I appreciate the time and thought people have put into responding to my question but things seem to have become complicated I suspect because the writer is responding to the latest in the thread without taking account of all that has gone before or because the writer is looking to a more "complicated" approach to what I am proposing. I think I have the answer to my question but, meanwhile, here's a recap drawing together the various points which have been raised.
I'm planning a layout for the last Kirkbean Playmobil Exhibition including two passing loops on an oval, at any one time, one oval will have a train parked on it and the other will be empty while its train circulates the oval. The idea is that a train will run clockwise for a while and then be parked on the empty passing loop and the other train will then be released from its passing loop and circulate anti-clockwise, being returned to it after a few circuits and so on.
Clearly, the passing loops need to be isolated and I originally thought of doing so through the points at each end of the passing loops. However, it occurred to me that if there were an isolating point at the entry end of each passing loop and an LGB semaphore signal US style at the exit end of each loop, I could isolate the loops that way and release the trains under signals.
. There will be a passing loop each side of the oval, one for trains running clockwise (call it the North Loop) and one for trains running counter-clockwise (call it the South Loop). In each case, the entry to the loop will be controlled through an electrically operated point connected to a 1015U split track. The exit side will have an electrically operated point and an electrically operated signal, the signal at stop being the means of isolating the train from the exit end through a1015U split track and from the entry end similarly.
I know it is possible to drive the signal via the exit point, but as the loop will be used for parking a train while another train runs round the oval in the opposite direction, I want point control and loco power to be separate.
Here's the track layout for the North Loop, repeated for the South Loop suitably modified:
The train approaches from the left and enters the loop. The split track at 1 is transmitting power and so the train continues until the loco crosses the split track at 2 and then stops. The loco is an LGB Spremberger and a half rail length between the split track at 2 and the split track at the signal at 3 is enough to isolate it.
After the loco stops at the signal, the entry point is switched back to the mainline, so the loop is now isolated from both ends.
At the passing loop on the other side of the oval, there is a train waiting to be released to travel counter-clockwise and this is done simply by releasing the signal at the exit end of the passing.
Once a train is on the main line running in either direction, both loops are fully isolated, by a point at the entry end and by the signal at the exit end.
The power supply is to the continuous, inner loop in this, all the interruptions via split tracks being on the isolated, outer passing loops.
In the light of Dan's post (#21), under DC there is no problem running a loco clockwise and then (after that loco has been isolated on a passing loop) running another loco anti-clockwise; all that is needed is to remember that if turning the control knob on the controller clockwise sends a loco clockwise and forwards around the oval, turning the control knob anti-clockwise sends a loco facing in an anti-clockwise direction forwards around the oval.
Complex to describe but not to wire up or to operate.
I take Dunnyrail's point about using EPL to its fullest, so if setting up and testing go smoothly I may investigate interlinking some operations between the two passing loops, although at some point I will need to intervene to decide when a train on the continuous loop is to return to its starting loop.
