This is my own idea for an 8'x 8' display layout to run three trains. Lionel never did "easements" on their plans with O31 curves, which is something I favor for better operation and appearance. Instead of copying the old plans exactly, why don't we think up some new ideas along similar lines?
Using non-derailing switches, if switches A and B are set for the curved route, a train will "random-route" itself on the inner mainline. Switches A and D would need to be the newer style with smaller switch machines; O22 switches probably wouldn't fit. SCARM file attached.