The pass was formerly traversed by the Northern Pacific Railway and the right-of-way is still intact and used as a rail trail. The Chicago, Milwaukee, St. Paul and Pacific Railroad (The Milwaukee Road) ran nearby, using the St. Paul Pass Tunnel south of Lookout Pass; its East Portal is at , southwest of exit 5 of I-90 in Montana. The tunnel was completed in 1908 and is part of the Route of the Hiawatha rail trail.