The
Seikan Tunnel (??????
Seikan Tonneru or ????
Seikan Zuido) is a 53.85&_160;km (33.46&_160;mi)
railway tunnel in
Japan, with a 23.3-kilometre (14.5&_160;mi) long portion under the seabed. Track level is about 140-metre (460&_160;ft) below seabed and 240-metre (790&_160;ft) below sea level
[1]. It is the longest undersea tunnel in the world, although the
Channel Tunnel between the United Kingdom and France has a longer under-sea portion. It travels beneath the
Tsugaru Strait — connecting
Aomori Prefecture on the Japanese island of
Honshu and the island of
Hokkaido — as part of the
Kaikyo Line of
Hokkaido Railway Company. Although it is the longest traffic (railway or road) tunnel in the world, faster and cheaper air travel has left the Seikan Tunnel comparatively underused. Its claim to the record for the longest tunnel will be taken when the
Gotthard Base Tunnel, a European railway tunnel, is completed in around 2018. It is also the deepest rail tunnel in the world.
[2]Connecting the islands of Honshu and Hokkaido by a fixed link had been considered since the Taisho period (1912–1925), but serious survey only commenced in 1946, due to the loss of overseas territory at the end of World War II and the need to accommodate returnees. In 1954, five ferries, including the Toya Maru, sank in the Tsugaru Strait during a typhoon, killing 1,430 passengers. The following year the Japanese National Railways (JNR) expedited the tunnel investigation.[3]
Also of concern was the increasing traffic between the two islands. A booming economy saw traffic levels on the JNR-operated Seikan (a contraction of principal cities Aomori and Hakodate[4]) Ferry doubled to 4,040,000 persons/year from 1955 to 1965, and cargo levels rose 1.7 times to 6,240,000 tonnes/year. In 1971, traffic forecasts predicted increasing growth that would outstrip the ability of the ferry pier facility, which was constrained by geographical conditions. In September 1971, the decision was made to commence work on the tunnel. A Shinkansen-capable cross section was selected, with plans to extend the Shinkansen network.[3]
Arduous construction in difficult geological conditions proceeded. 34 workers were killed during construction.[5]
