Actually, one more thing.
A couple of minutes later, the AI decided to link that second coal mine that was right next to an already existing station (see screenshot n°6). Here is what it did:
Why didn't it link directly to the already existing line? The line it built instead is very strange; it uses bridges to go over town roads instead of going around them, and it goes over already existing track to link to the same main line immediately afterwards. Moreover, as I already pointed out, it would have been more clever to link to the mainline closer to the destination (ie at the bottom of the screen) than further away.
There seems to be a lot of places where the AI could have reused existing track and doesn't. I think what causes that is that the AI choses where it will connect the line and then tries to figure out how to connect the two places. This results in strange behaviours sometimes.
The AI tried to link the green line to the place circled in blue. Something went wrong obviously, because it stopped building during the process. I could have linked it to the place circled in red (it seems more logic to me...).
Also, it seems that the AI doesn't like to use the same rail for two different cargos. At some places on the map there are for or six tracks instead of two, simply because it transports two or three different cargos, despite them traveling roughly the same route.
I will post the savegame once I think the game is over.
On a side note, is an option for trains to drive on the right a possibility?