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. (July 2007)
The Flathead Tunnel is a 7.01-mile (11.28 km) railroad tunnel in the Rocky Mountains of northwest Montana near Trego, approximately 28 miles (45 km) west of Whitefish. Owned by the BNSF Railway, it is the second-longest tunnel in the United States.
The tunnel, which opened in 1970, was built by the Burlington Northern Railroad as part of a new 60-mile (97 km) bypass of part of the existing route that had to be abandoned due to changes caused by the construction of Libby Dam.
The tunnel is used by about 50 freight trains each day as well as Amtrak's Empire Builder. Speed through the tunnel is approximately 50 mph (80 km/h). Fans and a door at the east portal are used to ventilate the tunnel and clear it of diesel locomotive exhaust.