The US standard railroad gauge (distance between the rails is 4 feet, 8.5 inches.
That's an exceedingly odd number.
Why is that gauge used?
Because that's the way they built them in England and English expatriates designed the US railroads.
And the ruts in the roads?
Roman war chariots formed the initial ruts, which everyone else had to match for fear of destroying their wagon wheels.
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.
In other words, bureaucracies live forever.
Imperial Roman army chariots were made just wide enough to accommodate the rear ends of two war horses.
Now, the twist to the story:
Thank you Cousin Mel