I’m thinking about running a double line flying (wye) junction from a double main line off to a yard and connecting branch short line. I have been researching prototype flying junctions like the Fretin Triangle. Any helpful hints/ lessons learned from model railroaders who have incorporated one into their layout would be most appreciated.
It would take a huge amount of space.
Just looked at the Fretin Triangle - which would occupy a basketball court if built accurately in HO scale. The track levels aren’t marked, but there’s a lot of ‘over and under’ weaving - no problem given the prototype’s size, but not really practical in a model to fit in a finite space.
I sketched out a simpler version, where one route passing across other tracks went over, and the other went under. It would still require about twelve feet on the yard side, and ten feet from the center each way along the main - HO scale, maximum grade 4% with vertical easements, four inches railhead to railhead at overpasses and underpasses. The killer is those long, almost straight grades up and down. Tweaking the mainline wouldn’t help much, since there is one point where there are tracks on three levels.
Of course, it would be smaller in N-scale and smaller still in Z. With only six turnouts, not very complex in any scale. The alternative would require three level crossings, which would decrease the space required (27.5/30" curve radii) by a factor of (almost) four.
I vaguely recall a John Armstrong layout based on the PRR Zoo Junction in Philadelphia. The primary emphasis was passenger traffic, with trains snaking over and under…
Chuck (Modeling Central Japan in September, 1964)