The Gotthard Base Tunnel (GBT) is a railway tunnel across the Alps in Switzerland. With a length of 57 km (35.4 mi) and a total of 151.84 km (94.3 mi) of tunnels, shafts and passages, it is the world's longest rail tunnel, followed by the undersea Seikan Tunnel in Japan.
The project, which costs CHF 9.83 billion, consists of two tunnels with one track each. It is part of the Swiss AlpTransit project, also known as New Railway Link through the Alps (NRLA) which includes the Lötschberg Base Tunnel between the cantons of Bern and Valais. Like the Lötschberg tunnel, it will bypass winding mountain routes across the Saint-Gotthard Massif and establish a direct route suitable for high speed rail and heavy freight trains.
Tunnel construction began in 1993. Boring operations in the east tunnel were completed on 15 October 2010 in a cut-through ceremony broadcast live on Swiss TV. When it opens for traffic in late 2017, the tunnel will cut the 3.5-hour travel time from Zürich to Milan by an hour and from Zürich to Lugano to 1 hour 40 minutes.