Q: How do I wire a double crossover? Each crossover results in a reversing loop. Should I use a PM42 or AR1? This is O scale (2 rail) if that would have any bearing on your answer.
A: Without a drawing to see how things are laid out, this can only be a guess, but a couple rules do apply. The reversing sections must be longer than the longest train. And there should be only one train in the reversing section at a time. It also seems to be a good idea to keep the reversing sections away from the crossovers themselves. Since these types of track layout are already complicated, adding the double reversing sections just seems to be asking for trouble. The "0-Scale" also does apply here since your locomotives are likely to be drawing heavy current, so using AR1's may not be a good choice here. Also, remember that the "reversing section" is really a separate power district. In traditional model railroading, we view the reversing section as an area clearly defined by gapped tracks, clearly defined so that we know when to throw the DPDT reversing toggle. In DCC, the reversing areas can be much larger, with the electronics handling things while we operate our trains.