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Emission Standards » United States

Cars and Light-Duty Trucks

Federal Standards (US EPA)

The most recent emission standards for light-duty vehicles are the Tier 3 standards, that follow the earlier Tier 2, Tier 1, and pre-Tier 1 federal emission regulations.

Two sets of standards had been defined for light-duty vehicles in the Clean Air Act Amendments (CAAA) of 1990: Tier 1 and Tier 2 standards. Once Tier 2 standards were fully phased-in, the EPA adopted the Tier 3 emission regulations. The succession of these regulations can be summarized as follows:

  • Tier 1 standards were published as a final rule on June 5, 1991 and phased-in progressively between 1994 and 1997.
  • Tier 2 standards were adopted on December 21, 1999, with a phase-in implementation schedule from 2004 to 2009.
  • Tier 3 standards were finalized on March 3, 2014, to be phased-in between 2017 and 2025.

Tier 1 standards applied to all new light-duty vehicles (LDV) of less than 8500 lb gross vehicle weight rating (GVWR). The Tier 2 rule extended the applicability of the light-duty emission standards to medium-duty passenger vehicles (MDPV) with GVWR between 8500 and 10,000 lbs. Tier 3 regulations additionally include emission standards for chassis-certified heavy-duty vehicles up to 14,000 lbs (Class 2b and Class 3).

The successive tiers of emission regulations do not begin with a sharp cut-off date. Rather, each new tier of emission standards is phased-in over a number of years. During the phase-in period, manufacturers are required to certify an increasing percentage of their new vehicle fleet to the new standards, with the remaining vehicles still certified to the preceding tier of emission regulations.

The US emission standards establish (a set of) certification emission limits applicable to each certified vehicle, as well as fleet average standards. The fleet average standards—for NOx at the Tier 1 and Tier 2 stages and for NMOG+NOx at Tier 3—distinguish the US emission regulations from other light-duty emission standards for criteria pollutants across the world, which typically include only certification/type approval limits.

California Standards (ARB)

California emission regulations for light duty vehicles are designated Low Emission Vehicle (LEV) standards. The succession of California standards—including the LEV I, LEV II and LEV III stages—has closely followed (or, more accurately, preceded) the respective federal standards.

The California standards have been mores stringent than the federal ones. The tendency, however, has been that of increasing harmonization—the federal Tier 3 regulations are closely aligned with California LEV III standards.

California standards were adopted by a number of other states who needed emission standards more stringent than the federal regulations—especially at the LEV II stage. States that adopted California Clean Car Standards—including the California LEV II and GHG emission standards—are listed in the following table.

Table 1
States adopting California LEV II clean cars standards
StateLegislationYear AdoptedMY Effective*
New JerseyP.L. 2003, Chapter 26620042009
ConnecticutPublic Act 04-8420042008
WashingtonHouse Bill 139720052009
VermontAmendments to Subchapter XI20052009
New YorkChapter III, Subpart 218-820052009
MaineAmendments to Chapter 12720052009
Rhode IslandAir Pollution Control Regulation No. 3720052009
MassachusettsAmendments to the state’s LEV regulations20052009
OregonDivision 257; OAR 340-256-0220; Division 1220062009
ArizonaExecutive Order 2006-1320062011
PennsylvaniaAmendments to Title 25, Chapters 121 and 12620062008
MarylandSenate Bill 10320072011
Florida†Executive Order 07-1272007
New MexicoExecutive Order 2006-6920072016
* Generally refers to GHG standards, LEV II standards became effective earlier in some states
† Pending ratification by the Legislature

Source: Maryland Department of The Environment, 2007