Watch the video and admire the engineering:
Here is the brief description of project:
On April 10, 2014, the slide of the Milton-Madison Bridge was completed. At nearly a half-mile long, this is the longest bridge slide of its type in North America, perhaps the world. The slide occurred over a two day period with the actual slide time being approximately 12 1/2 hours. The total slide distance was 55 feet, going from temporary piers to refurbished, permanent piers.
The old bridge was where the new bridge is today – after the slide. The new bridge was built on temporary supports NEXT TO the old bridge. The old bridge still carried traffic. After the new bridge was built, traffic was switched to the NEW Bridge on the temporary alignment. The old bridge was demolished. The existing piers were rehabilitated. After that work was complete, the new bridge slides back over where the old bridge used to be. By reusing the foundations and piers the owner saved many tens of millions of dollars.