In addition, since the maintenance cost is large, such as the need to pump a large amount of spring water even after completion, even a huge investment is regarded as a sunk cost, and it is said that it is more economical to abandon it, and it was ridiculed variously as "Showa's Three Idiots Assessment", "useless long things", and "quagmire tunnel".

[7] The tunnel plan was handed over to the Japanese National Railway in 1946 with preliminary geological surveys and feasibility studies,[7] 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.

[13] 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[8][14] by detonating a dynamite charge on the last few meters of the earth.

[14] The tunnel was opened on 13 March 1988,[11] 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.

[11] Similarly, the commuter ferry service between the two islands[9] run by Japanese National Railway[18] had also ended.

Deregulation and competition in Japanese domestic air travel has brought down prices on the Tokyo-Sapporo route, making rail more expensive in comparison.

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.

Initial surveys undertaken in 1946 indicated that the eastern neck was up to 200 metres (656 feet) deep with volcanic geology.

The western neck had a maximum depth of 140 metres (459 feet) and geology consisting mostly of sedimentary rocks of the Neogene period.

[28] The area is folded into a nearly vertical syncline, which means that the youngest rock is in the centre of the strait and encountered last.

To establish a greater understanding, a horizontal pilot boring was undertaken along the line of the service and main tunnels.

[27] Beneath the Tsugaru Strait, the use of a tunnel boring machine (TBM) was abandoned after less than two kilometres (1.2 miles) owing to the variable nature of the rock and difficulty in accessing the face for advanced grouting.

A 2002 report by Michitsugu Ikuma described, for the undersea section, that "the tunnel structure appears to remain in a good condition.

The effectiveness of the escape shafts at the emergency stations is enhanced by having exhaust fans to extract smoke, television cameras to help route passengers to safety, thermal (infrared) fire alarm systems, and water spray nozzles.

[26] Before the construction of the Hokkaido Shinkansen, both stations contained museums detailing the history and function of the tunnel that could be visited on special sightseeing tours.