If Tim Eyman's Initiative 1125 becomes law, it might cause a funding gap for the Highway 99 tunnel, to replace the aging Alaskan Way Viaduct.

Eyman told The Seattle Times he turned in what he estimates to be 327,043 signatures Friday in Olympia, making it a "slam dunk" I-1125 will qualify for the ballot.

Among other clauses, it would allow only flat-rate tolling, similar to the $2.75 fee charged eastbound-only on the new Tacoma Narrows Bridge. But the Highway 520 floating bridge and the Highway 99 tunnel are supposed to use variable tolls -- so that on Highway 520 the rates range from zero overnight, to $3.50 each way in the peak commute hours. An environmental-impact statement released Thursday for Highway 99 examines tunnel tolls ranging from 84 cents to an average $2.44 to a peak of $4.21.

The tunnel needs enough toll revenue to support $400 million in construction bonds the state Legislature required, to supplement $2.4 billion in gas taxes and federal bridge grants to replace the old Alaskan Way Viaduct.

"A flat toll rate would not achieve our objective as far as financing the project," said Highway 99 administrator Ron Paananen, asked about I-1125 during a news conference Friday about a newly released environmental-impact statement. "We would have to work with legislators and the governor's office, as far as handling that difference."

There are many other variables that can affect the highway funds, not to mention traffic flows.

The state DOT has been studying a gradual evolution toward region-wide tolling on multiple highways, under both Secretary Paula Hammond and predecessor Doug MacDonald. Gov. Chris Gregoire and Senate Transportation Chairwoman Mary Margaret Haugen, D-Camano Island, have called for a new round of transportation taxes in 2012.

Eyman's measure could win, lose, or be voided in part or whole by lawsuits. The state toll revenue projections could be way high or low.

One strategem that seems unavailable is for the state DOT to legally "lock in" variable tolls before I-1125, by writing those into a bond covenant. Paananen said toll-backed bonds won't be sold until 2014-15, toward the end of the deep drilling operation through downtown Seattle. (Courts allowed Sound Transit to keep collecting its car-tab tax until 2028 because 30-year bonds were already sold, despite a repeal clause in Eyman's winning I-776 nine years ago.)

Eyman said he's not singling out Highway 99, but flat tolls everywhere. He argues that variable tolls favor the rich, who can afford peak rates, and hurt the poor, who have less flexibility to commute at other times.

"Tolls have always been flat. That's the way it's been done for 100 years in our state. It's fair and it works," he said. Eyman had no specifics Friday as to how a tunnel funding gap should be closed, except he thinks flat tolls would be just as lucrative.

I-1125 also seeks to forbid Sound Transit light rail from running on the I-90 floating bridge, and to ban potential I-90 tolls from being applied to the underfunded Highway 520 project.

Bellevue developer Kemper Freeman, who has campaigned against Eastside light rail, has contributed $525,000 to Eyman's organization, which hires paid signature gatherers.

Eyman opponent Andrew Villeneuve, founder of the Northwest Progressive Insitute, points out that in Initiative 912 six years ago, voters defeated Eyman and upheld gas taxes, including those to replace the viaduct.

"If you wreck the corridor by dropping the ball, and not getting the facility built, that's bad for economy, and bad for trade with other countries," he said.