details can be found on the EPA’s Testing and Measuring Emissions website. Key steps in fuel economy data collection and verification under the US CAFE system are:

1. Manufacturers test 90 percent of vehicle sales by configuration and report the data to EPA.
2. EPA reviews and judges the acceptability of manufacturer reported data.
3. In addition to reviewing manufacturer data, EPA conducts confirmatory test for 10-15 percent of fuel economy data vehicles and determines the fuel economy of test vehicles based on comparison of its own results and the data from manufacturers.
4. After manufacturers submit the actual production data of a model year, EPA calculates and verifies the average fuel economy of the manufacturers.⁵
5. EPA has the authority to confirm the manufacturer’s road load determination, used to properly reflect in-use loads on the vehicle while driving.
6. EPA requires in-use verification testing of vehicles in-use.