This might actually work!

I got the toughest part of the project finished today. The rest should be smooth steaming.

The tough part was the section of the track that goes under the stairs. If you recall when I installed the track to POLA in this same space I made protestations about never doing that again. Well time heals all wounds and I went ahead. However, this time it was a lot easier, despite my arthritic hip acting up.

 First, because I needed 5 inches of clearance under the stair landing to accommodate my O scale locomotives, Atlas flex track, and roadbed, I could get my eyes at track level to see what I needed to do. The HO track was too close to the stair landing for me to see easily the track. Also, the access holes in the stair stringers were much bigger, again for O scale. allowing me to see what adjustments were needed.  The stair stringers don't seem to be sagging with all the material hogged out. I can reinforce them if I notice any issues.

Pre-fabbing the track in the garage. 

Secondly, I prefabricated the benchwork and track sections in the garage on a nice large flat surface. The improved access made it much easier to lay these tracks.  I used my curve templates to get nice flowing and consistent curves using Atlas flex track.

I put a joint in the track and benchwork between the curve and the straight section where the tangent ends and the easement  starts. Basically I made two large sections of snap track. That joint has two dominoes to hold it in alignment, but  they are only glued in one side. So I can remove the tangent section if needed.  I reinforced that joint with a piece of 1x3 that is screwed in from underneath, again removable if needed. I was able to reuse  the joists from the POLA staging yard too. The joists help support the tangent piece.

I haven't test run an engine yet, as I want to put safety walls along the roadbed to prevent errant cars and engines from falling to the floor. But hand pushing a box car looks good.

Tomorrow I'll finishing the road bed and connect it to the rest of the layout.  I only plan to use flex track in the tunnels and the closet sections. All the other track will be hand laid as before.

A view down the tangent track. 

There is a 12 inch long tangent between the two curves in the closet.