Sound Transit, WSDOT plan light rail bridge over I-5

Railway Track and Structures, Jan, 2007

Commuters are seeing a new light rail overpass taking shape across I-5 in the Seattle area. Sound Transit is building the overpass, located at the Boeing Access Road near Seattle's southern border. Crews will employ a construction method and schedule that keeps the freeway open during the day, limiting lane closures and traffic impacts to nighttime hours.

The construction will utilize precast concrete segments in a balanced cantilever design, a method first used in the Puget Sound region last summer when Sound Transit built a light rail bridge crossing the Duwamish River. For the I-5 overpass, two large bridge piers have been built, one on each side of the freeway just south of the existing Boeing Access Road overpass. Starting with the pier adjacent to southbound I-5, giant cranes will hang the pre-cast segments one at a time on alternating sides to keep the structure in balance. Steel tensioning cables running through the segments will keep them in place as the structure extends in each direction. After the structure is built over the southbound lanes of I-5, the structure over the northbound lanes will follow, and the two structures will connect above the freeway.

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Also, the federal government has given approval to enter final design for the University Link light rail extension. This enables Sound Transit to begin negotiations with the Federal Transit Administration as part of the agency's efforts to secure a $750-million federal grant for the project.