> It’s fair to say that few of us now marvel at moving walkways, those standard infrastructural elements of such utilitarian spaces as airport terminals, subway stations, and big-box stores. You've gotta be referring to escalators here. Never seen a moving walkway in a big-box store, or a subway station for that matter.
There are at least some in the Paris subway, including one that went at 12 km/h but was decommissioned in 2011: https://en.wikipedia.org/wiki/Moving_walkway#Trottoir_roulan...
I do think a concept with parallel tracks moving at different speeds would have been easier to use and more reliable though. But it might not have been revolutionary/over-engineered enough to attract attention and subsidies.