When I first got this as an e-mail I also went to confirm what I could, and the URL quoted higher up has a fairly good summary. The only bit I couldn't confirm as fact was the space shuttle railway route.
I looked in a big old volume, I think the Cambridge Encyclopaedia of Technology but can't now confirm that, in its articles on roads. Carriage ruts once established became very deep and if you didn't make your carriage to fit them the carriage couldn't use the roads. Roman ruts were still in use in modern times.
The gauge didn't originate with Caesar. The Greeks used standard ruts, and although the city-states normally didn't maintain inter-city roads, some routes such as those to Delphi and Olympia were carefully maintained. They even had passing-passes and sidings like a mdoern railway.
Standard animal-width gauges have been found variously in Mesopotamia before that, and I think the oldest were Neolithic ones in Malta.
