Factorio Forums

Greetings,

I am pretty new to trains and especially signals and chain signals. Either I don’t understand how they work, or they are not working correctly.

Before we start: I wanted to set up a new loading/unloading station. After I was happy with my design, I added signals and chain signals and decided to fill it with a bunch of dummy trains to see if it works the way I want it to. So I connected the two tracks to the top of the screenshots and the two tracks at the bottom of the screenshots and added some dummy stations to let the trains drive around for a bit: However, the trains don’t fill up the “buffer” tracks even if they are empty.

So, I have a train coming from the top. Since all 3 buffer tracks are full, it has to wait: The train on the right buffer track leaves. In my understanding, the waiting train should then go to the now empty buffer track. However, it seems like the train has decided that it wants to stay on the middle track, even though the signal at the beginning of the buffer track is already green. It is a little hard to see in the screenshot but the chain signal has turned blue at this point: It takes 7 or so in-game seconds until the train notices the empty track and chooses to go there: A few seconds later, the same thing happens with the next waiting train. It waits for the right track even though there are two empty tracks to choose from: I have the same thing happening with trains coming from the right side of the setup: Here, the train even waits until both tracks are free before going: In all the examples shown so far, it takes roughly 5–10 seconds until the train finds the new path.

However, the last two screenshots show the same problem as earlier. Here, I blocked the trains on purpose to stop them from leaving. This time it takes 35 seconds (!!) for the train to see that there is a new path:
I would really like to understand train signals and chain signals better. However, I’ve been stuck for an hour now and have no clue what is going on. I have already searched for signals on the wrong side of the track, and I am pretty sure I haven’t missed any.

I appreciate any kind of help!

Greetings,
Mc_Muffin

Unfortunately, there is not enough information for us to debug. Train issues can be tricky to analyze, some subtle issues are really hard to spot. Your 1st screenshot, the map, doesn't show the signal positions (they're green and red dots), and it doesn't show the station names. No schedule information. No block information in the zoomed in screenshots (the colored block info you see if you hold a signal in hand). If you could post a save, it would be best.

In general, Factorio isn't like a car driver who chooses a lane ad hoc according to the traffic. Instead, when a train is about to depart, it determines the destination (if there are multiple destination stations with the same name), then calculates a path to the chosen destination and then follows this path no matter what trains have moved since creating the path. So it can happen trains want to drive through a track occupied with a train while an adjacent lane is free. There are repath events/situations that will change the path en route. Route calculation and repathing is described here: https://wiki.factorio.com/Railway/Train_path_finding

Thank you for your quick answer.

But isn't the whole point of those “waiting areas” (which I've seen in a couple of YouTube videos) that the trains can wait there if the actual train station is occupied? If the path is calculated at the time of departure, then the whole point of the waiting areas seems useless, doesn't it?

I mean, a train leaves a train station. It “sees” that at that point the left lane is open, so it chooses this path with its path calculations. However, by the time it arrives at the waiting area, that lane could be occupied by another train (which is probably what happens in my screenshots), and so the train never searches for another open lane?

Or should I design my “waiting areas” so that I can pretty much guarantee that there is always one lane open in the waiting area upon the arrival of a new train?

You can just put train stops in the holding bays and add them to the schedule without any wait conditions.

Mc_Muffin wrote: Fri Jan 30, 2026 9:41 pm Thank you for your quick answer.

But isn't the whole point of those “waiting areas” (which I've seen in a couple of YouTube videos) that the trains can wait there if the actual train station is occupied? If the path is calculated at the time of departure, then the whole point of the waiting areas seems useless, doesn't it?

I mean, a train leaves a train station. It “sees” that at that point the left lane is open, so it chooses this path with its path calculations. However, by the time it arrives at the waiting area, that lane could be occupied by another train (which is probably what happens in my screenshots), and so the train never searches for another open lane?

A train in motion train will try to repath under a number of different conditions, such as not being able to reserve a signal as it approaches.

The problem you're seeing, as I understand, are with trains that are fully blocked so they had no choice but to slow down and wait at a signal.

Thinking through the logic, I can think of a number of ways that would make it rather complicated and error-prone to implement train at rest in a way that would be able to respond instantly to the kind of situations you're looking at. So, the devs went with a "try again after waiting for a given period" solution that is reliable, albeit at the cost of introducing the kind of delays you're observing.

Thank you for all you answers. I think that I now have a deeper understanding of how these signals work.