Some recent threads on the forum have mentioned helixes, connected levels, etc. This got me thinking about whether I could squeeze a helix into my own 12 x 18 train room. A multi-deck layout seemed like an intriguing way to get a longer main line in the same space. So that in turn got me thinking whether it was even possible to design a "multi deck" layout using SCARM. The answer is YES! with a few qualifications.
As far as I know SCARM only lets you use one baseboard. So I made the "upper deck" from a couple of extruded polygons. To prevent any terrain weirdness and maintain a consistent appearance I did the same thing with the lower level, although it wasn't required. For simplicity's sake both decks have the same terrain profile, although I'm sure that they could be as different and complex as needed.
All of the track on upper levels has to be "bridge" track with its track supports removed. The 3D polygons forming the upper deck have to be as thick as any valleys you're planning to create, at least where those valleys are going to be placed. Any mountains, tunnels on the upper deck, and their portals have to be manually created as figures. Depending on how much time you're willing to put in, the results can be a bit crude-looking, but still useful for planning purposes, and not really any more crude than other terrain created using 3D figures. If you're actually going to build your terrain by sculpting layers of foam, this might not be too far off from the real thing!
As you might know, tunnels and portals made this way don't impede the operation of trains using the Model Trains Simulator extension. So you can still travel the routes on both decks and even use the "camera" icon to see the cab view from the upper deck!
I strongly recommend that you create additional layers to keep things separate between the upper and lower decks. Track, terrain, etc., overlap in the top-down view (as they do in real life.) So it's important to be able to "turn off" a layer and hide objects, which prevents them from being accidentally selected when editing.
Some things I learned from this excercise about planning my own layout are: There really isn't enough space in my train room for a helix. If I do build one, it should probably be in the adjacent garage with two holes through the wall where trains can enter and exit. (They would disappear for a while, and magically appear on the other level!) Adding twice as much track and more trains on the upper level sounds like a good thing. But having two more "crews" in the train room will make what's already a tight, narrow space even more crowded.
I learned that trains disappear out of sight for a LONG time in the helix. So although it adds much length to the mainline, it doesn't proportionally add to the operating enjoyment. Perhaps a multi-track helix could be used as a means of staging. But it is a very useful construct if you have enough space for one and want to build a multi-deck layout. The grade in the helix is about 2.8% which is steep but manageable. Going all the way around the room on a continuous slope (in my case almost 50 feet), a grade of almost 5% would be needed to achieve what I would consider the minimum separation of 24" between decks. And that leaves NO flat track for switching, industries, etc. So in my case two flat decks connected by a helix is the best way to do it.
With that 24" separation, neither deck would be at an ideal height. The lower one would likely be a back-aching 32-36" and the higher one at 60" which is pretty much eye level for me and hard to reach.
I've attached three 3D screen captures to give you an idea of what the finished product looks like. And also the SCARM file, so you can experiment or use my layout as a starting point. Try turning off various layers to see how this changes the 3D view. The track layout is just a single mainline with dogbone loops to give you a feel for operation on two levels. There's plenty of room to add passing sidings, etc., to permit multi-train operation.
Thanks again to @Mixy for designing a great program that made this possible!
