Light-duty vehicles

This section provides an overview of the key aspects of criteria emission standards applicable to recent emissions regimes, namely Tier 1, Tier 2 and Tier 3.

Emissions standards for light-duty vehicles (LDVs) in the U.S. - both those applicable federally and to the state of California - have a long history and have undergone several updates over the years. Under the Clean Air Act of 1970, California was allowed to devise its own air quality and emissions standards, provided that they were at least as stringent as federal standards. The state has consistently availed itself of this authority in developing standards stricter than those applicable federally. Other states interested in following California’s lead (13 in total: Colorado, Connecticut, Delaware, Maine, M