Factorio Forums

> What did you do?
An automatic train network was set up with many trains, tracks and signals.
> What happened?
Two automatic trains collided despite proper signaling.
> What did you expect to happen instead? It might be obvious to you, but do it anyway!
I expected one of the trains to wait until the other one cleared the intersection.

I tried to annotate what is happening here: (1) A train enters and exits the intersection as expected. I believe this causes the fast petrol train to repath.
(2) Another train comes up to the intersection and stops because the block is reserved.
(3) A very fast petrol train comes up and reserves a loop that comes back around and includes the intersection.
(4) After the petrol train leaves the intersection, the train in (2) enters it. When the petrol train loops back around, it crashes.

Here's a video of what's happening:
https://www.youtube.com/watch?v=KunZCXAM5IM

I attached the save in question, as well as a screenshot of where it's happening about 10 seconds after the save is loaded. (I couldn't run over there quick enough to resave at that location.)

Save file: Screenshot of where to look:

The looping train is probably moving so fast that it reserves the collision block for the second time (via the stopping point) before it has actually cleared the block for the first time. This might be related to the old self-intersecting route bug.

I think this may be related to what happens here: viewtopic.php?f=7&t=48209 .
A train leaves a block (in your case the intersection) that it will enter again, without enough space to break in between. This means that when it leaves the block, it should still have the block reserved. It wrongfully gives up its reservation after the first time it exits this block.

I loaded the save and tried it in the current stable (0.15.34) and no crash happened on the location, so I guess it was fixed in the meantime.