Factorio Forums

Hi folks, just starting out with my first multi-train lines, so I hopped into the advanced rail tutorial. The first few examples with chain signals I understood, and after a little while, I figured out the intersection challenges. But with the curving, multi-intersection challenges, I am really struggling to understand how to place the chain signals, and figuring out the logic that each chain signal is following.

This latest tutorial test I have made work but only by fluke.

First of all I am trying to understand the logic, so maybe you can help me with this example. Ignore the red trains for now. Whatever I do, I can't stop the bottom cyan train using one signal and I don't understand why. Here is the example before any user interaction. If you run the trains, the cyan train at the bottom travels to stop at the red signal below the top cyan train.
https://steamuserimages-a.akamaihd.net/ ... 476B54D04/

Example A:
To stop the cyan train, I have tried placing a single chain signal along its path in the location where my cursor is. No joy, the train carries on to the red signal. Note that the chain signal starts off red if you put it in this position.
https://steamuserimages-a.akamaihd.net/ ... B4572E3E3/

Example B:
Restarting the tutorial, I tried placing a single chain signal further up connecting to the other section. Same result. Note that the chain signal starts green in this case.
https://steamuserimages-a.akamaihd.net/ ... 1F1E061D8/

And same result if I put both chain signals down at once (both chain signals start off red). Adding a chain signal opposite the red signal at the top also makes no difference.

I thought that the first chain signal the cyan train hits should be looking at the path ahead, and seeing if any upcoming sections are occupied/red signal. If any of them are occupied, the chain signal shouldn't let the train through. In these examples I don't understand why the chain signals are letting the train through, and also why they are still letting it through even though the chains are coloured red.

Can anyone explain? I feel like if I don't understand the logic, I stand no chance of figuring out how to use chain signals in the game. Also if anyone has the optimal solution for this tutorial and feels like sharing the logic behind what each train is deciding in the answer, that would also be great.

I feel like when the devs look at the tutorials again, it would be good if they looked at the last part of this one. Up until that point I thought they did quite a good job of showing how the chain signals worked. I feel like they need to go through some of these later examples step by step, to show the player exactly what order a chain signal is looking at. Examples explaining multiple trains on curving tracks would be good too, rather than just shove you into a much harder tutorial level. The main problem is that when you find a solution, its quite possible you just fluked it, or don't really understand the logic behind why it worked. It's also annyoing that in the tutorial you can only see the rail sections when you are placing signals, but not when watching the trains.

Cheers

Full signal after the train leaves the intersection.

Chain signal every place two rails touch. (No, it's not gay if two rails touch)

Chain signal the junction entrance.

Congratulations! You are now a twin lane highway master. The tutorial is pretty naughty because it doesn't have you use chain signals in places you really should. Ignore it and automate these rules in your head.

Some train signal tutorials that would really be nice:
- Building a simple train stacker
- Building a single lane side road
- Double headed trains vs. loop trains

Example A: Signals are directionwise right of the tracks, so this signal starts out red because it sees the bottom cyan train ahead of it, but only trains coming from the intersection would pay it any mind. The cyan train looks to it's right and sees a green full signal so it keeps going. (Btw. Having a signal on the left of the track (in direction of travel) but not on the right is a equivalent to having a permanent red signal there, signals without counterpart on the other rail side make a block transition one-way only)

Example B: Same issue, the signal is looking onto the intersection (and all the signals leading away from it). It would only serve any effect for trains coming from the top right rail going south.

"And same result if I put both chain signals down at once (both chain signals start off red). Adding a chain signal opposite the red signal at the top also makes no difference.": See above, same issue.


Aside from that you seem to have the right idea about signals.

I found the tutorial problem you mention to be poor specifically because it does not give you enough chain signals to properly signal the whole junction.

You can solve the tutorial problem with a bit of simplification though. Just treat the whole mess past the straight rails as a single block like this:


The general key to knowing how to use a chain signal in a system where trains can only run on a track in a single direction is pretty simple. You want every intersection to be it's own distinct block. Use a chain signal to enter the block and a regular signal to exit the block. Be sure that there is enough room between the exit signal and the next signal down the line for a train to stop without blocking the intersection with its back end.
If it helps you personally to logically define the blocks, you can use more signals. The setup below functions identically, it just uses a little bit more resources to place everything.

For a bi-directional track, you want to use a chain signal at the entrance to the track, with a regular signal at the exit. There is no need for signals in between the entrance and the exit.

There is a special case I haven't really seen mentioned. That is dealing with the junction between a double track system and a single track branch. When a train enters a group of chain signals, it reserves it's whole path through the segment. The seemingly redundant signal indicated by the red arrow in the image below exists specifically to prevent the train from reserving it's path through the junction until it actually gets there. This can be very important when dealing with trains on long single track branches.

ColonelSandersLite wrote:I found the tutorial problem you mention to be poor specifically because it does not give you enough chain signals to properly signal the whole junction.

Ehm, just replacing the 6 inner signals with chains gives a perfectly signalled junction.

my biggest issue was overcoming using too many main signals where i should have used chain signals.

main signals allow trains to approach... chain signals make trains wait until the entire chain is clear. use the in game color coding to make sure the entire intersection is separated from the incoming tracks as in the screenshots, but make sure there are not any main signals within that box... only chain signals.

These chain signals are totally redundant. You don't need chains before merges, only before intersections. The key point of chain signals is to prevent a train from "entering the box", i.e. they should never enter an intersection where they can block someones valid exit route if their own exit route is blocked. For merges, the exit of both lanes is the same, so train A can never block train B, as train A's path being blocked implies train B's path being blocked as well.

You also don't need signals before splits.

vanatteveldt wrote:

These chain signals are totally redundant. You don't need chains before merges, only before intersections. The key point of chain signals is to prevent a train from "entering the box", i.e. they should never enter an intersection where they can block someones valid exit route if their own exit route is blocked. For merges, the exit of both lanes is the same, so train A can never block train B, as train A's path being blocked implies train B's path being blocked as well.

I prefer to use signals before merges, but in the example shown I would remove the regular signal after the merge, and change to two signals before the merge to be regular signals. (Note that this does not means that the posted image is broken, just that there is more than one way to signal most intersections, and some of those might be better than others.

In your images you are placing the signal on the wrong side of the track. You can tell by the directions of the arrows. Signals should be placed on the right side of the tracks in the direction the train will travel.