It didn’t happen as quickly as Chairwoman Lisa Cupid wanted, but her Democratic colleagues came around: A majority on the Cobb County Board of Commissioners now say they support a mass transit referendum in 2024.

At a work session this week, all three Democrats backed a 30-year sales tax that could generate billions of dollars for mass transit, setting the stage for a vote in November 2024.

Formal votes to authorize the referendum, set the project list and the amount of the sales tax — up to 1% — won’t come until later. But Tuesday’s discussion gave county transportation officials the go-ahead needed to begin preparations for what’s likely to be a uphill battle for transit supporters in the sprawling suburb.

Cobb County has long had a complicated relationship with mass transit. The northwest Atlanta suburbs famously opted out of MARTA in the 1960s, dashing the hopes for a true regional transit system at a time when the interstate highway system allowed white flight and development to accelerate outward from the capital city’s core.

Today, Cobb has its own transit system, CobbLinc. But connections to MARTA remain sparse and inconvenient for commuters.

County transportation officials say the proposal would be a major step toward a true regional transit system, funding new services, such as bus rapid transit lines that could connect South Cobb and cities along the I-75 corridor to MARTA stations in Atlanta.

The money could also help with Cobb’s portion of a regional project to install bus rapid transit routes along the top end of I-285. Late last year, commissioners agreed to spend $547,000 on its share of a $16 million study for the project, a first-of-its-kind collaboration with MARTA and three other metro Atlanta counties.

If the sales tax is approved, Cobb’s long-term transit plans also call for expanding local bus routes and improving connectivity between key county nodes such as the Cumberland area, South Cobb, and cities such as Marietta and Smyrna.

Commissioner Monique Sheffield, who represents South Cobb, said she struggled with the 30-year length of the tax, but ultimately decided long-term investments are needed. Since 1990, the county has grown from a population of 447,745 to 766,000 today. By the time a 30-year tax would expire, demographers anticipate Cobb will have more than 1 million residents.

“Our decisions on transportation and transit should be contemplated through the lens of a generational investment,” said Sheffield, a Democrat from District 4. “How will our decisions today benefit your grandchildren and their children?”

The Democratic majority will have to authorize the ballot measure along party lines. Many county residents have no desire to spend their tax dollars on transit, and Republicans Keli Gambrill and JoAnn Birrell, who represent less dense suburban and rural areas, oppose the 30-year tax. They prefer to consider a 5-year transportation tax that could be used for roads and sidewalks.

“In West Cobb they are OK with not having transit,” said Gambrill, the District 1 commissioner. “They don’t want that.”

Conservative opposition to transit became a campaign issue for cityhood supporters, even though cities have no control over whether the county holds a transit referendum. Voters rejected all three cityhood questions on Tuesday.

Cupid had initially pushed for a referendum this fall, but the delay could work in transportation advocates’ favor. It will be a presidential election year, which has higher turnout than midterm elections.

Waiting has an opportunity cost, as well. The sooner the election is held, the sooner the county can hope to capitalize on federal transportation funding that is often awarded to places willing to make sustained local investments of their own.