It's all a matter of enforcement and who is responsible for it. Most PD don't know and don't care to, but don't let CHP or DOT officer under your hood. Even though you don't have to go smog your truck every other year, can still be wrote up for not having the proper federally mandated equipment. So the next time you get pulled over for speeding, be nice, take your ticket and say thank you. You don't want to piss 'em off if you don't have your smog equipment hooked up and he decides to check.