The tunnel was constructed for the Great Northern Railway by the Walsh Construction Company and S.J. Groves and Sons (collectively known as Walsh–Groves) at a cost of nearly $44 million (equivalent to $316 million in 2023).[3] It is part of a 60-mile (97 km) rerouting of the Great Northern Hi-Line that became a necessity due to construction of Libby Dam and subsequent creation of Lake Koocanusa.[1][4]
Work began on May 12, 1966.[3] Drilling was completed on June 21, 1968 when President Lyndon B. Johnson ceremoniously triggered a final explosion from a circuit connected via telephone to the White House.[5][6]
Finishing work continued for the following two years, and the tunnel, along with the entire rerouted rail line it is a part of, opened on November 1, 1970. An opening ceremony was held on November 7, 1970 and included the passage of the first official train through the tunnel, a 21-car passenger special carrying 1,200 area residents who were offered the opportunity to travel a circular route from Libby and back on both the new and old rail lines.[7][8]
Official records indicate that two people were killed in two separate incidents during construction, both occurring after drilling was complete.[3][6]
As of 2022[update] the tunnel is used by about 40 freight trains each day as well as Amtrak's Empire Builder.[9] Maximum speed through the tunnel is 50 miles per hour (80 km/h).[10] The north portal contains a ventilation system to clear the tunnel of diesel locomotive exhaust and provide cooling air to eastbound locomotives, as there is an uphill grade heading eastbound.[11][9]
