Which Japanese expressway is the longest?

Which Japanese expressway is the longest? The answer is the Tōhoku Expressway.

The Tōhoku Expressway extends about 679.5 kilometres from Kawaguchi in Saitama Prefecture, within the Greater Tokyo Area, to Aomori Interchange in Aomori Prefecture. It is designated E4 and forms the main north–south road link between the Kantō region and northeastern Honshū.

The route passes through or near major cities including Utsunomiya, Fukushima, Sendai, Morioka and Aomori. Much of it parallels National Route 4 and the Tōhoku Shinkansen, although the expressway diverges northwest in northern Iwate and Aomori. It is operated by East Nippon Expressway Company.

People often confuse it with the Tomei Expressway because Tomei is one of Japan’s busiest and best-known routes linking Tokyo and Nagoya. Tomei is important, but it is substantially shorter. The Tōhoku route is six lanes between Kawaguchi and Utsunomiya, then generally four lanes farther north.