Cheat the minimum track curve, I mean. O.K., this has been said before by me in a number of ways, but it all boils down to this. For whatever reason, downsizing is happening in everything. But we don't have to give up our hobby just because we can't have a big layout. The solution is smaller set-ups (with more detail perhaps), and being content with what you have! Yes we will be spending less because we have less to spend. And we have to be more creative with what we build. But by no means do we have to stop participating in the hobby. The only way to have continuous running of our trains in a small space is to use the smallest curve possible. Not the thing that some hobbyist like to brag about, their tight curves. In fact it has become a status symbol to have very wide curves. But the tight curve is very possible with flexible track like GarGraves and I encourage the practice so we can build small layouts that can be transported and set up in small spaces. Even small table-top set-ups for a coffee table, buffet, end table, or sofa table are possible. Yes, you only need about 24 inches depth for either HO or O gauge. That is correct, just look over some examples on this site.
So to recap, the tight track curve is the solution to our economic and space problems. We don't need special train rooms, basements, or attics. We can fit these small set-ups in our regular living spaces; don't even need spare rooms. I recommend using smaller 4 wheel steam locomotives, and smaller diesel switchers, short cars (rollingstock), and shorter trains, on these small set-ups and it all works! And we can rotate our buildings and scenic details, as well as our equipment, to keep our interest at a high point. If we need a challenge, we can repaint and super-detail everything. Believe me, there won't be enough time in the day if you go the super-detail route. Best piece of advice -- learn to be content with your compromises, the secret to peace of mind with life in general, and this hobby in particular.
Here are a few ideas to get the ball rolling:
1. Think Murphy bed for your bed squeezing in a small layout in the room, although a Murphy bed style layout/table is also an option.
2. A shelf layout that is only 24 inches deep at the return loops, narrower elsewhere.
3. A layout on a large coffee table (26" by 56")
4. An around the room layout that is only about 8 inches deep in most places, at about chair-rail level. Normal furniture can fit in, with lift-out sections at doorways and windows.
5. A semi-permanent dining room table layout that folds in half for temporary storage.