Accelerated Bridge Construction

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Construction began late last year, with a combination of pre-made components being shipped in while the construction of two new superstructures on temporary supports were mounted alongside the current bridge.
“We assembled these pre-cast elements into a single span,” Sivakumar explains. “With one superstructure in the median area between the two existing bridges and another north of the westbound bridge. While all this was happening, [the construction crew] built a new superstructure underneath the existing bridge.” And all this was happening without any effect on traffic.
“People see what’s going on, but there’s no impact to them,” says Sivakumar.
At 5 p.m. on Saturday, September 21, the DOT closed I-84 and the first round of demolition began, with crews working for four hours to rip apart the dilapidated structure. And then the slide began.
Four 100-ton jacks began pushing on the new roadway plates, each set atop a “slide track” with a teflon surface that slips across the underside of the polished, stainless steel plates. But each jack only has a stroke of around 30 inches, so every two and a half feet the plates slide, the crews move the jacks forward to push the new roadway further.
“It’s a slow process,” Sivakumar admits. But the bridge was in place eight hours later, and Sivakumar says it could have been done in four to six hours, “but it was pouring that night.”
The final step was to raise the approaches of the road on either side of the bridge to match the new structure’s height and length, so an army of asphalt trucks, pavers, and workers descended on the two sides to build up the additional space and make it strong enough to handle the hundreds of thousands of tractor trailers that would roll over it in the coming years.
The westbound span was opened to traffic at 12:55 p.m. the following day, widened into a single span bridge that was 80 feet long and 57 feet wide — more than twice the width of the previous bridge — with three lanes and two full-size shoulders.
This Saturday, October 19, the eastbound span will be slid into place, and if weather isn’t an issue, Sivakumar says the new span could be open even earlier.

That's pretty cool, but I can't imagine how nerve wracking it would be to do this the first time.  I know I'd be shitting my pants as they started jacking the deck over.