I think the idea is large pedestrian only paths, interruptible in rare occasions by emergency vehicles or for moving large things (perhaps car priority during very limited hours?)
Sure the roads on average can be a lot narrower, assuming perfect coordination, but it will still be a needed pretty much in all the same places...
Before cars, we had roads. They were not empty.
A big problem with cars was that people had to stop walking on (or near!) roads.
If you watch film of early cars, people still happily walked amongst them. The problem isn't so much with cars themselves, but with increasingly impatient people; the intensifying rat race.
What is a rat race? I've heard it all my life but until this moment I never questioned what it actually meant.