I've never seen anyone post a layout that combines methods for creating height and crossing tracks, so I thought I would post this. If you are short of space and you can make that crossing, all the sudden you have more space!
The dimensions are not important, but the left side in my example is roughly 4x8'.
As you see, the layout is simply a blue separate loop-to-loop line with an orange loop-to-loop line bent around and partially stacked above it. An interchange to move cars or trains between lines is shown in white but is not strictly necessary.
All the loops are level. The blue line descends from its yard to a tunnel loop on the right. Orange line trains climb to a mountaintop above the blue tunnel on the right.
Due to their divergent nature, the parallel tracks resemble a "<" sign or a mountain switchback.
Method #1 to save 50% - Going up and down at the same time
While the orange track is climbing off the table, the blue track isn't staying level. It is descending to a lower level or in my case a tunnel. Every inch of available track is thus exploited up or down to create separation. The grade or vertical distance travelled doesn't need to be the same for each line. In my example, the orange line is longer so it can do more of the elevation change.
Method #2 to save another 50% - Going back the way you came
When you can go back the way you came, you don't need to account for a track "back down" to ground level.
Method #3 to potentially save more - Extend the runs
If necessary, the run of the orange line could be extended around the curve. If really necessary, the run could be extended past the switch. Obviously, the heights of the two lines must agree at the interchange to exchange cars.
