In 1992, to cope with NOx pollution problems from existing vehicle fleets in highly populated metropolitan areas, the Ministry of the Environment adopted the "()", called in short The Motor Vehicle NOx Law. The regulation designated a total of 196 communities in the Tokyo, Saitama, Kanagawa, Osaka and Hyogo Prefectures as areas with significant air pollution due to nitrogen oxides emitted from motor vehicles. Under the Law, several measures had to be taken to control NOx from in-use vehicles, including enforcing emission standards for specified vehicle categories.