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