Seikan Tunnel, the longest tunnel in the world

In March 13, 1988, the Seikan Tunnel, which connects Hakodate-shi in Hokkaido with Aomori Prefecture in Honshu, was opened to traffic. The length of the tunnel is 53.85 km making it the longest undersea tunnel in the world. The length of the submarine portion is 23.3km.

A design has existed for the Seikan Tunnel (connecting Hakodate-shi in Hokkaido with Aomori Prefecture in Honshu) since the Greater East Asia War. In 1923, Kakuji Abe, a merchant dealing with marine products in Hakodate introduced the idea in the “Great Hakodate Theory” which explored the future of Hakodate.
At the time, there was already a plan to connect the four Japanese Islands by railway called, “Design for a high speed train running throughout Japan”.

In 1946, the plan for the Seikan Tunnel project was pushed forward and a geological survey was started in Honshu and Hokkaido. However, the realization of the huge project was very difficult and continuing a detailed investigation proved impossible in Japan after its defeat in the war.

On September 26, 1954, Typhoon No.15 caused a large-scale sea accident to occur. The Seikan ferry, Toya-maru as well as the Seikan-maru No.11, Kitami-maru, Hidaka-maru and Tokachi-maru sank. 1,430 passengers and crew were killed.
 
Triggered by this large-scale sea disaster, the design of the Seikan Tunnel, connecting Honshu and Hokkaido, was rapidly realized.
On March 23, 1961, the digging of the inclined tunnel in Yoshioka, Hokkaido started .

On March 24, 1967, the digging of the pilot tunnel in Hokkaido was started.

On November 27, 1971, the groundbreaking ceremony for the main tunnel took place.

In May, 1976, the Seikan Tunnel was nearly submerged by an abnormal flood, but overcame the difficulty.

On January 27, 1983, the pilot tunnel went through.

On March 10, 1985, after much difficulty, the main tunnel penetrated.

From the geological survey in April, 1946 to the opening to traffic in March, 1988, the tunnel took 42 years to be fully completed. From the start of construction in 1964 to completion took 24 years.

The construction costs, which included the Seikan Tunnel and the tunnel approaches of the Tsugaru Straits Line, etc., were 689 billion yen. It was the project of the century.