SEATTLE — One of Sound Transit’s latest light rail projects is featuring what the transit agency says is a first-of-its kind rail line on a floating bridge.
The Seattle Times reports that after more than a decade dealing with the technical challenges involved, the agency is installing tracks on the Interstate 90 bridge across Lake Washington as part of a route from Seattle to Bellevue and Overlake, Wash., scheduled to open in 2023.
The most significant part of the engineering to make the project work are eight steel platforms, called “track bridges,” where the rails pass over the hinged joints of the highway bridge, which can rise or fall up to 2 feet depending on water levels, and also move because of wind, waves and traffic. The track bridges will allow the rails to stay in line even when the platforms move to accommodate the motion of the bridge, thanks to flexing bearings similar to those used to protect buildings from earthquake motion. Trains will be able to operate at 55 mph across the bridge.
To offset the additional weight on the bridge from the rail line, concrete barriers along tracks the are being replaced with cable fencing to prevent a derailing train from falling into the lake.
— Updated at 4:55 p.m. CDT on July 25 to restore missing words in last paragraph, clarify attribution on claim that floating bridge is a first.
