An extension of the Tōhoku Shinkansen through the undersea Seikan Tunnel to Japan's northern island, the Hokkaidō Shinkansen, operated by the Hokkaido Railway Company (JR Hokkaido), began operations on 26 March 2016.
Work on the first section of the line started in May 2005 and involved converting 82 kilometres of the former Kaikyō Line, which passes through the Seikan Tunnel to dual gauge operation. The new arrangement combined the existing narrow gauge (3 feet 6 inch 1067 mm) line with a new standard gauge (4 feet 8 1⁄2 inches 1435 mm) line.
The old narrow gauge line remains in use in both directions. As a result, it takes just over an hour for the fastest shinkansen services to cover the full 148.8 kilometres from Shin-Aomori to Shin-Hakodate-Hokuto because the maximum speed on the dual-gauge section of the line is 140 km/h.
The restriction comes because about fifty freight trains use the dual-gauge section each day and limiting them to times when the shinkansen services do not operate is not an option.
The line's current arrangements have ten Hayabusa services running back and forth between Tōkyō and Shin-Hakodate-Hokuto every day along with one return Hayabusa service between Shin-Aomori and Shin-Hakodate-Hokuto, along with a return Hayate service between Morioka and Shin-Hakodate-Hokuto, and another between Shin-Aomori and Shin-Hakodate-Hokuto.
All services require seat reservations (there are no non-reserved carriages), and standing tickets are available if the seating is fully booked.
Shin-Hakodate-Hokuto will remain the terminus until JR Hokkaidō open the extension of the line to Sapporo around March 2031. At that point, since around 76% of the 211.3 km extension will be underground, speeds of up to 360 km/h in the new tunnels will mean the journey from Tōkyō to Sapporo should take roughly five hours.
More... Route details and map: http://www2.jrhokkaido.co.jp/global/english/shinkansen/