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When a trio of homeless men allegedly lit a pile of construction materials ablaze beneath an I-85 overpass in Atlanta, Georgia, in late March, the conflagration destroyed a 100-foot section of the bridge, which plummeted to the ground and brought traffic to a halt. With a chunk missing from a major transportation artery in one of the world’s most congested cities, highway officials knew they had to act fast—that stretch of road carries about a quarter of a million vehicles every day.
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Using not-so-new techniques formulated to address America’s long list of aging spans, the Georgia Department of Transportation rebuilt the collapsed overpass in a little less than two months, replacing 350 feet of roadway.
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As infrastructure projects go, that’s a lightning-quick turnaround that could serve as a model elsewhere. The majority of America’s roadways received a D grade earlier this year in the quadrennial infrastructure report card issued by the American Society of Civil Engineers. Bridges fared somewhat better, earning a C+, and officials from ASCE attribute the better grade to a building technique known as Accelerated Bridge Construction, or ABC.
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There are more than 600,000 bridges in the United States, and nearly a quarter of a million are more than 50 years old. Since the White House has stated it would like to spend as much as $ 1 trillion on infrastructure—a detailed plan has yet to take shape—it’s possible transportation planners could get needed funds to restore these aging spans. ABC, which first emerged about 30 years ago, could play a big part in upgrading more than 56,000 bridges that ASCE deems structurally deficient.
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“ABC is bridge construction that uses innovative planning, design, materials, and construction methods in a safe and cost-effective manner to reduce the on-site construction time that occurs when building new bridges or replacing and rehabilitating existing bridges,” according to the Federal Highway Administration. Basically, highway planners use more prefabricated materials so that work crews need not perform several labor-intensive, weather-dependent construction processes such as subframe placement, steel reinforcement installation, and concrete work on-site at the bridge.
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By bringing in finished footings, headers, decking, and other parts, fewer workers are needed on-site. As FHWA pointed out in the ABC manual it published in 2011, this bears a number of benefits—notably fewer, shorter-duration traffic disruptions and therefore less danger for both travelers and workers.
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Benjamin Beerman, a civil engineer with the Federal Highway Administration, said the process also aims to limit traffic-related disruptions to essential services including police, fire, and ambulance vehicles, school busing, mail delivery, and garbage pickup. There are also environmental and safety improvements.
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“From a national perspective, the industry is getting better at recognizing how these other aspects interrelate with one another and how innovations in planning, design, materials, and construction can be used to address the need to minimize on-site construction time,” he said. In the past, cost-reduction goals often led to slower completion, which in turn had impacts outside the construction zone.
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“ABC is a balance between construction costs and customer service, the ability to recognize there’s more to bridge construction than the bridge itself, and the understanding of how quickly our industry can build.”
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In addition to using prefabricated bridge parts and reducing the number of workers standing mere inches from traffic, ABC also aims to minimize temporary roadway realignments, traffic detours, temporary bridges, and other common construction aids so that a span can be assembled much more quickly and traffic can continue apace. Here’s a video that shows the basic concept.
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When construction of the interstate highway system began in the 1950s, most workers were building structures in areas where nothing else existed. Today, the challenge faced by planners and construction crews is that America is built out, and they must work to replace and rebuild the aging structures amid packed traffic and population centers.
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