I lived right next to one of the bridges they replaced on I-80 in Utah. They were replacing a big stretch of the freeway so they set up a "bridge farm" where they built seven bridges on stacked cargo containers and got them ready to go. Then they load a bridge on a massive machine with hundreds of wheels and basically drive it down the one side of the existing freeway to the site of the new bridge, drop it into place, secure it, and load up another bridge. They'd drive each bridge over the bridge they had just put in place basically building their way as they went. It was amazing how quickly they did it (just 41 days which included driving the bridges into place at 0.5 mph). They did a different section with four bridges in just 48 hours. I felt they made up for the terrible I-15 reconstruction for the olympics with how smoothly this I-80 project went (and the I-15 expansion in Davis county which also used this offsite bridge construction techinque).