An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Green Vehicle Guide

The Road to Cleaner Cars… (Text Only)

See: Infographic version of this information

1970: Clean Air Act (CAA) passed; emission standards set for cars and light-duty truck

1975: Emission Standards Take Effect

1979: Congress amends the CAA and passes more stringent standards

1981: Congress further tightens standards

1990: CAA amended again; Tier 1 standards set

1994: Tier 1 Standards Take Effect

2000: Tier 2 standards set; cars and light trucks now held to same standards

2004: Tier 2 Standards Fully Take Effect

2014: Tier 3 standards set

2017: Tier 3 Standards begin phase-in

2025: Tier 3 Standards Fully Take Effect