Japan Railways just announced that the connexion using the Seikan tunnel (53km long under the sea) with shinkansen bullet trains between Shin-Hakodate and Shin-Aomori will start operating next March. This will be the first time that the famous shinkansen bullet trains operates in the northern Japanese island. When the the rest of the currently under-construction sections are finished it will be posible to travel from Sapporo until Tokio in four hours by train. It will also be posible to move from Sapporo until Kagoshima, separated by more than 1500km using only bullet trains… but for this case it will still probably be much better to use planes 🙂
Inauguration ceremony. Photo by Asahi.com
By 2020 we will be able to travel from Tokyo to Sapporo in four hours riding the bullet train
More information at JR website