Of course, if you're building a kit car or rebuilding a salvaged car or any number of edge cases, BAR has to certify the vehicle, but for a "normal" car you can get away with almost anything. Bald tires, no seatbelts, windshield wipers falling off, glass smashed up all to hell, wheel bearing so shot it looks like you're driving a paint shaker.
Granted, it's illegal and you could get a ticket for it, but you'll see plenty of smashed up cars with no headlights or bumpers or whatever driving around on the roads in CA. It's just a matter of not running across a police officer who feels like spending the time to ticket you for blatantly illegal (lack of) equipment.
I met a guy at the La Jolla Concours d'Elegance who had imported an ('82?) Trabant. He had gotten it registered with the CA license plate "IRNCRTN". Apparently, Cal DMV saw that it was over twenty-five years old, gave him an exception and the plates, and then demanded that he have it smogged.
A two-stroke Trabant.
I believe he showed the DMV the bottle of oil that he poured into the gas tank after every fillup, and asked them if there was a smog check place willing to hook what is essentially an old lawnmower up to their million-dollar diagnostic apparatus. This seemed to work.
My understanding is that they can't test for NOx without rollers and the smog shops couldn't afford it.
In any case, you'd end up with cases where cars put together by show judges couldn't pass because it didn't match some book. A lot of cars used to have to have crazy gadgets that interfered with spark advance.
All for pass or not pass.
Truth is, I'll bet you could drop the whole system and not see a change in air quality at this point. Super-dirty early cars get a bye (aircooled VW) and late model are rarely modified or worn out. If you feel the need to test, do a good job and then simply charge for the amount of emissions that come out.
I have the feeling that the emissions industry has metastasized into a political power. Not unlike car dealerships.
regarding Kei cars/trucks, my working theory is that most of the objections are safety related. Lots of DOT standards that the rest of the world ignores. Oddly, motorcycles are perfectly legal.
That’s basically what happened in Ontario Canada. They dropped the program because it wasn’t providing any value. New cars would maintain good emissions control for 10 years and beyond that, salt does a good job of destroying cars anyway.
CO2 is a different story with pickups and SUVs. Ultimately, it’s how much you drive and how you drive, and that’s better addressed with gas taxes.