The US standard railroad gauge (distance between the rails) is 4 feet 8.5 inches. That’s some 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.

Why did the wagons have that particular odd wheel spacing?  Because, if they tried to use any other spacing, the wagon wheels would break on some of the old, long distance roads in England,  that’s the spacing of the wheel ruts.

So who built those old rutted roads?  The Romans built the first long distance roads in Europe (and England) for their legions. These 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 own wagon wheels. Since the chariots were made for Imperial Rome, they were all alike in the matter of wheel spacing. Therefore the U.S. standard railroad gauge of 4 feet 8.5 inches is derived from the original specifications for a Roman war chariot.

Bureaucracies live forever.  So, the next time you are handed a Spec/Procedure (SOP) /Process and wonder, "What horse’s ass came up with this?" You might be exactly right. Roman army chariots were made just wide enough to accommodate the rear ends of two war horses.
 

So, when you see the Space Shuttle sitting on its lauch pad, there are two big booster rockets attached to the sides of the main fuel tank. These solid rocket boosters (SRB’s) are made in Utah. The engineers who designed the SRB’s would 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 happens to run through a tunnel in the mountains and the SRB’s had to fit through that tunnel. The tunnel is slightly wider that the standard railroad track and the railroad track, as we now know, is about as wide as two horse’s behinds. So a major Space Shuttle design feature of what is one of the world’s most advanced transportation system was determined thousands of years ago by the width of a horse’s ass.

And you thought being a horse’s ass wasn’t important.