The U.S. standard railroad gauge (distance between the rails) is 4
feet, 8.5 inches. That is an exceedingly odd number.

Why was that gauge used? Because that's the way they built them in
England, and the U.S. railroads were built by English expatriates.

Why did the English build them that way? 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? Because the people who built the
tramways used the same jigs and tools that they used for building
wagons, which used that wheel spacing.

So why did the wagons have that particular odd spacing? Well, if
they tried to use any other spacing, the wagon wheels would break on
some of the old long distance roads in England, because that was the
spacing of the wheel ruts.

So who built those old rutted roads? The first long distance roads in
Europe were built by the Roman Empire for their legions. The roads
have been used ever since.

And the ruts in the roads? The ruts in the roads, which everyone had
to match for fear of destroying their wagon wheels, were first formed
by Roman war chariots. Since the chariots were made for or by
Imperial Rome, they were all alike in the matter of wheel spacing.

The U.S. standard railroad gauge of 4 feet-8.5 inches derives from
the original specification for an Imperial Roman war chariot.

Specifications 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 have some idea... The Imperial
Roman war chariots were made just wide enough to accommodate
the back end of two war horses.

Wait. There's more.

When we see a space shuttle sitting on its launching pad, there are
two booster rockets attached to the side of the main fuel tank. These
are solid rocket boosters, or SRBs. The SRBs are made by Thiokol
at their factory in Utah. The engineers who designed the SRBs might
have preferred to make them a bit fatter, but the SRBs had to be 
shipped by train from the factory to the launch site. The railroad 
line from the factory had to run through a tunnel in the mountains.
The tunnel is slightly wider than the railroad track, and the railroad
track is about as wide as two horses rumps.

So a major design feature of what is arguably the world's most
advanced transportation system was determined over two thousand
years ago by the width of a horse's ass!

--Source: unknown (an unnamed Mexican physicist).

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