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Overnight bridge replacements possible?

IT’S SAFE to say that the worst part of road construction—from a driver’s point of view—are delays.

It’s pretty much a necessary evil, especially with bridges.

But, as far as bridges are concerned, in some cases that necessary evil is becoming a thing of the past.

A technique known as Accelerated Bridge Construction is changing the game.

It’s an amazing process in which a bridge can be replaced overnight.

It works like this: Piers can be built beneath or next to a bridge while traffic continues driving on it. In turn, the superstructure (the deck) is prefabricated offsite, then is brought in and “slid” into place.

That’s what was done on the 135-foot Interstate 84 bridge at the New York and Connecticut border late last year, according to a Wired article about the project.

The piers were built under and next to the bridge. The new superstructure was brought in and slid into place the night of Sept. 21. Traffic was using the bridge the next day.

Done the traditional way, that project would have meant two years’ worth of road closures and an additional cost of $2 million.

Those are the key benefits with ABC—time and cost savings.

The technique has been used for years, but now it seems to be picking up steam as a way to replace bigger, highly traveled bridges like the one on I–84.

The Federal Highway Administration is touting ABC as a key in the efforts to deal with a quarter of the nation’s 600,000 bridges that are in need of fixing or replacing.

The Virginia Department of Transportation wants to get the number of the state’s structurally deficient or obsolete bridges below 8 percent, said local spokeswoman Kelly Hannon.

Currently, 9 percent of the Fredericksburg District’s bridges are structurally deficient or obsolete, including the Falmouth and Chatham bridges.

No local bridges have been replaced via the ABC method.

But VDOT has used “prefabricated elements” on bridge projects for decades, says Annette Adams, head Fredericksburg District structure and bridge engineer.

She considers ABC on every bridge project, though.

Hannon said VDOT’s Fredericksburg District has crews that focus specifically on fast, efficient bridge work.

They can “perform an intense 5- to 10-day bridge superstructure replacement. In some cases, the project is a total bridge replacement,” Hannon said in an email.

They don’t use the ABC method, but the crews get the work done faster than in the past.

Why not use the ABC technique on the Rappahannock Canal Bridge project, which will shut down Fall Hill Avenue for about nine months?

Without addressing the canal bridge specifically, Adams and Hannon said each project is different. In some cases, the ABC method isn’t practical.

That’s probably the case with the canal bridge project, which involves raising the bridge and adding a trail beneath it.

Maybe one of these days we’ll get to see an overnight bridge replacement locally—perhaps even on the Falmouth and Chatham bridges.

Scott Shenk: 540/374-5436