I am probably over thinking this, but…
This is a simplified model of the lower return loop (hidden) and the mainline double track crossover before it enters the main yard. The crossover is what creates the ‘reverse’ scenario.
The mainline crossover is about 34 feet from the start of the hidden return loop.
In this scenario, where would you add double gaps to create the reversing section? I am using a DCC Specialties PSX-AR controller to control the reverse section. In my previous layout I double gapped both mainline tracks and made the whole reverse loop a reversing section. The outside loop of the return loop is about 40 ft long which is longer than any train I would run.
Thoughts?
Thanks,
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Hi @Onewolf42. I have a similar setup for my staging yard. I have my gaps (blue) as shown in the sketchup below. Will that give you enough length?
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That was my first idea also. But a train coming from the right on the lower track using the turnout to cross over, the length of the reversing section is only the length of the turnout. Still looking it over. Maybe isolating the upper upper track from the crossover turnout to the start of the yard on the upper track, along with the lower track, as proposed, would give the OP the length he needs. He also could extend the reversing section from the turnout on the lower track more to the right, if possible, for added length.
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That is a fair point, @floridaflyer1. @Onewolf42, what length of mainline do you have to the right of that gap on that mainline? Shifting that turnout to the left would give more length there, if that is an option.
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I would do as Casey did wok those left most gaps, but the gaps on the right ought to be placed before the crossover, not after. Keep the crossover as part of the non-reversing section so that you don’t have to gap the center of the crossover.
Rich
Is there some technical reason why I shouldn’t just double gap both tracks right where the return loop balloon starts? And have the return loop balloon as a reversing section?
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That will work but then all your track feeders in the yard reversing section would have to through the auto reverser. Generally the less complex the reversing section the better.
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Maybe the simplest/safest option would be to just use the lower mainline between the staging turnout ladder on the left and the crossover on the right as the reversing section. That section is about 420" long and my longest trains will be about 220-230".
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Needless to say, I like my idea best. 
Rich
And for posterity sake, here is the bigger picture.
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I believe that when the divergent route in taken at the crossover a short will occur at the turnout as the outer rail of one track will now be connected to the inner rail of the other track. I’ve been wrong before but I believe the track must be gapped between the two turnouts at the crossover and the reversing section made as long as possible toward the right of the crossover. The frog end of the lower crossover can be gapped anywhere up to the start of the yard.
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Not under my plan because the crossover will be in the non-reversing section with the same polarity of the rest of the track in the non-reversing section.
Rich
That was my understanding as well @floridaflyer1. I think there needs to be a double gap at the crossover. @Onewolf42, somewhere else along you layout, is there a similar loop where one side of the double track loops back on itself? Basically, are you planning on being able to have continous running with trains running in one direction on one side of the double track and back on the other? If so, then the polarity would be opposite and you would need the double gap. However, if that is not the case, I think@richhotrain’s plan would work.
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Casey, your plan would work with the gaps in the center of the crossover because then, and only then, is the reversing section that you propose fully isolated.
In my proposed plan, the reversing section is fully isolated by the gaps just after the yard on the bottom and the gaps just before the crossover on the lower track. No need for gaps on the crossover.
If possible, you alway want to keep crossovers outside of the reversing section.
Rich
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I think Rich’s/my plan of having the lower mainline track between the staging track ladder and the mainline crossover works fine. The will be no turnouts/crossovers in the reversing section.
The double track mainline goes through the main division yard, passenger station/service and eventually falls off the edge of the benchwork. 
Before it reaches the edge of the benchwork the Oregon Short Line heads off to the left. I wanted to (mostly) model a single track mainline of the Union Pacific and the OSL was the best candidate. The single track mainline continues on the lower level (40" elevation), enters the helix (which is double track: outer for going up, inner for going down) where is enters the middle level (60" elevation). The single track mainline basically retraces the path of the lower level about halfway and then starts climbing (1.65%) until it crosses the aisle at 80" elevation and head into the upper level (inside the center platform with 28" high floor). The single track mainline goes around the center platform (20ft x 17ft) and hits the turnout which starts the upper level return loop/staging tracks. (which is a true reversing loop).
Here is the lower level where the OSL goes left and the double track mainline goes over the edge (representing Nevada/California).
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Without gaps at the crossover, the positive( to use an old term) track on the lower track connects to the negative track on the upper track when the divergent route is chosen, the point of reversal is at the point the two crossover turnouts meet.
Looking at the layout plan the outer rail of both tracks coming into the crossover from the right have the same polarity. when the crossover is activated, the outer rail of the lower track connects to inner rail of the upper track, thus causing a problem
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You and I are seeing something different. I see in the crossover that Lower mainline R connects to upper mainline R and lower mainline B connects to upper mainline B.
Let us assume there is no return loop. Do you still see a problem with the crossover?
Now add the reversing section in the lower mainline left of the crossover. It’s polarity will match either the upper mainline or the lower mainline at the crossover.
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You are correct, we see different things, I see lower R connecting to upper B. I see R as the outside rail on both the upper and lower tracks. and B as the inner rails on both. when the turnout is thrown, assuming power routing TO, rail R on the lower connects to B on the upper.
Let me try another way, a loco enters from the right on the lower track, the engineer is located over the inside rail(B). The loco goes through the crossover, and now the engineer is over the outside rail(R), that’s a reversal and, without gaps as soon as the power routing turnouts are thrown a short will occur. In a case of a non- power routing TO, the short will occur as soon as power is applied to the layout. Another way to look at it. assume the upper track is at the upper edge of a loop on a 4X8 board and the lower is on the bottom of the board, now install right hand turnouts at the upper left and lower right of the loop and connect the divergent tracks. Where would you have to put the reversing section?
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Are you saying that this otherwise normal crossover requires a reversing section/controller? I don’t see it.
The entire lower level track has the same polarity except the reversing section on the lower main line left of the crossover.
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Seems like a lot of energy being expended on a simple problem and a simple solution.
In its simplest form, the top half of the following diagram shows the issue on Onewolf’s layout. Those sparks show the short at the point of opposite polarities,
The bottom half of the diagram shows the solution. Wire everything on the right with the same polarities. Gap (the green circles) the section coming out of the yard on the lower track and make that the reversing section.
Rich
