I have bought a fair amount of Atlas 2 rail track. ( more than I will ever use). I have Lima O scale trains to run on it. I'm not sure but guessing it takes 12 pieces to make a circle, I do know but can't remember what I have but I do know it's tighter than what Atlas offers anymore, and I have a full box of it, which I think is enough for two circles.
My passenger cars if I remember correctly are 21" ( I have 4 of them I believe lol ) I haven't set these up other than a test track, to run the engine. I plan to make a second level in one corner of my layout and put these up there.
Just an idea for another brand of 2 rail which I believe you could get DCC into.