There’s also variation in - how power is delivered through the overhead wire (direct or alternating current, switching frequency, voltage), often even within a

There’s also variation in - how power is delivered through the overhead wire (direct or alternating current, switching frequency, voltage), often even within a country, for example because high speed rail needs more power and cannot use what’s used elsewhere (https://en.wikipedia.org/wiki/List_of_railway_electrification_systems https://en.wikipedia.org/wiki/List_of_railway_electrificatio...) - platform height (again, often even within a country. See https://en.wikipedia.org/wiki/Railway_platform_height https://en.wikipedia.org/wiki/Railway_platform_height) Two centuries of work leads to significant technical debt.