5 ms·

The difficulties with gps seem over stated, Which Track? Trains don't randomly switch tracks except in yards, instrumenting each switch to understand when a tr

The difficulties with gps seem over stated, Which Track? Trains don't randomly switch tracks except in yards, instrumenting each switch to understand when a train switches tracks seems like an easy problem. Tunnels? First there aren't "that" many and there aren't many long enough that a single long train shouldn't count it as occupied in the interest of safety. It also shouldn't be a high effort to add a satellite or wireless repeater with a known location at at least each end of a tunnel. An arduino with GPS tracking an accelerometer (or gyro), a compass, add a few wireless location nodes around tunnels and other dead spots and every difficulty here is solved. The accelerometer can even early report rough tracks or switches. What excuses the economist entertains while we have successful tracking in many other forms of transport.

matthewmacleod 4y ago
Of course, in reality you can't build safety-critical systems that operate in challenging rail environments by slapping together an Arduino, a GPS receiver, and an IMU and saying "problem solved lol". None of the things you have described are "easy problems". In fact, they are pretty difficult! Systems need to be robust, interoperable, reliable, provably correct, fail safely, deal with surprising edge cases, have long service lives, and any number of other challenges. In any case, all you've really done here is re-invent technology that already exists. In ETCS level 2, for example, the signalling system uses known-location transmitters on the track as references and the train calculates its position in-between using on-board sensors like axle encoders, IMUs etc. This is just a short article about an interesting new technology for providing the "train position" component of the system by building a magnetic map of the rails. Pretty cool idea – if it's accurate enough, it provides a more robust source of absolute positioning information, which is key to allowing the rollout of realising "moving-block" approaches in which trains' movement authorities are updated in real-time, allowing higher traffic density. And it's not like nobody's thought about GPS/GNSS either – there have been extensive projects looking into the feasibility of those systems. The Russian ABTC-M system uses GLONASS, and I'm sure some implementations of PTC in the US use GPS. But again, these are difficult challenges incorporating lots of different technology and you don't solve them overnight.
- sitkack 4y ago
  They should be solved asap. Increasing rail utilization is key to many of the problems we are facing. Rail can move cities, nothing else can do that. Many of these things would be solvable by solar powered cameras on 4G/5G/starlink. Vibration sensors in the tracks, transponders in the cars, wheels, engines, etc. We need way more signals than we currently have.
  - bobthepanda 4y ago
    Generally speaking, LIDAR or cameras on trains don’t solve much, because trains’ braking distances (and therefore what they need to “see”) extends for hundreds of meters, sometimes over a kilometer, and around curves, walls, etc. It’s a different problem space. Rail utilization will certainly help at the margins, but only maybe one or two trains an hour. The real meat and potatoes is generally more tracks, and removing conflict points on existing ones.
    - sitkack 4y ago
      You can dead reckon speed, location from camera lidar data, just like what they were doing with the magnetic map in the article. I made no statements that the train would be locally self engineering using the cameras.
      - bobthepanda 4y ago
        If dead reckoning is what you're relying on, you need * the last junction you passed and how you exited, and * number of turns of the wheel. The issue is that rewiring junctions is very expensive, upgrading trains to be compatible is expensive, etc. Even more so if you cannot upgrade an entire network all at once, and you need to account for mixed operations with both new and legacy compatible systems.
    - kposehn 4y ago
      Lidar on trains has some uses, but you're quite correct that it isn't the primary sensor. However, automating trains on heavy-haul networks like the US & Brazil is a big opportunity. The pressure to reduce crew costs means longer trains and less network fluidity; automating them allows much shorter point-to-point consists on the same infrastructure. As long as they have the right sensors they can run much closer together - even couple & de-couple en route (with some extra equipment).
KaiserPro 4y ago
> Which Track? Trains don't randomly switch tracks except in yards, Track spacing is often much less than the dilution of position, which is less than ideal. This means that the area that the GPS thinks the train is, is bigger than the track width. Trains in the UK are often in cuttings, urban canyons etc, which means that the error margin could be up to 100m without much effort. > instrumenting each switch to understand when a train switches tracks seems like an easy problem. Only if you ignore that those sensors are now life critical, so is the connection, and the software that joins it all up. > Tunnels? First there aren't "that" many and there aren't many long enough that a single long train shouldn't count it as occupied in the interest of safety. again see DoP. But safety distance is related to speed. the slower the trains the shorter the distance, which means you are more likley to bump into GPS DoP issues. Also tunnels normally have cuttings, which again limit the number of satellites visible. > It also shouldn't be a high effort to add a satellite or wireless repeater with a known location at at least each end of a tunnel. again see safety critical equipment, you'll need fail safes > The accelerometer can even early report rough tracks or switches. Whats the percentage drift per second of those sensors? How often is the calibration frequency? how much vibration can it handle before it becomes inaccurate? whats the mean time to failure? As a point, the "new" thameslink trains refused to open its doors at the thameslink station, because the station was in a tunnel, and the GPS wasn't available. This meant that the train said it didn't know where it was, so no doors open. As a general rule of thumb, life critical stuff needs to be simple, well tested and well characterised. Failure of a system might cause a death, subtle failure is even more dangerous. This means expense.
- smileysteve 4y ago
  > Track spacing is often much less than the dilution of position, Which is why I spell out to instrument the current reporting switches (which are the current systems (and yes they fail)) > As a general rule of thumb, life critical stuff needs to be simple, well tested and well characterised. For context, my state leads in railroad crossing deaths, in part because the existing signaling infrastructure is too sparse or dilapidated. >
Animats 4y ago
> The difficulties with GPS seem over stated. If anything, they are understated. GPS is so easy to spoof that it should not be used in a vital system. Most train control systems have two completely separate systems. One keeps trains from running into each other, and the other makes the railroad run efficiently. The first usually depends on brutally simple and fail-safe wayside equipment. The second is based on direction from a control center somewhere. The second system is capable of keeping trains separated on its own, and it's so tempting to get rid of all that wayside safety equipment, with all that gear in trackside boxes needing maintenance visits.
NamTaf 4y ago
This is hilariously hand-wavey of the complexity and strikes at my frustrations between how most IT engineers see the world vs how real-world engineers do. There are parallel tracks within metres of one another. Switching yards have tonnes of them and require precise knowledge of what’s in what. GPS isn’t SIL. Trains operate in cluttered environments with reflection and echo abound. That causes drift above the separation of tracks. There’s way more than “a few” dead spots, and what happens if those repeaters fall over? There’s tonnes of reasons why high tech isn’t used in train safety-critical systems. The fact you suggest an arduino as an appropriate platform for this is frankly absurd and underscores your misunderstanding of the whole issue. Close enough isn’t good enough. Crashing doesn’t just mean you reboot or reload the program and try again. It means people die. Edit to add: A good rule of thumb I’ve learnt after 15 years in the game: if you look at the solution to an engineering problem and then start a sentence with “why don’t they just…”, you probably don’t understand the problem well enough.
- olivermuty 4y ago
  To be fair, «why don’t they just» has also made a lot of startup founders very wealthy over the last 15 years ;)
  - NamTaf 4y ago
    I’ll cop that, though I’m fairly confident in saying it’s the exception that proves the rule, in that those ones end up knowing the problem space so well that they sort of horseshoe around to seeing new insights others miss.
    - bobthepanda 4y ago
      also, even though some startup founders have become very rich questioning the basics with technology, many more have failed.
- jen729w 4y ago
  > how most IT engineers see the world vs how real-world engineers do Reminds me of… # Programmers: Stop Calling Yourselves Engineers “It undermines a long tradition of designing and building infrastructure in the public interest … The title ‘engineer’ is cheapened by the tech industry.” https://www.theatlantic.com/technology/archive/2015/11/programmers-should-not-call-themselves-engineers/414271/ https://www.theatlantic.com/technology/archive/2015/11/progr...

matthewmacleod 4y ago

Of course, in reality you can't build safety-critical systems that operate in challenging rail environments by slapping together an Arduino, a GPS receiver, and an IMU and saying "problem solved lol". None of the things you have described are "easy problems". In fact, they are pretty difficult! Systems need to be robust, interoperable, reliable, provably correct, fail safely, deal with surprising edge cases, have long service lives, and any number of other challenges. In any case, all you've really done here is re-invent technology that already exists. In ETCS level 2, for example, the signalling system uses known-location transmitters on the track as references and the train calculates its position in-between using on-board sensors like axle encoders, IMUs etc. This is just a short article about an interesting new technology for providing the "train position" component of the system by building a magnetic map of the rails. Pretty cool idea – if it's accurate enough, it provides a more robust source of absolute positioning information, which is key to allowing the rollout of realising "moving-block" approaches in which trains' movement authorities are updated in real-time, allowing higher traffic density. And it's not like nobody's thought about GPS/GNSS either – there have been extensive projects looking into the feasibility of those systems. The Russian ABTC-M system uses GLONASS, and I'm sure some implementations of PTC in the US use GPS. But again, these are difficult challenges incorporating lots of different technology and you don't solve them overnight.

sitkack 4y ago
They should be solved asap. Increasing rail utilization is key to many of the problems we are facing. Rail can move cities, nothing else can do that. Many of these things would be solvable by solar powered cameras on 4G/5G/starlink. Vibration sensors in the tracks, transponders in the cars, wheels, engines, etc. We need way more signals than we currently have.
- bobthepanda 4y ago
  Generally speaking, LIDAR or cameras on trains don’t solve much, because trains’ braking distances (and therefore what they need to “see”) extends for hundreds of meters, sometimes over a kilometer, and around curves, walls, etc. It’s a different problem space. Rail utilization will certainly help at the margins, but only maybe one or two trains an hour. The real meat and potatoes is generally more tracks, and removing conflict points on existing ones.
  - sitkack 4y ago
    You can dead reckon speed, location from camera lidar data, just like what they were doing with the magnetic map in the article. I made no statements that the train would be locally self engineering using the cameras.
    - bobthepanda 4y ago
      If dead reckoning is what you're relying on, you need * the last junction you passed and how you exited, and * number of turns of the wheel. The issue is that rewiring junctions is very expensive, upgrading trains to be compatible is expensive, etc. Even more so if you cannot upgrade an entire network all at once, and you need to account for mixed operations with both new and legacy compatible systems.
  - kposehn 4y ago
    Lidar on trains has some uses, but you're quite correct that it isn't the primary sensor. However, automating trains on heavy-haul networks like the US & Brazil is a big opportunity. The pressure to reduce crew costs means longer trains and less network fluidity; automating them allows much shorter point-to-point consists on the same infrastructure. As long as they have the right sensors they can run much closer together - even couple & de-couple en route (with some extra equipment).

KaiserPro 4y ago

> Which Track? Trains don't randomly switch tracks except in yards, Track spacing is often much less than the dilution of position, which is less than ideal. This means that the area that the GPS thinks the train is, is bigger than the track width. Trains in the UK are often in cuttings, urban canyons etc, which means that the error margin could be up to 100m without much effort. > instrumenting each switch to understand when a train switches tracks seems like an easy problem. Only if you ignore that those sensors are now life critical, so is the connection, and the software that joins it all up. > Tunnels? First there aren't "that" many and there aren't many long enough that a single long train shouldn't count it as occupied in the interest of safety. again see DoP. But safety distance is related to speed. the slower the trains the shorter the distance, which means you are more likley to bump into GPS DoP issues. Also tunnels normally have cuttings, which again limit the number of satellites visible. > It also shouldn't be a high effort to add a satellite or wireless repeater with a known location at at least each end of a tunnel. again see safety critical equipment, you'll need fail safes > The accelerometer can even early report rough tracks or switches. Whats the percentage drift per second of those sensors? How often is the calibration frequency? how much vibration can it handle before it becomes inaccurate? whats the mean time to failure? As a point, the "new" thameslink trains refused to open its doors at the thameslink station, because the station was in a tunnel, and the GPS wasn't available. This meant that the train said it didn't know where it was, so no doors open. As a general rule of thumb, life critical stuff needs to be simple, well tested and well characterised. Failure of a system might cause a death, subtle failure is even more dangerous. This means expense.

smileysteve 4y ago
> Track spacing is often much less than the dilution of position, Which is why I spell out to instrument the current reporting switches (which are the current systems (and yes they fail)) > As a general rule of thumb, life critical stuff needs to be simple, well tested and well characterised. For context, my state leads in railroad crossing deaths, in part because the existing signaling infrastructure is too sparse or dilapidated. >

Animats 4y ago

> The difficulties with GPS seem over stated. If anything, they are understated. GPS is so easy to spoof that it should not be used in a vital system. Most train control systems have two completely separate systems. One keeps trains from running into each other, and the other makes the railroad run efficiently. The first usually depends on brutally simple and fail-safe wayside equipment. The second is based on direction from a control center somewhere. The second system is capable of keeping trains separated on its own, and it's so tempting to get rid of all that wayside safety equipment, with all that gear in trackside boxes needing maintenance visits.

NamTaf 4y ago

This is hilariously hand-wavey of the complexity and strikes at my frustrations between how most IT engineers see the world vs how real-world engineers do. There are parallel tracks within metres of one another. Switching yards have tonnes of them and require precise knowledge of what’s in what. GPS isn’t SIL. Trains operate in cluttered environments with reflection and echo abound. That causes drift above the separation of tracks. There’s way more than “a few” dead spots, and what happens if those repeaters fall over? There’s tonnes of reasons why high tech isn’t used in train safety-critical systems. The fact you suggest an arduino as an appropriate platform for this is frankly absurd and underscores your misunderstanding of the whole issue. Close enough isn’t good enough. Crashing doesn’t just mean you reboot or reload the program and try again. It means people die. Edit to add: A good rule of thumb I’ve learnt after 15 years in the game: if you look at the solution to an engineering problem and then start a sentence with “why don’t they just…”, you probably don’t understand the problem well enough.

olivermuty 4y ago
To be fair, «why don’t they just» has also made a lot of startup founders very wealthy over the last 15 years ;)
- NamTaf 4y ago
  I’ll cop that, though I’m fairly confident in saying it’s the exception that proves the rule, in that those ones end up knowing the problem space so well that they sort of horseshoe around to seeing new insights others miss.
  - bobthepanda 4y ago
    also, even though some startup founders have become very rich questioning the basics with technology, many more have failed.
jen729w 4y ago
> how most IT engineers see the world vs how real-world engineers do Reminds me of… # Programmers: Stop Calling Yourselves Engineers “It undermines a long tradition of designing and building infrastructure in the public interest … The title ‘engineer’ is cheapened by the tech industry.” https://www.theatlantic.com/technology/archive/2015/11/programmers-should-not-call-themselves-engineers/414271/ https://www.theatlantic.com/technology/archive/2015/11/progr...