In 1998, NHTSA granted vehicles over 25 years of age dispensation from the rules it administers, since these are presumed to be collector vehicles. However, there are two exceptions to the rule. One is California, where vehicle emissions requirements make it difficult to register a classic vehicle from overseas. (California Smog Check is mandated for automobiles 1976 and newer.) In 21 states, mini trucks (JDM market kei trucks) of any age can be legally imported and registered as a utility vehicle with on-road use and top speed restrictions varying by state, although states that allow mini trucks to be operated on public roads prohibit their operation on Interstate highways.