Hartsfield-Jackson International Airport is starting a massive project to double the size of its parking decks, an effort expected to take at least eight years and hundreds of millions of dollars.

Parking is an important service that can cause frustration for travelers when they can't find a spot and are rushing to catch a flight. But it's also one of the biggest sources of revenue for the airport. And, the airport faces big competition from private off-airport parking lots.

SECONDARY PHOTO: April 23, 2013 - Atlanta, Ga: With the control tower in the background, a traveler walks toward the north terminal from the parking deck at Hartsfield-Jackson Atlanta International Airport Tuesday morning in Atlanta, Ga., April 23, 2013. Nearly a year after the Atlanta airport opened its new international terminal, it is already planning for the next expansion. Hartsfield-Jackson International Airport's master plan study shows the airport will soon need more parking, and will also need more people-mover train capacity inside the terminal, more security screening line space, more gates and more airfield capacity - such as another runway -- in the next 20 years JASON GETZ / JGETZ@AJC.COM

Credit: Kelly Yamanouchi

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Credit: Kelly Yamanouchi

More than 100 people interested in a contract to design the project to demolish the aging parking decks and rebuild new ones attended a meeting Tuesday at Hartsfield-Jackson. A separate contract is planned for construction of the parking decks.

The expansion of the world's busiest airport's domestic terminal parking garages is part of Hartsfield-Jackson's master plan unveiled last year, when the airport revealed the project was estimated to cost $550 million to $750 million in 2014 dollars.

Hartsfield-Jackson spokesman Reese McCranie said the existing decks are decades old and not structured to support the weight of four additional levels.

A key reason the project is expected to take so long to complete is that the airport must keep parking available for travelers while it demolishes each deck and rebuilds at the same site.

"That's a huge challenge," said Hartsfield-Jackson development program director of project management David Pino. "That is the task."

Maintaining traffic flows -- and revenue -- "is of paramount importance," Pino said.

To provide parking during the work, the airport plans to build a third parking deck next to the Georgia International Convention Center to accommodate about 6,000 cars. People using that deck will have to take the existing SkyTrain people-mover to get from that parking structure to the terminal.

"People won't be impacted until the fall of 2017, " McCranie said. "We will have a replacement deck in place once we start construction and replacement of the parking structures."

The new parking decks will double in size to eight levels, with a planned 15,000 parking spaces on the Terminal North side and 17,000 parking spaces on the Terminal South side. Also planned are pedestrian bridges on level four -- which would allow travelers to avoid walking across the busy roadway.

Today, the parking garages have four levels, with a total of about 13,000 spaces in the decks out of a total of 29,000 public spaces at the airport.

The airport also plans to build a third parking deck to accommodate about 6,000 cars while the old parking decks are being rebuilt.