OLYMPIA, Wash. (AP) - Tolls to finance a new six-lane floating bridge across Lake Washington could be nearly $10 when the proposed replacement along State Route 520 is opened in 2015, a legislative committee has been told.

Financing and cost estimates for replacing the overcrowded and aging Evergreen Point floating bridge between Seattle and the suburbs east of the lake were presented Monday at a House Transportation Committee hearing.

In the most optimistic outlook with tolls to finance construction, the round-trip charge for motorists would range from $5.66 to $8.13 in today's dollars and $6.90 to $9.90 when traffic begins flowing over the new span in 2015, lawmakers were told.

The low end assumes that the same toll would be levied on Interstate 90 across the Mercer Island floating bridge and that money borrowed for a new span would be paid back over 40 years.

By comparison, motorists face a $3 round-trip toll on State Route 16 over the Tacoma Narrows bridge after a second span opens this summer. That's tentatively scheduled to rise to an average of $4 in 2010, $5 in 2013 and $6 from 2016 until the bridge bonds are retired in 2030.

The latest cost estimate for a new Evergreen Point bridge is $4.38 billion. The Legislature has committed $552 million and last week the Regional Transportation Investment District covering Pierce, King and Snohomish counties pledged $1.1 billion if voters approve tax increases to raise $8.5 billion for various road projects.

That leaves a shortfall of more than $2.7 billion, plus $200 million for work that would be needed if the state decides to collect tolls on the eight-lane Mercer Island span and to make that bridge usable for a light-rail line or express buses.

Jeff Doyle, director of the Public-Private Partnership program for the state Department of Transportation, said none of the options for tolls only on State Route 520 made sense to the agency, an expert review panel, investment bankers or private investors.

The round-trip tolls for a 50-year project would be $10, a 75-year project $8.50 and a conventional 30-year project $16, all based on a completion date of 2015.

Charging motorists to drive on either bridge across Lake Washington for 40 years was the "best case for toll financing," Doyle said.

Rep. Alex Wood, D-Spokane, said committee members first saw the numbers a week ago. Rep. Dennis Flannigan, D-Tacoma, committee vice chairman, said legislators were considering tolls among other options for a new Evergreen Point bridge.

"I don't think we can go home without responding to the overwhelming cost of the project," Flannigan said.