Recently picked up the book Mopac Power, by Joe Collias. In the historical bit in the first chapter, he relates that the original Pacific Railroad was built to 1 5 foot 6 inch track gauge. This was not seen as a problem as the road's first dhief engineer believed the Mississippi River would never be bridged, and thus interchange would not be possible. They remained this way from charter in 1849 until July, 1869, when the system was regauged in fourteen hours. May have "only" been 300 miles by then, but think of the feat in terms of the tools available...
That was actually quite common as railroads tried to standardize. Both wide gauge and narrow gauge lines were handled about the same. They hired on extra gandy dancers and positioned them all along the line with the necessary tools. At a set time they all went to work moving one rail either in or out, depending on if the old gauge was narrow or wide. They usually had trains running again in about a day.
Another railroad which I recall reading of a system re-gauge was the Erie RR. What is truly interesting for me is that fellow believing the Mississippi would never be bridged. In world history, even at that point in time, so many previous "never" situations had already been disproven....
