Hey CROR410? Was your question more like how does CTC differ from ABS only? Heres how it work buddy. With CTC a train dispatcher can run trains any way on any track (double or triple track, or one line with sidings) He can decide which way traffic can flow. So theres a crew change point will call MP1 (CP 1) with controlled signals at both ends with a bunch of crossovers. (a O.S.) So at the eastend of MP1 there are four mainline tracks, two for west bounds to park and two for east bounds trains to change out.(that does change with traffic demands) Two miles west from MP1 there is another controlled signal, MP2 (CP 2, Control Point at MP 2). Ten miles from MP1 is another O.S. (set of crossovers) at MP10 (CP 10) So this is how traffic gets "spaced", all four tracks at MP1 are full, two west bounds waiting to leave and two east bounds. The west bound hot shot UPS train on main #1 gets a high green light and they blast off, once they clear MP2 a loaded coal train on #2 track gets a low yellow, and this is what JG was talking about,"slugging" "stalling" insted of pulling right a way they sit there and wait for a better signal. The UPS train is almost at MP 10 before the coal train decides to leave town. The red over any signal tells the crew they are crossing over to a different track. (they know the speed threw the turn out) Train dispatchers dont want trains spread out most of the time. When they do decide to hold trains its because something else is going on forcing him to hold trains. Sometimes if there is no east bound traffic close the dispatcher could run the UPS train up one track and run the coal train up two track and get them both out of town quick, crossing the coal train back over to one track at MP 10. With CTC that is possible.
Now with trains trying to get into town. An east bound stopped at MP1 waiting for a clear track to pull into. (four, three, two main??) A east bound leaves and clears main four and the east bound at MP 1 gets a low yellow and pulls into the track threw the crossovers at 20 mph. (they know the turn out speed) Once they clear another east bound stopped at MP2 gets a high yellow, they do the thing JG was talking about and decide there gonna sit there and wait for a better signal. (train dispatcher can see this, its a controlled signal) Finally they get a double yellow, approach medium is what we use to call it. Its not set up to space trains, its telling the crew that they are going in at MP1 into eather main four or main three, do twenty threw the turn out. Theres no spacing about it, it telling them what to do. If the light at MP 2 went from a yellow to a flashing yellow they might have a high yellow at MP1 or maybe a low yellow or a low green. Lights can tell you were your going, a double yellow means your going into three or four main. Anything else would be two or one track, different turn out speeds on those switchs.
All that make any sense? CTC gives the train dispatcher more control, ABS works like an interstate that we drive on, west bounds on this track, east bounds on the other. The fast ones catch the slow ones, the fast one leave the slow ones in the dust. (all though trains can run the other direction with special permission) As soon as a train clears a block another train behind him gets a signal to pull into that block, unless its controlled by the dispatcher, the lights tell the crew what action is required after passing that signal, it does not space trains, it tells us what to do. Dispatchers hold trains at controlled signals, but they dont call it spacing. Theres a reason behind the delay.