For example, by expanding the ranking information used, states can fine-tune their profiling. Credit losses increase quickly when the exemption fraction is higher than 50 percent. This, however, is also dependent on the specific profiling utilized by the state. The draft guidance contains a special note regarding the preliminary and evolving nature of the estimates of credit losses with low emitter profiling. This approach exempts cars until they reach a certain age, on the premise that virtually all cars are clean when sold and most remain clean for at least several years.
Many states now wait until a car is four or five years old before the first required inspection.
Some give the owner the option of inspection during these years. It is the state's choice whether to assess a program fee on new cars while they are exempt from testing. EPA recommends that states exempt cars from testing until they are at least four years old. States with a simple system of scheduling inspections on the anniversary of a new vehicle sales date should have no difficulty analyzing scenarios for themselves. Overall, the loss of credit for exempting the four newest model years is quite small, and EPA believes most states can find ways to compensate for it if needed to keep the SIP approvable.