The reason is the older cars do not have the connection that fits the emission equipment used to check them. At least that is what the letter my mom received said. It told her to leave the paperwork in the vehicle and show it if anyone questions her.
Perhaps, I am missing something. That does not make sense to me. Aren't the newer cars safer and produce less emissions than older cars?
Newer cars have diagnostic equipment onboard that continuously tests for emissions and will light up your check engine light if there's a problem. That's why inspections on modern cars are so quick - they plug in their computer, check the data in the car, and you're on your way.
Older cars (pre-1995) didn't have the tech (OBD2) to do that so they're exempt since I guess allowing people to potentially drive unsafe vehicles (because they don't even do any safety checks to see if your brakes work, that you don't have bald tires, cracked windshields, etc.) or that belch pollution is cheaper than having more employees and longer lines at the inspection stations.