During the mid 2000, an experimentation in the Montparnasse metro station in Paris transformed a moving sidewalk in order to have an acceleration ramp from 3 to 9km/h. It was slower(most of the time) than the 1900 expo's 10km/h. And there always was a "slower" sidewalk (3km/h, the default) next to it. The goal was to go up to 11km/h (it did at some point). And yet it failed, and was removed 15 years ago. Only the slow options remain.

https://fr.wikipedia.org/wiki/Trottoir_roulant_rapide#/media...

You can see it in action here: https://youtu.be/FBzlEG3tMuw?t=399