The Gotthard Base Tunnel (GBT) is a railway tunnel through the Alps in Switzerland expected to open on 2 June 2016. With a route length of 57 km (35.4 mi) and a total of 151.84 km (94.3 mi) of tunnels, shafts and passages, it will be the world's longest and deepest traffic tunnel and the first flat low-level route through the Alps.