The Vereina Tunnel is a railway tunnel situated in eastern Switzerland, which at 19,058 m is the longest tunnel on the Swiss RhB railway network as well as the world's longest metre gauge railway tunnel. In length, it is followed by the Furka Base Tunnel (15,442 m) and the Albula Tunnel (5,865 m).
The tunnel was built to improve all-weather transport links in the eastern part of Canton Graubünden, as the Flüela Pass (between Davos and Susch) is prone to heavy snowfall and avalanches in the winter months. Construction began in 1991 and the tunnel opened to traffic November 19, 1999. The total cost of the tunnel came to CHF 812 million.
Service is based on hourly regional trains between Scuol-Tarasp and Chur, complemented every 30 minutes by car shuttle trains transporting road vehicles between the two valleys linked via the tunnel and by freight trains. The tunnel is single track, with passing loops (each two km long) in the middle and near the two portals. Electrification is the RhB overhead standard of 11 kV 16.7 Hz AC.