The Stampede Pass railroad tunnel is arched in the center; that is, daylight is not detectable at either end of the tunnel when looking through to the other end; unlike both the first (2.6 mile, 1900) and second (7.8 mile, 1929) Cascade Tunnels of the Great Northern Railway at Stevens Pass, which were "boresighted" and ran in a straight line and at a constant downward angle from northeast to southwest. Steam engines ascending in either direction within the confines of the Stampede Tunnel was the cause of many train crews and passengers being nearly choked to death by the buildup of exhaust gasses within the tunnel; this led to a forced-air ventilation equipment being added at the west end of the tunnel at a later date. The grade is 2.2 percent on the east side from the town of Easton and 2.2 percent on the west side from the town of Lester.