Specification Funnies with a Twist
The United States standard railroad gauge (the distance between
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the rails) is 4 feet, 8.5 inches.
That's an exceedingly odd number.
Why was that gauge used?
Because English expatriates built U.S. railroads, and that's the
way they built them in England.
So why did the English build them that way?
Because the first rail lines in England were built by the same
people who built the pre-railroad tramways, and that's the gauge
used for the tramways.
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 with that wheel spacing.
Why did they use that odd wheel spacing for the wagons?
Because if they used any other spacing, the wagon axles would
break when driven on heavily rutted long distance roads. The
wagon wheel spacing was the spacing of the road ruts.
So who built those old rutted roads?
The first long distance roads in Europe were built by Imperial
Roman legions, and have been in use ever since.
The ruts, which everyone had to match lest they destroy their
wagons, were made initially by Roman war chariots. All the
chariots made for or by Imperial Rome were alike in wheel
Thus, we have the answer to the original question.
The United States standard railroad gauge of 4 feet, 8.5 inches
derives from the original specification for an Imperial Roman war
The next time you are handed a specification and wonder what
horse's ass came up with it, you may be exactly right.
The Imperial Roman war chariots were just wide enough to
accommodate the back ends of two war horses.
Now the twist. There's an interesting extension of this tale
relating railroad gauge to horses' behinds.
When a Space Shuttle is sitting on its launch pad, we can see two
big rockets attached to the sides of the main fuel tank.
These are the solid rocket boosters, or SRBs.
Thiokol makes the SRBs at a factory in Utah.
The engineers who designed the SRBs might have preferred to make
them a little fatter, but the SRBs have to be shipped by train
from the factory to the launch site.
The railroad line from the factory runs through a tunnel in the
mountains, which is only is slightly wider than the railroad
track, and the SRBs must be hauled through that tunnel.
Remember, U.S. railroad tracks are only as wide as two Roman war
This means a major design feature of what is arguably the world's
most advanced transportation system was determined by the width
of a horse's ass!