Video: Alaskan Way Viaduct replacement set

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SEATTLE – The Alaskan Way Viaduct will be replaced with a bored tunnel deep under First Avenue in downtown Seattle.

An official announcement from Gov. Chris Gregoire, Seattle Mayor Greg Nickels and King County Executive Ron Sims is expected Tuesday morning at 8:30 a.m. And the decision is already soliciting cheers and protests.

The head of the King County Council says the tunnel will be two miles long and will be covered by surface streets. The tunnel will likely be a stacked tube with two lanes in each direction.

"They’re the Port of Seattle. They’re the freight and maritime people. They’re the farmers from Eastern Washington. It’s really a state highway and all that traffic will now be underground,” said Bob Donegan, Viaduct Advisory Committee.

The tunnel would start at Royal Brougham way on the south end near the two stadiums. It would emerge near Thomas Street, north of the Battery Street Tunnel.

Most notably, it would be east of the current viaduct. That would allow the viaduct to stay open and keep traffic moving during tunnel construction.

Some people seem to be happy about the tunnel idea.

“I’m in favor of anything that’s below ground to preserve the nature of the waterfront,” said one person we talked to.

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This is a WSDOT image of what the bored tunnel in Seattle might look like. It would be two lanes in each direction stacked under First Avenue.

The boring practice is proven. Sound Transit bored a tunnel through Beacon Hill for light rail.

But what about the sandy soil near the water’s edge? It makes some people nervous.

“Because of the length of time it will take and the problems that are potentially there that we don’t know about when you start digging underneath this not very reliable property,” said one woman.

“Don’t be freaked out. The engineers we talked to said the safest place to be in an earthquake is in a tunnel,” said Donegan.

Some business owners along First Avenue have concerns, ranging from the noise and the vibration caused by construction to the length of time it will take to complete the job.

State transportation officials had recommended either another elevated highway or improved surface streets. But other interested parties, including the mayor and the Seattle Chamber of Commerce, favor a tunnel.

The tunnel is the most-expensive option at $4.25 billion. The elevated and surface plans would cost more than $3 billion. The state has committed $2.8 billion for the project. The city will put in just under $1 billion; King County and the Port of Seattle are also involved.

The mile-long section of Highway 99 on the Seattle waterfront is 55 years old and carries about 100,000 vehicles a day. The aging roadway was damaged in a 2001 earthquake, and experts say it could come down in another major quake.

The proposal still needs to be presented to the state's legislature.

The Associated Press contributed to this report.