Failing an Emission Test
It varies by state in the U.S., but in general if a vehicle fails the test, then the owner is required to have it repaired. Many places tie the emissions test to the vehicle’s registration, so if the person does not get the required repairs, the registration is not renewed. After the repair, the vehicle is re-tested. If it fails again, the cycle continues until the vehicle passes.
Some states allow an owner to delay further repairs or in some cases, an exemption from future tests if the owner has spent a certain amount of money (like $400) on emissions-related repairs and the car is still failing. Low-income owners may be granted an extension or exemption after spending less than the standard requirement.
Also, some people own “classic cars” that are worth more money when they have all the original parts. Of course, many older models were built before emissions-reduction equipment was invented or included as standard on cars, so these vehicles tend to pollute a lot. Some places, because the value of these cars will go down if the car is altered by adding emissions-reduction equipment, grant the owners an exemption from emissions testing. Compared to the total number of cars on the road in most places, there aren’t that many people driving classic cars, so exempting them from testing doesn’t have a big impact on the clean air effort.