US: Heavy-duty: Fuel Consumption and GHG

Note: Phase 2 standards included regulations on trailers in addition to trucks. The legality of the EPA regulating trailers has been challenged, leading to a hold on trailer regulation implementation. The legal process is still ongoing, and there has been no final ruling released as of July 15, 2021.


Phase 1 standards apply to model years (MYs) 2014–2018 on-road vehicles with a rated gross vehicle weight of ≥ 8,500 lbs. Required CO2 and fuel consumption reductions vary by vehicle type and range from 6–23% compared to a model year 2010 baseline. Phase 2 standards are applicable for 2018–2027 and are estimated to reduce CO2 and fuel consumption 16% for heavy-duty pickup trucks and vans, 16%–19% for vocational vehicles, and up to 30% for tractor-trailers.

Standard type

Joint fuel consumption standards and GHG emission limits

Current Standard

MYs 2018–2027

All on-road vehicles with a gross vehicle weight (GVW) rating ≥ 8,500 lbs.


In 2010, President Obama requested that the National Highway Traffic Safety Administration (NHTSA) and the U.S. Environmental Protection Agency (EPA) work to jointly establish greenhouse gas (GHG) emissions and fuel efficiency standards for medium- and heavy-duty highway vehicles. The first joint GHG emissions and fuel consumption standards for medium- and heavy-duty vehicles were adopted in the United States in 2011. This was the first time that either heavy-duty GHG emissions or fuel efficiency had been regulated in the United States. This “Phase 1” regulation covered MYs 2014–2018 and applies to all on-road vehicles rated at a GVW ≥ 8,500 lbs.

The rule has several important elements. It:

  1. Drives efficiency improvements in many important aspects of the heavy-duty vehicle for the two highest fuel consumption classes: tractor trucks and pickup trucks
  2. Sets separate standards for engines and vehicles
  3. Establishes standards for four major greenhouse gases in addition to fuel consumption limits

EPA developed GHG emissions standards under the authority of the Clean Air Act, while NHTSA developed fuel efficiency standards under the 2007 Energy Independence and Security Act (EISA). The emissions included in EPA’s program are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and hydrofluorocarbons (HFCs). The EPA program began with MY 2014, while the NHTSA program became mandatory starting with MY 2016 vehicles. Under EISA, NHTSA is required to have four full years of lead-time following the finalization of the rule; EPA has no such lead-time provision under the Clean Air Act.

Overall, the stringency of the program ranges from 6% to 23% reduction in fuel consumption in the MY 2017 timeframe, as compared to the MY 2010 baseline. The stringency levels vary according to vehicle subcategories based on weight classes and vehicle attributes. The rule is best understood as three separate regulatory programs linked to specific provisions for tractor trucks, pickup trucks and passenger vans, and vocational vehicles. In addition, the engines that power tractor trucks and vocational vehicles are regulated in a stand-only program.

Technical standards

Applicability and exceptions

The affected medium- and heavy-duty fleet incorporates all on-road vehicles rated at a GVW ≥ 8,500 lbs. and the engines that power them, except those covered by the GHG emissions and Corporate Average Fuel Economy (CAFE) standards for MYs 2012–2016 light-duty vehicles. CO2 and fuel consumption standards are applicable to the following categories of vehicles:

Phase 1 and Phase 2 CO2 and fuel consumption standards
  Phase 1 Phase 2
Proposal 2010 2015
Final rule 2011 2016
Model years 2014–2018 2018–2027
Percent CO2 and fuel consumption reduction Combination tractors (Class 7 and 8) 9%–23% 12%–27%
Trailers 3%–9%
Vocational vehicles (Class 2b-8) 5%–9% 10%–24%
Commercial pickups and vans (Class 2b and 3) 10%–15% 16%
Engines 5%–6% 0%–5%

Most vehicles covered by the regulation carry payloads of goods or equipment, in addition to passengers. To account for this in the regulatory program, two types of standard metrics have been adopted:

  1. Gram CO2per ton-mile (and gallon of fuel per 1,000 ton-mile) standards for vocational vehicles and combination tractors
  2. Gram CO2 per mile (and gallon of fuel per 100-mile) standards for pickups and vans

CO2 and fuel consumption standards

EPA and NHTSA have joint final standards for the three main heavy-duty regulatory categories: combination tractors, heavy-duty pickup trucks and vans, and vocational trucks.

Combination tractors

Differentiated standards were adopted for nine subcategories of combination tractors based on three attributes: weight class, cab type, and roof height. Phase 1 and Phase 2 final standards are shown below. Phase 2 added standards for Class 8 Heavy Haul Tractors, which are heavier than 120,000 lbs.

Phase 1 and Phase 2 final combination tractor standards
    Baseline: Phase 1 (2017)a Phase 2 (2027)
    g CO2/ ton-mi gal/1,000 ton-mi g CO2/ton-mi gal/1,000 ton-mi
Class 7 tractor Low roof 119.1 11.7 96.2 9.4
Mid roof 127.2 12.5 103.4 10.2
High roof 129.7 12.7 100.0 9.8
Class 8 tractor (day) Low roof 91.3 9.0 73.4 7.2
Mid roof 96.6 9.5 78.0 7.7
High roof 98.2 9.6 75.7 7.4
Class 8 tractor (sleeper) Low roof 84.0 8.3 64.1 6.3
Mid roof 90.2 8.9 69.6 6.8
High roof 87.8 8.6 64.3 6.3
Class 8 heavy haul Low roof 48.3 4.7
aThese baseline values are different from the standards in the Phase 1 standards because the Greenhouse gas Emission Model (GEM — discussed later) was updated for the Phase 2 regulation to better reflect real-world usage and impacts.

The regulation also defines two sets of standards for tractor engines for MYs 2021, 2024, 2027, and beyond: (1) CO2 standards and (2) fuel consumption standards. Engine-based standards must be met by heavy-heavy-duty (HHD) and medium-heavy-duty (MHD) diesel engines used in combination tractors. If manufacturers met the MY 2021 standards a year earlier for MY 2020, their MYs 2024–2026 standards were slightly relaxed, but they are still required to meet the MY 2027 standards for MY 2027.

Engine standards for engines installed in tractors
Category Year CO2 emissions (g/bhp-hr) Fuel consumption (gallon/100 bhp-hr)
MHD engines 2017 (baseline) 481 4.78
2021 473 4.65
2024 461 4.53
2027 457 4.49
HHD engines 2017 (baseline) 465 4.67
2021 447 4.39
2024 436 4.28
2027 432 4.24

Heavy-duty pickup trucks and vans

These vehicles must meet CO2 and fuel economy standards in an approach similar to that taken for light-duty vehicles, but with different standards for gasoline and diesel vehicles. EPA has established CO2 standards in the form of target standard curves, based on a “work factor” that combines a vehicle’s payload, towing capabilities, and whether it has 4-wheel drive. The Phase 2 standards will phase in with increasing stringency in each MY from 2021 to 2027, requiring 16% CO2 emissions reduction by MY 2027 compared to MY 2017 baselines. The EPA standards include a separate standard to control air conditioning system leakage. NHTSA has set corporate average standards for fuel consumption that are equivalent to EPA’s standards (but does not include EPA’s air conditioning leakage standard).

Both agencies provide manufacturers with two alternative phase-in approaches. One approach phases the final standards in at 15-20-40-60-100 percent in model years 2014-2015-2016-2017-2018. The other phases the final standards in at 15-20-67-67-67-100 percent in MYs 2014-2015-2016-2017-2018-2019.

Vocational trucks

This vehicle segment has been divided into 18 regulatory subcategories based on fuel type (diesel or gasoline), weight class (light, medium, and heavy), and duty cycle (urban, multi-purpose, and regional). As with tractor trucks, there are per-vehicle fuel efficiency and greenhouse gas requirements in MYs 2021, 2024, and 2027.

Phase 2 vocational vehicle CO2 and fuel efficiency standards
Weight class Duty cycle 2017 (baseline) 2027 (final)
g CO2/ton-mile gal/1000 ton-mile g CO2/ton-mile gal/1000 ton-mile
Diesel Gasoline Diesel Gasoline Diesel Gasoline Diesel Gasoline
LHD (Class 2b-5) Urban 482 502 47.3 49.3 367 413 36.1 46.5
Multi-purpose 420 441 41.3 43.3 330 372 32.4 41.9
Regional 334 357 32.8 35.1 291 319 28.6 35.9
MHD (Class 6-7) Urban 332 354 32.6 34.8 258 297 25.3 33.4
Multi-purpose 294 314 28.9 30.8 235 268 23.1 30.2
Regional 249 275 24.5 27.0 218 247 21.4 27.8
HHD (Class 8) Urban 338 354 33.2 34.8 269 26.4
Multi-purpose 287 314 28.2 30.8 230 22.6
Regional 220 275 21.6 27.0 189 18.6

Engine standards for light heavy-duty (LHD), medium heavy-duty (MHD), heavy heavy-duty (HHD) diesel engines and for heavy-duty gasoline engines up to MY 2027 are shown below.

Phase 2 engine standards for engines installed in vocational vehicles
Category Year CO2 emissions (g/bhp-hr) Fuel consumption (gallon/100 bhp-hr)
LHD engines 2017 (baseline) 576 5.66
2021–2023 563 5.53
2024–2026 555 5.45
2027 552 5.42
MHD engines 2017 (baseline) 558 5.48
2021–2023 545 5.35
2024–2026 538 5.28
2027 535 5.26
HHD engines 2017 (baseline) 525 5.16
2021–2023 513 5.04
2023–2026 506 4.97
2027 503 4.94
Gasoline engines 2016 (no change in MY 2027) 627 7.06


Phase 2 includes the first CO2 emission and fuel efficiency standards for trailers hauled by Class 7 and 8 tractor trucks. The original standards were finalized for MYs 2018, 2021, 2024, and 2027.  Since 2017, there has been a court-ordered stay on the enforcement of these trailer standards, and the legal challenge has not yet been resolved.

The standards for box-type trailers entail a bin system of aerodynamic bins numbered I–VIII to certify new trailers. Manufacturers will have to switch to higher numbered bins over time. Other compliance technologies include low resistance rolling tires, automatic tire inflation systems, and trailer weight reduction. Final MY 2027 trailer requirements are shown below:

Phase 2 trailer CO2 and fuel efficiency standards
Trailer type Standard (g CO2ton-mile)a Fuel economy (mpg) Percent CO2 reduction
Reference 85–87 (long) 147–151 (short) 6.2–6.3 (long) 6.7–6.9 (short) 0%
Long dry box 77 7.0 9%
Short dry box 140 7.3 5%
Long refrigerated box 80 6.7 8%
Short refrigerated box 144 7.1 5%
Partial aero long dry box 79 6.8 7%
Partial aero short dry box 141 7.2 4%
Partial aero long refrigerated box 81 6.6 7%
Partial aero short refrigerated box 144 7.1 5%
Non-aero box trailers 3%–4%
Non-box 3%–4%
aIncludes assumed 20,000 lb. (short van) and 38,000 lb. (long van) in payload; Equivalent NHTSA fuel consumption standards in gallon/1,000 ton-mile are based on 10,180-gram CO2 per gallon diesel; Assumes trailers are pulled by a standard tractor.


The requirements for tractors and vocational vehicles include both engine and vehicle standards. Engine manufacturers are subject to the engine standards. Testing is conducted over one test cycle:

  • Tractor engines are tested over the steady-state Supplemental Emissions Test (SET)
  • Vocational engines are tested over the Federal Test Procedure (FTP) transient test
  • Heavy-duty pickups and vans are tested over the light-duty FTP and the Highway Federal Economy Test

Chassis manufacturers are subject to the vehicle standards. Compliance for tractor trucks and vocational vehicles is determined based on a vehicle simulation model, called the Greenhouse gas Emission Model (GEM), which was developed by the EPA as part of the Phase 1 regulatory development process and has been subsequently updated several times, including as part of the Phase 2 rulemaking. The regulation does not require chassis dynamometer testing due to the large variety of vehicle configurations and the scarcity of heavy-duty chassis dynamometer test facilities.

Instead of using a chassis dynamometer as a way to evaluate real-world operation and performance, various characteristics of the vehicle are measured, and these measurements are used as inputs to GEM. These characteristics relate to key technologies applicable to a given truck category. This includes inputs such as engine- and transmission-specific data, aerodynamic performance, weight reduction, tire rolling resistance, the presence of idle-reducing technology, and vehicle speed limiters.

Useful life

EPA CO2 emissions must be met over the engine and vehicle’s useful life. The useful life definitions for engines and vehicles that use the respective engine categories were identical to those defined for criteria pollutant standards for MY 2004 and later heavy-duty engines in the Phase 1 regulation. The Phase 2 standards increased the useful life for LHDDE only for GHG emissions, not criteria pollutant standards. Useful life is measured either in miles driven or years of use, whichever comes first:

  • LHDDE and commercial pickup trucks and vans: 150,000 miles or 5 years
  • MHDDE: 185,000 miles or 10 years
  • HHDDE: 435,000 miles or 10 years

Other standards and provisions

N2O and CH4 standards

N2O and CH4 standards introduce emission standards for nitrous oxide and methane:

  • Engine testing (tractors & vocational): N2O = 0.10 g/bhp-hr; CH4 = 0.10 g/bhp-hr
  • Chassis testing (pick-ups and vans, FTP-75 & HWFET): N2O = 0.05 g/mi; CH4 = 0.05 g/mi

Testing requirements start from MY 2015 and are consistent with N2O and CH4 requirements for light-duty vehicles. The standards were designed to cap emissions at current levels to prevent N2O and CH4 emission increases in future engines.

A/C leakage

EPA adopted standards to assure that low-leakage components are used in air conditioning systems designed for heavy-duty pickup trucks and vans, and semi-trucks. The standard for larger A/C systems (capacity above 733 g) is measured in percent total refrigerant leakage per year, while the standard for smaller A/C systems (capacity of 733 g or less) is measured in grams of refrigerant leakage per year.

Costs and benefits

NHSTA and EPA estimate total benefits from the rule of over 1,000 million metric tons of avoided GHG and nearly 2 billion barrels of oil saved over the lifetime of the vehicles sold from 2014–2018. The rule builds on a congressionally mandated study by the National Academy of Sciences (NAS) and previous work by the ICCT and many other stakeholders.

Projected costs, benefits, and vehicle payback periods are listed in the table below. Payback periods are longer for Phase 2 than Phase 1 standards but are still well within the average ownership cycle of the first vehicle owner.

Phase 1 and Phase 2 costs and benefits
  Phase 1 Phase 2
Vehicle technology costa Combination tractors (Class 7 and 8) $6,215 $12,300
Trailers $1,100
Vocational vehicles $378 $2,700
Commercial pickups and vans (Class 2b and 3) $1,048 $1,350
Average payback periodb Combination tractors (Class 7 and 8) 1 2
Vocational vehicles 1 4
Commercial pickups and vans (Class 2b and 3) 2 3
Energy and climate impact Greenhouse gas emission reduction by calendar year (million metric ton CO2) 76 (2030) 108 (2050) 139 (2040) 167 (2050)
Fuel reduction by calendar year (billion gallons per year) 6.0 (2030) 8.7 (2050) 10.2 (2040) 12.3 (2050)
Greenhouse gas reduction over regulated vehicle lifetimes (million metric ton CO2 equivalent) 273 1,098
Fuel reduction over regulated vehicle lifetimes (billion gallons) 22 82
Monetary impactc Fuel savings (billion) $50 $169
Other benefits (billion) $7 $88
Total costs (billion) $8 $29
Overall benefit-to-cost ratio 7:1 8:1
aFor tractors and vocational vehicles, these values include the additional costs related to engines.
bYears after technology purchase in which cumulative fuel savings are greater than the additional initial technology cost.
cBased on 3% discount rate; “Other benefits” include value of health and monetized CO2 benefit.


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