California: Heavy-duty: Emissions

California: Heavy-duty: Emissions

Overview

Although California’s emissions standards for heavy-duty vehicles align with federal U.S. standards, California recently imposed its own regulations, including additional testing, stricter emissions limits for public buses, and optional heightened NOx standards for heavy-duty vehicles (HDVs).

Standard type
Conventional pollutant emission limits

Applicability
Vehicles with gross vehicle weight rating (GVWR) > 10,000 lbs.

History

In 2004, federal emission standards for heavy-duty vehicles were harmonized with California standards, with the intent for manufacturers to use a single engine and/or machine design for both markets. However, California certifications for model years (MY) 2005–2007 require additional SET testing beyond federal requirements, and NTE limits of 1.25 × FTP standards. California also adopted more stringent standards for MY 2004–2006 engines for public urban bus fleets.

In December 2021, the California Air Resources Board (CARB) adopted a new Heavy-Duty Engine and Vehicle Omnibus Regulation and associated amendments that update standards, testing, and compliance mechanisms for nitrogen oxide (NOx) and particulate matter (PM) emissions from on-road heavy-duty vehicles for model years (MY) 2024 through 2031.

Technical standards

Model years 1987–2003

MY 1987–2003 California emission standards for heavy-duty diesel truck and bus engines are summarized in the following table. Applicable from 1994­ to 2006, sulfur content in the certification fuel was reduced to 500 ppm weight percent (wt).

California emission standards for heavy-duty diesel engines, g/bhp·hr
Year NMHC THC CO NOx PM
Heavy-duty diesel truck engines
1987 1.3 15.5 6.0 0.60
1991 1.2 1.3 15.5 5.0 0.25
1994 1.2 1.3 15.5 5.0 0.10
Urban bus engines
1991 1.2 1.3 15.5 5.0 0.10
1994 1.2 1.3 15.5 5.0 0.07
1996 1.2 1.3 15.5 4.0 0.05

Useful life and warranty periods: Compliance with emission standards must be demonstrated over the useful life of the engine. The regulation was adopted as follows, for both U.S. and California:

  • LHDDE: 8 years or 110,000 miles (whichever occurs first)
  • MHDDE: 8 years or 185,000 miles
  • HHDDE: 8 years or 290,000 miles

Applicable federal standards: Federal useful life requirements were later increased to 10 years, with no change to the above mileage numbers for the urban bus PM standard (1994–present) and for the NOx standard (1998–present). The emission warranty period is 5 years or 100,000 miles (5 years or 100,000 miles and/or 3,000 hours in California), but no less than the basic mechanical warranty for the engine family.

Consent Decrees: In 1998, a court settlement was reached between the Environmental Protection Agency (EPA), Department of Justice, CARB, and engine manufacturers (Caterpillar, Cummins, Detroit Diesel, Volvo, Mack Trucks/Renault and Navistar) over the issue of high NOx emissions from heavy-duty diesel engines during certain driving modes. Since the early 1990s, the manufacturers used engine control software that caused engines to switch to a more fuel efficient (but higher NOx) driving mode during steady highway cruising. EPA considered this engine control strategy an illegal “emission defeat device.”

Provisions of the Consent Decree included the following:

  • Civil penalties for engine manufacturers and requirements to allocate funds for pollution research
  • Upgrading existing engines to lower NOx emissions
  • Supplemental Emission Test (steady state) with a limit equal to the federal test procedure (FTP) standard and NTE limits of 1.25 × FTP (with the exception of Navistar)
  • Meeting the 2004 emission standards by October 2002, 15 months ahead of time

Clean Fuel Fleet Program: The Voluntary Clean Fuel Fleet (CFF) program was a federal standard that applied to 1998–2003 MY engines, both CI and SI, > 8,500 lbs. GVWR. In addition to the CFF standard, vehicles must have met applicable conventional standards for other pollutants.

Clean Fuel Fleet Program for Heavy-Duty SI and CI Engines, g/bhp·hr
Categorya CO NMHC+NOx PM HCHO
LEV (Federal Fuel) 3.8
LEV (California Fuel) 3.5
ILEV 14.4 2.5   0.050
ULEV 7.2 2.5 0.05 0.025
ZLEV 0 0 0 0
a LEV — low-emission vehicle; ILEV — inherently low-emission vehicle; ULEV — ultralow-emission vehicle; ZEV — zero-emission vehicle

Model years 2004 and later

In 2004, EPA signed emission standards for MY 2007 and later heavy-duty highway engines (CARB adopted virtually identical 2007 heavy-duty engine standards in 2001). The rule included emission standards and diesel fuel regulations. For additional information on heavy-duty emissions, see the US Heavy-duty Emissions page.

Optional NOx standards (THROUGH MY 2023)

In 2013, CARB adopted an optional low-NOx standard for on-road heavy-duty engines. In this program, manufacturers can voluntarily opt to certify their engines at levels below the 0.2 grams per horsepower-hour federal standard, which has been in place since 2010. There are three levels of certification: 0.1 g/hp-hr, 0.05 g/hp-hr, and 0.02 g/hp-hr, which correspond to reductions below the current federal standard of 50%, 75%, and 90%, respectively. A significant number of engines are certified well below the 0.2 g/hp-hr limit, which gives the ARB confidence that the optional NOx levels are achievable targets in the near-term.

With this optional NOx standard, engines that are certified below the standard could utilize incentive efforts such as the Carl Moyer Program , which provides funding for vehicles and equipment that provide emission benefits beyond what is required by regulation.

MY 2024 and beyond

In December of 2021, CARB adopted a new Heavy-Duty Engine and Vehicle Omnibus Regulation to mandate NOx standards. This regulation phases in more stringent emissions standards starting in MY 2024 and updates them again in MY 2027 to achieve a 90 percent reduction in NOx emissions by 2031. These changes will lead to an estimated 30% overall fleet-wide reduction in heavy-duty NOx. Emissions by 2050. Although CARB and the EPA have historically harmonized standards and new regulations concerning heavy-duty vehicles, CARB’s proposal was released before the EPA announced updates of the continuation of the Advanced Noticed of Proposed Rulemaking for the Cleaner Trucks Initiative. . The standards are more stringent than previous national-level regulations but are weaker than those imposed by the CARB rule.

This adopted regulation also enumerates new testing procedures starting with MY 2024, replacing the NTE (Not-to-Exceed) method with one of two options (manufacturer’s choice): a 3-bin moving average window (3B-MAW) method (described in section 86.1370.B.6), or a ramped modal cycle (RMC) which combines multiple test modes into a single test (described in section 86.1362 of U.S. EPA’s Improvements for Heavy-Duty Engine and Vehicle Test Procedures, and Other Technical Amendments). The 3-bin moving average window test sorts windows into three bins based on the CO2 output during the testing window normalized to the Family Certification Level (FCL) of the engine family, which is the CO2 emission rate at the maximum power output. The normalized rate is sorted into idle, low-load, and medium to high load windows which are compared to the FTP limit. Every window will need to fall below 2 times the limit for the corresponding cycle from 2024 to 2029 and 1.5 times the limit starting in 2030.

For Otto engines, windows will not be binned by CO2 emissions, and all will be compared to the FTP emissions limit.

Emissions standards

Exhaust emission standards (g/bhp-hr) for light, medium, and heavy heavy-duty engines are the same from MY 2024 to MY 2026:

Exhaust emission standards for light, medium, and heavy heavy-duty vehicles MY 2024–2026 (g/bhp-hr)
Test Procedure NOx NMHC CO PM
FTP cycle 0.050 0.14 15.5 0.005
RMC cycle 0.050 0.14 15.5 0.005
Low-load cycle 0.200 0.14 15.5 0.005

Light and medium heavy-duty vehicles have the same exhaust emissions standards (g/bhp-hr) for MY 2027 and subsequent models:

Light and medium heavy-duty vehicle emission standards for MY 2027 and beyond (g/bhp-hr)
Test Procedure NOx NMHC CO PM
FTP cycle 0.020 0.14 15.5 0.005
RMC cycle 0.020 0.14 15.5 0.005
Low-load cycle 0.050 0.14 15.5 0.005

Heavy heavy-duty vehicles have an additional phase-in period from MY 2027 to 2030 before final standards are set starting in MY 2031. The MY 2031 NOx standards are slightly less stringent to account for the longer useful life that comes into effect for MY 2031:

Exhaust emission standards for MY 2027–2030 heavy heavy-duty engines (g/bhp-hr)
Test procedure Intermediate useful life oxides of nitrogen NOx NMHC CO PM
FTP cycle 0.020 0.035 0.14 15.5 0.005
RMC cycle 0.020 0.035 0.14 15.5 0.005
Low-load cycle 0.050 0.090 0.14 15.5 0.005
Exhaust emission standards for MY 2031 and subsequent heavy heavy-duty engines (g/bhp-hr)
Test procedure Intermediate useful life oxides of nitrogen NOx NMHC CO PM
FTP cycle 0.020 0.040 0.14 15.5 0.005
RMC cycle 0.020 0.040 0.14 15.5 0.005
Low-load cycle 0.050 0.100 0.14 15.5 0.005

Under the updated regulation, heavy-duty engines must comply with emission standards for the duration of their useful life. The useful life requirements will increase as model years advance, and as technological advancements make longer useful lifetimes feasible. The next phases are shown below for light, medium, and heavy heavy-duty diesel vehicles and heavy-duty Otto vehicles. The useful life periods are tracked in terms of miles, years, or hours—whichever metric comes first.

Useful life periods for light, medium, and heavy heavy-duty diesel and heavy-duty Otto vehicles
Model year Useful life (miles)
LHDD MHDD HHDD HDO
Current–2026

110,000 miles

or

10 years

185,000 miles

or

10 years

435,000 miles

or

10 years

or 

22,000 hours

110,000 miles

or

10 years

2027–2030

190,000 miles

or

12 years

270,000 miles

or

11 years

600,000 miles

or

11 years

or

30,000 hours

155,000 miles

or

12 years

2031 and subsequent

270,000 miles

or

15 years

350,000 miles

or

12 years

800,000 miles

or

12 years

or

40,000 hours

200,000 miles

or

15 years

AVERAGING, BANKING, AND TRADING

CARB’s Low NOx Omnibus regulation proposal has also specified California provisions for averaging, banking, and trading credits to increase flexibility of meeting the new standards. Manufacturers may participate in California’s ABT program starting with MY 2022 vehicles, but all manufacturers are required to enroll in the program beginning with MY 2024 vehicles.

A fraction of federal credits generated through the federal ABT program from MY 2010 through MY 2021 may be transferred to the CA program only for MY 2022.

CA ABT credits may only be used up to five model years after the year the credits were generated, except for credits generated by zero-emission vehicles. For zero-emission vehicles, credits are available from MY 2022 through MY 2026. Starting in MY 2027, banked zero-emission credits will no longer be available.

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