[solalf]

Well this is actually still very common in Paris! A number of subway stations have adopted them for long corridors connecting platforms of different lines within the same station. They move people at 4km/h on average, but the one in Montparnasse station goes up to 9km/h (used to be 11!). They’re mighty useful to hurried Parisian commuters.

https://fr.m.wikipedia.org/wiki/Trottoir_roulant_rapide

[jgtrosh]

The 11km/h central lane was wicked fast. It was really exciting as a kid... But always broken.

[mahkeiro]

Though you needed a good balance for the slowing/accelerating sections.