In most political campaigns, each side goes in with a pretty good idea of who its voters are, and the final week is only about getting the rock-solid ones to the polls — never mind the loosely committed or might-be-persuaded.

Then there’s the July 31 transportation referendum. With a number of polls suggesting that the measure will fail, Citizens for Transportation Mobility, the lead advocacy group urging voters to “Untie Atlanta” by voting yes, is going after unlikely and undecided voters with zeal.

CTM strategist Paul Bennecke said the organization has identified about 25,000 people who favor the transportation improvements but are ho-hum about actually voting, and it’s trying to give them the extra nudge to get to the polls.

“All along we’ve planned our effort around impacting the voter turnout model, meaning we need to turn out new and low-propensity primary voters who support the transportation referendum,” Bennecke, the Republican half of the campaign’s bipartisan brain trust, said via email. “It’s one of the hardest things to do in a campaign, especially a primary election on a summer day in July, but we feel it will make the difference.”

Meanwhile, foes of the $6.14 billion transportation measure are working on several fronts, despite lacking anything like the financial resources enjoyed by the Untie Atlanta campaign.

“This is a grassroots, guerrilla campaign going on, and the best thing happening now is all of the anti-T-SPLOST people are coordinating,” said Sen. Vincent Fort, D-Atlanta, who was recently joined by representatives of the NAACP, the Sierra Club and the state’s Tea Party Patriots for a press conference outside the state Capitol. “I’ve never seen anything like it.”

It’s no surprise that tea party adherents would oppose the 10-year, one-cent sales tax. But the presence of some NAACP leaders and the Sierra Club on one side, lined up against Atlanta Mayor Kasim Reed and the Atlanta Bicycle Coalition on the other, shows just how impossible it is to draw a straight line dividing supporters and foes on this issue.

Alan Abramowitz, an Emory University political science professor, said that fracturing, particularly among the African American community, is a considerable setback for T-SPLOST supporters.

“The African American vote is absolutely crucial to it. Traditionally, African American voters have been much more willing to support public spending and tax increases,” he said

On the other hand, he said, the pro-T-SPLOST campaign’s unconventional strategy of targeting unlikely voters has some merit.

Primary races have historically low turnouts, meaning that the CTM could actually swing the election by turning out a few thousand extra votes.

And unlike a partisan election, Abramowitz said, he suspects that many potential voters haven’t yet chosen sides, something that will change as the media storm heats up.

“I think a lot of people are just starting to focus on it, and that’s what gives this thing a chance,” he said.

Certainly, as anyone with a mailbox and television in Atlanta has likely noted, the pro-T-SPLOST campaign has the resources to far out-advertise the opposition. Funded by large donations from some of Georgia’s best-known businesses, CTM expects to shell out between $3 million and $5 million this month.

With no clear party lines and no specific geographic base, the campaign’s challenge is to engage voters with a wide range of political ideologies, in widespread locations with diverse transportation needs, said Kevin Ross, CTM’s Democratic strategist.

To that end, the campaign has created 11 different spots for cable television, each targeted to a different part of the region, promoting individual projects that will be built if the tax hike passes. They are accompanied by similarly targeted mailers as well as radio spots.

“This is a very complex election, a complex campaign,” Ross said. “In some respects, statewide campaigns aren’t this complex, because you tend to have the party element that gives it a little bit more definition.”

Opponents may have less money, but they’re not without tools to spread their message, said Sheila Brown, community coordinator for the state’s NAACP.

The NAACP is mobilizing its members through social media, email blasts and by hosting transportation forums, she said. It’s also reaching out to churches, asking them to place anti-T-SPLOST materials inside their Sunday bulletins.

The group’s efforts are aided by prominent radio hosts within the black community, such as Derrick Boazman, who joined in the press conference at the Capitol.

“Whatever forums we can use, we plan to,” Brown said.

The Sierra Club, meanwhile, is dispatching members to speak at public events, arguing that the project list is too weighted toward highways.

For its part, the Tea Party Patriots is working the phones, said Debbie Dooley, Georgia state coordinator. The group purchased both Republican and Democratic voter lists and has organized home-based phone banks to reach voters.

J. Kyle Tilley, of Dallas, plans to vote no, but not because of any outside persuasion. Unemployed since the housing crash, the former building materials salesman made up his mind as soon as he learned the initiative involved a 10-year, one-cent tax.

“The ads do not help nor hinder my decision to vote no,” said Tilley, now a stay-at-home dad to three young children, via e-mail. “After decades of misusing road funds, it will be hard for me to vote for any taxes.”

But Teresa Burrell said the pro-T-SPLOST ads persuaded her to vote yes.

“I knew no details at all before, and the ads have helped me decide how to vote,” she said via email. “I live in Douglasville, but the traffic situation affects all of us, and I will support it because of all the different ways that ads have shown it will help with the gosh-awful traffic.”

- Staff writer Shannon McCaffrey contributed to this article.