The chariot ruts in Roman roads affected what?
Early Roman chariots were built to fit the width of two war-horse's rear ends. After time, chariot and wagon wheels etched grooves into the surface of the road, forcing other conveyances to match up to the same wheel spacing. Eventually this measurement was adopted as the American standard railroad gauge of 4-feet, 8.5 inches. Modern rail tunnels were designed to accommodate this size specification, which in turn effected the maximum breadth of freight and payloads. As the train system was used for the delivery of the space shuttle's solid rock boosters, their ideal width had to be modified in order to fit the tunnel dimensions.