Japan has a nationwide system of national highways distinct from the expressways. The Ministry of Land, Infrastructure, Transport and Tourism and other government agencies administer the national highways. Beginning in 1952, Japan classified these as Class 1 or Class 2. Class 1 highways had one- or two-digit numbers, while Class 2 highways had three-digit numbers. For example, routes 1 and 57 were Class 1 highways while 507 was a Class 2 highway.

National Route 6 is a Japanese highway from Tokyo to Sendai that goes through the cities Mito, Iwaki and Sōma. It traces the old Mito Kaidō route from Tokyo to Mito, and, for much of its 353.6-kilometer (219.7 mi) route, it runs parallel to the Jōban railway line and the Jōban Expressway.