The return loops behind the paper mill were both 15", as well as buried in a lift out mountain, both were on grades to enable one to cross over the other, c55 with a bit of superelevation. The tunnels concealed the "model railroadiness" of the over/under tight curving tracks, and also masked the unpleasant aesthetics of longer cars white-knuckling their way through the turns.
Because I was fanatical about quality control during that part of the build, it was one of the most operationally reliable parts of the layout.
The Thomas Sub track had the steeper climb, but traffic was mostly hoppers and 4 axle power, with occasional 60' hi cubes for charcoal service. The Connellsville line managed long cars jus fine, but only with truck mounted couplers to manage the wide swing. Being 15 years ago, that was pretty much what was available, so the auto racks and 89' parts cars did fine.
So, as long as you're thoughtful at installation, and don't stretch the limits of your rolling stock, you should be fine.
Lee
