To explane the picture above with a second picture below. A double track route (having two opposing one way tracks) is used by the blue and black line. Both lines are entering a terminal station where they are ending. The track from the railroad depot is connected with both station platforms by using a semi double slip switch (shown by the arrow 3) Signal number 1 (near the depot) is guarding the traffic towards the station. A trains of the blue line are stopped there when an opposing blue train is leaving the station until it has past point B and the way is clear to move further to the blue line station platform. If a blue train at signal 1 is waiting for a leaving black train it waits until the black train has passed point A. If a black train at signal 1 has stopped to give way for a from the station leaving black train it shall wait until the opposing black train has past point A. But a black train moving towards signal 1 don’t wait for a leaving blue train because the routes of the opposing trains don’t interfere. One way signal 2 is used to create the left (coming towards you) one way track.