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I-90 Floating Track Bridge

In an engineering first, light rail vehicles will someday travel over a floating bridge in Seattle, Washington. As part of Sound Transit’s East Link extension project, two lanes of the Homer M. Hadley Memorial Bridge will be replaced with dual-track light rail in order to take the region's light rail system over Lake Washington to link Seattle with Redmond.

 

I-90 Floating Track Bridge
The Hadley Bridge consists of a 1.1-mile floating span linked via transition spans to concrete approach spans on either end. Hinged expansion joints secure the transition spans to the floating and fixed spans. The transition spans can rotate in response to changes in the lake water level, and they also accommodate rotations of all three primary axes caused by wind and other loads, and longitudinal displacement resulting from temperature changes. These rotations do not impact the daily motor vehicle traffic on Interstate 90, which traverses the Hadley Bridge, but a rail system would have to remain elastic under these conditions yet also be supported sufficiently rigidly to carry a light rail vehicle traveling at speeds up to 55 miles per hour.

The project team, led by WSP USA (as engineers), devised the Curved Element Supported Rail (CESuRa) track bridge system, which can withstand and compensate for the dynamic, multidimensional movement of the bridge deck at the expansion joints.

The design phase was completed in December 2012. Fabrication and testing of the prototype test track commenced in January 2013. Construction of the test track began in February 2013. Vehicle testing began in August 2013 and completed in November 2013. Construction is scheduled to begin in 2016.

The project has received the ACEC-Washington Best in State, Silver Award, in the “Future Value to the Engineering Profession” category.