Complicated reversing loop?


Please see attached sketch. I want to set up this reversing loop on the 'B' Line so I can reverse a train from either leg or just do a straight-through loop. I think I can do this by placing insulators where indicated at the double-crossover. Any problems so far?

Now my question is about how to connect the 'A' Line so I can switch it over to the B Line and back again through a double-crossover. Should I;

1. power the entire 'A' Line from the reversing loop and just let the whole thing get switched by the auto-reverser?

2. add insulators at the double-crossover between the A Line and the reversing loop, and power the A Line separately?


My first thought was option 2. but there's not room for a train-length between the two double-crossovers so the auto-reverser might be doing a lot of switching at each axle as the train passes between the two lines. Is this OK? Would it be better if I make a wide rail gap at the double-crossover from the A Line so the rolling stock wheels won't make a short? Any disadvantage to doing this?


In case it matters, I'm running HO scale, DCC, modern diesels, all metal wheels, (future) lighted passenger cars. I appreciate any suggestions.



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Scarpia's picture



I'm not a wiring expert so please take the following with a grain of salt.

First, the double crossovers will need to be gapped anyway to operate properly, basically isolating the entire center frog section of the crossover. You'll only need to add an additional gap on the end near Loop A (both tracks) to separate the loop into a separate power district, one controlled by an auto reverser.

Loop B doesn't need to be separated from Loop A, but I think I would, in order to avoid having a train in A flop the polarity on your in B. I would think that separating it from A, and wiring it as another block like the rest of the layout should avoid that problem. In this manner, Loop A will correct itself based on the traffic, regardless of where the the trains enter or exit.

This is a case where I would strongly recommend frog juicers for the crossovers; I think a slight investment in this case will pay off in dividends quickly.

I hope that helps!

HO, early transition era local time GMT +4
On30, circa 1900    


Reverse Loop

I would run a single reverse loop from about the "P"  in reverse loop to the first switch in the lower double crossover.  Make it a train length long.  It does not need to run from switch to switch. 

If you can't get a train length then use double gaps to prevent individual wheel shorts.  This probably precludes lighted or otherwise powered cars from working properly at these gaps.  The possibility of these cars shorting exists depending on how the power pickup system is designed.  A car with all wheel pickup will short out the system as the pickup length would be longer than the short double gap used to prevent individual wheel shorting.  Testing individual cars would identify any problems before the long train is run with visitors present.

An auto reverser would be the easiest way to power this reverse section.  A different solution would be needed for a DC layout

Linkages can be built to reduce the number of switch machines needed.  Master Comstock posted pictures about a year ago of a single machine design that I did in the '90s.

Note that each switch on each double crossover would need to have it's frog wired according to your standard frog control method regardless of linkage used.  A commercial double crossover like Walthers  has the center crossing gapped and wired correctly. 

Dang, I didn't mean to get this wordy--


cv_acr's picture

Reversing Section

I would run a single reverse loop from about the "P"  in reverse loop to the first switch in the lower double crossover.  Make it a train length long.  It does not need to run from switch to switch. 

I concur. I don't know how much track is actually there, or how long your trains are, but ideally, if it's long enough, run the reversing section from just to the left of the crossovers between the two loops, to just to the left of the first switch in the crossover at the bottom. (Exactly what Terry was suggesting). Don't include the switches or the "B" loop in the reversing section.

Note that each switch on each double crossover would need to have it's frog wired according to your standard frog control method regardless of linkage used.  A commercial double crossover like Walthers  has the center crossing gapped and wired correctly. 

Right, although that's completely unrelated to the reversing loop. (Not saying it doesn't need to be considered, it does; it's just a completely different issue that's in addition to and completely unrelated to the reversing circuit).

What Chris said

Chris is right.  The frog issue has nothing to do with the reverse loop.  However, I have found that some tend to forget to include the everyday things when solving problems and I tend to mention them in passing as a reminder.  Maybe a belt and suspenders issue on my part.


The right way


You are attacking this the wrong way, just because the loop on the left is your reversing loop it is not actually the problem. Normally you would just do the whole loop from the crossover as a reversing block, but as you have the extra crossover and loop (non reversing) very close there would always be problems especially with coach lighting without some tricky wiring, I can tell you how to do that but the way you have asked the question tells me it could be trouble sometime later if there was a problem and you did not fully understand enough to diagnose the real cause.

The method you need is to isolate the crossings as per my alterations to your plan here

The two red lines are isolation on both rails on all tracks. The right hand ones must be at least one train length from the crossover (longer if possible as your trains will grow) Power this section via the reverser.

You will need to isolate the crossovers and power the frogs as usual if they are not done by the manufacturer. I have marked them in for you.

There is one proviso with this that ONLY ONE train may be in the reversing section block at anytime when a reversing move is made, the loops and rest of the layout is no problem as is straight through moves.


The 'A' and 'B' tracks need to be wired in phase so that a train crossing over will not cause a problem, just follow from the inside rail of the 'A' line over the crossing you be on the outside rail of the 'B' line and wire that to the same side of your system then do the same with the other rail. Don't forget the isolators on the crossover.


On second review

If the trackage on the right side of the drawing forms another loop then I would add a second train length reversing section, preferably in the lower track or somewhere away from complicated trackwork.  This would be in addition to the "reversing loop" section.  While the double crossovers appear to be the point that the reverse loop ends, any part of loop track can be the reverse section so the double crossover can be treated as a regular section of track.

This leaves both double crossovers as well as loop B and the "rest of the layout' as regular track with no special wiring.  Train length tracks, if available in these locations, eliminate the potential design complications caused by lighted or otherwise powered cars. 

Each of the reversing sections can only hold one train at a time so most, if not all, of the "only one train at a time in this area" problems go away.  This does cost an additional reverser.


No Terry, you are mistaken

No Terry, you are mistaken as that would not work at all. The loops on each end, while they form part of a reversing loop are not the problem, it is the fact that there are actually four reversing loops (two loops with two different possibilities each and they are all overlapped. Multiple reversers would spend all day fighting with each other as they would be controlling the same track work. Reversers have to be on the part of the track that is causing the short. The only way for this to work is as I described.


Thanks and another question for Tony

Thanks to all who replied.

Tony, I like your approach and I think I'll go in that direction. Let's see if I'm understanding you correctly; the loop won't actually be the reversing section, rather the section in the middle will be. I'll wire up the green loop in phase with the black one.

I'm using all DCC-friendly Peco turnouts so does that mean I can omit the isolators at the crossovers?

And assuming that, can my 'train-length' be between your two red lines? I won't have room for a train-length between the black crossover and the right-hand red line.


4 reversing loops


Take out the track that is labled reversing loop and the straight section above "insulating joiners' and please tell me where the other reversing loops are.  I don't see them on the sketch.

As drawn, loop b is an oval and the section containing both double crossovers form a short section of double track that is connected to the rest of the layout via a single track when deleting both of the tracks I have described as reversing sections.




possible point of confusion


Thinking more after I pushed the button, the possible point of confusion is where I gapped my reverse sections.

Both are single track with no turnouts or crossings contained within the reversing sections.  No part of either double crossover is included in either reverse section.

Not enough coffee yet this morning,


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