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U.S. EPA Standards

The US Environmental Protection Agency was established to study and set federal standards for a variety of environmental programs, including vehicle emissions regulation.

EPA's Office of Transportation and Air Quality (OTAQ) is responsible for controlling air pollution from motor vehicles and fuels. Where federal standards are not met, EPA can issue sanctions and take further steps to assist the states in reaching recommended levels.

Vehicle emissions regulation in the US began with the passage of the Clean Air Act of 1970. This was amended in 1977, which tightened standards for the first time.

In 1990, the CAA was amended again, mandating even tighter emissions standards called "Tier 1." While the 1990 amendment prevents EPA from tightening federal standards until 2004, it gave the agency time to study and develop "Tier 2" standards.

In 1998, EPA submitted its recommendation to Congress for the Tier 2 tailpipe emissions standards, which will take effect in 2004.

Note: The state of California was granted by the CAA autonomy in formulating and implementing its own emission standards, which are set by the California Air Resources Board. To date, California has the most stringent measures for regulating emission standards in the US (e.g. LEV, ZEV).

List of current US emissions standards

  • Tier 1 - current federal standard

  • Tier 1-D - current federal diesel standard

  • HDT - Heavy Duty Truck

  • TLEV - Transitional Low Emission Vehicle (California)

  • LEV - Low Emission Vehicle (California)

  • ULEV - Ultra Low Emission Vehicle (California)

  • SULEV - Super Ultra Low Emission Vehicle (California)

  • ZEV - Zero Emission Vehicle (California)

Go to the BAQ 2004 website
Vehicular air pollution > Emissions standards

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