Lötschberg Base Tunnel

The Lötschberg Base Tunnel (LBT) is a 34.57 km (21.48 mi) railway base tunnel on the BLS AG's Lötschberg line cutting through the Bernese Alps of Switzerland some 400 m (1,300 ft) below the older Lötschberg Tunnel. It runs between Frutigen, Bern, and Raron, Valais.

The Lötschberg Base Tunnel was built as one of two centrepieces of the New Railway Link through the Alps. Construction of the LBT began in 1999 and achieved breakthrough during 2005. It was completed in June 2007 and the first train operations began in December 2007. This initial project was estimated to cost SFr4.3 billion ($3.59 billion).

The LBT was saturated within a few years of opening due to a 21 km (13 mi) single-track section. Without a second bore, its overall capacity is greatly reduced. During 2016, a planning contract was awarded for the completion of the second track of the LBT, which has been estimated to cost 1 billion Swiss francs. The resulting plan was presented in spring 2019. In early 2024, Parliament decided to complete the second bore, with an estimated cost of SFr 1.7 billion. Construction for this continuation is expected to start in 2028.