Backward Compatibility

The U.S. Standard railroad gauge (distance between rails) is 4 feet, 8.5
inches. That's an exceedingly odd number. Why was that gauge used?

Because that's the way they built them in England and U.S. railroads
were built by English expatriates.

Why did the English build them like that? Because the first rail lines
were built by those who had built pre-railroad tramways and that the
gauge they used.

Why did they use that gauge then? Because the people who built tramways
used the same jigs and tools for railroads that they used for building
wagons, which used that wheel spacing.

So why did wagons use that odd wheel spacing? Because that is the
spacing of the old wheel ruts.

And who built these old rutted toads? The first long distance roads in
Europe were built by Imperial Rome for their legions.

And the roads have been used ever since. The initial ruts which everyone
else had to match for fear of destroying their wagons, were first made
by Roman war chariots. Since the chariots were made for or by Imperial
Rome, they all had the same wheel spacing.

Thus, we have the answer to the original questions. The U.S. standard
railroad gauge of 4 feet 8.5 inches comes from the original
specification for an Imperial Roman army war chariot.

So, the next time you are handed a specification and wonder what horse's
ass came up with it, you may be exactly right. Because the Imperial
Roman chariots were made to be just wide enough to accommodate the
back-ends of two war horses.