The Senate Wednesday approved the plan to replace the Alaskan Way Viaduct with a deep-bored tunnel, which is expected to cost $4.2 billion.

The Senate passed the measure 43 to 6 but it will also have to be approved by the state House of Representatives.

Mayor Greg Nickels, King County Executive Ron Sims and Gov. Christine Gregoire announced the tunnel as their preferred option last month.

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 also have the option of traveling north or south bound on Alaskan Way.

Gregoire also said there will be investments in improved bus service, east-west city streets, a new seawall, relocated utilities, and an upgraded waterfront.

 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 Aurora Avenue North near 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.

At a recent open house, alternatives for reaching the Ballard and West Seattle neighborhoods were presented to those worried about the closure of the Western Avenue exit off the viaduct toward Northwest Seattle if the tunnel is built and access to parts of Southwest Seattle.

For people in the north end, access to the tunnel would be from Aurora Avenue North, which would transition from a surface highway to the bored tunnel between Mercer Street and Denny Way, replacing the current route via the Battery Street Tunnel and the Alaskan Way Viaduct. At the Mercer Corridor, access to Aurora Avenue North and the bored tunnel would be provided in all directions.

For those in West Seattle, transit officials are telling residents that by taking SR 99, drivers could continue north through the new deep bored tunnel to emerge just south of Mercer Street. For better access to Downtown Seattle, they could exit SR 99 at Royal Brougham and travel along the new Alaskan Way six-lane boulevard from Columbia Street to King Street as well as the new four-lane boulevard along the Central Waterfront.

I-5 will continue to provide another alternative for drivers traveling north, transit officials said.

The bill that passed Wednesday supports the tunnel plan and also calls for a study of a use of tolls.