You were right, after changing the junction to a roundabout and still having it fail, I finally noticed this little guy, hiding behind a tall electric pole and blending in with the wall gate lights: Which I think was causing the track to become one-way.

Ever since I started playing Factorio, I've always used a single-track rail system, with chain signals that prevented a train from leaving unless the whole path to its destination is clear. However, I have become interested in more advanced rail signaling and setups. I think I have a basic ...