Will - all that yours on the "Art Website"? impressive.
Turns out the upper/outer level is a minimum of 72" diameter - I don't know for sure because I had a box of used Ross track that went over 88". Taking a page from many on the forum, where it fit, I would place the largest diameter curve I had on hand in the middle and finish with the 072. My second level has a mix of 072, 062, 054 and 042. The inner is no more than 42" with the depot having 031" at the tightest diameter. A couple of my MTH premiers supposedly minimum 072 run just fine on the tighter curves.
For me it was important to be able to run an engine on all three tracks - given the biggies were not going to be able to do that - so all the tracks need to be interconnected. Basically I wanted more than a 30 second loop around the track.
My biggest issues are - forgetting to put bridges back in place when changing from a test run to run on the layout (and the other tracks with the missing bridges) and forgetting to electrically connect all the tracks into one common feed. I get to a turnout, get halfway through and oops no power. DRAT!
Overall running the big iron in a small space is really hard to do - other than a big circle. I was playing with SCARM and realized I need 19 feet just to have a modified dogbone with 072 - double mainline needs a touch bigger. This one is 13x23 and where do I put a multiple track passenger station (14 feet minimum length) - back is the only feasible place.
The Black Diamond RailRoad is built on a similar foot print and will probably be what I model on my next layout - with a little customization of course.
