Sound Transit and WSDOT announce revised schedule for light rail bridge crossing I-5; travelers advised of nighttime traffic impacts

Starting after the New Year’s holiday, commuters will see a new light rail overpass taking shape across I-5. Sound Transit will build 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.

 “Building this bridge represents a major milestone for delivering Link light rail service from downtown Seattle to the airport in 2009,” said Henry Cody, Sound Transit’s construction manager for the Tukwila light rail segment. “By utilizing an approach never used before in our region at this site and at three other locations, Sound Transit is saving time and taxpayer dollars. Additionally, we have worked with the Washington State Department of Transportation (WSDOT) to schedule the construction at night when traffic volumes are lowest.”

The construction will utilize pre-cast 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.

Lane closures, including approximately nine nights when I-5 will be closed in a single-direction at a time, will occur on Sunday through Thursday nights and possibly some Saturday nights over the approximately 2-1/2-month construction period. Details, including current schedule information, are available at x843.xml.

Sound Transit plans, builds, and operates regional transit systems and services to improve mobility for Central Puget Sound.