Factorio Forums

on every signal pair on both sides of the track; if you mouse over one of the signals is the other one highlighted?

if not then it's not a valid bidirectional pair

You are mixing one way tracks and two way tracks with multiple parallel tracks. Why not keep it limited with 2 parallel tracks going in opposite directions? You can have a lot of trains going over a track if they all go the same way.

Inside the green circle you need a signal, which you have done in your night time picture.
Inside the red circle the signals are mis-matched.
They don't appear to be opposite each other which would prevent the train from returning back the way it came.