A History of Engineering Specifications
- a whimsical e-rumor -
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 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.

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's the spacing of the wheel ruts in
the ground from years of travel by wagon.
So who built those old rutted roads? The first long
distance roads in Europe (and England) were built by
Imperial Rome 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 be exactly right,
because the Imperial Roman war chariots were made just wide
enough to accommodate the back end 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 it's launching
pad, there are two booster rockets attached to the side of
the main fuel tank. These are solid rocket boosters, or
SRB's. The SRB's are made by Thiokol at their factory in
Utah. The engineers who designed the SRB's might have
preferred to make them a bit fatter, but the SRB's 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' 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 ass.
Don't you just love engineering?
(author unknown)