Railroad tracks, a horses ass... and rockets! [Long] The US standard railroad gauge (the distance between two rails) is 4 feet 8.5 inches... an exceedingly odd number. Why was that gauge used? Because a number of the early railroad lines in the US were built to fit standard-gauge locomotives manufactured by English railroad pioneer George Stephenson. The English expatriates who immigrated to America built them to the same dimension they had built them in England. Why did the English build them l…