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Rails Signaling for Dummies
By Wall-Nut
This is a beginners guide for everyone who has problems getting into rail signaling for trains.
The Only Rule
For a long time I struggled with train signaling. And most of the guides I could find only talked about more advanced applications, but not the basics.

There are many guides, both on Steam and the Factorio Forums that explain the game mechanic behind this. (basically: the tracks between two signals are considered one "block", trains can occupy a block and thus prevent other trains from driving into an "occupied" block, chain signals check their AND next signal, bla bla bla)

But I find that the best way to learn how something works is through practice. So you should just get started and then learn as you go along!

And to get you started, here is just one basic rule when it comes to rails signaling!

"Place a chain signal going into a junction and normal rail signals on all of its exits"

Let me give you a basic example. In the picture below, there's a simple junction. Assuming trains are allowed to move in the shown direction, we place a chain signal going into the junction and rail signals on all exits. Note: All signals need to be put on the RIGHT side of the rails, when facing the direction of movement.

Afterward it should look like this:

Now for a more complicated example. If trains are allowed to move in ALL directions through the junction, you follow the same rule: chain signals going in, rail signal going out.

And you're done!

No, really, it's that simple!
The Only Exception
The only exception to this rule is, when leaving a junction DIRECTLY leads to another junction!

Technically, it's not even an exception, because you're just following Rule Number One again! Remeber, "Going into a junction, place a chain signal". So when leaving a junction leads to another junction, instead of a rail signal, you should place a chain signal!

Here's an example!

The rail signal in the red circle has been replaced with an chain signal. And then the basic "rail signals on all exits" part of the rule applies.

Assuming again that you can move in all direction through both junctions, it should end up looking like this:

If you wish to signal crossings, it works similar to junctions, except you would only have one normal signal leaving the crossing.

A two-way crossing should look like this:

Sometimes you will want trains to deliver lots of materials to a factory and might end up with several train stations right next to each other.

If you have more then one train delivering one kind of material, you can make a "parking area" so all your trains will patiently wait their turn, like this:

For this, you just need to branch a rail off into several tracks, leave enough space for your preferred number of wagons (hover over a signal to display indicators for your train length) and then merge them again into the track going to your train stations.

Make sure the signal before your parking spaces is a chain signal and begin every parking space with a rail signal and finish them with another chain signal. Place another chain signal after the lines merge into one again.

Below is an example, the signals marked blue are chain signals and the red ones are rail signals:

If you correctly signal your rails like this, you should get well-behaved trains all neatly lined up, like so:

Don't forget to put a rail signal before your Unloading Station as well!
Two Lines
Another very popular way of making sure your trains don't crash into each other all the time is to use two raillines, each one only going in one direction, like this:

Now this example has a space of two rails inbetween (notice the extra rails in the middle), big power poles for energy and rail signals along the lines to regularly make "blocks" so your trains don't have to wait all the time (again, not going into detail here, just trust me on this).

This may seem like a lot for just a little bit of track, but once you have robots placing these down, it will be easy and quick. Everything is arranged in a repeatable pattern so you can just place these blueprints down one after the other without a worry. Until then, you can make do with just a single, two-way rail, in my experience.

Since each line only goes in one direction it can be a little complicated to branch off of the main line. So if you need ideas, the following pictures show some examples of how I usually do just that.

A single line branching off of the main line:

A single line going into the main line:

T-Junction (a two-rail line branching off of another two-rail line):

A four-way crossing:
(I know these look crazy. but trust me, it works)

A roundabout:

I don't want to get in on the (quite heated) debate over four-way crossings versus roundabouts. I find that crossings are easier to navigate in manual mode, while roundabouts provide an easy opportunity to do a U-turn. So I personally use both.

Now for one last tip: I really like to blueprint a simple c-shaped, curved rail. It really helps building these junctions without having to do them over and over again because you misaligned something:
Debug Mode
The last tip I have for you is to use the "debug mode". You can toggle "show rail blocks" under F4. Among many other things, it will also show you your rail's "blocks" (that you probably keep hearing about, when it comes to rail signaling. and don't quite understand).

It can turn a hot mess like this:

Into this:

It's quite simple if you use this. Each colour represent one "block" and as long as there is a train anywhere on the block, the rails going into this block will be red. And chain signals will also turn red if the next signal ist red, including other chain signals (you can make a chain signal ... well, chain by stringing several of them together). Just go ahead and place some signals all over the place with debug mode on, it will help you get a feel for this whole "block" buisness!

If you still find it confusing, don't worry about it! Just use the rules and examples in this guide and you'll be good. But I found, this really helped me understand all this talk about "blocks".

And now you're an expert on rail signaling!

I hope this will help any players who were as confused by rail signaling at first as I was.

Thank you for reading!

If you'd like a blueprint book string for my rail designs, you can use this link[www.dropbox.com].
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Rodent Chef Jul 7 @ 3:16am 
This guide was posted 3 years ago but it is still incredibly helpful! My 15 trains havent crashed into one another for 20 hours now (first time playtrough btw). To others I highly recommend making 2 lanes for both directions and not 1 lane for both directions. Thanks for the guide!
Black ginger Jun 7 @ 8:40pm 
I still don't get it.
Baby Artist Feb 23 @ 1:17pm 
The trains seem to act stupid whenever i try to use signals. Wish there was a more easier way.
Waffletron Mk. VII Dec 4, 2019 @ 7:27am 
I didn't understand any of this before I read this guide, but now I know how it works! Thanks!
bearhiderug Nov 27, 2019 @ 4:53pm 
Nul Atlas Nov 21 @ 2:29pm
Still don't understand
Piratebear Nov 24, 2019 @ 9:06am 
Good guide. More examples would be cool. Although they exist in abundance. Still.
Nul Atlas Nov 21, 2019 @ 12:29pm 
Still don't understand
Captain Mintberry Crunch Oct 29, 2019 @ 8:58am 
Thank you for this amazing guide!!!!!!!
Impatient Oct 27, 2019 @ 4:26pm 
3. If you want to write a good rail signal guide start with factorios basic concept of track sections! What are they, how are they delimited, when are trains allowed to enter and exit track sections, how does train length affect exiting a track section, what effect has a chain signal on entering a track section and so forth ... . By approaching signaling from that perspective, a lot more things become clear much faster (and also to you it would become aparrent why a Y-split does not need an entering signal).

Impatient Oct 27, 2019 @ 4:26pm 
Dude, ... don't write rail signal guides yet ...
1. In the second picture the chain signal on the entering side is unnecessary, as it is not a crossing but just a Y-split. There is no danger that this Y-split ever gets gridlocked.

That kind of ignorance alrerady shows it s dangers ...

2. the signal setup in the 3rd picture is completely wrong! It only works if only one train each uses the left tracks. If you meant it like that you have to provide that contextual information. For single track, two way setups it is very important to know how many trains want to use the track! If there are more trains involved than one for each of the left tracks, that setup WILL gridlock!