Case in point is the "metro line". The metro will be an elevated line that I am imagining will snake through the city. As such, before any city planning can be done, the exact track layout for the two-track metro line needs to be determined (which is also constrained by the outer loops of the 'main line railways).
My original approach was to use Unitrack curves - the 216 and 249 radius curves -which would then connect to Atlas flex track for the non-curved sections. I decided not to use existing Kato viaduct sections as the walls are a bit too overwhelming and would block the trains. I wanted something a bit different, so I knew I would be scratch-building some sort of viaduct/elevated structure. So my original concept was to use 1/8" thick PVC foam board (one of my materials of choice!) as the base, and then mount the Unitrack to this material - with some sort of siding to make it look like an elevated trestle or viaduct system.
So what I decided to do was abandon Unitrack and go with some classic snap track - in this case I'll be using Minitrix's R1 and R2 radii curves (which also means much tighter curves at 194.6 and 228.2 radii - which should be better for my cityscape than the wider curves. I am a bit concerned that these might be TOO tight, but as this is going to be a metro system, it's not like I'll be running any TGVs or traditional passenger cars on this line - well, at least that option is gone now!).
So I started with a new plan for my viaduct. After several different attempts using various easily available and cost efficient materials, I ended up with a plan that will use Evergreen Scale Models 1/4" thick plastic strips along with 1/4# wooden dowels available at the hardware store.
And so, the initial straight section is complete! If this approach works out, then I'll proceed to creating the curves and the station section using the same basic format.