I completed the upper deck over the weekend. The basement is still a bit of a mess, so I'll take more pictures shortly.
So the new challenge is determining exactly how to tie in the helixes. On the west side, the mainline will go down a grade to enter the helix under the Stanley Works. I'll be using the masonite I cut for the spline on the last layout. The masonite spline is great for this because it automatically creates easements into the curves, and it also makes steady vertical curves. I've done a quick mock-up and it looks like this will work well.
The real issue is on the east side of the city. I moved the helix I've built to see how it will fit in place there. I could move it into position provided I'm sticking with the idea of placing it behind the support column, instead of around it.
The problem is that the geometry I was hoping for doesn't really work. So I measured out how it would differ if I moved it to be around the pole. It helps, but not not really enough. I looked at a number of possibilities, including entering the helix in the opposite direction. In the end it creates as many problems as it solves.
After a lot testing, I've come up with an approach that I think will work pretty well. It will obviously depart from the prototype, but I think it will actually improve operations. Besides, I haven't come across any pictures from that side of town...
So on the modified east-side of town the mainline will also dip into the hidden helix quickly. The siding will extend to serve several industries on top of the helix. Since the inner track on the mainline which will run passenger and freight is 26", I'll reduce the radius of this helix to that radius. In addition, the turnout to make the helix single-tracked will be placed before it gets to the column which will save me 4" and allow me to move the helix enough to open up the geometry a bit.
When I get a chance I'll see if I can get one of my buddies to draw up a plan to post.