The tunnel was constructed from 1912-1914 by the Chicago, Milwaukee, St. Paul and Pacific Railroad (The Milwaukee Road) as part of its line from Chicago to Seattle, completed in 1909. It replaced a temporary surface line over Snoqualmie Pass at ; this grade from Hyak to Rockdale later became U.S. Route 10, now the eastbound lanes of I-90. The tunnel is aligned east-west and electrification in 1917 eliminated smoke dissipation issues.