Pathfinder question

[Vitus]

Hello,

I've been trying to understand how does the pathfinder behave in special situations recently. I have pretty good knowledge about the general behaviour of pathfinder (first twoway red end-of-line, penalty concept, presignals, PBS and so), however, I haven't managed to understand, nor find the pattern in some very specific situations, which are documented in attached savegame.

I consider this kind of knowledge very useful for #openttdcoop games; mostly because of the crazy things that are going on from time to time (trains without orders, SRNWs and so).

Most of the figures and questions are in the savegame. I'll just comment on few.

SRNW figures hopefully don't need much commenting.
The whole reversing "stuff" is behaving very strange, though. The fact, that stations need PF "fix" is pretty clear (as there's difficulty setting forbidding reversing in stations), however the reverse itself doesn't seem to work as actual penalty, because the trains would choose the first station in that case.

Figures with orderless trains. Now, that's where I don't understand anything. Seemingly useless rail pieces are changing whole train routes and so on... Is there any pattern or general rule to use in this situation? The first station in the orderless network should also get trains, however, the forced split fails for every passing train. It's even stranger when you consider, that these trains shouldn't care for PF traps and so, because they don't have orders at all.

Overflow figures are pretty clear, however, there's one not-very-understandable case, where the pathfinder behaves differenty (figures 1 and 2). What does actually influence whether the train will choose route to depot instead of rushing against the middle two-way signal?

Most of the time, the main question comes down to "how can this little piece of track influence whole network".

Thanks for your time,
Vitus.

The savegame needs only one NewGRF (Logic Engine 0.6, which should be available through BaNaNaS) and it was made in nightly (r19894).

edit: typo, savegame info

[Vitus]

I'm attaching new version of the savegame. It contains additional commenting, which hopefully makes it more understandable.

[Vitus]

Yet another version, this time with two new orderless network figures.