Driven the east-side belt route of I-215 lately?

Near the offramp to 4500 South is a massive structure. Men in hard hats have been building it for the past four months, and it almost looks as if it were a concrete launch ramp to nowhere.

"The last thing people think is that we're going to pick it up and move it," said Tracy Timothy, crane operator on the project.

But that's the plan. Over a 36-hour period in October, workers hired by the Utah Department of Transportation will pick up the structure, move it across the freeway, and then lift it into place as the new 4500 South bridge over I-215.

The technique, known as rapid bridge replacement, has been used in cities throughout Europe. The goal is to replace a bridge within weeks, days or even hours and save commuters the lengthy road closures that happen when structures are rebuilt in place.

UDOT is hopeful it will only need to close I-215 for 36 hours to remove the old bridge and install its replacement, while 4500 South is expected to be closed for 10 days so crews can build approach ramps, stripe lanes and install fencing.

"We have to do a lot of projects," said Rukhsana "Shana" Lindsey, UDOT director of research and bridge operations, as she explained why her agency was doing a rapid bridge replacement. "We want to do (those projects) with as little impact as possible."

UDOT has done some types of accelerated replacements using prefabricated road pieces, but it has never replaced an entire bridge structure. A Dutch company, Mammoet, which specializes in moving heavy objects, has been hired to maneuver the new structure into place.

The company will use 16-ton jacks to lift the structure from its platform near 4500 south. The bridge will then be placed atop a machine called a self-propelled modular transporter that UDOT says looks like a flatbed trailer.

The transporter vehicles have several dozen wheels that are controlled by a computer. Workers will walk behind the machines, using a sort of joystick to move the new bridge across I-215 and over to 4500 South. The bridge will then be placed on strong support walls that crews are now constructing.

Lindsey says the bridge will function the same as a structure that is rebuilt in place.

"The only change is that we are building it off to the side," she said.

Bud Shumway, project superintendent for the bridge's contractor, said work has been challenging — and never dull. "It's the first time we've done it, and we didn't know what we were doing," he said. "At first, looking at it on paper and then imagining it was overwhelming."

Shumway said that motorists exiting I-215 at 4500 South will often slow near the construction site and ask what he is building. Workers have joked they're building a Wal-Mart or some other big building.

"It's the first one of its kind" in Utah, Shumway said.

UDOT plans to replace the 4500 South bridge on the weekend of Oct. 26. Viewing areas will be set up for the public to watch.

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E-mail: nwarburton@desnews.com