New Seattle tunnel designed to ride out catastrophic 9.0 quake, DOT says

Workers paint massive stick figures on the sides of the SR99 Waterfront Tunnel (Photo: WSDOT)

SEATTLE – The new Highway 99 tunnel opening in early February has been constructed to withstand a powerful once-in-2,500-years earthquake of roughly 9.0 magnitude off the Washington coast, state Department of Transportation officials said Monday.

And that, in its most basic terms, is why the tunnel is such a dramatic improvement over the Alaskan Way Viaduct, according to transportation officials.

In 2001, the Nisqually earthquake shook the Seattle region and the viaduct along with it. The viaduct was repaired and strengthened, but the aging structure was still vulnerable to collapse or major damage in an earthquake.

The new two-mile tunnel beneath Seattle will eliminate that danger. State transportation officials say the tunnel's sophisticated systems are designed to help keep vehicles moving and travelers safe – including during earthquakes.

"The viaduct was built in the 1950s and seismic design is now light years ahead of what we knew back then," said David Sowers, deputy administrator of the Alaskan Way Viaduct replacement program. "Ultimately, replacing the viaduct is all about keeping people safe and this new tunnel meets the gold standard for safety."

Its seismic design, along with cutting-edge safety features, combine to make the new tunnel one of the safest in the world, he said.

Robert "Red" Robinson, director of underground services at geotechnical engineering firm Shannon & Wilson, echoed that viewpoint.

"That tunnel is by far the safest place to be in an earthquake," he said.

In a new video, seismic and structural experts explain what keeps the S.R. 99 tunnel safe during earthquakes:

The viaduct will close for good on Friday at 10 p.m. and the new S.R. 99 tunnel will open in early February. However, it will take up to two additional weeks to complete a new northbound off-ramp into downtown Seattle. Drivers should expect traffic disruptions for up to six weeks.

For more information about how to survive the period between the viaduct closure and the tunnel opening, visit the KOMO News Alaskan Way Viaduct Closure Survival Guide ...

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