One tricky chain signal !

[eldarne]

Hi everyone !

I'm sorry for such a basic question (I guess ?), but I've been working trains for 2 days now and it's driving me crazy (no play on words ^^)

I have a particular case and I can't comprehend why a chain signal is behaving like it behaves.
It's not that it doesn't work. But it slows down all trafic & I need my ore FASTER !

The picture speak for itself I think. You can see that the train entering the station on the left, makes the chain signal for the exit go red. But the railway is free in front of him. It should be blue for me.

Thanks to anyone taking the time to help me and explain me what's wrong.

[twepy]

The most basic rule of trains in Factorio is that only one train is allowed in a block, which is a section of track separated with signals. Your intersection isnt properly divided into separate blocks and as a train is occupying the intersection block that chain signal doenst allow another train to enter. Factorio signals arent like the path based signals of OTTD, where trains that have a free path over the intersection the game would allow multiple trains to enter a intersection.

[Loewchen]

I can't comprehend why a chain signal is behaving like it behaves.

Quite simple, the block after the chain signal is occupied by the train changing direction South to East. Chain signals do not allow to have more than one train in one block, just like regular signals. If you want a train to be able to go north in this situation, you need to put the chain signal between the fork and the vertical track, not before the fork.

[eldarne]

I would understand the problem if the train leavinf the station was going down. But it is going up. And up is free, isn't it ? So the chain signal should see it and give the go to the train.

I must say that I searched a lot and then tryed and failed so much time before arriving to this.

I understand the basics, but when you have this kind of station with lanes going up down left and right, it besomes tricky to spot what is part of a "block" or not.

Can't you just have a feedback for what area is covered by a block ? Because I'm starting to go crazy following the right pass of the lane with my mouse and try to visualize the "block".

[torne]

The debug menu (hit f4) has a basic visualisation of which block is which (there's a recent FFF about making this a proper visualisation outside of debug)

Every piece of rail that touches is part of the same block, unless divided by signals. This includes in directions it's impossible for the train to actually go, as well as directions the train doesn't currently intend to go.

The problem in this case is that there's no signal separating the train currently in the intersection from the block the top right train is trying to enter: that block continues all the way down to the signal before the merge onto the southbound track.

[twepy]

Bit crude but i visualised the block:


Notice the color of the signal with the yellow arrow? Its red, because the block the signal guarding occupied with a train and it doesnt matter where the train is in the block.

[eldarne]

Ok I got it ! Well, I think I got it at least =)

Thanks for the debug menu tips ! It was really useful !

One question though : what does the little "F" and "B" that pops when I activate the "block" view in the debug menu means ?

Thank you so much for the fast answers !

*Thanks for the schematic twepy. Helped me a lot to visualize blocks !

[twepy]

Then you probably show-rail-segments activated not show-rail-blocks, the latter doesnt show any letters.

[eldarne]

I had indeed activated both menu (just in case ^^)

Here is my new system =) I think everything looks good this time. Thanks to you !
The problem was I couldn't even place the signal I needed. So I made it bigger.

This debug menu is really great ! Helped me a lot !

[Ripshaft]

haha good to hear, yeah figuring out how to think about these things is something those of us who grew up with things like TTD take for granted, but we all had just as hard a time figuring it out ourselves too... except we didn't have forums back then... oh god we're getting old.

Though to move you further on, your use of regular signals should be reserved to the 'exit points' of your intersection, if you want multiple trains to be able to use the intersection at once, in as many ways as possible. If you replace the non-exit signals with chain signals you'll be able to support more non-stop trainage through that intersection. (edit: without getting into a traffic jam - which can happen in your current setup when the intersection gets stressed... which will happen without fail in factorio lol)

[eldarne]

I reworked the system. It still had some problems on the other lane this time ^^

But I made it work properly. And I now test it heavily with 4 trains going in and out to test the limts.

Thanks for the tips about chain signal being used at entrance. I presumed it was it so I used it at "big entrance" only. Do you confirmed I should use it at every non-exit point ?

[Ripshaft]

I reworked the system. It still had some problems on the other lane this time ^^

But I made it work properly. And I now test it heavily with 4 trains going in and out to test the limts.

Thanks for the tips about chain signal being used at entrance. I presumed it was it so I used it at "big entrance" only. Do you confirmed I should use it at every non-exit point ?

Yeah, the way it works is that it'll look for any clear path to a normal signal - and this check can be passed from one chain signal to the next, so if only your exits are normal signals, your entrances will allow any train through that can find a clear path to the exit. Using normal signals generally works but it can cause weird and annoying problems like jams because a train will enter the intersection because the first part shows green (since the first part is clear) but as soon as it gets through it, the next part is not clear, and the train stops in the middle of the intersection... this in turn stops another train entering the intersection, and before you know it you have a complete jam. Chain signals within the intersection instead will let you completely avoid that problem.

[torne]

The way I learnt to think about regular signals vs chain signals in a complicated intersection is to follow this process:
1) Put a regular signal everywhere there needs to be a signal (i.e. everywhere you need to separate the blocks to allow trains to pass by each other)
2) Then, look at each signal in turn, starting from the exits and working "backward":
a) Imagine there's a train of whatever the longest size train you use stopped at this signal
b) Is that train blocking any other routes?
c) If it is, you need to replace the previous signal in its path with a chain signal.

However, when you have a small, compact intersection like the one here, where there's not enough room anywhere inside the intersection for a train to stop, then you always just end up with a simple situation of "all entrances are chain signals; all signals inside the intersection are chain signals; all exits are regular signals". You usually only need to think about it in more detail if the intersection is big enough to contain suitable places for a train to wait inside of it.