According to the Federal Highway Administration, accelerated bridge construction “uses innovative planning, design, materials, and construction methods in a safe and cost-effective manner to reduce the onsite construction time that occurs when building new bridges or replacing and rehabilitating existing bridges.” The entire project may take as long as conventional construction, but the time on site is much less. There’s less inconvenience to the public because the road closure is only for a short time. For example, demolition and replacement of a bridge might take place over a weekend, as in this video. Consequently, the safety hazards due to traffic in a construction zone are much less.
Video: Utah DOT replacing a bridge on Interstate 80 in Salt Lake City. Demolishing the old bridge and sliding the new bridge into place took just one 3-day weekend in April 2023.
As we seek to upgrade our transportation infrastructure, it’s worth considering accelerated bridge construction for some of the work. The US interstate highway system got its start in 1956 with the Interstate Highway Act. Although the last parts of it weren’t complete until the 1970s, the entire original construction is beyond its design life—and it shows.
How does it work?
Accelerated bridge construction entails building large portions of the bridge somewhere other than in its final location. This could be at a precast concrete plant or near or on the construction site.
[A]ccelerated bridge construction enabled the agency to reduce traffic delays while it replaced northbound and southbound bridges on I-15 over East Nichols Canyon Road. The project…first involved building a new center bridge between the two I-15 bridges. After it was built, northbound traffic was shifted to the new bridge, and the northbound bridge was demolished and replaced. Northbound traffic was then shifted to that new northbound bridge, while southbound drivers were shifted to the new center bridge. The southbound bridge was then demolished, and a supporting structure was built for a new deck. After that, the center bridge’s deck was disconnected and slid into place…to serve as the new southbound bridge.—Don McLoud, “Time-lapse video: dish soap aids Utah’s million-pound bridge slide,” 25 July 2022.
Video: In a 2022 Utah DOT project, the new bridge temporarily replaced the northbound bridge and then permanently replaced the southbound bridge. Dish soap aided the sliding of the new bridge into place.
In some cases ultra high-performance concrete helps to speed construction. Precast concrete requires closure pours to connect the segments. Also, bridge sections that slide into place need to connect with the abutments. These closure pours need to gain strength quickly so that the bridge can open to traffic. While ultra high-performance concrete costs more per cubic yard than regular concrete, the volumes necessary aren’t that high. And opening the bridge on time saves drivers both time and money.
Utah DOT leads the way
When the FHWA first implemented accelerated bridge construction, Utah DOT was an early adopter of the technology. They also did a lot to get the politics right. In public works, it’s essential to enlist the support of the public. Utah DOT publicized the projects widely so everyone would know ahead of time about the closure of a major route. Normally they would schedule them over a weekend to minimize disruptions. In the end, it wasn’t difficult to convince the public that complete closure of a major artery over a weekend or two is preferable to months of partial closures and traffic delays.
Where possible, the DOT would arrange for the public to watch the construction, setting up campsites from which they could safely observe the work. Although construction isn’t as fast as it appears in time-lapse videos, it’s fast enough to see progress in real time. People could show their kids how it all comes together. And that kind of participation fosters a sense of ownership.
The DOT also needed the support of the politicians who would vote to fund the projects—or not. At first, accelerated bridge construction was somewhat more expensive than conventional construction. To get the politicians on board, the DOT pledged to complete a project during the term when it received funding. That way politicians campaigning for reelection could point to specific projects they had accomplished. Accelerated bridge construction meant the public would associate minimal inconvenience with the new bridge.
When to use accelerated bridge construction
It may seem obvious why you’d use accelerated bridge construction in an urban setting. After all, closures disrupt far more traffic in a city, and inconvenience far more people. But cities also usually have more alternate routes, so detours are relatively short.
In a rural area, on the other hand, closing a bridge might force traffic to divert many miles out of the way, as there may not be any nearby alternate routes. The less time that goes on, the better. Delays cost money for everyone who has to detour for several miles. For emergency vehicles, delays can have serious consequences.