Trains are still not able to assess properly where they are, even using satellites and inside train sensors. Of course there is research on that, but it's still an unsolved problem. (Current alternative is to put markers in the track, but that's also expensive at scale.)
> Trains are still not able to assess properly where they are, even using satellites and inside train sensors. Of course there is research on that, but it's still an unsolved problem
Throwing up our hands about how hard a problem this is seems like a ridiculous position to stake. If we can design self-driving cars, that operate safely in far less controlled environments, we can figure out the linear offset of a large vehicle traveling along a physical rail running along a fixed pre-determined path.
> If we can design self-driving cars, that operate safely in far less controlled environments
Self-driving cars aren't supposed to drive quicker than they can look ahead, which makes the problem way easier because you don't have to figure out how to detect obstacles ahead of time and can simply rely on vehicle-local information to stop if necessary. And because cars can brake way more rapidly than trains, it means you can still drive reasonably quickly even within that limitation.
Plus in an emergency, cars have steering as an additional degree of freedom to attempt getting out of any nasty situation that may have developed.
(And of course the socially expected safety standards for cars are quite a bit lower than for public transport…)
Trains on the other hand have braking distances on the order of a kilometre or so, and high-speed trains at full speed several kilometres, so trying to get by on local data only is hopeless and the usual strategy is instead having central signalling system that can accurately track trains and coordinate their movements.
I said nothing about "throwing up out hands", this is a current research topic. But you can hardly blame the workers for not using a system, the researchers haven't invented yet.
> If we can design self-driving cars
We can not design self-driving cars to the safety standard that is required for railways. They are way less safe than the current half-manual system for railways. What you suggest is using less automatic safety systems than what we currently do.
Why is it that these fatal train accidents have happened multiple times in Spain, but never in Japan, even though Japan has been doing it high speed rail longer, and at 10x the passenger volume than Spain? Do they have some alien safety technology unavailable to Spain?
The were several other train accidents, where it was found out, that the drivers have made races, who can stay above the speed limit longer. But I think that was already in the 90s. There is/was definitely something at fault with the safety culture.
But there was a recent incident in Germany as well (https://en.wikipedia.org/wiki/Burgrain_train_derailment), which is somewhat similar to the earlier accident in Spain this year. Targeting high value projects, while not paying for proper maintenance is not something that only happens in a single country.
There were two fatal train accidents in the UK this year, one of them being a rear-end collision, despite no one even citing them in this thread, and definitely not claiming the UK having low safety culture. Sadly the Spanish "black legend" is still very much in force, portraying Spain as some lower place than it actually is.
Yes, you can say that high-speed rail crashes are not limited to one country (though Spain has had multiple this year alone), but you can't say that it has ever happened in Japan. So for you to argue up and down this thread that everyone calling out issues with Spanish high speed rail safety is wrong, as if it is some sort of intractable problem, is bananas.
I have not stated anything that is specific to Spain in this thread? I do think there is something wrong with the safety culture in Spain, I mean obviously, there was an accident.
> but you can't say that it has ever happened in Japan.
That sounds very unlikely to me, and in fact Wikipedia indicates otherwise: https://en.wikipedia.org/wiki/Shigaraki_train_disaster
That is not a high-speed rail line... so, no?
Ok, so railway safety for me doesn't stop at the end of high-speed lines. But, maybe Japan does indeed clear the measure you suggested, so congratulations to Japan, I guess?
Yup, so it seems that high-speed rail safety is not an unsolved problem. Wonder what the lessons are? Hmm...
"Sadly" anything involving safety with humans is never a solved problem, because safety culture needs continuing training and effort.
> I said nothing about "throwing up out hands", this is a current research topic. But you can hardly blame the workers for not using a system, the researchers haven't invented yet.
This you? Who's fault is it then? You said the tech doesn't exist (lets take that at face-value for the sake of your argument), so then if not tech, then what? You're just left with people. So are you saying it is their fault or not? Or is it just nobody's?
Yes. General safety culture. However asking who is at fault instead of asking how to prevent it from occurring again, is also an indication of a lack of safety culture.
In addition: https://news.ycombinator.com/item?id=50297950 https://news.ycombinator.com/item?id=50293093
You can do both
indeed. Japan is a compliance and shame based society. that alone is the foundation of a very strong safety culture, something that southern europe is famous for lacking.
> that alone is the foundation of a very strong safety culture
It's a mixed bag. That can also cause safety violations, they were suicidal incidents, because punctuality is placed over safety, in Japan. https://en.wikipedia.org/wiki/Amagasaki_derailment
The train to control center calls leaked, and they not sound like aircontrol talk we have heard latelly, more like "meh, paperwork". People! You are handling multi-ton things capable of going faster than 300 Km/h.
Japan railway crew have stricter procedures when they are alone: https://en.wikipedia.org/wiki/Pointing_and_calling
Has there ever been a case where two self driving cars collide with each other? I hate to be part of the peanut gallery, but as a totally naive person when it comes to railway safety research it really does seem amazing train collisions can’t be easily prevented with gps, lasers, sonar or various other trivial ways. Even the crash in question seems like it might have been easily prevented by having a second human in the loop. Maybe I and others just suspect the difficulty isn’t so much technological as it is financial.
As far as I am aware, there has been no non-supervised train in a general train network. (They exist in closed systems.) However whether the train is self-driving is really not the issue here. In current railway safety systems (even from the 80s) a crash is about the same probability as random bitflips. However reality is too messy, so that the availability is not satisfactory enough to not use a human fallback, and then you are back to the assisted human error rate.
Current operation of a train is basically self-driving and supervising driver. So if you suggest "just use self-driving", you make the system less safe, not more, because it means just getting rid of the human supervisor. This is not currently done, because it would be too insecure. It might be done in the future, but rather because less safety is going to be accepted in favor for getting rid of the costly human.
A self-driving train will happily cause a crash, if the target is "drive with high-speed in that segment currently occupied by another train". The issue is that that becomes a target, not that there is a human in the loop.
> A self-driving train will happily cause a crash, if the target is "drive with high-speed in that segment currently occupied by another train".
Sure, if you allow trains to ignore safety completely, then accidents will occur. That is a ridiculous statement.
Yes, if the dispatcher issues faulty movement authorities, it's futile to look for the error in the train. That was my point.
> Has there ever been a case where two self driving cars collide with each other?
I don't think that's relevant to trains. Cars can avoid a collision much more easily than trains can. Cars can swerve, and if they are at a distance at which line of sight tells them they will hit an obstacle, they are moving slow enough to stop before hitting that obstacle. Trains have to stay on tracks, and they need up to 4 kilometers to stop moving.
The constraints are very different, so the solutions and tradeoffs will be different too.
> We can not design self-driving cars to the safety standard that is required for railways.
That is completely false. PTC does that, and we've had it for several decades. There are several self-driving cars operating in the world right now. I have never heard of a PTC system causing accidents; those occur in places where the system isn't required (like entering Grand Central).
You keep pretending that avoiding train collisions is too magical to achieve with current tech, but train traffic is easy to limit (but slightly harder to optimize), and systems exist to do that, because rail is unique amongst all forms of travel: if you drop speed to zero for any trains at risk of collision, they are safe. Planes will plummet; most cars are human-operated and you can get rear-ended, etc.
> That is completely false. PTC does that, and we've had it for several decades.
I think you are misunderstanding the sentence you quoted.
It says something about the safety of self-driving cars. That is they don’t meet the standards required for railways. In other words the expected safety for a self-driving CAR is lower than the expected safety of a RAILWAY. (Caps for emphasis, sorry about the shouting.)
Your comment reads as if the quote claims that we cannot make “self-driving trains”. It does not say that.
> You keep pretending that avoiding train collisions is too magical to achieve with current tech
I don’t think that they do that. Definietly not in the comment you responded to.
> That is completely false. PTC does that, and we've had it for several decades.
And they somehow work with radar, lidar and GPS from inside the train? No they work with classical block based systems and on signalboxes. So all the safety systems are outside of a train.
> You keep pretending that avoiding train collisions is too magical to achieve with current tech
Huh?? Railway interlocking exists for more than a century. It's very safe and I didn't wrote anything contradicting that.
Yeah and that's fucking ridiculous and a damning indictment of the glaring incompetence of train companies.
If I can have reasonably accurate gps readings of my phone while I'm on the train, there is zero reason for train companies to not have systems that are at least as accurate.
Does your phone's GPS work in a tunnel? What happens if GPS ever gets jammed (or worse, spoofed)?
Aviation also doesn't exclusively rely on GNSS positioning, so why should train protection, given that it's also extremely safety critical?
> Does your phone's GPS work in a tunnel?
My car's GPS does, using dead reckoning.
Trains can also use dead reckoning.
/me checks notes, I've heard that they move on inflexible things called "rails" that almost never change the location.
The thing is that trains move way faster compared to friction (which is needed for breaking and manoveering) than cars. The equivalent is if you would be driving 900-1200 km/h with your car[1]. Good luck being able to break in time on that speed and estimating your position with GPS.
Also the hard part is knowing the position of the others and their trajectory, which changes in between moving towards them and is done by a third party. The normal passing distance is smaller than the width of your vehicle and you can only change your own direction every few kilometers. That means that the others trajectory towards you can only become known after you are already past your last opportunity to change your trajectory and even within your breaking distance. Good luck!
[1] Friction for cars on the road is 0.010-0.015, for trains 0.001-0.002; train speed 120 km/h * 7.5 = 900 km/h equivalent for car; that's not even a high-speed train.
Part of the problem is multiple tracks. Those tracks may be only 10 feet (3 m) apart. (I don't know if high-speed rail lines in Spain are that close, and I don't know if the line where the accident occurred was double track.)
"Reasonably accurate GPS" trying to determine which track you're on at 150 mph is not as simple as you make it sound. Yeah, it can determine how far along the track you are. But when you get two trains moving toward each other, each at 150 MPH, do you really trust that GPS to tell you that they're on different tracks?
I agree that the problem here has no easy, general and automatic gps-based solution but I think it's helpful to keep the actual likely situations in mind. Usually we have the most trains/densest timetables close to major transport hubs where speeds are low anyway and driving 'on sight' is a good compromise of safety and keeping things working. Where speed really matters - outside of major hubs, straight ruralish routes - we simply don't usually have great density of trains AND tracks. At least from my travels in western Europe I don't think I've ever seen more than two tracks in the same direction on high-speed-segments. So if we keep that in mind and don't expect a general and automatic solution, a simple, gps-based fallback-system that requires all trains that are within a radius of X of each other (either in time or space) MUST coordinate, else they both shutdown/move on sight, could work reasonably well. In reality and for the involved parties (the trains that are close to each other), it's a very human-scale problem.
Trains can't change lanes without warning like a Nissan Altima on the Dan Ryan Expressway. The only way a train can move from one track to an adjacent track -- or get on the first track in the first place -- is if switches are set to allow the train onto that track. And on any modern high-speed line, those switches are centrally controlled by dispatch.
Keeping track of which parallel track a train was on automatically was a solved problem a hundred years ago, using relays and lights and hard-wired logic. Adding computers and GPS greatly increases the precision with which dispatch knows position and speed along the track, but knowing which track has not changed in the last century.
Yes, but as long as the central signalling system is working, it already knows where the train is, with no need to involve GPS. (And where modern signalling and train protection systems need increased precision as compared to the granularity of track circuits/axle counter sections, the solution usually involves a combination of on-train odometry plus track balises at occasional intervals in order to reset any inaccuracies that might have accumulated.)
What we're talking about here is some sort of TCAS-equivalent for the case where the central signalling is down – while it's easy to accurately localise trains with the aid of a central signalling system that authoritatively knows about the infrastructure layout, it's quite more difficult when you're trying to do the same thing in a decentralised, train-local fashion.
Yep, that's what I was trying to convey as well. There also seems to be RCAS, but it sounds like a newly invented system. https://www.dlr.de/en/kn/research-transfer/projects/next-gen...
And as of now, I suppose that RCAS (or RCAS-like systems) is best suited for (especially minor) single track branch lines that don't currently have a full-scale signalling system already up-and-running, but instead still rely on "Timetable & Train Order" and similar systems.
Single track means that at least outside of stations, collisions can be reliably identified without much danger of false positives (and for station areas you can just institute a blanket speed limit to compensate for the gap in RCAS coverage, which might not even be any lower than the speed limit required for traversing diverging/spring-operated/hand-operated points there anyway), and no already existing full-scale signalling system means that RCAS actually provides a significant safety benefit and is therefore likely worthwhile from a cost-benefit-analysis point of view, too, if you're actually regularly operating multiple trains simultaneously on that kind of infrastructure.
Whereas on multi-track mainline railways avoiding false positives is much harder and normally you should already have proper signalling and train protection systems in place anyway, so the additional safety benefits of RCAS would be much more marginal.
[dead]
>Trains can't change lanes without warning
Oh, they can, but it's usually a very traumatic event.
Basically what was the case with the previous accident in Spain.
It's very easy since there is limited ability for trains to change tracks, so the location history of the train is a strong indicator of which track it is on. Even Google Maps can tell you which lane you are in since god knows when, and cars can freely change lanes. And that's just consumer software. For something commercial like a train they could trivially solve this problem with something more robust. But I'm not familiar with the Spanish system; how much of the engineering did they do?
There are switches that move trains between tracks. Now you need every switch to report, keep a history of that. Many trains also separate and combine. Trains sometimes go backwards to be switched.
It's not impossible. But handwaving GPS placement of trains at the correct location, direction, and track deserves more than a handwave as trivial.
All of those failure modes can be accommodated. I fail to see anything here a competent engineer couldn't address. I speculate it's not a technical problem, but an operational and cultural one. This is not rocket science.
But it must be also cheaper and more reliable than the current system, otherwise nobody is going to implement it.
Two rtk receivers with LTE including a little battery backup would cost what, $2,000 per car tops?
Presumably switches already report their position to somewhere.
It's absolutely unacceptable for this problem exist in today's world.
> Presumably switches already report their position to somewhere.
Yeah and this somewhere already knows whether a crash is going to happen. In which case your solution brings no benefit. You can't rely on the correctness of a system, which you want to make an alternative to, to help in the case the original system fails.
This discussion focuses on a non-problem (granted partly due to an imprecise comment of mine). The system knows where all the trains are and also that a crash will happen, if the decision is made, that then indeed was made.
What is needed is that the system needs to convince the operator there is still a problem, after it proved itself unreliable. My suggestion would be a log of the constraints the prover encountered while determining whether there is a conflict. This certainly already exists somewhere in the background, but I am not aware whether that is currently shown to operators in deployed systems. It does exist somewhat in the research systems we use in university.
Multiple independent systems. Easy to ignore a single system, but two or more ? Would have to have a death wish
When I wrote that comment I would have answered, that you already need to distrust a system, that of course still have the authority to sound like it would be right. Also from other accident reports, my understanding is that relying on yet another system causes people to make even more errors, while when they start to manually assess the situation from first principles, they are able to grasp the fundamental error, because they are questioning every assumption, as they are reconstructing a world model different from the automatic system. But the latter takes more time and effort, so people tend to do the former.
The thing is that in modern automated dispatching you only have the same world model as the automatic system, so when there is an error you have the same world model as the system, but that just detected, that that does not equal the actual state of the world. And often the error is in fact a false positive.
But now, I actually think that this accident was caused by several systems being in effect: https://news.ycombinator.com/item?id=50298796
Yes, it can tell you. How perfectly, though? Perfectly enough to bet 60 lives on?
When Google Maps gets wrong what lane I'm in, nobody dies. It can be right 99% of the time, that's good enough. It's not good enough for a train system, though - at least, I suspect it's not. I'd want a lot more than "it works in my car" before I trusted it.
Can we just have it as an additional data point, on top of what we should already know from where the train should be from switching history? If we get 99% accuracy, is that enough to check with an operator “specify which track you are in, left or right” when the measured value is different than the expected?
In addition to that being unpractical, the train doesn't even know the state of switches, i.e. not whether it is on the same track as some other position. It's just that this is undecidable for a single train. (This is what my first comment was about, it's simply not known how to solve it on the level of a single train, likely because it is impossible.) However the answer for what to do if a train can't trust the network, is don't move. Or move by sight, which is limited to 40km/h for good reason.
On the other hand this is a complete non-issue and solved for more than a century on the network level. So there is zero need to invent satellite or vision based train detection at worst even using statistical systems, when you can use deterministic systems, for example using the fact that a train is out of metal, so it's detectable by the train closing a electric circuit between the rails. Or using the sensors that are installed at every signal, switch or other positions for precisely this question.
HN does railway safety... The Dunning-Kruger level in this thread is ridiculous.
As a passenger, I'm very glad software engineers haven't (fully) taken over aviation and railway safety yet.
Google maps gives me the directions for the express lanes when I'm in the normal lanes and vice versa like 50% of the time, and that's an order of magnitude greater error in distance than the distance between adjacent train tracks. And several orders of magnitude greater failure rate than is acceptable for a safety system.
RTK is more than capable of figuring out what track you are on
It can be on the other track right now, but change to your track in the future. Or in other words, the topology of the network changes in operation. Whether the track you are on and the track another train is on, is the same or not is not decidable without knowing the current network state.
Would that work in tunnels and forests too?
Tunnels are controlled by a single block - only one train can ever be allowed access at once, period. Until the "current" occupant train is verifiably out of the tunnel, that block is forbidden to all.
Forests are irrelevant; rail right-of-way contains no trees, and is wide enough to assure clear "view" of satellites.
You are just answering how the current system actually works. This discussion was about how a hypothetical system works based on GPS or radar alone.
> Tunnels are controlled by a single block - only one train can ever be allowed access at once, period.
Absolute nonsense. Do you have any idea how long some tunnels are?
There are actually different definitions for what a block is. It can be both a section where you can decide for trains to enter or where you can change their sequence (Zugfolgeabschnitt vs. Zugmeldeabschnitt, don't know the English terms) Also it can be a physical implementation of any constraint between components of different stations.
But yes there does not need to be a limitation on there only being a single train in a tunnel.
> a damning indictment of the glaring incompetence of train companies.
No, what I describe has nothing to do with the companies, that's the research state. It's just an indictment of you making bold statement about a subject, you don't now enough about.
> I can have reasonably accurate gps readings of my phone
Would you dare to cross on a rope over a deep valley, blind using only GPS readings of your phone? Because that's kind what you are suggesting, expect you also move a few hundred other people.
> Would you dare to cross on a rope over a deep valley, blind using only GPS readings of your phone?
Hang on, this is nothing at all like that - trains run on fixed tracks. The only bit of data we are interested in for collision avoidance is the linear offset along the track. Even the shittiest GPS fix of all-time would give a good-enough intersection with a fixed path to avoid crashing into a second stationary train in the open country-side (do you see any satellite line-of-sight blockers in the crash footage?)
> The only bit of data we are interested in for collision avoidance is the linear offset along the track.
So that is naive, but assuming that would be all that you need, with GPS you would also need the positions of all other trains. But why would you transmit all this information to every train, instead of just computing the collisions in a central node? (That's what is done now.) A better fit for what you suggest would be radar, and this does exist. [1] But that's where your original assumption is naive. You regularly pass other trains within <2m at high speeds, so linear offset is not all you need.
> But why would you transmit all this information to every train, instead of just computing the collisions in a central node?
Because central nodes can fail (as they did here, both human and machine), and providing this redundant data allows both the computer and the human-in-the-loop on the fast-moving chunk of steel to independently validate the decisions coming from the central node.
> You regularly pass other trains within <2m at high speeds, so linear offset is not all you need.
In this collision, both trains were on the same track. So while we obviously care about adjacency issues in the general case, this specific failure mode can be detected purely via a linear offset.
You can and do have redundancy in the central node already. Also that's not what failed here.
> In this collision, both trains were on the same track.
Yeah, but how do you distinguish that? So when I understand you correctly, what you want is: Find another moving chunk of metal in the radius of 2km, which moves toward you, but not in a direct or ballistic trajectory, but in a arbitrary complicated trajectory, but which can lookup in a database. Also you are operating in the real world, so there are potentially houses, trees and mountains in between. I guess that would be possible, but it would be really expensive. Your best bet would be to adapt a missile detection and targeting system from the military. A system which does exist and is somewhat similar is RCAS (https://www.dlr.de/en/kn/research-transfer/projects/next-gen...).
> Yeah, but how do you distinguish that?
By enumerating the tracks?
I feel like you are intentionally trying to turn this into a spherical cow situation by insisting on solutions that work in an information vacuum. All of this sort of problem in the real world is solved by sensor fusion from multiple data sources.
Trains are captive to a particular track - they can only change tracks at specific pre-determined junctions. With a pretty minimal sensor feed from each junction we can statically determine which track segment a given train is on. With GPS we can shrink that segment length down to a few kilometres. By sharing data persistently every single train can validate that central command-and-control is not about to run it into another train from behind...
There cases which are genuinely challenging engineering problems (i.e. derailments that impinge on adjacent tracks), but this trivial case of bumper cars is not one of them.
>> Yeah, but how do you distinguish that?
> By enumerating the tracks?
How do you distinguish that the <2km away detected moving train runs on your track on not on the one directly besides you?
> Trains are captive to a particular track - they can only change tracks at specific pre-determined junctions.
Yeah, but you do not know which one it runs on. Your entire point is that you do not trust the information the infrastructure knows. If you do allow to use information from the infrastructure, then why not use the sensors that already exist along the whole train network? It's also very unlikely that there is something electrically connecting the two rails of a track, that you would like to run over. So why wouldn't you trust that information, but some vague GPS signal?
> we can statically determine
But the current state of the art is, that you deterministically and provable know where a train is. Why would you use a more expensive, less safe system? The current focus to reduce errors in computing train conflicts is to prevent random bit flips due to radiation at the same time in three different computers running different software.
> I feel like you are intentionally trying to turn this into a spherical cow situation
The situation where you proposal makes sense, but the current system does not, is a spherical cow situation, that's my point.
> that you deterministically and provable know where a train is
You are the one who framed this conversation as it not being solved how to deterministically know where a train is. Everyone else in here has been kindly suggest that if perfect information is unobtainable, then we should work with what we have
Oh, I see how you could think that, without context. That's in fact not what I wanted to say. I meant that pretty literally. The infrastructure of course knows where the train is.
> Trains are still not able to assess properly where they are, even using satellites and inside train sensors. Of course there is research on that, but it's still an unsolved problem.
*Trains* on there own! This IS a hard problem, how to do that with any other infrastructure. It IS current research and not yet solved. That is for example relevant, if you want to be able to run trains at full speed <1m tolerance, so that you can have more than one train stopping at a station <60s. All while still not paying for infrastructure and maintaining backward compatibility with a century old trains. (I mean in the future you could use the same to also couple trains at full speed, but that's still sci-fi.)
> That is for example relevant, if you want to be able to run trains at full speed <1m tolerance, so that you can have more than one train stopping at a station <60s.
...is that something you'd ever want? In general, it is, but the way it's handled is by having those trains stop on separate tracks.
Running multiple trains through the same station track in under 60 seconds means that all passengers must embark and disembark in under 30 seconds. That's very tight. I would venture to say it's too tight and meeting this goal would make the trains worse.
(And if passengers aren't getting on or off the train, then the train isn't stopping at a station.)
In a society where building more rail is not welcomed, trying to get more out of the existing tracks becomes critical. In a metro, time for embark and disembark of 30s is not unreasonable. https://de.wikipedia.org/wiki/Fahrgastwechselzeit#cite_ref-d...
Redundancy in a central node is an oxymoron. Safety critical systems need to work 100% of the time if any single node fails, and stop safely if there are multiple failures and it can't work properly. Doesn't matter if each individual node is 100% reliable by itself because connections fail too.
You can still have redundancy in the computation, that isn't prevented by being in the same location.
> Safety critical systems need to work 100% of the time
Railway safety must be safe 100% of the time, but not available 100% of the time. Also the point of a signal box is to make decisions about the order of train assignment to track. You absolutely do not want multiple points of truths for that.
The way I think of it, divide the tracks into segments. Before you put a train on a segment, you must ask a question - is there a train on it. There are only two answers possible, No, and something else. If it is something else, stop. Don't let the train on that segment.
There are optimizations possible like make segments smaller etc but the original algorithm is trivial. If we can't figure things out, we make segments longer and we slow down the trains until we can. I am positive for a sufficiently large track segment and a sufficiently slow train, we can always answer the question with a no.
You've "invented" interlocking railway semaphores, after which the computer science concept was named.
https://en.wikipedia.org/wiki/Railway_semaphore_signal
https://en.wikipedia.org/wiki/Interlocking
Congratulation you are reinventing 1890 state of the art.
The problem is when the modern computer-dependent system replaces the ancient one, and so then the computer is down there is nothing at all.
Actually in this case it seemed that the opposite was the case, there was another fallback system, but you needed to disregard it, and operate manually, but the operators likely didn't notice that. https://news.ycombinator.com/item?id=50298796
Which is why you generally don't do that.
who said anything about only using gps? I'm saying in addition to their current system!
The exact comment I answered to. https://news.ycombinator.com/item?id=50287160
i don't see where it says they should use gps alone. In fact it even mentions starlink in addition to gps.
>Even GPS + Starlink + 1 monitor (is that 50k€?) could have prevented this.
My reading on that sentence was that even a simple setup would have been sufficient to prevent this. Not that it should be the only thing.
My reading indicates, that "Even X could have prevented this." means that X is able to solve the issue on it's own. Otherwise X would in fact not prevent it.
- I don't think X would actually work, without actually eventually recreating part of the current railway control system, and the current rail control system alone already works better.
- I don't think another less reliable more costly safety system helps, when the current one already stated that there is a problem, and it was ignored.
>My reading indicates, that "Even X could have prevented this." means that X is able to solve the issue on it's own. Otherwise X would in fact not prevent it.
X on its own would have solved this particular crash, yes.
X + existing setup would solve this crash + all the other crashed the existing setup solves.
Yes they are, those balises on tracks are the standard technique for both metro and mainline signaling systems at this point. Those balises, often combined with radio communication, are how fully autonomous trains have been operating for decades. (It's possible to use things other than balises, like track radio loops as in LZB or more recently beacons or LIDAR, but balises are standard and pretty affordable).
Yeah, that works and has been for a while. I was talking about non-track based safety systems. You can have balises in specific locations, but you can't have them every few centimeters on your whole network.
Why would you need that many? Trains can keep pretty reasonable track of the distance between two balises using odometers.
There are also other solutions, e.g. LZB uses a phase change of the signal every 100 meters as an additional precision signal.
Because balises cost money, are payed for by infrastructure companies. Their position needs to be decided a priori, so you can't have the whole resolution on the whole network in order to get as close to the physical limits between trains as possible. Also it would be nice to be able to implement automatic shunting without additional infrastructure costs.
There are now hybrid systems for ETCS L2 that allow virtual blocks as short as 1 meter long. Balis + odometer is quite robust (and indeed how most CBTC systems with moving block tech function).
I guess I'm confused by why non track -based solutions are necessary? ETCS L2 would gracefully handle a system restart and automatically force a 40kph speed limit until a train traversed the unknown track proving no occupancy, and allowing proceeding trains to go faster. This all works on a track-based system.
Because railway infrastucture companies would like to not pay for them, not build more tracks and still get more capacity due to "digitization".
Not sure what you're arguing, the line affected by this tragedy was migrating to ETCS L2. Its installation costs are getting lower too, I don't think there's an actual problem here.
I wasn't talking about a specific line at all. Research doesn't need a clear problem to try to find better solutions. Also Deutsche Bahn does think there is enough of a "problem", because they do support that research.
> Trains are still not able to assess properly where they are [...]
Isn't the ability to do so the basis of operation for e.g. the German LZB train protection system, which has been around since the 1960s?
If you mean that train protection systems don't (exclusively) rely on self-reported positions, your statement makes a bit more sense, but even that is changing with e.g. newer ETCS levels which do rely on self-positioning more and more.
I should have written that comment quite differently, it took a while for me to understand how it is read.
I did not say "train systems are ...", I said "trains are ...". This is referring to e.g. that odometry based on wheels results in a drift. GNSS is to imprecise and unreliable. I'm aware that you simply use balises, that's what I meant with "markers in the track". However that's based on the infrastructure again, so it's again not trains on their own.
https://news.ycombinator.com/item?id=50293093
It was simply supposed to be an example how GPS sounds like it should easily solve a problem, but does not without additional measures, that then do not need GPS anymore.
Would you mind sharing some more of the why it is still an open problem? (I know I know little about this subject.) I understand satellite positioning isn't definitive and did not suggest it should be the /primary/ risk mitigating factor. But even as a tertiary or lower risk mitigating factor, this would have been a worthwhile investment. (Sorry for the bleak introduction of economics.)
And some problems are just _open_ to outside looks. My assistant tells me that the room for error in trains on one dimension ('left - right') is mere 10s of centimeters. I understand that problem. But what track you are on, isn't that obvious to the human in the cabin? (Again, simplifying, not flaming. Production ready safety is _hard_.) So could a vision based solution help count tracks from left to right? (Assistant: "US PTC, on about 54,000 route-miles, uses GPS for the lead locomotive plus crew-entered track information and switch position".) So you use the dimension that matters most in crashes (forwards / backwards) from satellite, augmented with vision or human based left-right positioning. Some trains already have sensors to sense things like leaves on the track to adjust speeding and braking... So the sensor based approach is already there.
Perhaps I am read as suggesting that the problem is easy, and that is not my intention. But for cars this was solved decades ago for routing and years ago for self-driving. I use that daily. Flying is organised with a very clear 6 sigma approach. Crashes are nearly always situations where events / risks stack. Trains (in Spain)...?
Tl;dr - Safety is a function of (human; process; technology) and there is clearly something lacking for trains, when compared to other types of transport.
So that's a lot of questions, that I all can't answer in full.
> Would you mind sharing some more of the why it is still an open problem?
Because for train sensors, there is a small drift which accumulates too much, hence it is synchronized by magnetic position markers in the tracks.
> I understand satellite positioning isn't definitive
Yes, and the point is it might be some solution if we would have the safety systems from 1860. But we do not and hence it needs to be more accurate than the current system, and it is not and in addition also more expensive (and subject to remote influence and reliance on potentially adversary nation states).
> Sorry for the bleak introduction of economics
No, economics is basically the primary constraint for safety. We could pay million people to make sure a single person does not stumble if we want total safety, but that's completely pointless, and also these million people would starve, because no one is producing food anymore.
> But even as a tertiary or lower risk mitigating factor
But for that it's too expensive and still unreliable. There is RCAS[1], which I already linked elsewhere in the thread. That's basically cutting edge and too expensive to introduce everywhere. Also previous safety systems are already not rolled out enough, which is causing these accidents, so rolling out yet another expensive system is not going to improve much.
> But what track you are on, isn't that obvious to the human in the cabin?
Yes, but if it is already known, why use GPS to calculate the same information with more error?
> So could a vision based solution help count tracks from left to right?
If the train driver or dispatcher makes use of vision to assess the train position, the error will be higher than the current sensor/electric-resistance based system.
> Assistant: "US PTC [...]
BTW, that seems to be a verbatim quote from https://www.railwayage.com/cs/the-way-forward/
> US PTC
According to Wikipedia, ASFA being introduced in 1975 is rolled out in the entire Spain network. ETCS which is the European standardization seems to be rolled out on all high-speed lines or currently being rolled out.
> So you use the dimension that matters most in crashes (forwards / backwards) from satellite, augmented with vision or human based left-right positioning.
Duh, that just sounds like trains would be operating blindly in space currently and need to assess their approximate position.
> Perhaps I am read as suggesting that the problem is easy, and that is not my intention.
No, the issue is that you are suggesting far more complicated solutions to already solved problems, with simpler systems in operation for decades. The current system is that nobody in the train even has a say on where the train goes, so the problem you are trying to prevent doesn't even exist. This IS why it's way more safer than a car. There are movement authorities, that define from where you are allowed (and have to) drive with your train. The problem is not, that the train driver isn't able to know where he is and hence drives wrong or too far (that would be prevented by the on-board safety system), but that the movement authority itself is faulty.
On an up-to-date signaling box (withing the past 6 decades), even the train dispatcher is no say in safety questions. You could put a monkey in charge of it. There would be chaos, but they would not cause a crash. The current job of a dispatcher in normal operation is to assign resources to prevent deadlocks and to implement vaguely defined priorities. (Basically the equivalent of the public thinking a programmer is a code monkey, while the actual point is clarifying stakeholder interests.)
The actual issue here is, that while these safety system have a very small false positive rate, they do have a too large false negative rate for there to be an acceptable availability. Hence in the latter case, the human needs to take over and then you are back to a much higher false positive rate. The issue would be alleviated by relaxing the constraints on cost per availability. Either by allowing for less availability or by reintroducing more humans, so that the system situation can be assessed by humans directly.
These accidents are caused as follows: the automatic system fails, because the internal state of the system does not match the actual state of the world. Hence the human needs to take over. But the human also needs to rely on some system to know the world state. Which systems can he trust, given that the whole situation is that the systems report that he can't trust them? So he needs to make some decision and in most cases, that decision is still correct. But there is still an error rate to that, and then something like what we are discussing happens.
> But for cars this was solved decades ago for routing and years ago for self-driving.
This is absolutely not solved for the cars, and to the sense that it is, it was solved and rolled out from the 1870s onward for railways using mechanical computing systems, the switch to using electricity happened in the 1910s.
> Flying is organised with a very clear 6 sigma approach.
You are correct, that aircraft safety systems need to be designed to a higher reliability than railways, because on a rail you can always stop in case of an error, while in the air such a choice doesn't lead to a safe state. But if you compare these safety systems, basically aircraft is operated like railways used to be operated in the 1920s. (My peers actually had a task to compare them and find ideas from one that can be applied to the other. While there is a lot of automation to be taken from rail that can be applied to the aerial industry, there is not really much that can be applied the other way.) It is also operated with the amount of personal than 1920s railways. That's because there is a lot of money in aircraft, while railways are mass-transit and need to be cheap. If you would operate today's railway with the amount of human oversight than in the past, it would be a lot safer than aircraft.
> there is clearly something lacking for trains, when compared to other types of transport.
What are you talking about? Railways are so much safer than cars. https://news.ycombinator.com/item?id=50288518 Yes, there are less accidents in planes than in trains, but this is due to what I already explained.
Thank you for your time and knowledge.
GPS-based PTC absolutely does what you describe. It has long been solved.
No, it does not do, what I described. I was talking about solely determining it inside the train. At least Wikipedia indicates it is similar to LZB or ETCS. I am not familiar with PTC itself.
That's a research topic, because the infrastructure companies would like to not pay as much for maintenance and still have a high sequence of trains. Also with track based train control systems you can only have very high resolution in specific places, where you place your track-side infrastructure, but it would be nice to have that resolution anywhere you like.
PTC is a performance standard, not a concrete system. Some PTC systems do seem to use GPS for train positioning, which does seem surprising from a European train protection system perspective which all seem to completely avoid reliance on GNSS so far.
I guess a much less dense and largely overground network, mainly used by fairly slow moving freight trains as opposed to highspeed passenger connections, changes requirements somewhat.
Thanks.
I mean they are systems that rely on GNSS in Europe, but no safety systems, that would be simply to unreliable. For example I believe the railway announcements in Germany to depend on GNSS. They are also unreliable.