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Crews working under Seattle have hit a milestone as the SR 99 tunnel takes shape.

The final panel of the lower deck was installed this month (northbound lanes). The northbound stretch is constructed of 1,152 panels. Both levels — north and southbound — are now finished inside the SR 99 tunnel.

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Crews are not finished, however. There are still 300 traffic-monitoring cameras to test; ventilation systems to get up and running; and automated sprinkler systems to put out fires inside the tunnel. WSDOT says that “together, these systems will make the SR 99 tunnel one of the ‘smartest’ tunnels ever built.” The tunnel will be a living, breathing machine once it is finished. The two minute drive under Seattle will require an operation with control centers and mechanical systems for air, water, communication, power supply, and more.

Here’s a video from WSDOT showing the final piece of roadway being installed.

Tour the SR 99 tunnel

³ÉÈËXÕ¾ Radio’s Traffic Reporter Chris Sullivan toured the SR 99 tunnel. See his findings below.

Heading into 99 tunnel

— Chris Sullivan (@NEWSGUYSULLY)

More from inside the tunnel.

— Chris Sullivan (@NEWSGUYSULLY)

— Chris Sullivan (@NEWSGUYSULLY)

— Chris Sullivan (@NEWSGUYSULLY)