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Emission Standards » United States

Heavy-Duty Vehicles: GHG Emissions & Fuel Economy


US GHG emissions and fuel efficiency standards for heavy- and medium-duty vehicles have been jointly developed by the Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration (NHTSA), DOT. The NHTSA developed fuel consumption standards under the authority of the 2007 Energy Independence and Security Act (EISA), while the EPA developed a GHG emissions program under the Clean Air Act. The GHG program includes CO2 emission standards, as well as emission standards for N2O and CH4, and provisions to control hydrofluorocarbon leaks from air conditioning systems.

The standards are applicable to 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 MY 2012-2016 and MY 2017-2025 light-duty vehicles. The GHG/FE standards were adopted in two phases:

  1. Phase 1 regulation—adopted on August 9, 2011 [2324]—covers model years (MY) 2014-2018, with NHTSA fuel economy standards being voluntary in MY 2014-2015 to satisfy EISA lead time requirements.
  2. Phase 2 regulation—published on August 16, 2016 [2918]—applies to MY 2021-2027 vehicles. The Phase 2 rule also introduces new standards for trailers, a category not previously regulated. The EPA trailer standards begin in MY 2018 (for certain trailers), while NHTSA’s standards take effect in MY 2021, with credits available for voluntary participation before then.

The Phase 1/2 standards are applicable federally, as well as in California. However, the California Air Resources Board (ARB) deemed the federal Phase 2 program not sufficiently strong to meet California GHG emission reduction goals. The ARB started the development of California Phase 2 GHG emission standards for heavy-duty vehicles that would provide GHG emission reductions beyond those of the federal Phase 2 program. The California Phase 2 standards are expected to be proposed by the end of 2017.

Under the Phase 1 and Phase 2 regulations, different CO2 and fuel consumption standards are applicable to different categories of vehicles, including combination tractors, trailers, vocational vehicles, and heavy-duty pickups and vans:

  • Combination tractors (the semi-trucks that typically pull trailers): Phase 1 engine and vehicle standards begin in MY 2014 and achieve 7-20% reduction in CO2 emissions and fuel consumption by MY 2017 over the 2010 baselines. Phase 2 standards begin in MY 2021 and achieve 15-27% reduction in CO2 emissions by MY 2027 over the 2017 baselines.
  • Trailers: The standards start in MY 2018 and achieve 6-10% reduction in fuel consumption and CO2 emissions by MY 2027 over the 2017 baselines.
  • Vocational vehicles: Phase 1 engine and vehicle standards start in MY 2014 and achieve up to a 10% reduction in fuel consumption and CO2 emissions by MY 2017 over the 2010 baselines. Phase 2 standards start in MY 2021 and require a 10-18% reduction in CO2 emissions from gasoline vehicles and a 12-24% CO2 emission reduction from diesel vehicles by MY 2027 over the 2017 baselines.
  • Heavy-duty pickup trucks and vans: Phase 1 standards phase-in starting in MY 2014 and achieve up to a 10% reduction in CO2 emissions and fuel consumption for gasoline vehicles and 15% reduction for diesel vehicles by MY 2018. Phase 2 standards require a 16% CO2 emissions reduction from MY 2021 to MY 2027.

The majority of vehicles covered by the regulations carry payloads of goods or equipment, in addition to passengers. To account for this, the standards have been expressed using two types of metrics:

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

Testing & Compliance Determination. 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 SET test,
  • Vocational engines are tested over the FTP transient test.

The Phase 2 regulation introduced a new set of SET weighting factors, applicable only to GHG measurements (not applicable to pollutant emission measurements). The new weighting factors address the trend towards engine downspeeding.

Chassis manufacturers are subject to the vehicle standards. The regulations do not require chassis testing—vehicle standards compliance is typically determined based on a vehicle simulation model, called the Greenhouse gas Emission Model (GEM), developed by the EPA specifically for the GHG/FE regulations. The Phase 2 regulation introduced a number of changes to the GEM model.

Instead of using a chassis dynamometer as an indirect way to evaluate real-world operation and performance, various characteristics of the vehicle are measured and these measurements are used as inputs to the model. These characteristics relate to key technologies applicable to a given truck category—including aerodynamic features, weight reductions, tire rolling resistance, the presence of idle-reducing technology, vehicle speed limiters, and other factors.

CO2 and Fuel Consumption Standards

Combination Tractors

Differentiated standards were adopted for several subcategories of combination tractors based on three attributes: weight class, cab type and roof height. The standards phase in to the 2017 (Phase 1) and 2027 (Phase 2) levels shown in Table 1.

Table 1: Final Phase 1 (2017) and Phase 2 (2027) combination tractor standards
CategoryEPA CO2 EmissionsNHTSA Fuel Consumption
g/ton-milegal/1,000 ton-mile
Low RoofMid RoofHigh RoofLow RoofMid RoofHigh Roof
Final Phase 1 Standards (2017)
Day Cab Class 710411512010.211.311.8
Day Cab Class 88086897.88.48.7
Sleeper Cab Class 86673726.57.27.1
Final Phase 2 Standards (2027)
Day Cab Class 796.2103.4100.09.4499010.157179.82318
Day Cab Class 873.478.075.77.210227.662087.43615
Sleeper Cab Class 864.169.664.36.296666.836946.31631
Heavy-haul Class 848.34.74460

The regulations also define standards for tractors during the phase-in period: for MY 2014, MY 2021 and MY 2024.

In addition to vehicle standards, engine-based standards must be met by heavy-heavy-duty (HHD) and medium-heavy-duty (MHD) diesel engines used in tractors, Table 2.

Table 2: Engine standards for engines installed in tractors (SET cycle)
CategoryYearCO2 EmissionsFuel Consumption*
g/bhp-hrgallon/100 bhp-hr
MHD Engines20145024.93a
HHD Engines20144754.67a
* Equivalent NHTSA standards based on 10,180 g CO2 per gallon of diesel
a Voluntary in MY 2014 and MY 2015.

CO2 emissions are tested on the same engine that is tested for pollutant emissions—typically the highest rated engine within an engine family. While this is the “worst case” rating for meeting pollutant emission standards, it is typically the rating with the lowest specific CO2 emissions within the engine family.


The Phase 2 program introduced a new set of standards to promote the efficiency of commercial trailers. The first trailer standards become effective in MY 2018. The final 2027 standards are shown in Table 3.

Table 3: Final (MY 2027) standards for full-aero box vans
CategoryEPA CO2 EmissionsNHTSA Fuel Consumption
g/ton-milegal/1,000 ton-mile
Dry Van Long75.77.43615
Refrigerated VanLong77.47.60314

The Phase 2 rule also includes CO2/FE standards for partial-aero box vans, as well as design-based standards (tire rolling resistance level and pressure system) for non-box trailers and non-aero box vans. Both sets of standards are phased in over 2018-2021.

Vocational Trucks

At Phase 1, this vehicle segment has been divided into three regulatory subcategories—Light Heavy (Class 2b through 5), Medium Heavy (Class 6 and 7), and Heavy Heavy (Class 8)—which is consistent with engine classifications. At Phase 2, the standards were further differentiated depending on engine type (diesel, gasoline) and the duty cycle: urban, multi-purpose and regional. The final Phase 1 (2017) and Phase 2 (2027) vehicle standards are depicted in Table 4 and Table 5, respectively.

Table 4: Phase 1 final (MY 2017) vocational vehicle standards
CategoryEPA CO2 EmissionsNHTSA Fuel Consumption
g/ton-milegal/1,000 ton-mile
Light Heavy Class 2b-537336.7
Medium Heavy Class 6-722522.1
Heavy Heavy Class 822221.8
Table 5: Phase 2 final (MY 2027) vocational vehicle standards
CategoryEPA CO2 EmissionsNHTSA Fuel Consumption
g/ton-milegal/1,000 ton-mile
Vehicles with CI engines
Light Heavy Class 2b-536733029136.051132.416528.5855
Medium Heavy Class 6-725823521825.343823.084521.4145
Heavy Heavy Class 8 26923018926.424422.593318.5658
Vehicles with SI engines
Light Heavy Class 2b-541337231946.472441.858935.8951
Medium Heavy Class 6-729726824733.419630.156427.7934

Engine standards for light heavy-duty (LHD), medium heavy-duty (MHD), heavy heavy-duty (HHD) diesel engines and for heavy-duty gasoline engines are shown in Table 6.

Table 6: Engine standards for engines installed in vocational vehicles (FTP cycle)
CategoryYearCO2 EmissionsFuel Consumption*
g/bhp-hrgallon/100 bhp-hr
LHD Engines20146005.89a
MHD Engines20146005.89a
HHD Engines20145675.57a
HD Gasoline Engines20166277.06
* Equivalent NHTSA standards based on 10,180 g CO2 per gallon of diesel
a Voluntary in MY 2014 and MY 2015.

Heavy-Duty Pickup Trucks and Vans

The commercial pickup and van category includes those vehicles of GVWR from 8,501 to 14,000 lbs that are not regulated under the light-duty GHG/CAFE vehicle regulations. These vehicles must meet corporate average 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.

The EPA has established CO2 standards in the form of a set of target standard curves, based on a “work factor” that combines a vehicle’s payload, towing capabilities, and whether or not it has 4-wheel drive. The standards phase in with increasing stringency in each model year. 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 (though not including the EPA’s air conditioning leakage standard).

At Phase 1, manufacturers were provided with two alternative phase-in approaches. One alternative phased in the final standards at 15-20-40-60-100 percent in model years 2014-2015-2016-2017-2018. The other phased in the final standards at 15-20-67-67-67-100 percent in model years 2014-2015-2016-2017-2018-2019. Phase 2 standards are phased in over model years 2021-2027.

N2O and CH4 Emission Standards

The regulations introduced emission standards for nitrous oxide and methane:

  • Engine testing (tractors & vocational, both tested over the FTP cycle): N2O = 0.10 g/bhp-hr; CH4 = 0.10 g/bhp-hr
  • Chassis testing (pick-ups and vans, 55% FTP-75 + 45% HFET): N2O = 0.05 g/mi; CH4 = 0.05 g/mi (unlike the CO2 standards, averaging between vehicles is not allowed)

Testing requirements started in MY 2015, consistently with the N2O/CH4 requirements for light-duty vehicles. The standards were designed to cap emissions at the levels circa 2010 to prevent N2O/CH4 emission increases in future engines.

Other Provisions

Flexibilities. The regulations include certain flexibilities for vehicle manufacturers. The Phase 1 rule included optional compliance schedules, with more relaxed standards to be met from 2013, and with identical final standards. At Phase 2, optional sets of CO2 and fuel economy standards are available for some vehicle categories, which use different GEM model inputs.

A/C Leakage. EPA has 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.

Useful Life. The EPA CO2 emissions must be met over the engine’s and vehicle’s useful life. The useful life definitions for engines and for vehicles that use the respective engine categories are identical to those defined for criteria pollutant standards for MY 2004 and later heavy-duty engines and Tier 2 & Tier 3 standards for light-duty vehicles:

  • LHDDE—Phase 1: 110,000 miles/10 years; Phase 2: 150,000 miles/15 years
  • MHDDE—185,000 miles/10 years
  • HHDDE—435,000 miles/10 years