> Moving people in nyc at densities of 10ft by 20ft apart from the next human at the best theoretical case is astoundingly stupid

Are you sure? I would expect that it is average density of people over the length of the route that is important when it comes from moving people from some point A to some point B on a road.

With for example buses you have high density where the buses are actually at, but 0 density where they are not. The average over the entire route can easily be lower than the density for cars where you can have that 1 person per 20 feet over the whole route.

If an observer at a fixed point on the route sees more than about 50 cars pass between buses passing the cars will have higher throughput.