Since the chariots were made for or by Imperial Rome they were all alike in the matter of wheel spacing. Thus, we have the answer to the original question. The United States standard railroad gauge of 4 feet, 8.5 inches derives from the original specification for an Imperial Roman army war chariot.

The "Standard Gauge" of 4 feet 8.5 inches (1,435 mm) can be traced back to the early days of the British coal industry. George Stephenson, the "Father of Railways," adopted the 4-foot 8-inch gauge because it was the common width used for horse-drawn wagonways in Northern England. These wagonways were themselves influenced by the width of traditional carts and carriages, which were built to fit into the pre-existing ruts of old roads—some of which dated back to Roman times. The extra "half-inch" was added later to provide a bit more clearance for the wheel flanges on curves, helping to reduce wear and tear on the rails. As Britain exported its railway technology and locomotives globally, this specific measurement became the international standard. While it is often joked that the width is based on a "Roman chariot's rear," the truth is more about a long, practical evolution of human transportation dimensions becoming codified into modern industrial engineering.