Cascade Tunnel

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Cascade Tunnel eastern portal

The Cascade Tunnel refers to two tunnels at Stevens Pass through the Cascade Mountains, approximately 65 miles (105 km) to the east of Everett, Washington. The first Cascade Tunnel was a 2.63-mile-long (4.23 km) single-track railroad, built by the Great Northern Railway in 1900 to avoid problems caused by heavy winter snowfalls on the original line that had eight zig zags (switchbacks). The second tunnel, a 7.79-mile (12.54 km) single-track replacement of the earlier tunnel, was put in service on January 12, 1929, and is still in operation, connecting Berne in Chelan County on its east with Scenic Hot Springs in King County on its west. It is the longest railroad tunnel in the United States.


Original tunnel[edit]

Cascade Tunnel routes
The Oriental Limited emerging from the old tunnel in 1918. The train was being pulled by an electric locomotive.
Postcard illustration of the old and new tunnels from the Great Northern Railway.

The first tunnel began construction on August 20, 1897 and was completed on December 20, 1900. 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 smoke (fume) problem, as it was built with a 1.7% (1:58.8) gradient eastbound, which was too close to the ruling gradient of 2.2%. The tunnel was electrified, with the project completed on July 10, 1909, eliminating the problem. The unusual system used was three-phase AC, 6600 Volts at 25 Hz, from a 5 MW hydroelectric plant on the Wenatchee River just west of Leavenworth. The tunnel section only was electrified; 4.0 route-miles or 6.0 track-miles and 1.7 percent grade through the tunnel.

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 1500 hp[1] and weighed 115 short tons (104 t) each.[1] Initially three locomotives were coupled together and hauled trains at a constant speed of 15.7 mph, but when larger trains required four locomotives the motors were concatenated (cascade control), so that the speed was halved to 7.8 mph to avoid overloading the power supply.

However, 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 2.6-mile (4 km)-long Cascade Tunnel, killed 96 people (or 101 people according to Middleton), 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 one-half mile for the indeterminate future.

Current tunnel[edit]

Opening of the new tunnel, January 12, 1929.

The new Cascade Tunnel was opened on January 12, 1929. The new line had 72.9 route-miles or 93.2 track miles electrified, between Skykomish and Wenatchee. The ruling grade was still 2.2 percent, although 21 miles of 2 percent or worse grade was eliminated. The line length was reduced by 8.7 miles, and maximum elevation was lowered by 502 feet (153 m) from 3,382 feet (1,031 m) to 2,881 feet (878 m). The new electric locomotives had a motor-generator supplying DC traction motors, and the single-phase AC supply (11 kV, 25 Hz) required only one instead of two overhead conductors. Each Baldwin-Westinghouse Z-1 locomotive consisted of a pair of semi-permanently coupled 1-D-1 box-cab units. The pair weighed over 371 tons, and had an hourly rating of 4330 hp.

The new tunnel was started in December 1925, and was built in just over three years by A. Guthrie of St. Paul, Minnesota; the aim was to finish by the winter of 1928–1929 so that further maintenance on deteriorating snow sheds could be avoided. Frederick Mears assistant chief engineer who was in direct charge of the work for the new line.[2] While the new tunnel was being constructed, 21 miles between the original tunnel and Skykomish were electrified, even though 8 miles were abandoned when the new tunnel was opened. The three-phase electrification was abandoned from March 5, 1927 when 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 2500 ton eastbound train to 1 hour 45 minutes for a 3500 ton train, and 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).

Electrification was removed in 1956, after a ventilation system was installed to eliminate diesel fumes.[3]

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.

In Fall 2001 a single car derailed in the tunnel and was dragged the rest of the way out. It ripped out wiring that was attached to the sides of the tunnel.


The East Portal doors of the Cascade Tunnel opening so a train can pass through
West Portal of the Cascade Tunnel

The current Cascade Tunnel is in full operation and receives regular maintenance from BNSF Railway. The new alignment is a straight-line tunnel running between Berne and Scenic Hot Springs. It is currently part of the BNSF Scenic Subdivision between Seattle and Wenatchee, and Amtrak's Empire Builder runs through it. Because of safety and ventilation issues, this tunnel is a limiting factor on how many trains the railroad can operate over this route from Seattle to Spokane. The current limit is 28 trains per day.[4] Speed through the tunnel is 30 mph for passenger trains, 25 mph (40 km/h) for freight.

The gradient in this tunnel is 1.565% (1:64), with the rise from west to east. The gradient is 2.2% on the west side from the town of Skykomish. Most recently, telecommunications assets and track sections inside the tunnel were improved.[when?]

Ventilation operations[edit]

Because of the length of the tunnel, a somewhat unique system is used to ensure that the air inside remains breathable and reduce problems with excess fumes. For example, as a train enters the west portal of the tunnel, doors close on the east portal and huge fans blow in cool air through a second portal to help the diesel engines. As long as the train is within the tunnel, the fans work with reduced power to avoid pressure problems. After the train has left the tunnel, the red-and-white-checked door closes and the fans operate for 20 to 30 minutes with maximum power to clear the tunnel of exhaust before the next train passes through. In the opposite direction, the door opens when the train is about 0.6 mile (1 km) away from it. The fans are powered by two 800-horsepower electric motors, clearing the air through the seven miles of tunnel within 20 minutes. Present-day train crews carry portable respirators for use in the event of a fan failure or a train stalling inside the tunnel. In addition, there are emergency/safety stations spaced every 1500 and 2500 feet (460 and 760 m) apart, depending on the location within the tunnel, that provide additional air tanks and equipment to be used in the event of a ventilation/other failure.

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Coordinates: 47°44′33″N 121°04′10″W / 47.74250°N 121.06944°W / 47.74250; -121.06944