No, i will try to explain it. Normally, if you have two tracks, then every track is a single track for each direction. The signals are place exactly like this. If you have the need, because you have maintenance work on one track, you need a special order to get the permission to use the oposit track in the wrong direction. If this happens more then twice, you can have a special kind of signals to control the "wrong" side. This can be a kind of replacement signal, it is the Zs8. This needs on the end of the use of the wrong side a main signal or a kind of protection signal like a Sh signal. If you have two tracks, you can use in each direction in each moment, you have a "Gleiswechselbetrieb", which means bi-directional line operation . In this case, you have each signal on the right side and on the left side. The change of the track starts with a Zs6 signal. On the Schwarzwaldbahn yo can see the typ of signalisation. Even, this was installed, to have the oportunity for maintanace Work in each moment. The mountain "works" and moves a lot. So maintance work in the tunels is a frequent thing.
Regards
Bernd