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Emission Standards » United States

Heavy-Duty Vehicles: GHG Emissions & Fuel Economy


The first US GHG emission and fuel consumption standards for heavy- and medium-duty vehicles were adopted on August 9, 2011 [2324]. The rule was 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 regulation covers model years (MY) 2014-2018, with NHTSA fuel economy standards being voluntary in MY 2014-2015 to satisfy EISA lead time requirements. The affected heavy- and medium-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 MY 2012-2016 light-duty vehicles.

Different CO2 and fuel consumption standards are applicable to three categories of vehicles: combination tractors, heavy-duty pickups and vans, and vocational vehicles:

  • For combination tractors (the semi trucks that typically pull trailers), the adopted engine and vehicle standards begin in MY 2014 and achieve from 7 to 20% reduction in CO2 emissions and fuel consumption by MY 2017 over the 2010 baselines.
  • For heavy-duty pickup trucks and vans, the 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.
  • For vocational vehicles, the engine and vehicle standards start in MY 2014 and achieve up to a 10% reduction in fuel consumption and CO2 emissions by MY 2017.

The majority of 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 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.

The regulatory documents, fact sheets, and other supporting information can be found in the US EPA climate change website [2918].

CO2 and Fuel Consumption Standards

Combination Tractors. Differentiated standards were adopted for nine subcategories of combination tractors based on three attributes: weight class, cab type and roof height. The standards would phase in to the 2017 levels shown in Table 1.

Table 1: Final (MY 2017) Combination Tractor Standards
Category EPA CO2 Emissions NHTSA Fuel Consumption
g/ton-mile gal/1,000 ton-mile
Low Roof Mid Roof High Roof Low Roof Mid Roof High Roof
Day Cab Class 7 104 115 120 10.2 11.3 11.8
Day Cab Class 8 80 86 89 7.8 8.4 8.7
Sleeper Cab Class 8 66 73 72 6.5 7.2 7.1

The regulation also defines two sets of standards for tractors during the phase-in period: (1) MY 2014 CO2 standards and (2) MY 2014-2016 fuel consumption standards. Manufacturers may voluntarily opt-in to the NHTSA fuel consumption program in 2014 or 2015. Once a manufacturer opts into the NHTSA program it must stay in the program for all the optional MYs.

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 combination tractors, Table 2 (MY 2014 fuel consumption standards are voluntary).

Table 2: Engine Standards for Engines Installed in Tractors
CategoryYearCO2 EmissionsFuel Consumption
g/bhp-hrgallon/100 bhp-hr
MHD Engines20145024.93
HHD Engines20144754.67

An optional compliance schedule is available, with more relaxed tractor engine standards to be met from 2013 and numerically identical final standards to be met from 2016.

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.

Heavy-Duty Pickup Trucks and Vans. 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.

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 will phase in with increasing stringency in each model year from 2014 to 2018. 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).

Both agencies are providing manufacturers with two alternative phase-in approaches. One alternative 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 model years 2014-2015-2016-2017-2018-2019.

Vocational Trucks. 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. The respective vehicle standards are depicted in Table 3.

Table 3: Final (MY 2017) Vocational Vehicle Standards
Category EPA CO2 Emissions NHTSA Fuel Consumption
g/ton-mile gal/1,000 ton-mile
Light Heavy Class 2b-5 373 36.7
Medium Heavy Class 6-7 225 22.1
Heavy Heavy Class 8 222 21.8

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 4 (MY 2014-2016 diesel fuel consumption standards are voluntary).

Table 4: Engine Standards for Engines Installed in Vocational Vehicles
CategoryYearCO2 EmissionsFuel Consumption
g/bhp-hrgallon/100 bhp-hr
LHD Engines20146005.89
MHD Engines20146005.89
HHD Engines20145675.57
HH Gasoline Engines20166277.06

An optional compliance schedule is available for vocational engines, structured in a similar way to that for tractor engines.

Testing. 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.

Chassis manufacturers are subject to the vehicle standards. Vehicle standards compliance is typically determined based on a customized, sophisticated vehicle simulation model, called the Greenhouse gas Emission Model (GEM), developed by EPA specifically for this regulation. The regulation does not require chassis testing due to the large variety of vehicle configurations and the scarcity of heavy-duty chassis test facilities.

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.

Other Standards and Provisions

N2O and CH4 Standards. The regulation introduces 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 & HFET): N2O = 0.05 g/mi; CH4 = 0.05 g/mi

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

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:

  • LHDDE—110,000 miles/10 years
  • MHDDE—185,000 miles/10 years
  • HHDDE—435,000 miles/10 years