Explaining Accelerated Bridge Construction, the technique used for the collapsed Miami bridge

PHOTO: This March 10, 2018 drone image shows an early morning view of the main span of the a pedestrian bridge while being positioned to connect the City of Sweetwater, Fla., to Florida International University near Miami.PlayThe Miami Herald via AP, FILE
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The technique used to build the bridge that collapsed in Miami today was intended to cause less disruption and make installing new bridges easier.

The bridge that fell near Florida International University was put in place using Accelerated Bridge Construction (ABC) methods, and there is a school at the university dedicated to advancing those techniques.

Accelerated Bridge Construction a process where planners actively consider how bridge construction impacts local traffic flow and try to shift as much construction to be done in advance and off-site before moving those pieces onsite.

The Department of Transportation's Federal Highway Administration calls ABC "a paradigm shift in the project planning and procurement approach."

Janey Camp, a research associate professor in civil engineering at Vanderbilt University, said that ABC methods have been "gaining more visibility" in the past decade and were used for 10 bridges in Tennessee a few years ago.

Camp explained that a signature of ABC methods is "really condensing the timeline" of bridge construction.

"Instead of closing traffic for long periods of time as you build all parts of the bridge on-site, you can reduce the impact to the traffic if you can build some parts off-site and then move them to the site and then put them in place," she said.

PHOTO: This March 10, 2018 drone image shows an early morning view of the main span of the a pedestrian bridge while being positioned to connect the City of Sweetwater, Fla., to Florida International University near Miami.The Miami Herald via AP, FILE
This March 10, 2018 drone image shows an early morning view of the main span of the a pedestrian bridge while being positioned to connect the City of Sweetwater, Fla., to Florida International University near Miami.

According to the FHA, ABC leads to improvements in safety, durability, social costs and environmental impacts of construction projects.

Specifically, it improves site constructability, total project delivery time, and work zone safety for the traveling public, while reducing traffic impacts, on-site construction time, and weather-related time delays, the FHA states.

Camp, who is on the American Society of Civil Engineers' committee for America's Infrastructure, said that ABC is "a positive thing," noting that in many instances "you're replacing old infrastructure with new infrastructure while also [limiting] the impact it has to traffic flow."

The FHA states that approximately a quarter of all of the country's 600,000 bridges require repair or replacement, and the cost of traffic detours that are used during those repair periods "can exceed the actual cost of the structure itself."

Andy Hermann, a former president of the American Society of Civil Engineers, told ABC News that ABC methods are a "very good way to construct our bridges."

At this point in the investigation, it is difficult to point to a specific problem area as the possible cause of the collapse.

"It could be materials, it could be construction technique, it could be the engineering design itself," Hermann said.

"With the ABC type of construction, there are design loads that have to be taken into account for the actual moving of the bridge. ABC construction essentially builds a bridge off-site and then moves it into place for its final position. And when you do that you have different load points, different supports for the bridge that are different than the final supports. So you have to take account for that when you design the bridge,' he said.

Hermann said that if he were evaluating what went wrong in this case, he would start by looking at the different phases of the construction process.

"Did they put enough material into the bridge to withstand the moving loads? Look at the design itself, make sure everything has been accounted for. Look at the construction techniques, look at the materials. All these things are factors into a construction of bridge safety," he said.

ABC News' David Kerley contributed to this report.

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