Actually, California has the second toughest in the world, if only because Japan doesn't allow changes in emissions as the vehicles get older.  Yes, that's right - a ten year old Camry has to pass 2008 specs or else you have to buy a 2008 engine.  Joy.

That because Japan has their whole economic structure for automobiles designed around recycling them after a few years.   The personal property tax on a car also increases as it gets older in Japan instead of decreasing like is does here.   The Japanese governemt also gives tax incentives to buy a new car.   That's also why you see so many low mileaged JDM(Japanese Domestic Market) engines available here in the US.