For those interested in model toys, particularly that of the model train, one thing they will inevitably come across when commencing their hobby is the issue of how to wire their railway.
One of the most popular ways to do this is through the device called common rail wiring, the basic concept of which lies in always insulating the same piece of rail, while leaving the other one still connected. Sketch and/or draw a layout of your system that shows the dual tracks while marking the outer and inner rails as plus and minus respectively. In the example of an oval track layout, this means that the outer rail will always be positive no matter where it goes, and the inner rail will therefore also always be negative. The benefit of this is, once you have insulated the inside rail on every siding (even those controlled via on-off switches), the outer rail therefore becomes akin to common ground, while the inner rail resembles hot switched lead. This is why this method has become known as common rail wiring for the model train. Two different power packs are recommended for this system, both insulated from each other (such as in the cases where an oval is inside an oval), as they can then have the ability to control different areas of the layout in the same instances. Both packs need at least one wire to be attached to the common rail, with a second to go to either the insulated rail of the oval or to the sidings in order to be controlled.
The common rail system is a very popular one, primarily because it enables the system to pass on control from one of the packs to the other, with the model train on the track thus gaining power from the right side of the front truck at the same time as it is getting it from the left side of the rear truck. Minus the common rail, the model train would otherwise regard the insulated joint as a malfunctioning switch and would thus then just stall on the track. Just be prepared for the possibility of the model toys surging unexpectedly fast when crossing over the joint!
One last point remember to double insulate on the section of the track where you require the train to reverse back on itself this means that the positive rail will suddenly run smack bang into a negative rail, and thus an insulating gap and plastic joiner are essential here. A DPDT (double-pole, double-throw) switch will be required for this operation.
Aside from this, however, the common rail wiring should be the best solution for your model train toys system.