Location of the Tsugaru Strait in Japan
Connecting the islands Honshu and Hokkaido by a fixed link had been considered since the Taishō period (1912–1925), but serious surveying commenced only in 1946, induced by the loss of overseas territory at the end of World War II and the need to accommodate returnees. In 1954, five ferries, including the Tōya Maru, sank in the Tsugaru Strait during a typhoon, killing 1,430 passengers. The following year, Japanese National Railways (JNR) expedited the tunnel investigation. Also of concern was the increasing traffic between the two islands. A booming economy saw traffic levels on the JNR-operated Seikan Ferry double to 4,040,000 passengers/year from 1955 to 1965, and cargo levels rose 1.7 times to 6,240,000 tonnes/year. Inter-island traffic forecast projections made in 1971 predicted increasing growth that would eventually 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. Arduous construction in difficult geological conditions proceeded. Thirty-four workers were killed during construction. On 27 January 1983, Japanese Prime Minister Yasuhiro Nakasone pressed a switch that set off a blast that completed the pilot tunnel. Similarly on 10 March 1985, Minister of Transport Tokuo Yamashita symbolically bored through the main tunnel.
The necessity for the project was questioned at times during construction, as the 1971 traffic predictions were overestimates. Instead of the traffic rate increasing as predicted to a peak in 1985, it peaked earlier in 1978 and then proceeded to decrease. The decrease was attributed to the slowdown in Japan's economy since the first oil crisis in 1973 and to advances made in air transport facilities and longer-range sea transport.
The tunnel was opened on 13 March 1988, having cost a total of ¥1.1 trillion (US$7 billion) to construct, almost 12 times the original budget, much of which was due to inflation over the years. Once the tunnel was completed, all railway transport between Honshu and Hokkaido used it. However, for passenger transport, 90% of people use air travel due to the speed and cost. For example, to travel between Tokyo and Sapporo by train takes eight hours (Tokyo station and Shin-Sapporo station), with transfer from Shinkansen to narrow-gauge express train at Hakodate. By air, the journey is three hours and thirty minutes, including airport access times. Deregulation and competition in Japanese domestic air travel has brought down prices on the Tokyo-Sapporo route, making rail more expensive in comparison.
The Hokutosei overnight train service began after the completion of the Seikan Tunnel, and a later and more luxurious Cassiopeia overnight train service was often fully booked. Both were withdrawn following the commencement of Hokkaido Shinkansen services in March 2016, with freight trains being the only regular service utilising the narrow gauge line since that time. JR Hokkaido is exploring the use of "Train on Train" technology to remove the threat that the shock wave created in front of Shinkansen trains traveling at full speed pose to freight trains operating on Japanese standard narrow-gauge track in a tunnel setting. If successful, it will allow the Hokkaido Shinkansen to travel at full speed inside the tunnel in the future.
Shinkansen trains operate through the tunnel to Shin-Hakodate-Hokuto Station in Hakodate, connecting Tokyo and Shin-Hakodate-Hokuto stations in four hours and two minutes, at a maximum speed of 140 km/h (85 mph) within the tunnel and 260 km/h (160 mph) outside it, and 320 km/h (200 mph) to the south of Morioka. It is expected that by 2018 one daily service will be run at 260 km/h (160 mph) through the tunnel. The final stage is proposed to open to Sapporo Station in 2031 and is expected to shorten the Tokyo-Sapporo rail journey to five hours. The Hokkaido Shinkansen will be operated by JR Hokkaido.
- 24 April 1946: Geological surveying begins.
- 26 September 1954: The train ferry Tōya Maru sinks in the Tsugaru Strait.
- 23 March 1964: Japan Railway Construction Public Corporation is established.
- 28 September 1971: Construction on the main tunnel begins.
- 27 January 1983: Pilot tunnel breakthrough.
- 10 March 1985: Main tunnel breakthrough.
- 13 March 1988: The tunnel opens.
- 26 March 2016: Shinkansen services commence operation through the tunnel, regular narrow gauge passenger services through the tunnel cease.