More details have been released, including a projected four to five year construction period, on state elected leaders plan to replace the ailing Alaskan Way Viaduct with a deep bore tunnel, however, opposers have filed an initiative to stop them.

About 18,000 valid signatures will have to be gathered within 180 days to put it on a city ballot.

Dow Constantine, who represents West Seattle on the King County Council, has come out in support of the tunnel plan because of the value to West Seattle commuters.

"Every other proposal held the possibility of significant disruption for West Seattle commuters," said Constantine. "This deep bore tunnel creates the possibility of uninterupted traffic flow if we can figure out how to keep the viaduct safe for travelers until the tunnel is ready."

Since the Gregoire's plan means the viaduct could stay open while the tunnel is being constructed, it cuts down the amount of time traffic would be disrupted, he said.

"Waterfront businesses, which were threatened by lengthy construction, will be able to avoid the worst of those impacts," Constantine noted.

The plan calls for the tunnel to connect the stadium area with Aurora Avenue with exits near Royal Brougham Way South and north of the existing Battery Street Tunnel. Some traffic would be routed southbound onto Alaska Way and northbound onto Western Avenue.

The bored tunnel will be approximately two miles long and carry four lanes of traffic with 50 mile-per-hour speeds. Drivers will bypass downtown by entering the tunnel near the sports stadiums in the south and connect to State Route 99 north of the existing Battery Street Tunnel.

There are currently three lanes in each direction on the viaduct. The new plan does not include an exit, as it currently exits, from Western Avenue to access downtown, Interbay and Ballard.

About $2.81 billion has been set-aside by the state in gas taxes and federal bridge funds to pay for the $4.24 billion project.

The state's committed funds will be used for the new State Rroute 99 corridor from the sports stadiums to South Lake Union in a bored tunnel and restoring land under the existing viaduct to a four-lane surface street.

The funding plan also includes a local investment district.

The state legislature will still need to approve the plan, which is supported by Gov. Chris Gregoire, King County Executive Ron Sims, Mayor Greg Nickels, and Chief Executive Officer of the Port of Seattle Tay Yoshitani.

The agreement is the result of a year-long study of solutions for replacing the central section of the Alaskan Way Viaduct.

At a news conference Tuesday morning, Gregoire announced the project would begin in 2011 and likely end in 2015 with the tunnel completed.

"Building a deep bored tunnel will support a strong economy today and in the future," Gregoire said. "This decision will improve public safety, help ensure Seattle is a 21st Century international city, and generate thousands of new family-wage jobs in the Puget Sound region."

The viaduct was damaged in the Feb. 28, 2001 Nisqually Earthquake and has been steadily sinking since. It carries roughly 110,000 vehicles a day.

Nickels has favored a tunnel option and the recent decision falls roughly in-line with his plans. However, a 2007 vote resulted in little support for a tunnel option to replace the damaged structure.

"There are pivotal moments when great cities make history," said Nickels in a statement. "Today, we come together with a plan that creates more transit. We ensure that our city remains economically competitive. And we reclaim our destiny as a true waterfront city; tearing down an elevated highway and re-connecting Seattle to Elliott Bay."

The project costs for the city are $930 million to replace the central seawall and construct a waterfront promenade, relocate utilities, build a streetcar on First Avenue, and improve east-west streets. The county will seek new motor vehicle excise tax authorization from the legislature to fund over $190 million in transit capital and $15 million annually in operating expenses.

Yoshitani will ask the Port Commission to consider a $300 million investment in the replacement of the south mile of the viaduct and a new east-west connection to the container terminals.

The agreement also includes federal funds toward the Spokane Street Viaduct and Mercer Street projects, which are critical to east-west connections for West Seattle neighborhoods.

At the news conference, the "No Tunnel Alliance" held a rally in opposition to the tunnel plan.

The Alliance is chaired by activists Gene Hoglund and John Fox who say a tunnel would result in a "lack of connections" and "have a devastating effect on Seattle?s maritime and industrial businesses that provide many family wage jobs."

They claim the tunnel is too expensive and will do harm to the environment because slow or idling traffic will increase green house gas emissions.