Double Helix
This scene shows the east end of Chattahoochee yard. The mainline enters the helix on the left and winds its way up to the middle level. There's room for more staging tracks under the helix. Just to the right of the mainline will be a longer track representing the connection with the Apalachicola Northern. I used a more standard framing method for this helix rather than the threaded rod approach. The wood supports are much easier to install, but you can't control the grade as precisely as with the rods. There are probably some slight humps in this helix (you can kind of see a dip/hump on the upper level in the back). I just hope it's not enough to stall trains.
Below is a larger view of Chattahoochee yard with the new helix on the left (excuse the mess). The tracks on the right are in the approximate location they'll be positioned in the yard--the leftmost track is the mainline, next is the siding, then two yard tracks. Two or three staging tracks will be to the right of the yard tracks.
So all the subroadbed for the lower level is now in place. Now it's time to actually try laying some track!