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Crossing Lake Washington

Publish Date

East Link light rail employs cutting-edge technology to cross I-90 floating bridge

(Editor's note: Popular Science Magazine recently named the the technology behind running trains across a floating bridge as one of the most important engineering innovations of 2017!)  

As part of the East Link light rail extension, Sound Transit is doing something that’s never been done before – placing light rail on a floating bridge.

To safely transition light rail vehicles from the I-90 land bridge to the floating bridge, engineers and designers had to consider a number of factors including six different ranges of motion from Lake Washington: up and down, back and forth and side to side.

World-class solution put to the test


Sound Transit designed, built and tested a “track bridge” for the rails to rest on as they cross from the fixed to the floating portions of the bridge. 

The track bridge includes having the rails rest on a series of bearings and plates allowing them to move with changing lake levels and bridge movements. Sound Transit partnered with Parsons Brinckerhoff and Jesse Engineering of Tacoma to design and build two full-scale prototypes.

Passing the test

The two track bridge prototypes, along with two Link light rail vehicles, were shipped for testing to the Transportation Technology Center (TCC) in Pueblo, CO.

Once there, Sound Transit was able to mimic the forces and movements the track bridges will experience during normal and extreme conditions. The TCC is jointly operated by the Federal Railroad Administration and the Association of American Railroads to test new rail technologies.

After collecting more than 500 channels of data during each light rail vehicle pass, the track bridges passed all critical test criteria with the ability to provide safe and comfortable light rail operations at planned speeds up to 55 mph, the highest speed that Link operates.

East Link will provide a 15-minute ride between downtown Bellevue and downtown Seattle when it opens in 2023, no matter what time of day or traffic conditions. For more information about the project see the East Link project page.

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