Original tunnel emerging from the old tunnel in 1918. The train was pulled by a
Great Northern boxcab locomotive. Construction began on the first tunnel on August 20, 1897, and was completed on December 20, 1900. The tunnel was long.
John Frank Stevens was the principal engineer on the interim switchback route (opened in 1893, with grades up to 4 percent) and the first Cascade Tunnel.
Stevens Pass, located above the tunnels, was named after him. The tunnel had a fume problem from the coal-burning steam locomotives. It was built with a 1.7% (1:58.8)
gradient eastbound, which was too close to the
ruling gradient of 2.2%. Because of the steepness of the line, the locomotives had to pull hard to make the grade and thus burn more coal, which would lead to immense smoke in the bore. The tunnel was
electrified, with the project completed on July 10, 1909, eliminating the problem. The unusual system used was
three-phase AC, 6.6 kilovolts at 25 Hz, from a hydroelectric plant on the Wenatchee River just west of Leavenworth. The tunnel section only was electrified; or and 1.7 percent grade through the tunnel chamber. The motive power for the section consisted of four
GN boxcab locomotives supplied by the
American Locomotive Company; they used electrical equipment from
General Electric and were of and weighed each. Initially three locomotives were coupled together and hauled trains at a constant speed of , but when larger trains required four locomotives the motors were concatenated (cascade control), so that the speed was halved to to avoid overloading the power supply. The consulting engineer, Cary T. Hutchinson, published a detailed description of the system in 1909. The tunnel was still plagued by snow slides in the area. On March 1, 1910, an avalanche at
Wellington (renamed Tye after the disaster) near the west portal of the original Cascade Tunnel, killed 96–101 people, the deadliest avalanche disaster in U.S. history. This disaster prompted the construction of the current tunnel. The old tunnel was abandoned in 1929, after the new longer and lower tunnel was opened. During the winter of 2007–2008, a section of the roof caved in and created a debris dam inside the tunnel, making it impassable to pedestrians due to standing water and ceiling debris. A warning was issued to stay clear of the western side of the old tunnel for a distance of for the indeterminate future.
Current tunnel The new Cascade Tunnel was opened on January 12, 1929. While the new tunnel was being constructed, the Great Northern received delivery of
five new electric locomotives. The new locomotives had a
motor–generator supplying DC traction motors, and the single-phase AC supply required only one instead of two overhead conductors. Hence, the Great Northern re-electrified of the original route at single-phase (11 kV, 25 Hz) AC, including that were subsequently abandoned upon completion of the new tunnel, and used steam locomotives on the short remaining stretches of the old line. On March 5, 1927, the three-phase electrification was abandoned, and the new locomotives were placed in service between Skykomish and the east portal of the old tunnel; the time was reduced from 4 hours for a eastbound train to 1 hour 45 minutes for a train. Furthermore, for the first time regenerated power could be used by another train or fed back to the utility company (power from regenerative braking was previously dissipated in a
water rheostat at the power station). Two years later, the new tunnel opened. On April 4, 1996 an eastbound freight train broke through the doors at the east portal after they did not open properly. There were no injuries, but the broken doors slowed operations for a couple of days while replacement doors were brought up from the Seattle area. , one of the locomotives used on the new Cascade Tunnel , the other locomotive used on the current tunnel == Operations ==