This still doesn't allow train spacing of less than the braking distance. Braking distance of trains is large (due to high uncertainty in track friction), which still means trains are typically 1 minute or more apart when moving fast.
As long as you have comms with the trains around, it's clearly possible to safely go less than the braking distance, as long as you can be sure of the behaviour of the train ahead, even in the case of an equipment failure (ie. in case of a power failure, it will not slam the brakes on, but decelerate at X m/s^2).
As long as you have comms with the trains around, it's clearly possible to safely go less than the braking distance, as long as you can be sure of the behaviour of the train ahead, even in the case of an equipment failure (ie. in case of a power failure, it will not slam the brakes on, but decelerate at X m/s^2).