Subject: design considerations

Consider this when creating a design...

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 derived 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.

Why do YOU do the things you do?

Plus:

There's an interesting extension of the story about railroad gauge
and horses' behinds. When we see a Space Shuttle sitting on the
launch pad, there are two big booster rockets attached to the
sides of the main fuel tank.  These are the solid rocket boosters,
or SRBs.  The SRBs are made by Thiokol at a 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 to the factory
runs through a tunnel in the mountains.  The SRBs had to fit
through that tunnel.  The tunnel is slightly wider than a railroad
track, and the railroad track is about as wide as two horses'
behinds. So a major design feature of what is arguably the world's
most advanced transportation system was determined by the width of
a horse's backside.