Train wanting to go to depot stops at green signal

[Sanchimaru]

Hello, I have been quite a while away from the forums...
But lately I decided to start a new TT game. I found the following problem, and since it's been a long time, I can't recall how everything works. Sorry if this is a basic question, but I could find no documentation about it anywhere.

I use this kind of entrance for terminal stations:

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with a depot on the peak. There are 2 way signals at the station end, and pbs signals before the first track junction, as seen in the picture below.
So the train enters the junction heading to the station, but just inside the junction, it decides to go to depot. So it follows the path it reserved, but then stops at the green 2way signal, never reversing, advancing or changing orders.

What am I doing wrong? Since this is a very simple configuration, I have no idea what isn't working.

Thanks in advance

[aahz77]

I can reproduce the problem with r2075. Haven't tested older versions or Beta9 yet. Doesn't occur with regular entry/exit (non-PBS) signals.

EDIT: Sanchimaru, you don't do anything wrong. It's a commonly used setup, and the behaviour must be a bug.

[DaleStan]

To prevent that behaviour, use Go To depot/Service At depot orders.

[aahz77]

To prevent that behaviour, use Go To depot/Service At depot orders.

Hmm... why isn't it possible for the train to pass the green signal, and then turn around in the station to re-enter the pbs block towards the depot, just as it would do in a non-pbs-block??

[DaleStan]

Because a train that cannot find a route cannot pass a PBS signal. With a normal signal, it passes the signal anyway and just hopes, but to pass a PBS signal, the pathfinder must determine what tracks are to be reserved.

[aahz77]

Because a train that cannot find a route cannot pass a PBS signal. With a normal signal, it passes the signal anyway and just hopes, but to pass a PBS signal, the pathfinder must determine what tracks are to be reserved.

I cannot pass a signal that is leading OUT of the block? I understand that it's a two-way signal, so the track behind it which consists only of the station tiles, is technically also a PBS block (or isn't it?). As I understand it, the train should reserve the complete block consisting of all the platform tiles, pass the signal into the "platform" block, reverse at the end, and re-enter the junction block. It works for the normal situation in which the station is the destination and I don't get where the difference is.

[DaleStan]

I understand that it's a two-way signal, so the track behind it which consists only of the station tiles, is technically also a PBS block

Correct. And that's why the train can't pass it. Not because it can't leave the PBS block it's currently occupying, but because it can't enter the next PBS block

As I understand it, the train should reserve the complete block consisting of all the platform tiles,

But that's not a path to or toward the depot.
The pathfinder does not consider the possibility of U-turns, and the PBS engine would probably break horribly if it did.

[michael blunck]

Dumb question, but isn´t it this bug?

Correct routefinding issue with station platforms terminated by non-track tiles within the current PBS block caused by erroneous perception of said non-track tiles as the station platform end instead of the preceding tile.

http://svn.ttdpatch.net/trac/changeset/2082

If yes, try r2082 or newer.

regards
Michael

[aahz77]

I understand that it's a two-way signal, so the track behind it which consists only of the station tiles, is technically also a PBS block

Correct. And that's why the train can't pass it. Not because it can't leave the PBS block it's currently occupying, but because it can't enter the next PBS block

... which is the station block. But why? Oh, another sentence excuse me if I'm slow-thinking, but it's late for me....

As I understand it, the train should reserve the complete block consisting of all the platform tiles,

But that's not a path to or toward the depot.
The pathfinder does not consider the possibility of U-turns (...)

I didn't know that. And if its destination is the station, it finds a path (because no U-turn is needed) and reserves the path. Then turns after visiting the station, etc etc. All fine. I get it.

(...), and the PBS engine would probably break horribly if it did.

OK, please leave it as it is I don't play with services anyway. Just wanted to be sure that I have a correct understanding of what's going on and why.

If yes, try r2082 or newer.

I reproduced the problem (in r2075) with a regular station without any non-track tiles. Will check back tomorrow.

[Sanchimaru]

Thanks for the replies:

I downloaded r2082 and loaded the same game. Not only the problem persists, I think it's even worst, look at this new problem:

The train is just routing through a station a few tiles away, on its way to a far away terminal station on a one-way track.

[aahz77]

Not only the problem persists

+1 here

a far away terminal station on a one-way track.

This seems to be a normal situation:

The paths through the junction must be shorter than 64 tiles and cross 7 or fewer junction tiles. A train will never find a path that crosses more than 7 junction tiles.

(From the PBS Wiki entry)
A junction in this context may also be a PBS block consisting only of straight track, without any junction tiles, and then the 64 tile restriction applies.

[Sanchimaru]

The problem also persists in a newly started game.

This seems to be a normal situation:

Are you sure? I mean, look at the screenshot, the current order station is at sight, only 11 tiles away from the train's position. Also, there is nothing in the track, and the junction is just 2 tiles wide.
That behavior happens a lot when you try to send a train directly to a very far away station. But usually, just adding a waypoint helps, since the train is not travelling the whole distance, but only the distance from the junction to the waypoint. That is the basic purpose of waypoints, as even before the patch, buoys existed to help boats finding their way through long distances.
That was indeed the case here, the train got confused since the station was too far away, so I built a waypoint. Then, the "train xx seems to be lost" notice came shortly after.
If a train can't find its way from 11 tiles away of straight single line there must be a problem.

[aahz77]

This seems to be a normal situation:

Are you sure? I mean, look at the screenshot, the current order station is at sight, only 11 tiles away from the train's position. Also, there is nothing in the track, and the junction is just 2 tiles wide.
That behavior happens a lot when you try to send a train directly to a very far away station. But usually, just adding a waypoint helps, since the train is not travelling the whole distance, but only the distance from the junction to the waypoint. That is the basic purpose of waypoints, as even before the patch, buoys existed to help boats finding their way through long distances.
That was indeed the case here, the train got confused since the station was too far away, so I built a waypoint. Then, the "train xx seems to be lost" notice came shortly after.
If a train can't find its way from 11 tiles away of straight single line there must be a problem.

Building a station (or waypoint) inside a PBS block is never a good idea, as the train has to reserve a path towards an exit of the block, not just up to its destination. If the station is occupied, it might reserve another path through the block that doesn't lead through the station. Admittedly, if the block doesn't contain any junction tiles (as in your case), that shouldn't be much of a problem (terminus station platforms are an example of stations inside pbs blocks, and they work because it's the simplest possible case and the train doesn't have to reserve any track beyond the station).

However, in your case the train doesn't enter the block because it tries to reserve a path through the entire block, no matter how near its destination (your waypoint) is. And if the block is longer than 64 tiles, it won't find a route, thus not reserving a path.

The solution is to place more signals along the route, so that no block is longer than 64 tiles. I know that this makes it impossible to serve the station with more than one train, but then again, that would also be difficult with your current setup (so I assume you only have one train for such a branch line anyway).

[DaleStan]

However, in your case the train doesn't enter the block because it tries to reserve a path through the entire block, no matter how near its destination (your waypoint) is. And if the block is longer than 64 tiles, it won't find a route, thus not reserving a path.

Exactly. "Location of current order" and "end of PBS block" are two separate concepts. They usually happen to coincide, but they don't always. When they don't, it's "end of PBS block" that determines whether a train can enter, not "location of current order".

[Sanchimaru]

Understood, thanks for the information! it's not quite intuitive, but that's how it works

So, as for the depot issue, an advanced use of the train orders is required, including always a "service at depot" order for all trains going to that station, or eveng passing the junction. Trains won't even go to the depot if don't need to, running the basic schedule.

And about the second issue, I fixed it making a double track at the exit where the train was stuck. Just long enough to have 1-way signals.