Chuck,
Of course, you realize that you will have to let the following train know AT LEAST two blocks behind the leading train. In other words, when train #1 enters block #4 the signal governing block #4 will change to red, the signal governing the entrance to block #3 will change to yellow (to warn of block #4 being occupied) and this must be done while train #2 is still entirely within block #2. This, of course since you are only going to have 4 blocks, also means that since train #2 is still occupying block #2 the signal governing entrance from block #1 to block #2 will be red and that means that the signal governing the entrance from block #4 to block #1 will be yellow. In theory what you will have is two trains constantly following each other on yellow signals, or what they call an approach signal. The definition of an approach signal is "proceed, preparing to stop at the next signal. If exceeding medium speed, reduce to medium speed immediately. Medium speed is defined as a speed NOT EXCEEDING 30mph. This is all necessary to keep from having a train entering a block on a clear signal running at track speed then having the next signal red as by the time they see the signal there is no way that they will be able to get stopped short of the red signal safely or not even at all.
Of course, if there is a siding within the block you will need to get your signals to display a red over yellow for a "diverging approach", a red over green for a "diverging clear" and yellow over green for an "approach diverging" indication. That is if you are using color light signals rather than the light position signals which are entirely different and use nothing but yellow lights. Of course, if part of your layout is downgrade, then you will need an intermediate signal capable of showing a yellow over yellow which is an "advanced approach" which warns the train to be prepared to stop at the second signal and gives the train traveling downgrade additional time to get stopped.
If you wanted to run three trains with your four blocks we would have to talk about red over red over yellow or a single red on a mast with a number plate (which designates intermediate signals). These are both "restricting" signals which allow a train to entire a block that is already occupied by another train and will further restrict your speed to a maximum of 15 mph but often way less.
Like Pete says, "have fun wiring!"
prof
