Signals - I'm thick

[DaiStation]

How do I allow trains travelling in opposite directions to use the same piece of track?

At the moment I have:    ----s------------------g
(where s is a signal and g is a goods siding)
and a train at each place, each waiting for the other one.

[KrazyJay]

Only by removing the signal that divides the track in different sections.

[DaiStation]

Only by removing the signal that divides the track in different sections.

Then they'll never use the track.

Can someone please explain to me what the **** I am supposed to be doing?

[Lmallet]

Welcome to the forum DaiStation!

I suggest you first read through the Railway Signals page on the wiki here:

http://www.simutrans-germany.com/wiki/wiki/tiki-index.php?page=en_RailwaySignals

If you still have questions after reading, then feel free to ask!

[DaiStation]

Thanks! That's very helpful. At least I know I needed to add a passing loop now! It's much more fun when the trains move... 

I can't quite work out what my best plan is though when I've got a situation like this:

     |
     |
 .---+
 |   | 2
 |3  |
g-+---+
     |
    1|1

I put the red part in in order to add a passing loop, but I suspect that isn't what I should have done because I've confused myself again due to the extra junction Is it a double signal at point 1, a single at point 2 & 3? That's what I have done, and so far no problems, but I might just have not hit the "right" constellation yet.

[Lmallet]

So the "g" is a station?

Well, I could see situations where you might want a signal configuration such as this one, but without knowing what is north of the siding or south of point 1, I can't really comment.  Signals sometimes develop an "ecosystem" which can reach pretty far.  Could you clarify your drawing a bit?  Or even better, upload a screenshot or maybe even the savegame here http://files.simutrans-germany.com/, and post the link in this discussion.

Edit:  I don't think the wiki article mentions it, but stations actually act as signals themselves, so there is no need to add an additional one (except in some specific situations).

[DaiStation]

So the "g" is a station?

A goods siding, yes.

Well, I could see situations where you might want a signal configuration such as this one, but without knowing what is north of the siding or south of point 1, I can't really comment.  Signals sometimes develop an "ecosystem" which can reach pretty far.  Could you clarify your drawing a bit?  Or even better, upload a screenshot

I'll do a screenshot in a moment, once I find out how to post it. In the meantime:
    s->               s->
   .--...--.       .--------------.
   |   <-s |    s  |          <-s |
g---^--...--^-------^--------------^--g
                s v
                 s|s
                  |
                  |>- d
                  |
              .--<|
              |  2|
              |  ||
              |^ v|
              ||  |
              |3  |
            g-^--<|
                 1|1
                  |
                bridge
                  |
                  .
                  .
                  .
                  |
                  g
Key: g = goods siding
    d = train depot
    s = signal (s-> = signal, indicating direction of travel)
    number = signal (see above)
    ... = long stretch of line

Reading the friendly wiki article again, it says "Do not place signals at the entrance of the track sections, since this will cause trains to wait at the single track sections, causing dead locks." Hmm. What does it mean by "entrance of the track sections"? Before the passing loop? Immediately on the junction sections?

Yeah, and I still don't understand what's to stop deadlocks occurring outside of passing loops   Once I start putting signals in in other places I always seem to end up with a train at each end of a stretch, one driver saying "After you, dear chap," and the other saying "No, after you", then the first saying "No, really, I insist", and so on, ad infinitum. It's all very polite and British. No wonder our trains are always late.

Screenshot:

[Lmallet]

Ok, the screenshot made things a bit clearer.

Simutrans uses path-based signaling (or PBS).  This means that a train will reserve the track in front of it, and will keep reserving and moving ahead until it either gets to its destination, or runs into another reservation.  The train will reserve up to a signal, a station, or a turnout (this is why I mentionned that stations are signals too, turnouts can also act as signals in certain situations).  If you hit the "b" key, you will see these reservations in red.  Also, you can use the magnifying glass on a section of track to see who is reserving it.

There are a few places where you placed signals on single track sections.  The problem with that is that a train can occupy each of the blocks on each side.  If the two trains are running in opposite directions, they will deadlock at the signal.  Only use signals on single track sections if there will be a single train going past the signal, or if you are using it as a one-way indicator.

The section between two signals/stations/turnouts can be refered to as a block (as in per railroad terminology).  You need to have more blocks than the number of trains that can be occupying the section of your network.  Some quick diagrams:

G is a station.
S is a two way signal.
S> is a one way signal, the arrow points the direction.


               
             / -<S---------------------- \
GGGGG-------+--------------------------S>-+-----------GGGGGGG

The first example is roughly how you are using you signals, however notice the signals are at the end of the siding, and not at the beginning.  This is to allow trains to clear the turnout.  I would not run more than two trains in this configuration, as you essentially have three blocks (two blocks, with a third one that varies when the train clears its first turnout).


             / -<S--------------------<S \
GGGGG-------+--S>----------------------S>-+-----------GGGGGGG

The second example is how I usually build sidings.  In this case, you have four blocks, meaning you could run three trains.

             / -<S---------<S----------<S \
GGGGG-------+--S>----------s>-----------S>-+-----------GGGGGGG

The third example is the basis of double track networks.  Essentially for each signal you add in the siding, you create an additional block.  In this case you have six blocks, therefore it can handle 5 trains.

This is a rough explanation, someone will probably correct me on some minor points, but it should be enough to get you going again.

[DaiStation]

There are a few places where you placed signals on single track sections.  The problem with that is that a train can occupy each of the blocks on each side.  If the two trains are running in opposite directions, they will deadlock at the signal.

Yeah, that's exactly what I see.

Only use signals on single track sections if there will be a single train going past the signal

It happens even if I don't place any signals, i.e. with G----------G, presumably because, as you say, the stations are signals too.

From what you say, it seems any time more than one train will use a section of track, I need to add a passing loop on at least part of it.

You need to have more blocks than the number of trains that can be occupying the section of your network.

The first example is roughly how you are using you signals, however notice the signals are at the end of the siding, and not at the beginning.  This is to allow trains to clear the turnout. 

That's it! Those two points are the key things I didn't know/understand! Thank you so much!

[Lmallet]

From what you say, it seems any time more than one train will use a section of track, I need to add a passing loop on at least part of it.

That is exactly it.  The only way a train can pass another is to go around it using a passing loop.