"Hotlanta" has fizzled and it will take a bold plan like the Transportation Investment Act to help the region recover, a nationally known urban planner told a Thursday gathering of metro Atlanta leaders.

"You all have a lot of work to do," Brookings Institution visiting fellow Chris Leinberger told the 475 people attending the South Metro Development Outlook conference. An expert in land use and urban development, Leinberger outlined how metro Atlanta has fallen out of favor nationally as a business hub and is now competing with cities like Phoenix, Salt Lake City and Dallas, cities once overshadowed by Atlanta.

"You're not Hotlanta anymore," he said.

The 10-year-old conference, held at the Georgia International Convention Center in College Park, drew some of the region's top executives in business, education, civic and government, a strategic platform to pitch support for the July 31 transportation referendum. If passed, the penny-tax is expected to raise $8 billion and generate 200,000 more jobs over 10 years for a host of regional projects.

"This is the most important transportation investment you'll make in the early part of the 21st century," said Leinberger. "Why is transportation important? Transportation drives development. You invest in transportation for economic development, not to move people around."

A panel of four southside county leaders who helped craft the referendum -- Eldrin Bell (Clayton), Elizabeth "B.J." Mathis (Henry), John Eaves (Fulton) and Tom Worthan (Douglas) -- told the crowd the referendum represents a chance for the region to work together to fix its traffic woes, now among the worst in the nation.

Eaves said approving the initiative is "critical to getting our economy back up and running and to improving the transportation connectivity that will help us compete for jobs in the 21st century."

Clayton County wasn't granted everything it wanted in the final list, but Bell said the referendum is "more important than any individual county because we're all woven together in what we're going to do."

Noticeably absent from the conference were officials from Fayette County.

"If we’re going to do something like the TIA, we need to have a meaningful project list," said Fayette County Commissioner Steve Brown, who was unable to attend the conference due to a prior commitment. "The [public] transit thing is the major problem. Ridership is declining. The costs are exorbitant and 95 percent of metro Atlanta commuters choose to do something else besides ride transit."

One audience member stumped the panel by asking what happens if  the referendum fails.

Mathis responded: "There is no Plan B. If this fails, I see this whole region declining and going backward."

The Collaborative Firm, an East Point urban planning and development firm, hosts the annual conference.

"July 31 marks a major date for the future of this region," said Michael Hightower, managing partner of The Collaborative Firm. "[Transportation] is the biggest issue in the region and our state for years to come ."