> The minimum headway between trains is dominated by switch fouling: how long it will take a train to pass over the switch, and then for the switch to switch to

> The minimum headway between trains is dominated by switch fouling: how long it will take a train to pass over the switch, and then for the switch to switch to a different track, before the signal can go green again. The absolute minimum spacing between two trains running non-stop one after the other perhaps. Unless you imagine a system where at each station the line splits into two or three separate tracks, for all practical purposes however the actual limiting factor will be stations, as the combination of platform reoccupation time and dwell times will significantly larger than switch fouling time alone.