As campaigners for and against King County’s transit-and-roads Proposition 1 prepare for a final weekend push, numbers from the King County Elections office indicate the election is already more than halfway over.

As of Thursday, the county had received some 287,000 completed ballots — roughly 24 percent of the 1.2 million sent out beginning April 2.

Total predicted voter turnout is 38 percent, a projection based on other special elections, and one that still looks in the ballpark, said Kim van Ekstrom, elections spokeswoman.

Ballots must be postmarked by Tuesday.

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Ballots in special elections, in which voters decide on just an issue or two, often come in somewhat sooner than in elections with a full slate of candidates and issues for voters to consider, van Ekstrom said.

For Proposition 1’s friends and foes, this weekend is time to hit the streets and light up the phone banks for one more shot at voters who haven’t yet decided on the measure that includes a $60 car-tab fee and a one-tenth-of-a-cent increase in the sales tax.

“We’re still finding that a lot of people don’t know they have a ballot at home, or why they have a ballot at home,” said April Putney, campaign manager of Move King County Now, backing the measure.

Among the areas in which the measure’s supporters will be out in force are Kirkland and the University District, two areas that Putney said will be hit hard if Metro Transit makes the 16 percent service cut it says will be necessary if the measure loses.

Opponents, operating with far less money and fewer endorsements, still hope to get their message across that Metro needs to do more to cut spending instead of asking for more revenue.

Mark Baerwaldt, working with two groups opposing the measure, says it’s important for those who object to the tax and fee to “stand up and speak out,” whether that’s by doorbelling, posting yards signs or holding banners at busy intersections.

“It’s typical campaigning,” said Baerwaldt, who has worked on other anti-tax campaigns. “There’s nothing magical about it.”

In themes struck by the two campaigns, each portrays its position as the best way to help others.

Backers say a yes vote is needed to maintain bus routes that serve seniors, working families, students and people with disabilities.

They say people who drive to work would benefit as well, predicting that a defeat of the measure would put tens of thousands more cars on the roads every day.

But the opposing Families for Sustainable Transit says a no vote is a bigger help to working families, allowing them to keep more money in their pockets.

Together, the car-tab fee and sales-tax hike would cost the average family an estimated $11 a month, according to county economic analysts. Both would run for 10 years. The measure would raise an estimated $130 million a year, with about 60 percent going to Metro Transit for bus service and 40 percent to fund roads and other transportation needs in cities and in unincorporated King County.

Metropolitan King County Council Chairman Larry Phillips said the tax and fee are needed because of the Legislature’s inaction on a statewide transportation funding plan that might have included a more dependable source of funding.

On Thursday, Bellevue Mayor Claudia Balducci and Redmond Mayor John Marchione joined Seattle City Councilmember Tom Rasmussen in Seattle at the presentation of plans for a zip line from Seattle to the Eastside — a tongue-in-cheek preview of alternatives they said bus riders may need to consider if the measure fails.

The advantage that Proposition 1’s backers have in money and endorsements is immense.

Move King County Now has reported donations from 600-plus donors totaling $648,000 — more than 40 times the total raised by Families for Sustainable Transit and another opposition group,

Those favoring the measure also tout the backing of more than 275 organizations and community leaders, including business, labor, civic, environmental and educational groups, social-service agencies, large employers, 20 mayors, Democratic Party groups and seven Metropolitan King County Council members, including two Republicans.

The County Council voted unanimously to put the measure on the ballot, but not all members have signed on as supporters.

County Council Vice Chairwoman Jane Hague, a Republican, joined Democratic state Rep. Cyrus Habib of Bellevue this week to co-author a piece endorsing the measure in Eastside newspapers. Failure of the ballot issue, they said, would hurt Eastside workers and students.

The lead opposition group, Families for Sustainable Transit, lists 26 participating groups, most of which are Republican legislative-district organizations, and the endorsement of The Seattle Times.

Opponents say Metro should find ways to live within its income, which has climbed as sales-tax revenue increased after the recession.

Baerwaldt said it’s not his preference to be so outgunned in a campaign.

“If we had a lot of money and could flood the airwaves I would rather do that, but we’re doing what we can to get our message out,” he said.

He said if you’re fighting an unpopular tax, you may not need the most money.

And he noted that in 2011, Seattle voters solidly turned down a measure that would have created $60 car tabs for transit and street projects.

Roughly two-thirds of the money raised by Proposition 1 opponents has come from a single source, North Seattle businesswoman Faye Garneau.

Garneau, known for her work against tax measures and the successful effort to have Seattle City Council members elected by district, said she donated $10,000 to oppose Proposition 1 because, “I just feel that government is out of control and this is not a good time to be raising taxes. Government has to learn to live within its income.”

The largest donation to the pro-Proposition 1 campaign has been $50,000 from Local 1488 of the Washington Federation of State Employees, which represents University of Washington employees in a range of jobs on campus and at Harborview Medical Center. A union spokesman said many of those workers commute by bus and need quality transit service.

Local and international organizations of the Amalgamated Transit Union, representing bus drivers and other transit workers, each has given $20,000 to the campaign for Proposition 1.

Other top contributors have included Amazon ($25,000) and Vulcan ($20,000), each with workforces that rely on public transportation.

Large donations have also included $25,000 from Titan Outdoor, which handles advertising on buses; $20,000 from Veolia Transportation, which operates wheelchair-accessible vans; $20,000 from would-be NBA owner Chris Hansen’s Sonics Arena/ Horton Street; and $15,000 from the Downtown Seattle Association.

The pro-Proposition 1’s major expenses have been for mailers, Internet advertising and consulting services.

Seattle Times news researcher Gene Balk contributed to this report. Jack Broom:

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