The Mount Roberts Tramway, opened in 1996, wasn’t the first nor the longest aerial tramway, but it stands today as one of the most ambitious and successful ones ever built, thanks to several engineering innovations.
The Mount Roberts Tramway uses a cable transportation system known as a ropeway, first used in the European Alps in the late 1800s. Ropeways have been traditionally associated with ski areas, but today these systems are also used in other visitor attractions, material hauling and urban transportation. Leitner-Poma of America, the Mount Roberts Tramway builder, is a subsidiary of Pomagalski, S. A., the world’s largest supplier of ropeway transportation systems.
Compared to other aerial trams, the Mount Roberts Tramway is about average: 3,087 feet long and rising 1,745 feet in elevation. With its two 60-passenger cabins, the Mount Roberts Tramway can accommodate up to 1,050 passengers per hour.
An Engineering Marvel
While the Mount Roberts Tramway is typical in many ways, several features distinguish this system from others around the world. While a typical tram uses sockets to attach the hauling cable to the carriers, the Mount Roberts Tramway’s haul cable is spliced into a continuous loop, with the carriages attached using spring-loaded clamps. The innovative (and now patented) Poma design allows the rope to be released from the carriages and inspected over its entire length to monitor potential defects. The Mount Roberts Tramway was the first aerial tramway in the United States to use this system.
Another outstanding engineering feature of the Mount Roberts TraMKTRAM1mway is its lack of intermediate towers along the route to spoil the view. This is possible because the Tramway’s upper terminal tower is 165 feet tall–a height necessary to clear all obstacles along the route. Its more than 400,000 pounds of steel, all assembled by helicopter, not only support the Tramway cables, but also the fully enclosed, 3,000-square-foot viewing platform, from which riders get a spectacular panorama of the Juneau waterfront.
How the Tramway Works
For such engineering sophistication, the operation of the Mount Roberts Tramway is pretty simple. Two tracks of specially constructed wire rope provide the guiding “rails” for the carriage to ride on. A separate rope, attached to both carriers to form a continuous loop, pulls one carrier up the hill as it lowers the second carrier down. In this way, the two cars always move in opposition to each other: Whenever one moves up the mountain, the other moves down, and whenever one is docking in the upper terminal, the other is docking in the lower terminal. This type of operation is known as “jig-back.”
Each car rides on two track cables of 2-inch diameter, each having a breaking strength of more than 300 tons. The hauling cable is 1 3/8 inches in diameter and is automatically kept at the correct tension by a hydraulic system in the upper terminal. Track ropes are fixed to the foundations at each terminal and supported in specially designed saddles that distribute the load of the rope tension to the structure. The Tramway’s mechanical equipment drive, deflection wheels, motor, etc. are carefully incorporated into the terminal to minimize transmission of noise and vibration to the passenger boarding and deboarding areas.
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