Why We Do Things
The US Standard railroad gauge (distance between the rails) is 4 feet, 8.5inches. 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.
Why did the English people 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 use that 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's 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. The 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 the chariots were made for or by Imperial Rome, they were alike in the matter of wheel spacing.
Thus, we have the answer to the original questions. The United States standard railroad gauge of 4 feet, 8.5 inches derived from the original specification for an Imperial Roman army war chariot.
Specs and Bureaucracies live forever. Therefore, the next time you are handed a specification and wonder what horse's ass came up with it, you may be exactly right. Because the Imperial Roman chariots were made to be just wide enough to accommodate the back-ends of two war horses.
Why do YOU do the things you do?
There's an interesting extension of the story about railroad gauge and horses' behinds. When we see a Space Shuttle sitting on the launch pad, there are two big booster rockets attached to the sides of the main fuel tank. These are the solid rocket boosters, or SRBs. The SRBs are made by Thiokol at a 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 site. The railroad line to the factory runs through a tunnel in the mountains. The SRBs had to fit through that tunnel. The tunnel is slightly wider than a railroad track, and the railroad track is about as wide as two horses' behinds.
So a major design feature of what is arguably the world's most advanced transportation system was determined by the width of a horse's backside!
Mike, this is not entirely true, for allowable widths and heights of railroad equipment (and thus their loads) have changed many times over the years. The latest major modification to rail equipment clearance was the development of double-stacked containers which forced the vertical clearances of many bridges and tunnels to be increased.
Historical Note: When President Lincoln was assassinated, an especially palacial railroad car was chosen to transport his body from Washington to Illinois. However, this car was significantly wider than the standard equipment of the day, so out of respect for the dead president, the railroads on the route widened all the clearances to accommodate his car. (If I'm not mistaken, this was one of the first Pullman cars.) Soon after, this did become a "standard" car width and all railroads had to widen their right-of-ways.
By the way, the 4'-8.5" standard did not become standard for many decades after the widespread construction of railroads. Many of the early railroads had different gages that they used. It was only after the inefficiency and unsafe conditions created by these varied gages became too much that the American railroads agreed to one standard gage. As I recall, the decision (like virtually everything else) came down to, who had the most money, which was the Pennsylvania Railroad in those days.
So I think a far more accurate statement would be that a major design feature of what is arguably the world's most advanced transportation system was determined by golden rule (he with the most gold makes the rules.)
Finally, when the Czar of Russia was building railroads in his country, he specifically had the gage of Russian railroads build differently from that of the rest of Europe. His reasoning was that invading armies would not be able to use his own railroads in the event of an invasion. This odd gage turned out to be a major obstacle to the mobility of the German army during WWII. So, could it be said that a 20th Century German Army was defeated in part by Roman War Chariots?
In case you can't guess, I'm a Rail Fan.
Neil Faber, email@example.com