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SEATTLE - The first round of inspections for the State Route 99 tunnel since the Alaska Way Viaduct demolition is about to get underway. While crews work on their tests, some closures will be in effect this October.
While the tests will last two weeks, the inspection crews will only need to shut the tunnel down over the course of two weekends. Drivers will need to take detours during these days.
When is the SR-99 closed?
What's next:
WSDOT will begin reducing lanes at 9 p.m. on Friday, Oct. 4. Full closure will be in effect from 10 p.m. that night until 6 a.m. on Saturday, Oct. 5.
There will be another closure from 10 p.m. on Friday, Oct. 11 until Sunday, Oct. 13 at 6 a.m.
State Route 99 tunnel entrance under Seattle (FOX 13 Seattle)
What are the detours?
Southbound traffic will detour to the Harrison Street off-ramp and northbound traffic will detour to the Alaskan Way off-ramp. Additionally, the Sixth Avenue and Royal Brougham Way on-ramps will close at 9 p.m., according to the WSDOT project page.
Why are the closures happening?
The tunnel opened in 2019 and the federal government requires a set of inspections to be performed on this type of tunnel every six years.
The backstory:
The tunnel was decided on back in 2009 after years of debate following the Olympia earthquake that revealed worrisome structural integrity issues with the Alaska Way Viaduct.
The tunnel allowed transportation officials to reroute State Route 99 away from Alaska Way and under the city itself. This unique structure requires a complex ventilation and emergency preparedness system.
During the inspection, crews will test and assess various centrifuge fans, drainage systems, generators and other mechanical systems.
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