Under layout yards

I don't recommend using L girder if you want a lower level. It doubles the thickness of the benchwork and leaves less head space for the lower level. Also the greater the height difference between levels the longer the distance needed to have a viable grade percentage.

These levels are 18" apart, but the thickness of the benchwork eats up 4" off the top. L girder would double that, leaving you a working window of just 10".





This helix is how trains get in and out of my hidden yard.

Steve, eventually they will be wrapped with backdrop. In the case of the one in the photo, it will have the backs of buildings on the main street of Red Wing, Minnesota. The upper level will have a turntable and roundhouse. There will probably be a black fascia band that "caps" the sky, to provide some visual separation. There is a second helix which will have a similar treatment, though that one will be the Mississippi River valley. 

three track under layout yard

Some observations:

1. The greater the separation between levels the longer and steeper the grades need to be. 

2. The deeper the staging area the greater the clearance needs to be to reach over parked trains.

3. Track work needs to be nearly perfect.  You don't want any derailments.

Jan