US emission standard

In the United States, emissions standards are managed nationally by the Environmental Protection Agency (EPA). State and local governments may apply for waivers to enact stricter regulations.

Due to its preexisting standards and particularly severe motor vehicle air pollution problems in the Los Angeles metropolitan area, the U.S. state of California has special dispensation from the federal government to promulgate its own automobile emissions standards. Other states may choose to follow either the national standard or the stricter California standards. States adopting the California standards include Arizona (2012 model year),Connecticut, Maine, Maryland, Massachusetts, New Jersey, New Mexico (2011 model year), New York, Oregon, Pennsylvania, Rhode Island, Vermont, and Washington, as well as the District of Columbia. Such states are frequently referred to as "CARB states" in automotive discussions because the regulations are defined by the California Air Resources Board.

The EPA has adopted the California emissions standards as a national standard by the 2016 model year and is collaborating with California regulators on stricter national emissions standards for model years 2017–2025.

Light-duty vehicles are certified for compliance with emission standards by measuring their tailpipe emissions during rigorously-defined driving cycles that simulate a typical driving pattern. The FTP-75 city driving test (averaging about 21 MPH) and the HWFET highway driving test (averaging about 48 MPH) are used for measuring both emissions and fuel economy.

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