SR 99 Tunnel Nerve Centers Taking Shape

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SR 99 Tunnel Nerve Centers Taking Shape

Construction is underway on the north portal building, with crews currently building the underground structures for the ventilation and vehicular elevator shafts, and beginning work on the ground-level building that sits atop the cut-and-cover portion of the tunnel. Drivers and transit riders taking Aurora Avenue North can see the construction site running parallel on the west side of the Seattle Pacific Hotel. 

State-of-the-art systems will be the key to maximizing safety and efficiency inside the SR 99 tunnel. Lighting and intelligent transportation systems (video cameras, traffic counters, variable message signs, etc.) will help ensure smooth traffic flow, while the ventilation, drainage and fire-suppression systems will help the tunnel meet the highest safety standards. To manage these systems, two nerve centers – known as the north and south portal operations buildings – are needed at each end of the tunnel.

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The south operations building will sit on the south side of South King Street, just to the north of the tunnel entrance. Visible to northbound drivers, it will house maintenance vehicles, ventilation fans and emergency power.  Much of the underground structural construction is complete, and crews are beginning to install electrical systems while the building rises above the surface.

Rendering of the south operations building.

Rendering of the south operations building.

The north operations building will be located at the corner of Harrison Street and Sixth Avenue North, just to the south of the tunnel entrance. This building will house maintenance facilities, repair shops, radio equipment, the operations center, offices and crew rooms. Maintenance crews will primarily report to and work out of this building, which will also have a small parking lot.

Rendering of the north operations building.

Rendering of the north operations building.

The yellow stacks, each 84 ft tall, are part of the centrifugal ventilation fans that will be prominent features of both buildings. Each operations building will have four fans, and each fan will be capable of moving 160,000 cu ft of air per minute. For comparison, the eight fans would have been able to recycle all the air inside the old Seattle Kingdome (67 million cu ft) in a little under an hour.

The buildings will also provide crews with direct access to the tunnel via freight elevators, and serve as the end points for the tunnel corridors that provide passage for utilities and emergency egress. Both buildings will be built to specifications that match LEED Silver standards, but the designation won’t be official because there is no applicable category within the LEED certification system for these buildings – turns out they’re two of a kind.

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