I'm pretty good with spatial relations and designing things in my head. Despite building a 24x32 railroad with a four track main line and yards terminating on corners, I haven't used CAD and everything has worked out just fine.
There's a helix on the Milroy Secondary (behind Milroy on the upper level) and I had planned to use the airspace above it to represent Belleville, on my fictitious Pennsylvania Midland Railroad (which, in my world, took over the Kishacoquillas Valley Railroad).
The space directly above the helix had to be kept clear, but I had allowed 10 inches on two sides of the helix for Belleville, and much more on a third side. But when it came time to design, I just couldn't come up with something that met my needs. And then it happened...
The Belleville Epiphany!
What I did not take advantage of during design was the adjoining HVAC closet. I did some quick measurements and determined that I can run the Milroy Secondary through there, in a "nolix" design, and achieve the desired increase in elevation and minimize curves at the same time. The new route would be about four feet longer than the existing helix route.
Removal of the helix yields 20 inches on the two sides that were previously 10 inches and still leaves a four foot hole for the "mole" operator. The design wheels are still turning in my head, but the helix change is a "slam dunk".
The helix has been removed and construction on the new route will commence in January.