How Specs Live Forever

The US Standard railroad gauge (distance between the 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 the US railroads
were built by English expatriates. Why did the English people build them
like that? Because the first rail lines were built by the same people
who built the pre-railroad tramways, and that's the gauge they used.

Why did "they" use that gauge 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 the wagons use that
odd wheel spacing? Well, if they tried to use any other spacing the
wagons 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
roads have been used ever since. And the ruts? 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 were all alike in the matter of wheel spacing.

Thus, we have the answer to the original questions. The United States
standard railroad gauge of 4 feet, 8.5 inches derives from the original
specification for an Imperial Roman army war chariot.  Specs and
Bureaucracies live forever. 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.