Although some historians question the veracity of all the facts in the following story, it is accurate enough to make an interesting point.

The U.S. standard railroad gauge is four feet, eight-and-one-half inches. How did we wind up with such an odd railway width? Because that was the width English railroad-building expatriates brought with them to America. Why did the English build them this wide? Because the first British 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? Because the same jigs, tools, and people who built wagons built the tramways and used the standard wagon-wheel spacing. Wagon-wheel spacing was standardized due to a very practical, hard-to-change, and easy-to-match reality. When Britain was ruled by Imperial Rome, Roman war chariots, in true bureaucratic fashion, all used a standard spacing between their wheels.

Over time, this spacing left deep ruts along the extensive road network the Romans built. If British wheel spacing didn't match Roman ruts, the wheels would break. The Roman standard was derived after trial-and-error efforts of early wagon and chariot builders. They determined the best width that would accommodate two horse butts was four feet, eight and one-half inches. Thus the United States standard railroad gauge is a hand-me-down standard based upon the original specification for an Imperial Roman war chariot.

This doesn't end at railroads. Two big booster rockets attach to the sides of the main fuel tank that lifts the space shuttle into orbit. Thiokol makes these solid-fuel rocket boosters, SRBs, at its Utah factory. The engineers who design the SRBs ship them from factory to launch site by train. The railroad from the factory runs through a mountain tunnel only slightly wider than the railroad track. Even if Thiokol engineers wanted fatter SRBs, the railway gauge limits their design. Modern space shuttle design follows horses' butts.