ATLANTA — For decades, Atlanta has been the economic engine of the South, a dynamic city on the move. But if you’ve ever gotten behind the wheel here, it doesn’t feel that way.

The Atlanta metropolitan area has some of the worst traffic in America, with drivers routinely stuck in monumental, bumper-to-bumper jams that can turn a 10-minute trip into a miserable, one-hour slog.

Hoping to ease the gridlock, the region’s political and business leaders are pushing for a 1-cent increase in the sales tax to pay for billions of dollars in highway improvements and other transportation projects. The proposed tax is on Tuesday’s ballot.

Civic leaders say that Atlanta’s economic future hangs in the balance, with the metropolitan area in danger of losing business to more-livable cities unless it acts now to reduce congestion.

“Tampa, Charlotte, Denver, Dallas ... they all hope we lose,” said Metro Atlanta Chamber of Commerce President Sam Williams. “The competition has been taking advantage of this.”

Atlanta’s traffic problems have been 50 years in the making, a consequence of runaway growth. The metropolitan area’s population swelled from nearly 1.6 million in 1960 to more than 5.2 million in 2010, and many of the newcomers settled in suburbs radiating farther and farther from Atlanta’s core.

Now those commuters are clogging the highways that run straight through the city or form a big ring around it. While Atlanta does have a commuter rail system, it is laid out basically like a big plus sign and doesn’t reach many parts of the city. And there has long been opposition to expanding it.

The TomTom Congestion Index, compiled by the maker of automobile GPS devices, has ranked Atlanta the nation’s eighth-most clogged city. According to the 2010 census, Atlanta had the fourth-worst commute in America, with drivers taking an average of 30 minutes to get to or from work.

From billboards to beauty shops, the campaign for the tax has been hard-fought in recent weeks, and polls suggest the vote could be close.

Metro Atlanta is one of a dozen regions across Georgia that will vote independently on the tax increase, which could generate a total of more than $18 billion statewide for transportation projects over the next decade.

Atlanta stands to gain the biggest share. Supporters estimate the 1-cent increase would generate more than $8.4 billion between 2013 and 2022. The sales tax in the region is now around 5 or 6 cents on the dollar in most cases.

Each region developed a list of projects involving such things as roads, bridges, mass transit, ports, airports and bicycle and pedestrian facilities. Metro Atlanta’s list is heavy on road projects — including the widening or resurfacing of highways, the building of new ramps and reconstruction of a busy interchange — and light on mass transit.

Opposition in metro Atlanta has crossed political and racial lines, creating unlikely allies and adversaries.

Pro-business Republicans, including Gov. Nathan Deal, are finding themselves at odds with tea-party leaders in the GOP, who argue government can’t be trusted to manage the tax revenue responsibly.

The fiscal conservatives have made common cause with black Democrats, who say the plan doesn’t do enough to help poor people and minorities because it devotes little to mass transit and overlooks some sections of the city, and with environmental groups, which fear more pollution and development.

“We’re just united against a bad idea,” said Neill Herring of the Sierra Club. “We’ve got to break this sprawl habit.”

Supporters have bankrolled an $8 million campaign under the banner Untie Atlanta and say the transportation projects will create jobs via the construction work itself and the improvements that will ease congestion and make the city more attractive to companies looking to relocate.

“As a result of our failure to deal with our traffic issues as other leading cities in the world are doing far more rapidly, we risk entering a period of decline,” Mayor Kasim Reed said. “This is our region’s leadership moment.”

Nikki Strickland’s commute to work in Atlanta is 30 minutes each way on a great day. But if she leaves the house in suburban Alpharetta after 7:30 a.m., it’s too late. Then the drive takes an hour or more.

Her husband’s trek into midtown isn’t much better. “He can get completely stuck for hours if the wrong thing happens,” Strickland said.

She said she is considering voting for the tax but is conflicted. Taxing groceries — something everyone has to have, unlike a new car — isn’t fair, Strickland said. Moreover, she said, “I just don’t feel like Atlanta is serious about transit. And I don’t trust our institutions to do this. State government is so dysfunctional.”