This one, as they say, is an oldie but a goodie...

The US standard railroad gauge--the 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.

OK, so why did the English choose this gauge? Because the first rail lines were built by the same people who built the pre-railroad tramways, and that's the gauge that THEY used. Why did those folks use that gauge?

Because the people who built the tramways used the same jigs and tools that they used for building wagons, and wagons employed the 4 ft, 8.5 inch wheel spacing.

Fine. Why did the wagons use the 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 number is 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. These 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 these chariots were all alike in the matter of wheel spacing, we have the answer to our original question.

The US Standard railroad gauge of 4 ft, 8.5 inches derives from the original specification for an Imperial Roman army was chariot. Thus, specs and bureaucracies live forever.

The next time you see a specification, and wonder what horse's ass came up with it, you may be exactly right! That's because the Imperial Roman chariots were made to be just wide enough to accommodate the back-ends of two war horses.