The federal Clean Air Act provides the regulatory framework and standards for air quality. This framework is then adopted and modified by states through state implementation plans, or “SIPs.” As a result, many states require that cars of a certain vintage be tested as a means of achieving SIP goals for ambient air-quality standards. There is a profound inconsistency among the states in the treatment of historic vehicles and the enforcement of exemptions where they exist. For many owners, keeping a 20-year-old vehicle in “like-new” operating condition is prohibitively expensive.
This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/articles/2010/06/28/top-7-issues-for-the-historic-vehicle-association