The means of transportation from Hokkaido to Honshu was the Seikan ship until Seikan tunnel was completed. It took about 3 hours. However, it had some troubles. For example, the sea route was not safe. The Toyamaru accident in 1954 had 1155 dead and some missing people, caused by Typhoon Number 15 Roke. because of that reason, the plan that constructing Seikan Tunnel from Hokkaido to Honshu was becoming a reality. At first, the east route and west route was considered. In the west route, the deepest depth of water was 140 meters and the nature of the soil was easy to drill rocks, so west route was then chosen.