Since my last update I've been able to lay roadbed and track for the bottom and second level, and have started to work on the structure for the 'third level' of track and the street (or top) level.
In the below photo you can see me using the tried and true method of using white glue (actually, I used carpenter's / wood glue version of white glue just because it was handy) and pins to hold the track in place. I wasn't sure how the ends of the track were going to work, but with the help of my Dremel was able to get a nice even cut of the track to match the front of the diorama:
You might also notice some 'pipework' that I added to the top of the retaining wall. It seems like major retaining walls you see in urban areas always have some sort of stuff attached to them, so I figured some piping (created with styrene rods) would add another level of authenticity!
Below is the cork roadbed applied for the second level, a Kato two-track girder bridge, and another section of unused Kato double-track that I will convert to another bridge:
And below is the track laid down on the second level:
Finally, a shot of the last level of track (this time a single track line) which abuts another retaining wall which will be where the city level / street level facades will go:
From the other side, I am thinking of adding a road bridge over the tracks on the other end of the diorama to add more depth and dimension to the diorama. I'm intentionally trying to make this diorama as 'busy' as I can make it!