Four Feet, Eight and a Half Inches
Standard gauge railway lines are used throughout New South Wales & on Australian National Railways' interstate lines. It is also the primary gauge used in Britain, Europe, the USA, & many other countries. It is used on such high speed lines as France's TGV, Germany's ICE, & Japan's Bullet Trains.
Standard gauge, in railway terminology, means a distance between the rails of 4 feet, 8 ½ inches or 1.435 metres. That's an exceedingly odd number. Why was that gauge used?
Because that's the way they built them in England, & English expatriates built railways all around the world. Why did the English build them like that?
Because the first railway lines were built by the same people who built the pre-railway tramways, and that's the gauge they used. Why did they use that gauge in England, then?
Because the people who built the tramways used the same jigs and tools that they used for building wagons, which used that wheel spacing. Okay! Why did their wagons use that odd wheel spacing?
Because, if they tried to use any other spacing the wagon wheels would break on some of the old, long distance roads. Because that's the spacing of the old wheel ruts. So who built these old rutted roads?
The first long distance roads in Europe were built by Imperial Rome for the benefit of their legions. The Roman roads have been used ever since. And the ruts?
The original ruts, which everyone else had to match for fear of destroying their wagons, were first made by the wheels of Roman war chariots. Since the chariots were made for or by Imperial Rome they were all alike in the matter of wheel spacing.
Thus, we have the answer to the original question. The standard railway gauge of 4 feet, 8 1/2 inches derives from the original specification for an Imperial Roman army war chariot.
Proving Milspec endures forever