Tests require closures of westbound I-90 floating bridge

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On the weekend of September 16-19, Sound Transit and WSDOT will conduct technical tests on the Interstate 90 Homer Hadley Bridge. The tests will require overnight closures of westbound I-90 between Mercer Island and Seattle and both daytime and nighttime closures of the I-90 center roadway.

As population and congestion continue growing, Sound Transit is moving forward with studies of how to expand the regional transit system. Two major options for the I-90 corridor are under review: light rail, or a bus rapid transit (BRT) system that could later be converted to light rail. The bridge tests will provide information that engineers will use to design a light rail system across the I-90 floating bridge, including the scope of bridge improvements required and more detailed cost estimates.

Crews will close the I-90 center roadway express lanes at 6:30 p.m. Friday, Sept. 16 for most of the weekend. They will open the I-90 express lanes eastbound from 2 p.m. to 9 p.m. Saturday, Sept. 17 and from 2:30 p.m. to 6 p.m. Sunday, Sept. 18. The center roadway will reopen by 5 a.m. Monday, Sept. 19.

All lanes of the westbound I-90 mainline will close between Island Crest Way and I-5 in Seattle at 10 p.m. Friday, Saturday and Sunday nights (Sept. 16, 17 and 18). The westbound mainline will reopen by 7 a.m. Saturday and Sunday (Sept. 17 and 18), and will reopen by 5 a.m. Monday, Sept. 19.

Closing the westbound mainline at night on the weekend will cause the least amount of disruption for drivers compared to any other time. WSDOT encourages drivers to plan ahead and reschedule any nighttime trips west across the lake, if possible.

During the tests engineers will use sensitive equipment to measure slight movements of the bridge. Crews will use eight trucks loaded to weigh 148,000 pounds each to simulate two four-car light rail trains. Sensors will monitor the bridge as the two sets of trucks travel across at different speeds and pass at different locations. The closures are necessary so other vehicles don't compromise the results.

The test will add real world data to existing computer analyses that have modeled the types of motions and stresses that would be taken into account in a bridge retrofit. The test has strong potential to reduce costs since relying exclusively on computer analysis would likely require more conservative assumptions.

For motorists that may need to get from Mercer Island to Seattle overnight, the detour route will be north on I-405 to westbound Highway 520. Slightly more traffic is expected on Highway 520, but overnight volumes are typically small and adding traffic from I-90 should not cause delays. Crews will reopen the roadway as soon as possible each morning. Drivers can check live traffic conditions on WSDOT's Web site or call 5-1-1 for traffic information.

Over the next year Sound Transit will continue talking to the public about which transit system expansions will make the biggest difference in people's lives. These projects will be included in Sound Transit 2, a region-wide package of projects that will be built if approved by voters. For more information on options that are being studied visit www.soundtransit.org .


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