Each module traveled approximately a mile from the modular yard, overnight, across the airfield on self-propelled modular transporters (SPMTs) provided by Mammoet. The first set of modules were 29 ft wide, with the last four at 48 ft, says Pete Pemantell, Holder vice president. “They were also built with a lot more interior improvements” such as drywall, restrooms and elevator shafts. “The first ones were big empty spaces,” says Pemantell. While those were scheduled for one move a week, the team overcame the learning curve and scheduled the second batch for two moves a week. “We learned the process and gained confidence,” he says.

The completed moves of the first 10 modules “is a significant milestone because it represents about 50% of project completion,” said Frank Rucker, ATL’s senior deputy general manager for infrastructure, in a press release. “This is just Phase 2. We’ve still got a long way to go. It’s a very complicated construction because we’re operating with an active concourse.”

Over and Back

Over the next two years, the expansion of Concourse D will shift to non-modular construction techniques to increase the height and width of the concourse’s north section. Sections of the existing concourse will be temporarily closed to facilitate the removal and replacement of roofing, ceiling structures and other essential components.

“We have added the 30-ft-wide ‘boxcars’ on the east side, and now we’re adding to the end of the concourse to lengthen it,” says Pemantell. “As we finish that space, we will work back toward the midpoint of the concourse in a horseshoe sequence. On the return trip, we will be building over the top of the existing concourse.”

Since the new module heights are more than that of the existing concourse, “we’ll install columns on one side and beam over the concourse to join the modules,” Pemantell adds. “We will encapsulate the building, then demolish the existing roof and walls down to the boarding level inside the shell of the new building” using robotic equipment. As demolition moves forward, crews doing interior fit-outs will follow. 

“The modules we put in place last spring serve as hold rooms now, but once we’ve built up and over to the west, the seating will be removed and [the space] will be a circulation corridor,” he adds.

While the team had to ensure that at least eight gates were operational at all times on the north side of the concourse, it can demolish the south side to grade and start with bare foundations, Pemantell notes. When that work begins in late 2027, the remaining nine modules will be even bigger, with 96-ft widths, he says.

Making the Case

Initial plans for the project entailed expanding the concourse up to 105 ft, but keeping as many gates open as possible during construction and maximizing efficiency led to the idea of using modular, says Ross Payton, principal with Corgan, with which Goode Van Slyke leads the design team. Building new concourse sections offsite minimized the need to access the airfield during the day, requiring security checks. 

ATL’s use of modular follows that of its Dallas-Fort Worth and Los Angeles counterparts, but whereas the Los Angeles International Airport project added the modules to the existing concourse and Dallas-Fort Worth International Airport could completely demolish the existing building, “here, we facilitated [operational] gates along that concourse throughout construction,” Payton notes. 

The overall concept included a 31-ft expansion on the east side of the building and a 10-ft expansion on the west. The building footprint totals 211,000 sq ft at the apron and boarding levels with an additional 20,000-sq-ft airline lounge at the roof level. When completed in 2029, Concourse D will have 34 new gates that accommodate larger aircraft and provides 20% more seating at peak period, according to WSP, which along with joint venture partners H.J. Russell & Co. and Turner & Townsend Heery serves as program manager for the city of Atlanta’s aviation department’s overall $20-billion ATLNext capital improvement program.

In late 2022, the team began evaluating how to deliver the expansion of Concourse D, says Trevor Lee, senior project manager for H.J. Russell. “We didn’t start this project saying, ‘hey, we’re doing modular,’” Lee says. “We had to have our design team on board, we had to have our construction manager at risk on board, and we had to look at various different methods.”

All the moving parts had to be taken into account, including operation of the world’s busiest airport, which makes more than $350,000 in revenue per day per gate, Lee adds, leading the team to begin calculating how to best operate within the constraints of the project, including closing only eight gates at a time. For a forecasted construction period of 46 months, closing the entire concourse could’ve cost the airport upwards of $400 million.

“We looked at the pros and cons to each of those delivery methods, looking at budget, looking at schedule, looking at phasing, and the reason modular stood out was it was a business case,” Lee says.

Locating the modular construction site on the public side of the airport was a strategic move, too, meaning workers and material deliveries don’t have to go through normal airport security, increasing efficiency. Constructing the modules offsite allows work on the module itself and at the existing concourse to occur simultaneously, he adds, another boost to efficiency.

For instance, in phase one, Lee says the first steel delivery was made Dec. 4, 2023, kicking off steel erection in the modular yard one month before the gates were closed and foundation work started at the concourse.

The modular method does require two construction sites to be maintained: one where the modules are constructed and another at the concourse, taking up more resources. Extra permitting with the FAA is required, and added costs come with third-party quality assurance measures via special inspections.

Playbook Procedure

In preparation for the existing concourse to receive the modules, foundations and underground utilities were first installed. Constructed via structural steel with insulated metal panel curtain wall, the modules were placed atop the foundation slab. Utilities like chill water supply, return piping, electrical and duct work were then stitched to the existing concourse from inside the modules, Lee says.

Preparations began four or five days before the day of the move as the team did an hour-by-hour breakdown of each task and who is responsible, from structural engineers to trade partners. Both Lee and Pemantell call it a "run of show." While taking into account the experiences of LAX and DFW, "we wrote our own playbook," says Pemantell. "We drilled down into every risk. Each move had its own book. Each book had a timeline of events that had to happen."

Lee adds that each move started with a “go, no-go” decision at noon. If wind speeds are higher than 26 miles per hour or visibility less than 200 ft, or for other factors like severe weather, the move is called off. 

Ahead of time, the route was prepared to ensure smooth travel for the SPMTs, and pre-survey tests ensured the as-built conditions before baseline scans and the position of the SPMTs underneath the module itself.

“It’s almost like we have a command center right here at the mod yard,” Lee says. “To make sure we’re all on the same page, [we’re] talking to each other in real time. Then we execute the move.”

Once the module move starts, email and text messages went out to update the stakeholders that it’s underway, and another when it’s completed. Representatives from each trade and airside operations walked with the module, followed by support vehicles and a sweeper.

"We had contingencies—equipment on hand, for example if a module got stuck on a runway, we could handle it," says Pemantell. "We could demolish the module, load it up and get it out." That fortunately never happened.

With the last of the first 10 modules moved, foundation work will start for the next set, for which steel erection is set to begin in the second quarter of 2026. Those modules will be moved at the end of 2026 and into 2027.

The expanded concourse actually will have fewer gates—34 versus 40—but they will be able to handle larger aircraft that have 6,400 seats versus 5,400, notes Payton. As airport builders gain experience with the method, future modules could extend beyond 200 ft, he says, noting that "the initial modular move was about 90 minutes. By the final one, it was down to 45."