controlling (+/-)power to each of my 6 tracks in my 3 rail O gauge switching yard.

To kill power to single-ended tracks, I use SPST. For engine ready tracks, I use center-off SPDT, with one position for track power and the other for accessory power. The accessory power keeps the engine idle sounds going and the batteries charged. For double-ended tracks in the "division-point" yard, I insulated them into two segments in the middle, with a center-off SPDT in each half. Thrown toward the center, they get power from the panel rotary cab selector, and this is the normal position. Thrown away from center, they get power from the adjacent block. This allows me to switch the rear end of trains that still have road power attached. Presumably, I could switch both ends simultaneously, but I haven't tried to yet.