> I'm not sure whether the loading gauge (allowed size of train to fit under bridges) etc. is also standardized It sure is standardized; the problem is that th

> I'm not sure whether the loading gauge (allowed size of train to fit under bridges) etc. is also standardized It sure is standardized; the problem is that there are so many standards to choose from! See https://en.wikipedia.org/wiki/Loading_gauge https://en.wikipedia.org/wiki/Loading_gauge for an overview. Britain is a bit special, in that as the first country to have extensive rail infrastructure, it also has the smallest loading gauges around. Later built railway networks tend to have bigger loading gauges.