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There may not be a breeze coming off Elliott Bay the way there is during a drive along the elevated Alaskan Way Viaduct, but air will still be designed to move when drivers gain access to the new SR 99 tunnel beneath Seattle.

The Washington State Department of Transportation and Seattle Tunnel Partners released a new video on Thursday showing another component of the ongoing operational and systems testing taking place for the underground highway.

The video shows the workings of the tunnel’s ventilation system, which includes giant fans connected to those buildings with distinctive yellow smokestacks located at the Space Needle and stadium ends of the project. The locations are referred to as the north and south portals.

Yellow ventilation stacks are visible on the SR 99 tunnel’s south portal operations building. (Flickr Photo / WSDOT)

In the event of a car fire inside the tunnel, the giant exhaust fans in the portal buildings act like vacuums, pulling smoke through vents in the tunnel walls. The smoke travels the length of the tunnel ventilation corridor and up and out through the yellow stacks.

Testing is also being conducted on high-powered jet fans inside the tunnel, which are designed to push air through.

Testing on tunnel safety systems is ongoing, and an integrated systems test — in which all systems must work together — is still to come. A  previous WSDOT video referred to Seattle’s tunnel as “one of the smartest ever built.”

An opening date is approaching this fall, but has yet to be determined. SR 99 will need to be closed for three weeks and realigned at the tunnel ends before the new roadway can open.

Updates are available at the Alaskan Way Viaduct Replacement website.

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