The battle of the gauges
The distance between the rails, the gauge, seems like a detail. In early railways it was a matter of habit: George Stephenson used the gauge of the colliery wagonways that he knew, four feet eight and a half inches (1,435 mm), and it spread with his locomotives. Isambard Kingdom Brunel, engineer of the Great Western Railway, thought it too narrow. He chose seven feet and a quarter of an inch (2,140 mm) for a steadier, faster and more spacious railway.
The broad gauge did give a smooth ride and room for large engines. But where the two systems met, as at Gloucester, everything had to be unloaded and loaded again, and the confusion made the problem plain to everyone. A royal commission was set up, and in 1846 the Gauge Act made the Stephenson gauge standard for new lines in Great Britain, with Brunel's system left as an exception for the Great Western.
The end of the broad gauge
The Great Western slowly added a third rail to its broad-gauge track so that standard-gauge trains could use it, and in May 1892 it converted the remaining broad-gauge main line in a single weekend, with thousands of men moving the rails. Four feet eight and a half inches is now used on most of the world's railways, though Russia, Spain, India and others chose different gauges for their own reasons.