SR 99 tunnel slated for fall opening: What to know about tolling, viaduct closure & more

SEATTLE -- Bertha finished boring the path for a new tunnel under Seattle nearly one year ago.

Since then, construction crews have finished installing a double-deck highway end-to-end inside the tunnel. That leaves crews to finish installing and testing the $3.2 billion tunnel's advanced operational and safety systems.

So when will the tunnel open? How much will tolls cost? And what happens to the Alaskan Way Viaduct?

When will the tunnel open and what happens to the viaduct?

After the tunnel is finished, crews will close the Alaskan Way Viaduct for several weeks to realign the highway to the tunnel. The viaduct will be permanently closed, and it will take a few weeks before the tunnel will open to traffic.

Demolition of the viaduct will begin some time after the tunnel opens to traffic.

That paves the way for the Seattle Department of Transportation to build a new Alaskan Way along the downtown waterfront.

How much will tolls cost?

"Funding for the $3.2 billion viaduct replacement program comes from state, federal and local sources as well as the Port of Seattle and tolls on drivers using the tunnel. Of that total cost, the 2012 Legislature stated $200 million must come from toll funding," WSDOT says.

The Washington State Transportation Commission is responsible for setting toll rates: "The WSTC will consider multiple factors in order to determine the best rate to minimize traffic diversion onto other roads but still generate necessary revenue for the tunnel. They will use the results from the investment-grade study as a baseline for their work."

A study came up with two main possibilities: tolls ranging from $1 to $2.50 at peak times  -- which would raise the $200 million as required by state law -- and a second option kept trips closer to $1 to $1.25 at peak times.

A final decision has not yet been made.

One of 'smartest' tunnels ever built

The safety systems will make the SR 99 tunnel one of the smartest tunnels ever built, including:

What about the delays?

The project is about two years behind schedule after Bertha's main bearing was damaged in December of 2013 -- only about 10 percent of the tunnel had been bored.

Seattle Tunnel Partners and Bertha's manufacturer Hitachi Zosen came up with a plan to lift four million pounds of machinery up through a hole in the ground to repair the cutter head.

Two years later, STP resumed tunneling and completed boring the tunnel. WSDOT says the cause of the damage is under dispute and in litigation.

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Why build a tunnel?

Transportation officials explain the decision to replace the viaduct with a tunnel: