The first was 2.63 miles (4.23 km) in length and opened in 1900 to avoid problems caused by heavy winter snowfalls on the original line that had eight zig zags (switchbacks).

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.

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 unusual system used was three-phase AC, 6.6 kilovolts at 25 Hz, from a 5 MW (6,700 hp) hydroelectric plant on the Wenatchee River just west of Leavenworth.

A warning was issued to stay clear of the western side of the old tunnel for a distance of 0.5 mi (0.80 km) for the indeterminate future.

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.

[citation needed] The current Cascade Tunnel is in full operation and receives regular maintenance from BNSF Railway.

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.

Because of the length of the tunnel, an unusual system is used to ensure that the air inside remains breathable and reduce problems with excess fumes.

As long as the train is within the tunnel, the fans work with reduced power to avoid pressure problems.

The fans are powered by two 800 horsepower (600 kW) electric motors, clearing the air through the seven miles (11 km) of tunnel within 20 minutes.