Rails Signaling for Dummies (Space Age Update!)

This is a beginners guide for everyone who has problems getting into rail signaling for trains. (Now finally updated for Space Age DLC!)

The Only Rule

Note: I thought the new Space Age DLC was a good time to finally update this guide. It was originally from way back before even the 1.0 update. The pictures and some of the info were getting pretty out-of-date.

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. Assuming trains are only 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. Let’s say you are using two-headed trains (i.e. trains with an engine on either end that can move both ways). On is coming in from the west and one from the north, but them are both delivering copper ore to the same station for smelting into plates.

You simply follow the same rule for each individual track (red, blue and green) coming into the junction: chain signals going in, rail signal going out.

It will end up looking like this:


And you're done! … no, really, it's that simple!

The red train will patiently wait it’s turn until the blue one leaves to pick up more ore and then drive into the station.

Two Rail Systems

Unfortunately, two-headed trains can make it pretty hard to stop your trains from crashing into each other all the time. The more complex your railsystem gets, the harder it is too signal everything correctly without causing gridlock.

A popular solution for this is to use two raillines, each one only going in one direction, like this:

This way, every line only has one possible direction a train can be coming from, which drastically reduces the complexity of your junctions in terms of signaling.

Now this example has space inbetween the lines for powerpoles and roboports, if needed. There are also normal rail-signals along the lines in regular intervals to break up the "blocks" (more on that later).

This may seem like a lot for just a little bit of track, but once you have this blueprinted and can just place it all down with bots, 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.

Chaining signals

The way chain-signals work, is they basically “look ahead” into what’s coming next. But you can chain several chain-signals together to look even further ahead!

Look at the following example. The red train is waiting at the red signal (A) because the following railtrack is occupied by the blue train. It was allowed to move onto the track turning right, because the chain-signal (B) only looked ahead to the regular rail-signal (C) which was unoccupied.

But the red train is too long and blocks the rail going straight through the junction as well! This not only slows down your trains, it can also cause gridlock and make your entire trainsystem come to a halt.

So what you do here is to replace the rail signal in the previous picture (C) with an additional chain-signal (D). Now the red train will patiently wait at the first signal in the “chain” (E) without ending up stuck on the rail right turn.

Examples

Here are some examples of junctions for a one-way (i.e. two rail) system.
Since each line only goes in one direction it can be a little complicated to branch off of the main line.

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 pretty 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 when driving manually, while roundabouts provide an easy opportunity for your trains to do a U-turn. So I personally use both.

Elevated rails

The Space Age DLC also added elevated rails, which you can unlock once you’ve travelled to other planets. I’m not going to go into the details of how to do that or how to unlock them. But elevated rails can really help to increase the throughput of your junctions.

In the example below, I changed the normal crossing to use elevated rails, so now the east-west line and the north-south line are completely independent from each other! That means, the trains going straight across the junction don’t ever have to wait on each other before they can go through it themselves.

Visualization

A few updates ago they added visualization for train “blocks” when you’re placing signals. You no longer need to use “debug mode” to make these visible.

It can tell you the possible positions for signals, which direction the train can move in and it has an indicator for how many wagons can fit before the signal you’re trying to place.

You can change the length of this in the settings under interface and then “train visualization length”. Just adjust this to your preferred length of trains.

When holding a signal you can also see the ominous “blocks” I’ve mentioned before. They are represented by simple coloured lines on the rails. Each colour is a single block and as long as there is a train anywhere on the block, it is marked as "occupied" and signals will stop incoming trains from driving into an occupied block.

You can use this info to “break up” blocks, to make your trains run more smoothly. In the roundabout above for example, the entire inner loop is one, single “block”. That means, as long as there is a train anywhere on the loop, no other train can move through the roundabout.
You can separate a block by placing a few additional chain signals (Because we’re still going into junctions. Remember our one rule? You should really know it by heart by now.)
This way, you can break up the block into four independent quarters, allowing for less breaking and stopping for your trains. Your trains will be faster and the chances of gridlock occurring also decreases!

"Parking Lot"

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.

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

Make sure the signal before your parking spaces is a chain-signal, begin every parking space with a rail-signal and finish them with another chain-signal.

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

And don’t forget to put a regular rail-signal in front of every unloading trainstation.

If you correctly signal your rails like this, you should get well-behaved trains all neatly lined up and waiting their turn, like in the top picture.

Rail Planner

If you want to manually place curved rails, you probably know, you can use the “rail planner” function, by clicking on an existing rail with the rail item selected. This is limited to your player characters build range, however.

If you hold down shift to place “ghost” tiles instead, you can not only pplan rails much furhter away, you also automatically avoid obstacles. You can then place them by hand or, if you have construction bots unlocked, have your personal or roboport bots build them for you.

C-Curve

Now for one last tip: I really like to blueprint a simple c-shaped, curved rail. It’s super useful, because it’s a basic building block of so many railsystems and really helps building these junctions without having to do them over and over again because you misaligned something:

Thanks!

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 all for reading.

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And thank you for all the kind words and praise I have gotten over the years! This guide is the third highest rated Factorio guide on Steam ever and this update was LONG overdue. All the pictures had the super old graphics and train visualization wasn't even a thing yet, without using debug mode. Those were crazy times!
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[Prof_Rof]

Finally a guide that actually helps. Thanx

[Nutchapol]

the "A single line going into the main line" example is a bit wrong. the top row of signals should be Rail and Chain, not Rail and Rail.

[Cptn.Penguin]

@Dr. Proply thanks, you're right. I fixed that.
Glad you liked the guide :)

[Dr. Proply]

Thanks for the guide, really helpful. Spotted a minor typo, in the sentence:

"So what you do here is to replace the rail signal (B) with an additional chain-signal (D)."

(B) should be (C)

[Cptn.Penguin]

I finally got around to updating this guide a little bit. It's still only a basic guide, you can go way more in depth with circuit network stuff. But for everyone just starting out, I hope this guide helps. Happy new year!

[DFS Optimum]

First time player about to get into trains, I love you and your guide

[dud10982]

After 300 hours of playing I finally understand rail signals. You are a gentleman and a scholar.

[RAWKET LAWNCHAIR]

hero

[ryberg1]

thanks

[Hellrazer - wvx]

.... I'm not gonna start playing this game because I am scare I'll use hundreds of hours on it.
But it looks fun to play.