I don’t think we’ll eliminate 100% of cars/trucks, as they are very useful for certain applications. But if we removed all the cars from the road that are just people going some place, without any real cargo to speak of, the traffic on those roads would be significantly less.

Carmel, IN seems like an interesting case study. They haven’t going the route of adding in a bunch of public transit yet (that I’m aware of), but they have replaced nearly all their traffic lights with traffic circles, and have been removing surface level parking lots and creating more mixed use space. As a result they’ve been able to reduce lanes on roads, as traffic has decreased.