Whats the difference between Distpatcher Control or Automatic? I though with modern CTC the dispatcher can control any signal..or set the program to do it...or of course a train being in a block willl turn a signal to red.
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Mike,
For now, the short simple answer to your question is this:
In CTC, there are "Home" signals or much better described as "Control Points". These signals are the ones that can display an absolute "Stop" aspect. The dispatcher has control over these signals only. Once a favorable signal has been passed, that signal cannot display another favorable signal until the dispatcher asks or "Codes" it to do so.
Signals between Control Points are called "Intermediate Signals". The most restrictive aspect they can display is what at one time the rules called a "Stop and Proceed" (stop then proceed at restricted speed), but, thankfully in more recent years the name has been changed to "Restricting" (in order to keep the train moving at restricted speed). The dispatcher has no control over these signals as they are "Automatic block". Once a favorable signal has been passed, as the train continues on from block to block, the signal will automatically go from red to yellow to green for following movements.
Interesting. However, just curious, I have seen intermediates default to yellow...yet clear green either a couple blocks ahead...or many miles ahead??? If its a slow night, can't the dispatcher line the track up green for long distances? Does the computer help this?
Also I have seen a train in the block yet the intermediate turns green in the opposing direction...while the train is sitting there...as if green is unfolding behind the train so as soon as double track is reached the opposing train can proceed.
I have also seen the intermediates hold a train at red even when the block ahead was clear? Say a work crew was there.
OK, you want to get into the complicated stuff, eh? 
Yes, the dispatcher can and often does line signals up over long distances. With help from the computer he can put the signals on "Fleet" so that control points will line up behind a second or more trains following in the same direction or, a shifter needs to work back & forth by a controlled signal.
Intermediate signals, being automatic, can line up in the opposite direction of a train that has just passed that signals block. This depends a lot on how the signal system is designed (wired) out in the field.
There have also been times when, after meeting an opposing train, the signal relays would get stuck in the opposing flow of traffic. The dispatcher would then talk you by the stop signal and you would have to run restricted speed to the next control point. Being on the cab, you could watch the opposing signal line up behind you as you pass and clear the block behind.
Now, think of a long section of track (let's say ten miles long) with a control point signal (C) on each end and intermediate signals (I) in between.
For example, C-I/1-I/2-I/3-I/4-C.
You might also see two opposing (side by side) intermediate signals show clear in each direction. That is because the blocks are clear at least two blocks ahead and no "flow of traffic" has been set up by the dispatcher. In other words, there are no trains between the control points on either end.
So, neither C has been lined by the dispatcher and are showing red.
Signals I/2 & I/3 could be showing green in both directions.
Going left to right, signal I/1 could being showing green and signal I/4 showing yellow.
Going right to left, signal I/4 could be showing green and signal I/1 showing yellow.
With "stick signals", if a light bulb burns out the signal may derate to the next most restrictive signal. A green would derate to yellow and a yellow would derate to red.
A broken rail or a tripped slide fence circuit could also cause an intermediate signal to go red.
If a MoW crew is working between two control points, most likely the dispatcher is not going to allow a train into the MoW crew's working limits, unless, it is a work train and the two crews are working with each other on a track warrant or a "not to go past such & such milepost" is given to each crew on the track warrant.
Very informative and helpful. I appreciate this insight.
So technically between control points trains run in ABS style territory.
