[panglott]

California is known for having the toughest regulations in this area.

Kentucky had a limited emissions inspection regime from 1999-2005, when it was killed by the Republican governor. The only current inspection requirement I know of is if you purchase an out-of-state used vehicle. We have plenty of ancient cars on the road that have never been inspected.

Sometimes police officers will pull you over if you have obviously-broken headlights or such, and tell you to fix it, but not often.

[maxerickson]

Wikipedia has a decent article about where in the US emissions testing is required:

en.wikipedia.org/wiki/Vehicle_inspection_in_the_United_States