Some railroad trivia for you railroad game buffs ... the US standard railroad gauge is 4 feet 8.5 inches. That's an exceedingly odd number. Why was that 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.

Okay. Why did the wagons have that particular odd wheel spacing? 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. The roads were built by Imperial Rome for their legions, and they have been used ever since.

And the ruts? Roman war chariots first made the initial ruts, which everyone else had to match for few of destroying their wagon wheels and wagons. 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 question. The United States standard railroad gauge derives from the original specification for an Imperial Roman war chariot. So, the next time you are handed a specification and wonder which horse's rear 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 warhorses.

And now, the twist to the story: when we see a Space Shuttle siding on its launch pad, there an two big Solid Booster Rockets, or SRBs, attached to the sides of the main fuel tank. Thiokol makes the SRBs 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 340. The railroad line from the factory had to run. through a tunnel in the mountains. The tunnel is slightly wider than. the railroad tack, and the railroad tack is about an wide as two horses' behinds. So, the major design feature of what is arguably the world's most advanced transportation system was determined by the width of a horse's ass.