Japan ponders second Seikan tunnel

4 January 2021

Japan is once again considering a plan for a 31km TBM-bored undersea tunnel between its main island of Honshu and the island of Hokkaido in the north.

A proposal submitted in December 2020 by the Japan Project Industry Council (JAPIC) to transport minister Kazuyoshi Akaba envisages a multi-mode tunnel beneath the Tsugaru Strait that would complement the existing rail-only Seikan Tunnel. According to Nikkei Asia, the idea for a second tunnel beneath the Tsugaru Strait involves two decks, with the top deck for autonomous vehicles and the lower deck for freight trains. Non-autonomous vehicles are likely to be carried on Channel Tunnel-style roll-on roll-off trains.

The proposed tunnel is estimated would cost nearly US$7bn, but JAPIC expects this to be recouped in 32 years, assuming a 1.16% interest rate on project borrowing costs. From initial geotechnical studies, it is expected to take around 15 years to complete, compared to the 27 years it took to build the 54km Seikan Tunnel which opened in 1988. According to reports, the second tunnel would be shorter than the first due to a tweaking of the grade, depth and other factors.

JAPIC estimates benefits of around US$844m per year from the tunnel, coming mainly from increased agricultural shipments from Hokkaido – one of the country’s most important farming regions – and increased tourism.

A new tunnel would also provide opportunities to repair the Seikan Tunnel which is said to be experiencing water ingress at a rate of 20,000 lit/min.