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A similarly embarrassing state of affairs is the train traffic control system used by the NYC subway system: https://www.youtube.com/watch?v=Mjx3S3UjmnA https:/

A similarly embarrassing state of affairs is the train traffic control system used by the NYC subway system: https://www.youtube.com/watch?v=Mjx3S3UjmnA https://www.youtube.com/watch?v=Mjx3S3UjmnA

jholman 11y ago
Wow. Their end-goal upgrade, the one that they've installed on one line, and are installing on everything else looks so antiquated. My city's subway/elevated train system will be 30 years old this December. Train control is fully automated; there are no drivers on trains, and in normal operation there is no remote (human) operator either. It's been automated for 30 years. https://en.wikipedia.org/wiki/SkyTrain_(Vancouver) https://en.wikipedia.org/wiki/SkyTrain_(Vancouver) (Side note: during the BART strike, some HN commenters suggested computers to replace drivers, and other commenters said that wouldn't be safe. Such hilarious technophobia on HN.) I don't want to trivialize NYC's challenges and accomplishments: for one thing their system is far, far more complicated (468 stations on 34 lines, vs 47 stations on 3 lines), and for another we all know it's very hard to upgrade legacy systems. But I'm astonished that they would work so hard to modernize their 1930s technology to 1970s standards in the 2010s.
- wil421 11y ago
  Some less technology minded people would actually be freaked out by automated trains. The airport where I live has automated trains to go between gates and the cars very closely resemble the public trains cars without the seats. Most likely its not a technical challenge its a bureaucratic problem. Not to mention the unions aren't going to let the transit authority obsolete their jobs.
- benihana 11y ago
  Another thing about the NYC subway is that it runs 24 hours a day 365 days a year. Not many metros around the world can make that claim. Living in New York, the amazing thing about the subway system is how they keep it running. It's old and ridiculously complex, and despite what natives say, the MTA by and large does a good job running it. There's no political will to fix it right now. It's going to take trains becoming unsafe or costing so much to keep safe that people eventually notice and start making noise about it, I think.
  - warfangle 11y ago
    Yep. They do a pretty darn good job, considering what they have to work with. And I'm not talking just the technology - they have 31 billion dollars of debt to service, and constantly get the shaft from Albany when it comes to funding. They continue to take on debt because they have mandated projects and lack the funding to complete them.
- spacecowboy_lon 11y ago
  You know that the 30's gear on the Tube was more reliable than the 1970's stuff?
- bdonlan 11y ago
  The problem with some of these old lines is that they might have level crossings in which pedestrians or cars might occupy the tracks - so someone needs to be there to stop the train if that happens. Fully automated systems like the SkyTrain or Japan's Yurikamome line have grade-separated tracks (and in some cases platform gates as well) to ensure that sort of incursion doesn't happen.
  - warfangle 11y ago
    The NYC subway system has no level crossings where pedestrians can occupy the tracks. The only level crossing where another train might occupy the tracks is Queens-bound from the JMZ stop at Myrtle Ave & Broadway in Brooklyn. The M crosses at grade over the J/Z track.
jonawesomegreen 11y ago
That is fascinating, thanks for sharing. I had no idea the NYC subway was being run by a 100 year old electro-mechanical system.
- hga 11y ago
  The D.C. Metro system was planed in the '60 and constructed in the '70s, with the first operations starting in 1976. It too is based on electro-mechanical relays, although it's more ambitious, after the operator closes the doors and sees all is fine, he hits a "go" button and the system automatically takes the train to the next station, avoiding collisions as long as the "is there a train in the next segment" sensor system is working.
  - JonathonW 11y ago
    The DC Metro actually (mostly) hasn't used their automatic train control system in full automatic mode since a collision in 2009 that killed nine (for which the ATC system was directly responsible; a faulty circuit both forced a train to stop and rendered it invisible to the control system). Safe train control seems like it needs a little more sophistication than '60s or '70s tech was able to give. For one, it's common sense that a train that disappears from the system isn't really gone-- but the Metro system couldn't take that into account. Stuff like that should be pretty trivial today.
    - AnthonyMouse 11y ago
      > For one, it's common sense that a train that disappears from the system isn't really gone-- but the Metro system couldn't take that into account. Stuff like that should be pretty trivial today. It was pretty trivial in the 1970s. Require the sensor for an adjacent segment to be engaged before the sensor for an active segment will disengage. You can't do any computation with modern computers that you couldn't have done with relays in the 1970s, or the 1870s for that matter. Mechanical relays are slower, less reliable and more expensive than transistors... but they do the same thing.
    - Symbiote 11y ago
Animats 11y ago
They're showing a really old tower in that video. Most of the system does not use mechanical lever interlocking machines. It's mostly General Railway Signal NX, which is entirely relay-based. NX, (for eNtry eXit), is probably the first system with an intelligent user interface. The dispatcher has a track map, with lights showing which blocks are occupied. To route a train through the controlled area, the dispatcher pushes a button on the track map at the current location of the train. Lights then come on for all the places the train can reach from there. This takes into account other trains present, other routes already set up, and track or switches locked out for maintenance. The dispatcher presses an exit button where the train is to go, which locks in the route. All the signals and switches are automatically set by that one button press, and conflicting changes and routes are locked out. As the train progresses through the control area, the switches and track behind it are released, and can be used for other trains. It's designed to be fail-safe. There are "train stop" devices at every signal. These raise a big metal lever at the right of the rails. On the lead truck of each subway car, there's a big metal lever connected directly to an air valve for the air brakes. If a train passes a red signal, the air valve trip lever hits the train stop, which slams on the brakes and cuts power. The signal system even checks the position of the train stop devices; there are always at least two train stop devices up and locked between two trains, and train stops can't clear until the next one is up and locked. It's a good system. The main problem is the sheer number of relays and the amount of wiring required. Train detection is by checking if the rails are shorted together by wheels. In keeping with the fail safe concept, the power for that check is fed into one end of the block, and it's sensed at the other end. Thus, a rail break or a power supply failure causes the system to sense a train and set signals red. On electric railroads, the rails are also the power return for traction power. (The London system, with two power rails, is an exception.) So the sensing signals have to be different from traction power. They're usually audio frequency signals, with a different frequency used for adjacent blocks. At block ends, there's a low-pass filter capable of handling a few thousand amps, basically a big inductor. One of those failed in DC, causing a crash. Washington, DC has a similar system, but on top of it, they have a computer-controlled system for dispatching. This is quite common - a dumb, reliable system based on trackside equipment for safety, and a computer-controlled system for scheduling and dispatching. All this stuff has to handle snow, ice, snowplows, flooding, the huge traction currents (600VDC in New York), and lightning strikes on the rails as part of normal operation. So everything is in hulking iron and steel cases and very rugged. There's a relay-level simulator for NX.[1] Runs on Windows. [1] http://www.nycsubway.org/wiki/NXSYS,_Signalling_and_Interlocking_Simulator http://www.nycsubway.org/wiki/NXSYS,_Signalling_and_Interloc...

A similarly embarrassing state of affairs is the train traffic control system used by the NYC subway system: https://www.youtube.com/watch?v=Mjx3S3UjmnA https://www.youtube.com/watch?v=Mjx3S3UjmnA

jholman 11y ago

Wow. Their end-goal upgrade, the one that they've installed on one line, and are installing on everything else looks so antiquated. My city's subway/elevated train system will be 30 years old this December. Train control is fully automated; there are no drivers on trains, and in normal operation there is no remote (human) operator either. It's been automated for 30 years. https://en.wikipedia.org/wiki/SkyTrain_(Vancouver) https://en.wikipedia.org/wiki/SkyTrain_(Vancouver) (Side note: during the BART strike, some HN commenters suggested computers to replace drivers, and other commenters said that wouldn't be safe. Such hilarious technophobia on HN.) I don't want to trivialize NYC's challenges and accomplishments: for one thing their system is far, far more complicated (468 stations on 34 lines, vs 47 stations on 3 lines), and for another we all know it's very hard to upgrade legacy systems. But I'm astonished that they would work so hard to modernize their 1930s technology to 1970s standards in the 2010s.

wil421 11y ago
Some less technology minded people would actually be freaked out by automated trains. The airport where I live has automated trains to go between gates and the cars very closely resemble the public trains cars without the seats. Most likely its not a technical challenge its a bureaucratic problem. Not to mention the unions aren't going to let the transit authority obsolete their jobs.
benihana 11y ago
Another thing about the NYC subway is that it runs 24 hours a day 365 days a year. Not many metros around the world can make that claim. Living in New York, the amazing thing about the subway system is how they keep it running. It's old and ridiculously complex, and despite what natives say, the MTA by and large does a good job running it. There's no political will to fix it right now. It's going to take trains becoming unsafe or costing so much to keep safe that people eventually notice and start making noise about it, I think.
- warfangle 11y ago
  Yep. They do a pretty darn good job, considering what they have to work with. And I'm not talking just the technology - they have 31 billion dollars of debt to service, and constantly get the shaft from Albany when it comes to funding. They continue to take on debt because they have mandated projects and lack the funding to complete them.
spacecowboy_lon 11y ago
You know that the 30's gear on the Tube was more reliable than the 1970's stuff?
bdonlan 11y ago
The problem with some of these old lines is that they might have level crossings in which pedestrians or cars might occupy the tracks - so someone needs to be there to stop the train if that happens. Fully automated systems like the SkyTrain or Japan's Yurikamome line have grade-separated tracks (and in some cases platform gates as well) to ensure that sort of incursion doesn't happen.
- warfangle 11y ago
  The NYC subway system has no level crossings where pedestrians can occupy the tracks. The only level crossing where another train might occupy the tracks is Queens-bound from the JMZ stop at Myrtle Ave & Broadway in Brooklyn. The M crosses at grade over the J/Z track.

jonawesomegreen 11y ago

That is fascinating, thanks for sharing. I had no idea the NYC subway was being run by a 100 year old electro-mechanical system.

hga 11y ago
The D.C. Metro system was planed in the '60 and constructed in the '70s, with the first operations starting in 1976. It too is based on electro-mechanical relays, although it's more ambitious, after the operator closes the doors and sees all is fine, he hits a "go" button and the system automatically takes the train to the next station, avoiding collisions as long as the "is there a train in the next segment" sensor system is working.
- JonathonW 11y ago
  The DC Metro actually (mostly) hasn't used their automatic train control system in full automatic mode since a collision in 2009 that killed nine (for which the ATC system was directly responsible; a faulty circuit both forced a train to stop and rendered it invisible to the control system). Safe train control seems like it needs a little more sophistication than '60s or '70s tech was able to give. For one, it's common sense that a train that disappears from the system isn't really gone-- but the Metro system couldn't take that into account. Stuff like that should be pretty trivial today.
  - AnthonyMouse 11y ago
    > For one, it's common sense that a train that disappears from the system isn't really gone-- but the Metro system couldn't take that into account. Stuff like that should be pretty trivial today. It was pretty trivial in the 1970s. Require the sensor for an adjacent segment to be engaged before the sensor for an active segment will disengage. You can't do any computation with modern computers that you couldn't have done with relays in the 1970s, or the 1870s for that matter. Mechanical relays are slower, less reliable and more expensive than transistors... but they do the same thing.
  - Symbiote 11y ago

Animats 11y ago

They're showing a really old tower in that video. Most of the system does not use mechanical lever interlocking machines. It's mostly General Railway Signal NX, which is entirely relay-based. NX, (for eNtry eXit), is probably the first system with an intelligent user interface. The dispatcher has a track map, with lights showing which blocks are occupied. To route a train through the controlled area, the dispatcher pushes a button on the track map at the current location of the train. Lights then come on for all the places the train can reach from there. This takes into account other trains present, other routes already set up, and track or switches locked out for maintenance. The dispatcher presses an exit button where the train is to go, which locks in the route. All the signals and switches are automatically set by that one button press, and conflicting changes and routes are locked out. As the train progresses through the control area, the switches and track behind it are released, and can be used for other trains. It's designed to be fail-safe. There are "train stop" devices at every signal. These raise a big metal lever at the right of the rails. On the lead truck of each subway car, there's a big metal lever connected directly to an air valve for the air brakes. If a train passes a red signal, the air valve trip lever hits the train stop, which slams on the brakes and cuts power. The signal system even checks the position of the train stop devices; there are always at least two train stop devices up and locked between two trains, and train stops can't clear until the next one is up and locked. It's a good system. The main problem is the sheer number of relays and the amount of wiring required. Train detection is by checking if the rails are shorted together by wheels. In keeping with the fail safe concept, the power for that check is fed into one end of the block, and it's sensed at the other end. Thus, a rail break or a power supply failure causes the system to sense a train and set signals red. On electric railroads, the rails are also the power return for traction power. (The London system, with two power rails, is an exception.) So the sensing signals have to be different from traction power. They're usually audio frequency signals, with a different frequency used for adjacent blocks. At block ends, there's a low-pass filter capable of handling a few thousand amps, basically a big inductor. One of those failed in DC, causing a crash. Washington, DC has a similar system, but on top of it, they have a computer-controlled system for dispatching. This is quite common - a dumb, reliable system based on trackside equipment for safety, and a computer-controlled system for scheduling and dispatching. All this stuff has to handle snow, ice, snowplows, flooding, the huge traction currents (600VDC in New York), and lightning strikes on the rails as part of normal operation. So everything is in hulking iron and steel cases and very rugged. There's a relay-level simulator for NX.[1] Runs on Windows. [1] http://www.nycsubway.org/wiki/NXSYS,_Signalling_and_Interlocking_Simulator http://www.nycsubway.org/wiki/NXSYS,_Signalling_and_Interloc...