To All My Engineer Friends
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 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. 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? The first long distance
roads in England were built by Imperial Rome for their legions. The roads have
been used ever since.
And the ruts in the roads? The initial ruts, which everyone
else 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 United States 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 be exactly right, because the Imperial Roman war chariots were made
just wide enough to accommodate the back ends of two war horses. Thus, we have
the answer to the original question.
Now the twist to the story...
When we 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 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 SRBs had to fit through that tunnel. The
tunnel is slightly wider than the railroad track, and the railroad track is
about as wide as two horses' behinds.
So, the 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 butt.