Hokkaido Shinkansen

Hokkaido Shinkansen set to open on March 26 | International Railway Journal

The new line will be 149 km (93 mi) between Aomori and Hakodate.
Aomori: northern end of Honshu, Japan's main island
Hakodate: southern end of Hokkaido, Japan's northernmost big island

It will use the Seikan Tunnel: 54 km (33 mi) long, with 23 km (14 mi) underwater. The start of Shinkansen service there will mean the end of service of trains that use 1067-mm gauge.

One will have to change trains to continue to Sapporo, Hokkaido's biggest city. However, they are planning a Hakodate - Sapporo Shinkansen line. It will be 211 km (131 mi) long, and it should be done by 2030.

Hokkaido Shinkansen prepares for launch | International Railway Journal -- a long, detailed article.

Japan Railway Construction, Transport and Technology Agency (JRTT) is responsible for construction of the new line, which runs 23% on viaducts, 4% on bridges, and 65% in tunnels. In addition to the Seikan tunnel the line uses the 8.1km Oshima - Tobetsu, 6.2km Tsugaru - Oda, and 5.9km Tsugaru tunnels. The maximum line speed is 260km/h with trains operating at up to 140km/h in tunnels. Up to 51 freight trains a day will use the line at up to 110km/h with JR Freight developing the EH800 dual-voltage locomotive, which is capable of operating at 20kV ac on the conventional network and 25kV ac on the new section, for these revamped services. The twin-unit Bo-Bo+Bo-Bo locomotive has an output of 4MW at 25kV and 3.04MW at 20kV.

To accommodate the freight trains, 82 km of this line has been made dual-gauge, including the Seikan Tunnel itself.

The winter weather will be a challenge.

Heavy snowfall and temperatures as low as -20oC during the winter months, led JR Hokkaido to carry out tests during two winters ahead of the start of operations to confirm the line's performance as well as the durability of the trains and infrastructure. Using elevated sections reduces the risks of snow cleared by trains fitted with a snowplough from disrupting services by allowing the storage of accumulated snow in designated areas on the viaduct as well as enabling snow to drop through gaps in the deck to the ground below. In addition dual-gauge turnouts are protected using a "snow shed" while other turnouts are equipped with a snow melting system using an air jet which also clears snow or ice that has fallen from trains.

Construction on the 211-km Hakodate - Sapporo line started in 2012, and it should be done in 2031. The long construction time and the great expense of construction are because 76% of the line will run in tunnels, including at least 7 tunnels over 10 km long.

Japan opens Hokkaido Shinkansen | International Railway Journal -- between Aomori (Honshu island, the biggest one) and Hakodate (Hokkaido island) through the Seikan Tunnel.

The 148.8km line runs 23% on viaducts, 4% on bridges, and 65% in tunnels. In addition to the Seikan Tunnel, which opened in 1988, the new railway includes the 8.1km Oshima - Tobetsu, 6.2km Tsugaru - Oda, and 5.9km Tsugaru tunnels. The maximum line speed is 260km/h with trains operating at up to 140km/h in tunnels.

That means that only 8% of the track is at-grade. The Seikan Tunnel is 53.85 km long, with dual-gauge track.
Also,

The fastest Hayabusa services complete the 862.5km trip between Tokyo and Shin-Hakodate-Hokuto in 4h 2min. Hayabusa takes 2h 59min to cover the 713.3km between Tokyo and Shin-Aomori, where there is a two-minute stop to change drivers. The remaining 148.8km to Shin-Hakodate-Hokuto is covered in 1h 1min, with trains running at a maximum of 140km/h on 82km of the route.

Passenger-train service on the 1067-mm tracks has been ended.

Average speeds:

• Tokyo - Aomori: 239 km/h - 149 mph
• Aomori - Hakodate: 146 km/h - 91 mph