Factorio Forums

I've spent all morning figuring out train signals, and so far they seem pretty reasonable:
- normal signals effectively mean "is there a train in front of me?" or "is the track in front of me safe to drive onto?"
- chain signals just copy the signal in front of them

The part that I'm confused by, and maybe I'm mis-using the signals, is that they seem to also look at oncoming signals, instead of just the ones travelling the same direction. i.e. If I have a chain signal, it will copy the red-value from oncoming signals, and not just the ones in front of them that are also travelling the same direction. For normal signals, this means that the section of track that they look at for safety/emptiness, stops at oncoming signals, instead of the next signal travelling the same direction. This means that I can't do a seemingly simple thing (which other people have done, but failed to post simplified screenshots of...), which is to have a two-way section of track, with one-way sections for trains to pass each other.

This screenshot shows this problem - there's two sections of one-way passing track, and a section of two-way dangerous track, which I've marked with signals. The problem is that some of the signals stop early. For example, the chain signal in front of the green train should (in my understanding) be green, since the normal signal in front of it is also green - but it's instead copying the red signal from the signal that's pointing the other direction! This second screenshot shows a normal signal (one-way only) that's only looking as far ahead as the oncoming signal, and my understanding is that that would never be useful, since I wouldn't be able to have single-direction tracks (passing tracks / side-tracks) connected to bi-directional tracks. i.e. I either get to make my entire network single-direction, or my entire network must be bi-directional.

Could somebody help me understand how the signals are intended to be used? I am clearly using them wrong, because what's intuitive doesn't seem to be what's in the game.

P.S.
Sorry if this is explained somewhere else; I couldn't find anything on the wiki, or by searching these forums, that answered this specific question. (In fact, the info I've managed to find is either the trivial bullet points I wrote above, or subjects more advanced than this particular situation.)

P.P.S.
I can use double-wide, single-direction tracks, because I read through and uderstand this guide with simple rules of thumb. I would however, like to know how to use bi-directional tracks, so I can cut my rail usage by nearly half.

Train signals don't look at trains, they look at blocks. This tutorial should be helpful:
http://imgur.com/a/a8Hz0

In your specific case it's the block in front of the chain signal which is making it red: The train on the passing lane is "occupying" the entire red highlighted area because it's a single block. Thus the chain signal (and the incoming signal on the right) is red. A regular signal in place of the chain signal would also be red.

What you need to do is to split that block, like so: Now things work like you would expect

That seems pretty unintuitive to me. I get that the signals care about the other signals / tracks, and not the trains (specifically, the direction they are facing), but the fact that the blocks / sections of track do not respect the orientation of the signals, seems wrong to me. i.e. The player chooses the side of track to put a signal on (and thus its orientation), and then the game ignores that side / orientation (as shown by the block you've highlighted). I'll change my signals for now, but...ugh...

Thanks! :)

AileTheAlien wrote:That seems pretty unintuitive to me. I get that the signals care about the other signals / tracks, and not the trains (specifically, the direction they are facing), but the fact that the blocks / sections of track do not respect the orientation of the signals, seems wrong to me. i.e. The player chooses the side of track to put a signal on (and thus its orientation), and then the game ignores that side / orientation (as shown by the block you've highlighted). I'll change my signals for now, but...ugh...

Thanks!

Think about a railway which crosses another railway in perpendicular manner. The only way that would work is by making the section of rails that cross a single block. How far the block extends on each direction is controlled by rail signal placement.

The reason for that system is because it's a system of rules that both the player and the computer program running the game can understand.

A chain signal doesn't just "copy the signals in front of it". I think you've confused yourself by trying to interpret its behvaiour with that point of view. A chain signal says that the next section and the one following it are both clear to enter. Consider this screenshot:



Is it safe here for the the green train to pass the chain signal? Obviously not. The chain signal can't go safely green until the purple train has left the critical area. The only way the system can know when the purple train is out of the junction is if there is another signal on it's exit track.

Yea it doesnt simply copy the next signal, it in itself is also working as a normal signal. And it sais the block in front of it is occupied. Be it the train is still on the junction or has passed it in your pic. Just be real here, what would you do to make the signal go green?