So, I was going to play OpenTTD next but then...

[Thimple]

A tribute to Kovarex (FFF 81 - Chain Signals)

I love Factorio. I think it's one of the best games to have ever been produced. I've found after nearly 300 hours of playing though, that what I like the most is... trains!

Anyway, I was looking at other games that featured trains (a lot) and OpenTTD seemed to fit the bill, so I watched some tutorials on YouTube.

Then I got to this part:

https://www.youtube.com/watch?v=cN7cy_F ... Nil7&t=854

So, that's why I won't be playing OpenTTD any time soon.

What on earth did the OpenTTD programmers think they were doing?! Skip forward a minute or so until all the signals were changed to path signals and take a look. What do you see? EVERY signal is red. WTF?

In FFF 81, Kovarex explained that the underlying logic in TTD was different to Factorio, in that Factorio's trains know where they want to go, whereas in TTD the signals kinda direct them. You see in the YT video this happening, as a train gets to the red signal and it flashes green momentarily. OMG.

Frankly, I couldn't care less what the underlying logic is. A coloured signal is just that .. a 'signal', a visual indicator.

There is surely nowhere on this planet that puts a red light up and allows cars, trams, bikes, trains or whatever to hurtle towards it at full speed on the off-chance that there might be an exit when it gets there?

A red light means STOOOOOPPPPP, period (Amsterdam excluded).

It would appear, that 'signals' in OpenTTD are logical directors, but the visual feedback you get from them is... zero.

It seems Kovarex solved all that nonsense with chain signals and of course it all works fantastically well. It's clear, unambiguous, and logical.

In the Xterminator 'Base tour developer interview' vid:

https://www.youtube.com/watch?v=dCrjXs8 ... .be&t=2382

...you have to say ...beautiful too, surely?

I find it fascinating just watching the trains graciously give way, slow down, accelerate away etc.

Thanks Kovarex and the rest of the team for making such a superb game and for your continual support and improvements to it.

[Krazykrl]

Well, after playing a bit of OpenTTD... the PBS system in OpenTTD is a little easier to use. Since the train that triggers a PBS signal reserves only the tile segment pieces that the train will run on (instead of a defined block of rail that includes any railway switches, including associated rail inside that block that may not even interact with the requested path.)

According to the OpenTTD wiki: "Real signal is constantly red and only green temporarily when a train approaches in front of it and the path ahead does not collide with the path of another train. In a realistic junction setup, it is possible to allow multiple trains in the intersection of same block to pass-by safely due to railroad switch limiting which side of the junction the train can turn to. "

[DaveMcW]

One thing OpenTTD does better is rail tunnels.

[FunMaker]

I get your problem with Path Signals in OTTD, but the pathfinding in OTTD is over the top compared to factorio.
In factorio it is common that trains stay at signals because they have reserved a track quite some time in the past.
The train does not notice that there are 3 parallel tracks that it might drive because it wants the blocked track so badly...

In OTTD the train checks on every intersection if it is driving the best possible route. So if the track or trains blocking the track change: it might change.

I know that the reservation of tracks in factorio is because of the momentum the trains have(In OTTD the trains break "immediatly").

My suggestion for this problem would be:
If a train stands at a signal, remove the reservation and recalculate path every second.

Indeed the signaling that OTTD allows is nice but the signaling in factorio is simpler and more intuitive.

Another problem with factorios train momentum is, that signals that are set to red by circuit are ignored by trains with high momentum. In my opinion this is more odd than the "signal is red but path is clear" in OTTD.

[BlakeMW]

In OTTD you don't have to use path signals (no equivalent exists in Factorio) you can just use one-way signals (roughly equivalent to factorio signals) and presignals (roughly equivalent to factorio chain signals) and many players don't use Path signals at all. Path signals can be awfully convenient in OpenTTD because junctions based on path signals are simpler and more compact. And it does completely make sense why they default to red: because the meaning of the path signal is "thou shalt not pass unless thou have reserved a path", in other words the train isn't allowed through (red) until it has reserved a path through the block (green) and it can't reserve a path too far in advance because that could needlessly block other trains.

OpenTTD is an awesome game if you're into trains, especially with mods (what do they call them? newgrf packs or something?), you can get various historical locomotive/wagon packs for a prolonged steam age, you can modify values to make the trains accelerate really slowly and be bad on hills and there's all sorts of good fun to be had. There is a tendency in OpenTTD to be overly reliant on bridges and tunnels for junctions - of course you don't have to make your junctions using bridges/tunnels but it's awfully tempting to because you get awesome throughput. In Factorio you're forced to be honest since Factorio is purely 2 dimensional.

[Thimple]

@BlakeMW & Krazykrl

Yes, earlier in that YT tutorial vid, was an explanation of entry and exit signals (and combo signals), which made perfect sense logcally and visually.

I don't doubt at all that Path signals do their job logically, but visually i.e. them having a red light (that flashes green sometimes) is just redundant and simply confusing.

Obviously, you need the icon representation of the signal on the map, so that you know it's there and what its function is, but all the red lights are just useless visually to the onlooker i.e. us humans, because they don't convey any meaning, if you adhere to the convention that red means stop!

If you compare e.g. a typical Factorio T junction 2 lane main line, then I can see path signals would greatly simplify the junction; 6 in OTTD instead of 9 in Factorio (3 chain signals, 6 normal ones), but it's visually a meaningless light show, whereas in Factorio it's obvious what's going on and all the lights make sense.

https://www.youtube.com/watch?v=8LXOogE ... u.be&t=421

Talking of which....would I be right in assuming that in OTTD, using that YT tutorial vid as an example:

https://www.youtube.com/watch?v=cN7cy_F ... Nil7&t=971

...that T junctions (of that size) can't be signalled with pre/exit/combo signals in the same way as Factorio anyway, simply because of the space available?

There doesn't seem to be enough room there to add the necessary combo signals to break the block up into smaller sections?

Yes, from what I've seen, the rest of OTTD seems great gameplay wise.

@ DaveMcW

Yeah true.

Doubt we'll ever get terrain elevation / depression in Factorio, but you never know eh?

[BlakeMW]

Obviously, you need the icon representation of the signal on the map, so that you know it's there and what its function is, but all the red lights are just useless visually to the onlooker i.e. us humans, because they don't convey any meaning, if you adhere to the convention that red means stop!

I can't see the problem because that's exactly what the path signal says: stop unless I give you explicit permission to go. Also makes it more obvious at a glance that they are path signals rather than one way signals.

...that T junctions (of that size) can't be signalled with pre/exit/combo signals in the same way as Factorio anyway, simply because of the space available?

This is correct. In OpenTTD a rail piece takes up 1 tile and signals are placed on the rail but can only be placed on straight rail pieces and not on any form of junction (merge/split/crossing). In Factorio the signals are placed on a tile next to the rail and the rail pieces take up several tiles so it's a lot easier to sneak in signals.

[Thimple]

Obviously, you need the icon representation of the signal on the map, so that you know it's there and what its function is, but all the red lights are just useless visually to the onlooker i.e. us humans, because they don't convey any meaning, if you adhere to the convention that red means stop!

I can't see the problem because that's exactly what the path signal says: stop unless I give you explicit permission to go. Also makes it more obvious at a glance that they are path signals rather than one way signals.

The problem is, that the lights convey no sensible meaning to us at all! If you take every single train off all the lines, every path signal will still be red. Just what exactly is that supposed to 'mean'?

Let me give you another example:

If we imagine the situation where all the lights are green, and you 'could' say the opposite of "stop unless I give you explicit permission to go" i.e. "Go unless I give you explicit permission to stop"?...

But...the difference between the two systems of signalling is that only a complete maniac would accelerate towards a red traffic light!

If you imagine those signals without any lights at all, the trains would still work perfectly.

Another problem is inconsistency. Another part of the game is saying that a red light does indeed explicitly mean stop i.e. normal block signals, entry / exit and combo signals.

So...which is it game?! Does a red light mean stop, maybe stop or what? Make up your mind, eh? The only way to know for sure is to look at the map icons of the signals. Really confusing.

Why not make it a purple light for path signals?

[Muche]

I haven't played OpenTTD, my impression (just from watching linked tutorial video) is that one of the core differences is trains in OpenTTD have greater acceleration/breaking abilities (and lower maximum speed, although this may change in the later stages of the game). So a train going towards a red path signal does not need to slow down, it can safely stop in just one tile. Which is exactly the time when it tries to reserve a path and the path signal flashes green. The path signal flashes green for only a short amount of time, because the distance between the train reserving a path and passing the signal is so short.
So, what would happen if OpenTTD trains had worse acceleration/breaking? The train would need to reserve a path earlier (path signals would show green longer), alleviating part of the confusion.
The next step could be to change the colors the path signal is showing - no path reserved+all exits free: red to green, no path reserved+some exits blocked: red to blue, path reserved: green to yellow, block or all exits occupied: stays red. Doesn't this sound an awful lot like Factorio's chain signal?

[TruePikachu]

To handle the "core" issue, the path signals indicating red is not a bug or issue, and is actually realistic. In real-life interlockings (path signals are best used to simulate interlockings, similar to our chain signals), paths are set by a dispatcher; only once a valid path is set and "locked" (to prevent the path from being modified when a train is on it) does the signal indicate clear. In OpenTTD, since there's no concept of advance rail reservation, the path signals only attempt to establish their paths once the train is in the tile with the signal. Aside from this one behaviour, the system operates exactly the same as an advanced interlocking would.

Here in Factorio, the whole rail system is unrealistic. Firstly, the signal aspects displayed are usually of no use to an actual driver; for example, the "yellow" aspect indicates a scheduled train is approaching the signal -- this implies that a driver would never see the "green" aspect, since it would either be red or yellow when they reach it. Ignoring this, the chain signals indicate one of four states (in three aspects): either all exits are indicating clear, some exit is not indicating clear, no exits are indicating clear, or the block is occupied. This kind of information isn't useful for a normal train driver, since the driver just drives the train, they are not responsible for routing decisions.


In the real world, generally one wouldn't have "stop" signals after a series of "clear" signals; that is a SPAD waiting to happen. There is always going to be warning given in advance of a "stop" or a potential "stop" signal, through the "approach" signal aspects (which includes a distant signal indicating its most restrictive aspect). However, in games that let you change track instantly whenever there isn't a train on top like Factorio and OpenTTD, it is far simpler both in terms of gameplay and programming to be able to stop the train instantly (OpenTTD IIRC won't even SPAD, while Factorio will stop the train at the end of the track in all circumstances). In the real world, dispatchers generally aren't able to drop a signal to "stop" in front of an approaching train except in the case of emergency; if a train passes a "clear" signal, then there is a guarantee that the next signal will not be a "stop" signal.


Advance track reservation is a difficult topic in games; I don't think I've seen it done realistically in anything except for simulators. Factorio is the most realistic game I've seen in this regard, given that track for scheduled trains is reserved up to the train stopping point. It doesn't provide any such protection for manually-operated trains, however, which is one of the few issues I have with it. OpenTTD doesn't do advance track reservation at all, but it has an excuse because of train breakdowns which would complicate the whole logic and result in possibly-not-very-fun gameplay. Rail simulators such as Trainz simulate advance reservation nicely in my own experience (but I've heard of some cases where it fails). Finally, signalling simulators such as `railroad.exe` generally put the burden of reservation onto the player (in a realistic manner).



In the end, though, games are designed to be fun. There isn't a lot of fun to be had fighting with when or how paths are determined, nor is there fun in describing how such systems are unrealistic.

[makrom]

I think you are judging the game based on a very minor detail. OTTD is a great game (not necessarily a great train physics simulator though).
There are some key differences between Factorio and OTTD. OTTD has stations with several platforms, and trains don't stop at a designated platform. They can stop at any free platform, as long as the rail network permits it. And because it also has height, you can build very complex networks.

[Ikaheishi]

In the end, though, games are designed to be fun. There isn't a lot of fun to be had fighting with when or how paths are determined, nor is there fun in describing how such systems are unrealistic.

This. So much. Continuing on this point…

There's stuff I don't like about Factorio. There's stuff I don't like about Transport Tycoon, which OpenTTD is an (arguably) enhanced version of, game-play wise.

Yet, here I am. I play both Factorio and OpenTTD (a lot), in addition to many more games that have things I don't like. It doesn't matter; they're fun! And that is exactly what the point of games are: entertainment.

[HurkWurk]

path signals are not chain signals. they are "you can use this intersection" signals. thus, they only turn green when its your turn to go. its like a freeway onramp signal.

unlike chain signals, path signals indicate you can take any of a number of choices. chain signals control a single choice each.

[rcp27]

The OTTD system is probably a closer representation of how real world signals work: signals controlling a junction will show red until a path for a specific train is set, then the signal clears for the train to pass. This is fine in a real world railway context, but not so good in a gameplay sense. In the real world the signal's only purpose is to pass information to the train driver. In a game it is also useful to give information to an external viewer, namely the player. I am a bit of a train nerd and have played all kinds of train related games. Different games take different approaches depending on where they want to fall on the "exactly mimic real world trains" to "fun but not necessarily realistic" spectrum. Because of how trains are used in Factorio and how they fit into a broader gameplay context, a signalling system designed around maximum player feedback makes sense, even if it isn't how real world trains and signals work.

[Zool]

One thing OpenTTD does better is rail tunnels.

+9999

[Tekky]

In OpenTTD, since there's no concept of advance rail reservation, the path signals only attempt to establish their paths once the train is in the tile with the signal.

In OpenTTD, there already exists a Work In Progress patch that adresses this issue. Here is a link to the corresponding thread on the OpenTTD forums.

[Muche]

The difference between rail signals in Factorio, OpenTTD and IRL is they were designed for different systems.

Automatic trains in Factorio/OpenTTD technically don't need any signals you see, since they use underlaying signaling system; signals you see display some properties of that system.
A train approaching a block boundary theoretically has access to all information of the system (specifically other nearby trains and their reserved blocks).
Other properties of the system: track switching is very cheap, block reserving is cheap, path finding is somewhat cheap, all trains are identical (decision-wise regarding block reservation and honoring it by breaking in time; length, speed etc. don't matter here), trains know that other trains are identical to them, they know they know that, etc.
Traditional trains IRL do need those signals. A train driver approaching a block boundary knows only what the signal shows - in the most basic configuration whether the next block is free or occupied, in more advanced configurations next blocks as well.
Other properties of the system: track switching used to be expensive (manual), now it's cheap (electromagnetic), block reserving is expensive, path finding doubly so, trains could be considered not-identical decision-wise (I know I'll stop at red signal, but can't know for sure others will as well).
If you want to see the mix of both system, take a train and drive it in the manual mode. The result is usually mess and crashes.

One thing mentioned above is that OpenTTD's path signal is smarter in that it reserves as few tracks as possible, while Factorio's chain signal takes into account the whole block. I think this is due to Factorio being on lower level of "smartness". The player designs the railway system (and whole factory) to be as smart as they desire.
Sure, devs could make chain signal smarter, automatically create one block per train just surrounding it and moving them together along the tracks, automatically place smart chain signals at each track intersection if needed (and inevitably bias towards either RHD or LHD - whichever you don't like), but all that would rob the player of possibility to design their own system.
Thus, ideal Factorio signals show the status of the system in a particular block (aimed for the designed of the system), not what would be shown IRL in similar track configuration (aimed at user of the system).

OpenTTD seems to be somewhere in the middle - more smartness of the train system (since it deals with other transportation systems as well, so the player can't deal with each of them on too low level).
Maybe confusion of path signal is in that it acts on higher level but a player expects it to act on lower level?

[TruePikachu]

Strictly speaking, the Factorio chain signals are closest in idea to the pre-signals in OpenTTD.

[milo christiansen]

If you want to be exact, they are direct equivalents of combo pre-signals (the ones that combine exit signals and pre-signals).

OTTD has too many different signal types...

[TruePikachu]

If you want to be exact, they are direct equivalents of combo pre-signals (the ones that combine exit signals and pre-signals).

OTTD has too many different signal types...

If you want to be more exact, the chain signal is the combo pre-signal, and the block signal is the exit pre-signal.