@Mansen: I’m not sure I understood your point but the game does allow a signal to only trigger at one direction. The signal is only valid for one side. Signals must always be putted in the side of direction. If the track is both ways, and you put the signal to the right, it will trigger for trains going in the direction of the signal.
So in your screenshot, you can allow trains to be more effective, just put more signals, but since its a single track, they must be in one direction in other to not block the other direction.