Does the statement,
"We've always done it that way" ring any bells?
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
English expatriates built the US railroads.
Why did the English 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 have that particular odd wheel 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's the spacing of the wheel ruts.
So who built those old rutted roads? Imperial Rome built the first
long distance roads in Europe (and England) for their legions. The
roads have been used ever since.
And the ruts in the roads? Roman war chariots formed the initial
ruts, which everyone else had to match for fear of destroying their
wagon wheels. Since the chariots were made for Imperial Rome, they
were all alike in the matter of wheel spacing.
The United States standard railroad gauge of 4 feet, 8.5 inches is
derived from the original specifications for an Imperial Roman war
chariot. 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 army chariots were made just wide enough to
accommodate the back ends of two war horses.
Now the twist to the story. When you see a Space Shuttle sitting on
its launch pad, there are two big booster rockets attached to the
sides of the main fuel tank. These are solid rocket boosters, or
SRBs. The SRBs are made by Thiokol at their factory at Utah. The
engineers who designed the SRBs would 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 happens to
run through a tunnel in the mountains. The SRBs had to fit through
that tunnel. The tunnel is slightly wider than the railroad track,
and the railroad track, as you now know, is about as wide as two
So, a major Space Shuttle 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.