The nice thing with TTSD is that it won't have the same limit as TTD which let us have only three kinds of tracks. I suspect (but don't know for sure, as I am not on the coding team) that TTSD will have the following:
Normal train tracks, just like TTD
Electrified train tracks, just like Patched TTD
Monorails, just like TTD. However, I am hoping they will have the additional ability to run down/over roads and hop over buildings, just like real ones do.
Maglev, just like TTD.
Trams. These would operate on normal/electrified tracks, but also have the ability to run on tracks set into otherwise ordinary streets. When on dedicated tracks, they would obey signals like any other train. When on roads-with-tracks, they would act as if they were road vehicles, except of course with the restriction that they can't leave the tracks.
Subways. Really this is not a special kind of track, it is a new ability of all the other kinds of tracks to go underground, like in a normal tunnel, but with the ability to have turns, switches, signals, and stations down there. Of course you could use this to make a dedicated subway, or half in/half out like the London Tube, or just have an underground city-center mainline railroad station like in New York (Grand Central & Penn)
It is also possible there might be the following:
Elevated rails. I view this as basically the opposite of subways - instead of being underground, they're up in the air. The only special ability would be the ability to be built on top of other things (not buildings) such as roads or other tracks, just like the real ones are. Also the stations could be up in the air, built over the street or built on top of a ground-level station. Again, this could be a dedicated system, or it could connect to an ordinary suburban line.
High-speed line. Visually I suppose this would look just like normal electrified track except with a different (concrete?) colored ballast so you could tell it apart. I think its trains would also be able to operate over normal electrified track, but at slower speeds. Normal trains couldn't go on the high-speed line (different electrical frequency?) I think this would be a later addition as it isn't so obviously useful, you can use normal electrified lines for this easily enough.
I imagine the track laying would be very much the same as it already is with the Patch (buildonslopes, pre-signals, etc.) I'm hoping they will also have yellow warning signals (slow down, but don't stop, because a train is one block ahead) and signals on the BORDER of a square rather than right ON a square.
It has already been announced that TTSD will support viaducts (high-level bridges). If subways are implemented, then that would in effect also mean you could have curving tunnels.
I've seen some discussion about having train depots that are a realistic length. Personally I'm against this because it would take up WAY too much space, but that's another issue.
Somebody wanted third-rail electrification but I don't see that as very important. Maybe later.