Well, it took a lot of working out, but it's all been achieved with 3M Command poster strips and plastic hooks
I've used Command strips for years, ever since a Hot Wheels 'Wall Tracks' set I owned introduced me to them, they're my go-to for sticking anything up basically, so when I decided to try and extend the layout with a bridge, I realised they were probably the only means to attach it to the wall, short of fitting a shelf [which I didn't really want to do]
I took one of my Plarail girders to the hardware store and basically offered it up to a selection of Command strip hooks, and the best fit has been their 'decorating light clips', which are an almost perfect fit for the hollow inner of a standard Plarail yellow girder, so my method was to start at the solid floor end of my room and basically build the bridge, section by section across the stairway gap, sticking the girders to the wall with hooks and strips.
I left it overnight, deliberately overloaded with a 5 car train and the weight equivalent of ~5 Motor Tomica on the road, and it held up impressively, although it sagged slightly because the girders were only held on the bottom, so I added an extra Command poster hanging strip to secure the tops of every other girder to the wall, which almost immediately corrected the sagging, and so far, has held perfectly ^_^
The next stage is to curve the line around to meet a station and standard Plarail balloon track on a board that's going to sit above the stairs [which are L-shaped] in what would have been otherwise dead space [see diagram] - This is basically going to be a form of switchback, as i'm planning to fit a Plarail 'Auto Point' set to divert the trains onto another route, effectively allowing me to create a loop around my room; Considering that space at the end of the bridge was at a premium, and none of my Plarail components could dodge around a protruding section of wall, this was the best way to create a bedroom loop, by turning the trains back around before turning them off onto the rest of the loop; Honestly, i'm surprising myself with just how intricate this is going to be, this has certainly blown away any expectations I had for my layout going in
The road might well be another matter, although perhaps a Tomica road turntable could be the answer to my prayers lol
The blue sections are the track, it's a very rudimentary diagram but I think it gets the point across
Now all I got to do is hope and pray I got enough free time to sort out the rest of the room, cuz the layout isn't going anywhere without any space lol