Repeater Signals

[molten finch]

This could almost fall under the Path Signals roadmap (or be part of the solution for making it possible?).

A Repeat Signal simply repeats the status of the signal ahead.

They can be used to isolate multiple blocks in complex junctions to allow through traffic to take priority over those that are waiting for an empty station track.

If used to isolate junctions you may choose to place them in such an order;

CHAIN - REPEAT - REPEAT - BLOCK

This would force the CHAIN to read the BLOCK via the REPEAT signal/s.

[vivid shuttle]

That's pretty much what the presignal does, doesn't it?

It doesn't repeat a specific signal though, it 'repeats' all the "exit signals" of the block ahead (green = all available, red = all blocked, yellow = some available, some red, train will only cross if going to a green one)

Do yo have a specific scenario in mind where the behavior of the presignal doesn't cover the needs that a repeater would?

[molten finch]

That was also my expectation. Based on my understanding of the chain/pre signal behavior from tests last night, if the junction path exceeds a train's length and the destination path is unoccupied, it permits a second train to enter the intersection. This second train, consequently, blocks the intersection until the first train occupies and vacates the destination path initially perceived as open.

Implementing a repeater functions like a block/home signal, effectively preventing the second train from perceiving the destination path as available, ensuring it only detects that its immediate route is obstructed.

[ashen igloo]

Maybe I don't understand what you mean, but I was having this problem with a roundabout I made, where inputs had presignals, between each input and output was a signal, and at each output was another signal.

My trains were constantly getting gridlocksed, but the only thing I changed was changing the ignal between the inputs and putputs to a presignal (so now, to enter from the south, and exit to the west you go through pre>pre>pre>sig).

This basically fixed the issue.

[molten finch]

I'll have another play tonight and see if there's something I'm missing. This was exactly the expectation I also had, but perhaps my use was a little more unique in that I can fit an entire train between a set of signals.

I had PRE1 - PRE2 - PRE3 - SIG. With the expectation that any trains waiting at PRE1 would wait until PRE2, PRE3 and SIG were available.

However due to the layout of this particular junction I can fit an entire train between PRE3 and SIG, and in doing so PRE1 treats the block between PRE2 and PRE3 as being available. This then let's a train entire the block between PRE1 - PRE2 completely blocking any through traffic on a parallel track from passing.

[ashen igloo]

Why does the train stop at pre2?

[molten finch]

I'm really unsure. Here's the scenario. Both the blue and pink trains are heading to the station at the top. It has only one available track.

But the pink train hasn't entered the station yet so the pre signals still show some roads available. And allows the blue train to enter the junction

The orange train is heading straight through, but cannot pass the junction. Due to the blue train overlapping. And now the pink train has entered the station and there are no available tracks for the blue train, so it holds position blocking the entire junction.

I'm unsure if this is typical behaviour of the pre/chain signal, as it certainly wasn't my expectation based on my understanding of its purpose. I'm also unsure if there are any other factors I've not recognised. This happened on multiple occasions in the same session which lead me to the question of a repeater function over a chain.

[ashen igloo]

You're trying to do a lot with a little space, but i think one option is to just cut up the track the pink train is in in pic 1 with another presignal.

In terms of game improvements, I think just being able to fine-tune place signals would solve this

[molten finch]

Those spaces aren't available for signal placement as they overlap voxels. I'm running all tracks parallel with no gaps.

I definitely could change the layout to allow the existing function of signals to work. But I'm trying to utilise the most function in smallest space - which is what has lead me towards repeaters.

If the kids are behaving themselves tonight I'll record some game footage to explain better. I have my doubts they'll offer such kindness. 🫣

[ashen igloo]

No, I get it. I can picure what this lookslike. I'm saying if not "repeater signals" then being able to place pre and reg signals in these tight areas would be the next best bet for train logic.

[molten finch]

Just the bottom crossover alone would fix the entire issue of blocking the path for passing trains.

The other alternative I could look at with current functionality would be removing PRE3. Theoretically this should stop the blue train attempting to enter the junction allowing the orange train to take priority. It's potentially not a required signal for this exact junction layout.

[near elbow]

Id just suggest to put the connection between the rail of the blue and orange train further to the left

This just seems to be too much for too little space or you could rebuild the orange trains line a little further down and put two way signals in between the paralel tracks

[near elbow]

But generally i dont think we need a new signal type aside path signals

[molten finch]

OMG. Captain Slow over here again. I worked out why they're not behaving correctly. 🤣

[molten finch]

https://youtu.be/tMg4tfUuYno

Ok. So Pre-Signals are now working as they should. However there is still the occasion where it allows two trains to enter the block ahead stopping the train on the mainline in the dark blue junction blocking the path for through-traffic on the lower main.

This exact scenario is where a Repeater Signal would be the perfect solution as the Pre-Signal would read the Repeater as the only path forward, only allowing a single train to enter the block when an available Home Signal is green.

20sec into the video is the first occurrence of the Pre-Signal allowing 2 trains to enter the block ahead.

[vivid shuttle]

Ideally that will be a thing of the past with the (planned) path signals as the bottom line could still be taken by a train going straight even if the top part of the junction is occupied

And this can happen because trains only reserve a single block (regardless of the signal ahead).

It makes me wonder if it would be better if train reserve the track UNTIL the next block signal. That would alleviate this issue but also the one that many people encounter with "kissing trains" (bidirectional stations)

this is what "kissing trains" looks like (and an explanation)

[molten finch]

I was considering that too and for the sake of testing I was going to also use a pre-sig on entry with a home at the minimum overlap so it would only show available as a train begins to leave. But unfortunately with a station blocking signals there's no real solution from the test.

The purpose would purely be to release any train that has prematurely been released and blocking the junction. More of a failsafe than an outright solution.

I think what makes the particular scenario that I'm testing more problematique is that the pathfinding logic appears to be that of "the train with the shortest distance to the destination is given priority" even when it arrives last.

Perhaps the solution isn't so much that a repeater is required, but a priority based on how long a train has been waiting

[near elbow]

@molten finch what if you were to place a repeater signal after a merging track section how would it choose priority or would it just in case prefer to stay closed off ?

[clear herald]

Hello, just small insight. You can check how it works in factorio. There is this exact problem solved with reserving a path.
The way its done is that chain signals reserves next block signal. If next signals is chain signal, reserve that one, and next signal. If next is block signal then it will reserve that one and doesnt check what is next. This way you can create chain of chain signals that will reserve full path untill block signal.

Factorio image for visualisation (please ignor how its set up). You can see that marked signal (red circle) is red even tho no train is there, but that block is reserved as part of chain of chains. All yellow signals are reserved signals. The last yellow dot is first block signals and that one is reserved too. The signal after it is not reserved anymore (red arrows)

Hope I wrote in a way that makes sense

[vivid shuttle]

I have hundreds of hours in Factorio so I am very familiar with how trains work there! 😛

Factorio's signals and VT's signal behave identically. The only difference is that train reserve a path in front of them (precision to the rules you listed: it reserves enough space for the train to come to as stop), whereas VT trains do not.