A wagonway width became a railway standard
The familiar measurement is 4 feet 8½ inches, or 1,435 millimeters. It is the distance between the inner faces of the two rails—not the width of the train. It became common because early railways inherited a measurement already used on some British wagonways, where horse-drawn carts carried coal and other goods.
George Stephenson, an influential early railway engineer, used that gauge on projects in northeastern England. As steam railways expanded, his choice spread with them. Once a route had been built to a particular width, changing it meant rebuilding track and potentially replacing or adapting rolling stock. Reusing an established gauge was simpler, and each new railway using it made the choice more practical for the next.
Compatibility made the measurement stick
A railway gauge determines which trains can run directly on a track. If two connecting lines use different gauges, trains may have to stop while passengers or freight are transferred, or the railway must use special equipment to handle the mismatch. Shared gauge, by contrast, makes it easier for trains and cargo to move across company and regional boundaries.
British railway practice helped carry the measurement abroad, and it became widely used in the United States as well. But it is not unique to those countries, nor is it the gauge of every railway: broader and narrower gauges were also adopted in various places. The important advantage was not that 4 feet 8½ inches was inherently ideal. It was that enough railways had already built around it.
That is why an inherited wagonway dimension could outlast the horse carts that first used it: once a network depends on a shared measurement, changing it can cost more than keeping it.
