Last weekend, in Denver, a new bridge appeared over a stretch of US 6/6th Avenue Freeway in less than 2 days.
This is one of the first bridge installations of it's kind here in the states -- assembled by the freeway and then "rolled out" over the highway last weekend, the main part of the project only caused a full closure of the heavily-traveled freeway for only 2-1/2 days. The freeway closed Friday night after rush hour and reopened by Monday Morning.
This bridge is part of Denver's RTD light rail expansion and will accommodate a new rail line serving the Western Suburbs of Denver.
More information on this interesting project and the time-lapse video on the "rolling bridge" can be found at http://www.rtd-fastracks.com/main_1
UDOT has been doing this since 2007. They started with two bridges over I-215 and then every westbound bridge on a thirteen-block stretch of I-80.
For major urban freeways with adjacent land nearby, this is the best way to go.
Somewhat similar, it seems, is Texas' plan for the old Texas Stadium location. Build the interchange there, and then tie it into all the surrounding roads once the bridges/ramps are built.
They did that for a new section of the Chicago L over Wacker Drive back in 2002. They built a new "bridge" to remove columns from the middle of Wacker Drive, and then in one weekend they demolished the original structure, rolled the new one into place, and reconnected everything. It was brilliant.
http://www.chicago-l.org/operations/lines/images/NorthMain/ROW%40Wacker-NewBridge03.jpg
http://www.chicago-l.org/operations/lines/images/NorthMain/ROW%40Wacker-NewBridge05.jpg
You can see more photos here (they're at the bottom of the list of photos) http://www.chicago-l.org/operations/lines/northmain-brown.html