Trains just ignoring passengers

[CapAp]

I'm tired of losing levels because trains just ignore passengers in overcrowded stations. It happens constantly.

[guth]

I agree. I can (sort of) accept that the "AI" is a little stupid, but sometimes it's so stupid that it simply must be a bug. And it's a bug that I feel has appeared in a recent update.

One pretty extreme case is that when I put a new train at the end of a line, it sometimes (but very rarely) ignores that end station completely, even though that station only belongs to that single line and there's no other train coming to that station in a very long while. I think this exact scenario started happening maybe a few weeks ago.

[dholland]

@guth: I know you've made videos of some of your games. If you have a game with this bug on video, you could make a short video clip and send it to the devs.

I've experienced a lot of bugs with the AI over the several years I've played this game. I think bugs with extreme mode are clearer to demonstrate, because there is no teleportation clouding the issue. In normal mode, since the A* algorithm for pathfinding was never intended to work with teleportation (!) it's not surprising that the AI can get confused when a train or line is moved. I don't remember examples of this kind of bug when no train or line is moved, although I don't play extreme much.

If the bug only happens when a train is moved (either from the network or the inventory) it could be that in some cases the reservation of passengers for trains is not being updated properly after the train is moved. The passengers could have been reserved for more distant trains, and this reservation system is not updated to include the moved train, so no passengers can be picked up as they're all reserved by other trains.

Edit: a possible workaround in normal mode if the bug happens is to remove the station from all networks and ghost from the station to another unconnected station. Hopefully, there's now only the ghost train to serve the station and it will work in this case.

[guth]

Well, I delete all videos where I don't basically win (in extreme mode). :)
But I'll keep it in mind.

Yes, in normal mode you can usually fix problems caused by the bad AI, but in extreme mode, it can mean the end of the game.

[BlackSpy]

I had a happy accident on today's extreme map where a train ignored some passengers in error, but that meant it had spaces when it got to the next, overcrowded, station. Hurrah for bad AI!

[guth]

I think it does that on purpose, though. At least in some circumstances.

[crypto29]

This unexpected behaviour occurred during my game today in normal mode, and I cannot recall seeing this previously. It occurred immediately after moving a train, and despite ample seats, the station became overcrowded.

[Robert]

When this happens again, do you mind taking a screenshot as quickly as possible and posting it here with a description?

As a bit of background, writing AI for Mini Metro is a lot trickier than it looks. I assumed it would be a doddle but rapidly discovered that it's impossible to write something that acts sensibly in all cases. If we had unique stations and fixed timetables, then yep, it's be a lot easier, but because the simulation is so dynamic it's hard to know what's going to happen past a few seconds into the future.

We've spent years on this problem and I believe that where the current issues come from is passengers not hopping on train A because they think that it'll be faster if they wait for train B on another line (or train A, but coming back the other way). However this route might be expecting to make a transfer to train C, but then if before train B arrives the passenger realises that they've missed the transfer window, they won't hop on train B anyway and will wait for train A to return. So it makes sense from code but makes the passengers look incredibly stubborn and is very frustrating. We can't fix this without making passengers much less likely to take transfers, which then could lead to worse overall behaviour!

Having said all that though, if a train leaves a station at the end of a line and doesn't pick up everyone that it possibly can, then that's definitely just a bug.

[guth]

I'm not the thread starter, but thanks for responding, Robert.

I've just uploaded a couple of short videos that clearly demonstrate two somewhat different cases where the AI made the game end earlier than it could have. They don't show the extreme case I talked about above, and I can maybe see why the AI might think it was a good idea to do like it did in these videos. But it's still pretty stupid. :)
Both are extreme mode games in Sao Paulo. The 2nd one is from my daily challenge run from October 15, 2019.

https://youtu.be/33R8iPwLEWI

https://youtu.be/OxOb6IfROZs

Maybe you could use neural network(s) for the AI...?

And while I have you on the line, Robert... (I hope you don't mind...)
Just in case you're not aware of how tedious it is to get really high scores in normal mode, please take a look at this video that I uploaded a while ago:

https://youtu.be/vbwcPGuvMVY

Because of this I never play normal mode anymore.
Please try to avoid making extreme micromanagement a successful strategy in the upcoming Mini Motorways. Unless, of course, if other people like it...

[Robert]

Thanks for those two videos, they're very helpful. We've got a Mini Metro update planned for later in the year so we'll see if we can reproduce the issues and tweak the logic.

We're aware of the degenerate play required for high scores in normal mode, we have thought a lot about the underlying issues and are aiming not to replicate them in Mini Motorways. It's really no fun for anyone!

[nelson]

Robert, as I am one exploiting this "degenerate play" with "ghost lines", I have a suggestion: Make it impossible to delete a line while there's still a train running on the tracks, or (alternatively) also deleting all the passengers currently on board if you choose to delete a line, would help a long way to stop the use of "ghost lines" - and it would be thematic too (after all, a train can't run without tracks, can it?)

[guth]

Yeah, that would definitely make things better (at least).

[guth]

Robert, for some reason I've never really thought that it was the passengers' decisions to take a train or wait. In my mind it was the trains who decided (just like this thread's title implies), which really is less logical. So, I'm rethinking how stupid the AI in my two videos really is. I mean, why should a real passenger care if a station is getting overcrowded? He just makes an educated guess which train is the best for him to reach his destination, and sometimes real people even guess wrong. But let's assume passengers don't really like it when it gets too crowded, so maybe they could be more prone to take early trains if the station is getting overcrowded? Would that be doable?

Anyway, I'd personally much rather see a fix for the "degenerate play" in normal mode than a fix for trains ignoring passengers.

And btw, since you've got an update planned for later this year, maybe you could add yet another map. And if so, make it unlike any other map. Make it crazy!

Now, I'll be quiet...

[BlackSpy]

If there was a crazy map, I'd vote for something cylindrical, or even spherical. Your asteroid base's light rail system or something....

[Robert]

Haha we'll see what we can do! It has been suggested that we not do a regular city map but something totally left-field - we haven't decided yet (or if we have time to do a map for this update)

[guth]

Robert, I have another example video of strange AI behaviour:
https://youtu.be/Y91fVLH7dpg
Why does only one "star" passenger hop on the new green train that I place? I can't come up with any reason for that. I let the video run for a little while so you can see what happens to those poor star passengers.