Two years after elected leaders announced a deep-bore tunnel would replace the Alaskan Way Viaduct, there might still be a few people who haven't chosen sides.

Campaigns are pursuing them.

Ballots must be postmarked by Aug. 16 in a Seattle mail-in election. Referendum 1 deals with a process clause telling the City Council how to enact permitting agreements with the Washington State Department of Transportation, before a scheduled September groundbreaking.

More importantly, the referendum amounts to the public's only advisory vote on the $2 billion, four-lane tube.

In a last-ditch bid for swing votes, pro-tunnel Let's Move Forward and anti-tunnel Protect Seattle Now are sending some surprising messages.

Tunnel backers are portraying a plan for highway lanes as a boon for transit. And the opponents, many of whom want to reduce driving, are courting car commuters by publicizing the cost of tunnel tolls.

Here's a critique of three points made by each side:

• Pro-tunnel signs: big bus

The white bus icon on the green Let's Move Forward yard signs is so big, it's practically driving off the edge. Transit is a time-tested winning angle in Seattle, where huge margins voted yes to boost Metro bus service in 2006, and to expand Sound Transit rail in 2008.

But the tunnel isn't meant to be a transit project. State lawmakers decided it would have general-purpose lanes. And they did not allow King County to enact a 1 percent car-tab tax for Metro that leaders promised.

Conceivably, a tunnel could serve public or private express buses, from Greenwood to a game in Sodo, or West Seattle to South Lake Union, for instance. No one proposes such routes at Metro, now struggling just to prevent service cuts.

The Highway 99 project does provide a little transit — some $31 million for buses during construction, and then bus-only exits would operate near the tunnel at South Lake Union and Sodo. County Executive Dow Constantine says without a highway tunnel, there would be longer traffic jams that delay buses.

• Anti-tunnel prop: blue tollbooth

Opponents have seized on the high cost of tolls as a reason to vote "reject."

The state predicts a range from $1 overnight to $5 (2015 dollars) in the southbound afternoon peak, to cover $400 million of the construction costs.

As a show of solidarity with motorists, Protect Seattle Now has brought a "$5 TOLL" booth to Aurora Avenue North and other busy streets.

But a suggested tunnel alternative — relying on surface streets, more transit and Interstate 5 — would require thousands to leave their cars behind.

Tunnel opponent and Mayor Mike McGinn, when running for office two years ago, agreed with studies suggesting that 50,000 of the viaduct's 110,000 daily car trips need to be phased out, for a non-highway option to succeed.

"The public knows we need to make this transition, and the way you make this transition is how you invest your dollars in the future," he said. "And an investment in a 1.7-mile buried highway that doesn't even connect to downtown and serve transit is just a really poor investment in our future."

The toll proposal does pose a genuine problem, because studies say 40,000 or more drivers would dodge tolls by using nearby streets. Anti-tunnel campaign manager Esther Handy said the booth serves as a quick reminder. The Federal Transit Administration worries spillover traffic would clog access to the Third Avenue busway and state ferry terminal. Project Administrator Ron Paananen says the state needs to find a way to reduce the rates.

• Pro-tunnel ad: "McGinn and Eyman"

In a Let's Move Forward TV ad, a driving grandmother says: "Now Mayor McGinn and Tim Eyman want to stop the project, tear down the viaduct and replace it with, nothing?"

The pair are portrayed as a kind of Axis of Evil, due to liberal Seattle's distaste for anti-tax balloter Eyman, and the pro-tunnel campaign's portrayal of McGinn as obstructionist.

It's true Eyman has dabbled in the tunnel spat for fun, and to promote his Initiative 1125, which has qualified for the November statewide ballot. His measure would ban tolling that raises prices at rush hour and lowers them off-peak, as DOT desires, to raise money or control traffic volumes for several highways. But the two are not partners.

Eyman, of Mukilteo, said Friday he prefers fixing the old viaduct. McGinn would remove it, and he opposes I-1125.

• Anti-tunnel statement: "No exits downtown"

For obvious reasons, a tunnel 200 feet deep won't provide midtown ramps like those on the current viaduct, at Seneca and Columbia streets.

Tunnel opponents stress the "no exits downtown" in boldface in the Voters' Pamphlet. But the state is trying to compensate with a wider six-lane Alaskan Way from the ferry terminal to Sodo. Drivers coming in from the south would exit at Sodo, then enter downtown by turning uphill from Alaskan Way.

In any case, the viaduct's midtown exits serve only the traffic to or from the south. With the tunnel, routes entering downtown from the north would be much like today. A more serious criticism, made by Cary Moon of the People's Waterfront Coalition, is that cars would cut through historic Pioneer Square, especially if high tolls cause motorists to avoid the tunnel. And the environmental-impact statement presumes buses will go through Washington and Main streets.

• Pro-tunnel flier: "waterfront parks"

Let's Move Forward suggests that the "Practical, State Funded Solution" includes waterfront parks, open space, salmon habitat and stormwater improvements.

But the city, not the state, would need to fund the parks and open space, thought to be around $123 million. Potential sources could be fees on nearby landowners, or a voter-approved tax measure.

The state is paying to demolish the old viaduct — freeing up nine acres of open space — and to build a waterfront boulevard with bikeways. Tunnel opponents note that similar parks would be part of any nonhighway plan. A tunnel would reduce and contain runoff that now splashes off the viaduct.

Anti-tunnel brochure: "tax increases"

The tunnel "would result in significant tax increases to cover the remainder of the $700 million project funding deficit," opponents say. This is conjecture.

King County taxpayers will be contributing through the Port of Seattle, which pledged $300 million. Port officials insist the money is available without a property-tax hike. However, they likely would sell bonds around 2016, covered by prolonging the existing property-tax stream — instead of trimming the tax rate, or having those dollars free for environmental projects and paying old debts. Another $400 million is to come from tolls.

In the event of a shortfall, the state would need to raid other highway funds or find dollars through other tolls, statewide gas taxes or car fees. These costs are borne by motorists.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com