Gotthard Base Tunnel

The Gotthard Base Tunnel runs 57.1 km under the Swiss Alps. It opened in June 2016, with two single-track tubes where trains can travel at up to 250 km/h, beneath as much as 2,300 m of rock.

Japan's Seikan Tunnel (53.9 km) is the longest with an undersea section.

Context

The Gotthard Base Tunnel is part of a Swiss project to move freight and passengers through the Alps on a nearly flat route instead of climbing over mountain passes. Because it sits at the base of the mountain rather than near the summit, trains avoid steep gradients, and the tunnel allows heavier freight trains and faster passenger services.

It consists of two single-track tubes joined by regular cross-passages for safety, with up to about 2,300 metres of rock overhead. The route is about 57.1 kilometres long when both tubes are measured, and it passed the older Seikan Tunnel in Japan as the longest railway tunnel. Excavation took many years, using huge tunnel-boring machines and conventional blasting in some sections, and the tunnel officially opened in June 2016 with regular service following in December of that year.

The tunnel is a part of a wider Alpine rail corridor, and the benefit depends on the rest of the line being upgraded. The Seikan Tunnel remains the longest with a section under the seabed, as the existing note says, so 'longest' needs the qualifier 'on land' or 'railway' to be precise.