The tunnel is 54 kilometres long, and descends to a depth of 240 metres below the surface of the sea. It took 17 years and ¥538,000,000,000 to build, and opened in 1998. As well as regular passenger services, it's used by 50 freight trains a day, as well as sleeper services from Tokyo and Osaka. Work is in progress to upgrade it for use by the Hokkaido Shinkansen (bullet train), which is currently under construction. When complete, the new Shinkansen line will reduce the travel time between Tokyo and Sapporo from ten hours to five, but this project isn't without its problems – not least that Shinkansen trains run on a wider track than other Japanese trains, so the tunnel will need an extra rail to accommodate both types of train.