You can see an gif here at http://imgur.com/0gfW9ewWas prompted by https://www.reddit.com/r/factorio/comme ... _railroad/

Red by logic does not allow for train repath when there is an obvious path available. While the video is recorded in 0.13.4. It still exists in 0.13.10
End user input
I understand why a red by logic can get away with not repathing a train, say, for a crosswalk.
Suggested alternative/solution
Allow for a 2 stage red signal logic. for example.
Close signal if item > 10
Demand repathing if item > 20