A Very Interesting Piece of History
The US standard railroad gauge (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 English expatriates designed 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 the English use that gauge then ? Because the people who built the tram ways used the same jigs and tools that they had used for building wagons, which used that wheel spacing.
Why did the wagons have that particular odd wheel spacing ? Well, if they tried to use any other spacing, thewagon wheels would break on some of the old, long distance roads in England, because that's the spacing of the wheel ruts.
Since the chariots were made for Imperial Rome, they were all alike in the matter of wheel spacing. Therefore the United States standard railroad gauge of 4 feet, 8.5 inches is derived from the original specifications for an Imperial Roman war chariot.
The engineers who designed the SRBs would 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 from the factory happens to run through a tunnel in the mountains, and the SRBs had to fit through that tunnel. The tunnel is slightly wider than the railroad track, and the railroad track, as you now know, is about as wide as two horses' behinds.