Factorio Forums

Factorio v1.1.74 (steam/win64)

I'm experimenting with loop junctions and long trains (100 cars). The signalling within the loop junction is all chain signals so the train reserves its path before ever entering.

However, I recently witnessed (and can reproduce) a case where the train changed destinations while part way through a U-turn, attempted to loop 540 degrees instead, and crashed into itself. I believe, but cannot verify, that the change occurred because of a train-limit change on the original destination. Instead of continuing along its original path through the junction, it immediately generated a new path to the new destination and did something it wasn't supposed to do. It didn't attempt to stop; it was actually accelerating the whole time.

I have a save just before the train enters the junction. I have mods installed but this particular train and its stations are all vanilla.

Trains can never path to avoid their own tails.
This is simply a reason to avoid loop junctions. You could maybe try removing all the signals inside the junction, but that limits throughput.

Trains don't lose their reservation at a station when the train limit decreases, only if the station becomes disabled.

Thanks for the pointer. I suspected that might be the case and already have plans to fix my design.