Not just for cars, but also for cargo... just have a constant gondola-like conveyer that detaches a platform from the line to slow it enough to allow for cargo to get on, then re-zip-it backinto the line and speed it along, de-rail it once it hits its exit/location...

ideally though, in cities, there would be no surface streets and all cars would have their own level below that of bikes pedestrians.

What would SF look like if a superstructure was built above all streets and all pedestrian and bike traffic was moved up there? (sure, SF may be a poor example, so just select [city])

Look at Singapore's vast underground connecting malls between facilities. Those are pretty amazing.

I grade US urban/city planners rather poorly.