With final piece of roadway in place, the SR 99 tunnel begins to take shape

It’s been almost a year since Bertha the tunnel-boring machine completed its job drilling the tunnel that will eventually replace the State Route 99 Viaduct, and in the drill’s wake, crews have been busy building a road. Now, that work is largely done—although there’s still plenty of work to do getting the tunnel ready for cars.

Crews have been assembling 1,152 panels (made offsite by Tacoma Concrete Tech) that make up the lower, northbound deck since November. Yesterday, the last piece of that road was placed, marking the completion of both the north and southbound roads.

On a media tour on Tuesday, the tunnel looked very much still under construction—and those northbound roadway panels were still covered in a wrap designed to keep a layer of concrete wet while curing. Crews still have to finish up that concrete layer, which will smooth out the roadway over the panels.

But, with road signs starting to appear in the ceiling above, the tunnel is starting to resemble its final form.

Sarah Anne Lloyd

On the side of the roadway, egress corridors run between the decks of the roadway or out of the tunnel in the event of an emergency—here, and in the tunnel’s utility rooms, the concrete slabs laid by the drill are still visible.

Ceilings on the lower deck stretch up 16 to 17 feet—on the upper, arched roadway, they range anywhere from 16 to 22 at its peak. When complete, the tunnel will have a 15-foot clearance.

As Seattle Tunnel Partners crews finish the scope of the contractor’s work, the Washington State Department of Transportation (WSDOT) has started testing the tunnel’s internal systems. The majority of the devices that keep the tunnel safe and operational have already been installed in the operations buildings, but just are just under halfway done inside the tunnel itself.

Each of the around 3,000 devices that keep the tunnel operational and safe—like elements of the fire control system—is tested at least three times, said WSDOT program design manager Susan Everett in a media availability after a tour.

That includes manual fire-pulls, which send a signal to the tunnel’s operator, and emergency phones lining the corridor, which reach a 911 operator. Heat sensors also warn the tunnel’s operator of a potential fire, and start a countdown to a deluge of water—which the operator on duty can either postpone or accelerate as the issue is investigated.

The tunnel also includes a ventilation system, which, said Everett, will be dormant most of the time. “They could operate during congestion times” when traffic slows to under 30 miles per hour, said Everett, but during other times a “piston effect will provide ventilation” as cars move through the tunnel.

In addition to the ventilation and fire control systems, more than 300 cameras are installed monitor traffic and identify incidents.

The tunnel’s construction includes 95 miles of electric wiring, 21 miles of sprinkler pipes, 15 miles of lights, 13 miles of fiber optic cables, and 8 miles of linear heat detectors. As crews continue the work, for now it also includes 107 porta-potties.

Eventually, the tunnel will also include cell service—Everett reiterated that this isn’t part of the emergency system and that using your cell phone while driving is illegal—at the request of various cell service providers, who will be installing equipment in the tunnel at a later date.

After Seattle Tunnel Partners has completed their portion of the work and all systems have been tested, WSDOT then has to shut down SR 99 entirely for about three weeks to “do the traffic switch” and “rechannelize into the tunnel,” said WSDOT deputy administrator David Sowers.

WSDOT hopes to have a schedule for that closure six to eight weeks in advance, but it’s too early to nail down an exact timeline—while Seattle Tunnel Partners’s current schedule shows the contractor completing its work in mid-August, there are no guarantees. Sower said some “major milestones” for the project are coming up in May that should give WSDOT a better idea as to whether the contractor schedule is accurate.

The earliest the tunnel will open to traffic, said Sower, would be “probably October [2018].”

The tunnel was initially projected to open in December 2015. After a two-year delay halted the drill from completing work until April 2017, the projected opening date was moved to early 2019, putting a fall opening date slightly ahead of that revised schedule.

After the tunnel opens to traffic, the aging Alaskan Way Viaduct will come down. Some minor demolition could start before the end of the year, but “ideally we wouldn’t start major demolition until [at the earliest] January 2,” said Sower.

Eventually, the two-mile, tolled tunnel will carry cars from around the stadium district to Aurora Avenue North near Seattle Center. The current estimated cost of the project is $3.2 billion.

• Alaskan Way Viaduct Replacement [WSDOT]