This plan builds a single-track return-loop to return-loop layout, with a elevation-climbing loop in the middle to gain 6" in height. There are actually three passing tracks, with the smallest about 10.5', so two trains can pass each other in three places, for a number of interesting operating patterns. With a relay-arrangement using 3-rail detection and slow-down tracks, two trains in conventional-mode can run continuously passing each other in the middle-right passing track.
There is also an On30 elevated train for a third train and more operating interest. The mainline run is decently long, with an out-and-back run. The trains can run each reverse loop in the opposite direction each time for more variety.
With the three passing tracks, two trains can be waiting and staged in two of the passing tracks, for four visible trains, two running, and two staged.
The mainline is O48, with three O48 turnouts and the rest O60 and O72. The grade climbing up and around the loop is 2.5% - reasonable for easy operations. The inside passing tracks are O36 with some O48 to be almost O37. The mainlines will support O42 locomotives and equipment operation.
A work in progress:
The 6' width of the layout needs access around the two long sides, and the tunnel-end, so one can reach into the tunnels from the end. 6' is just a bit more than an easy reach from each side, but otherwise the rest of the layout is easily accessible.