I've always had small layouts, but the one I have now is the smallest one ever, so "real estate" for operating accessories (which often have a large footprint) is at a premium.
Thus came the idea of an elevated section of track across the entire back of the layout, with operating cars placed there, to put some "activity" to the layout.
I have a Lionel Powermax transformer dedicated to this elevated section, with some extensions built off it for a floodlight tower and an illuminated junction tower. I also have a couple of snap together truss bridges on this section along with a girder bridge. Visually it gives a small layout a lot more dimension.
So, what I did was to use very narrow sipping straws - cut with a slit down them lengthwise - and then I slipped them over the center rail. They're just a few inches in length. So I can easily turn on or turn off an operating car, by pushing to the left or right just an inch or two, to allow the center roller pickup to come in contact with the "live" rail.
When I want to turn the car off, I roll it back an inch or two, so that the center roller is now over the sipping straw piece. I just had to figure out how many cars would be parked on this elevation, and then to space the straw insulators in the right places so that the car could be moved just slightly to turn it on or off.
Right now I have an aquarium car, a vibrator searchlight car, the walking brakeman car, the chase gondola and a toxic waste car all up there. I can have a couple cars on at one time and not trip the transformer.