A look at the safety systems inside the SR 99 tunnel

SEATTLE — With the last of 1,100 roadway panels now in place in the new State Route 99 tunnel, the project focus is shifting to how to keep travelers safe in case a car fire compromises air quality.

"We have over 3,000 devices that need to be tested and commissioned," said Susan Everett, program design manager for the Washington State Department of Transportation.

On Tuesday, crews worked on a fire-suppression system.

Touring reporters saw big fans that will push clean air into the tunnel if needed.

New video released by WSDOT shows how much of the time, traffic will keep the air moving through what's called the piston effect.

If a car catches fire, heat sensors and cameras alert operators.

Deluges of water can be targeted at small zones of the tunnel.

There's an emergency escape corridor beside the roadway with its own ventilation system.

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Now that the tunnel looks much like it will when it opens to traffic later this year, project leaders can't help but be excited.

"It's an impressive engineering feat, no doubt about it," said David Sowers, WSDOT deputy program administrator. "It's the world's largest bored tunnel. I get goosebumps when I go in the tunnel because it's such an accomplishment."

Contractors project they'll be done with their work in the tunnel in mid-August.

The process of realigning SR99 to the tunnel from the Alaskan Way Viaduct it replaces will lead to at least three weeks of highway closures.

Officials say they hope to give drivers a heads up of six to eight weeks prior to that closure.