@rplst8 posted:One other thought on going 2-rail. Why do most HO trains run on 18" radius, but 2-rail O scale trains need like O96 (48" radius) or O108 (54" radius)? In O, the equivalent to 18" radius is 33". A few I've seen need 22", but even that is like 40" in O scale. Therefore O72 to me seems like it should be doable for a minimum radius in 2-rail O.
Big steam locos might need wider curves, but even 6-axle diesels & longer modern freight cars can take 36" radius curves. Of course they can look a bit silly doing so, just like HO models on 18" radius, but "can't be done" is just a myth. Here's a YouTube link showing my Atlas SD40 on the 36" curves at one end of my layout. First car in the train is an MTH Centerbeam on Atlas roller-bearing trucks.