Careful attention should be given when selecting idle emission standards (cutpoints) as this choice will effect several factors of an I/M program. The cutpoints used will determine how many vehicles fail the emission test which in turn will determine the cost of inconvenience to consumers for maintenance as well as the additional capacity needed to reinspect those failed vehicles. With stricter cutpoints, more vehicles will be maintained and the repairs made will result in higher emission reduction benefits. There is also some potential for cutpoints to influence the balance between hydrocarbon and carbon monoxide reductions. Not all I/M prgrams will be in areas requiring reductions of both ozone and CO. Some programs may consider selecting cutpoint which would achieve acceptable emission reduction benefits for only one of these pollutants by failing most or all vehicles for that pollutant (E.G. HC for ozone) while keeping the total number of failed vehicles constant. For all of these reasons, simply adopting another area's cutpoints may not be in the best interest of the I/M program if more effective cutpoints can be found to fulfill the program's emission reduction needs.

Cover title. "January, 1981." "EPA-AA-IMS/81-1."