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I mean things like: beyond city scale, you can't assume all the technology has been tested together, you can't assume you actually know where other trains are,

by o11c 1y ago

I mean things like: beyond city scale, you can't assume all the technology has been tested together, you can't assume you actually know where other trains are, etc.

IAmBroom 1y ago
I work in rail. In any automated system, you don't assume anything; you either know it absolutely (fail-safe systems), or you revert to pure manual control at line-of-sight of the operator, which is far slower. And yes, all the technology has been tested together. Before a train can enter a new region of authority, it must have permission from that authority, which means they must prove that the train can work with the local tech.
TylerE 1y ago
You can't assume those things in a subway, either. GPS doesn't work underground.
- LeafItAlone 1y ago
  The trains ride on a track. The tracks have sensors. The sensor positions are known. Now you know where all of the trains are. GPS satellites could drop out of the sky and you’d still know where the trains are.
  - TylerE 1y ago
    Yes, and those "sensors" have very limited precision. There's only one every several hundred yards.
    - kkysen 1y ago
      The latest tech for CBTC uses UWB for train positioning, which has a precision of a few inches.
      - rexpress 1y ago
        New York did some trials with UWB several years ago, which were claimed to have been successful. Since then, there has been very little news of permanent deployment or future developments either in New York or elsewhere. Not sure whether this means that the various signalling suppliers are waiting for a customer to take on the technical risk of being the first to deploy UWB CBTC, or that there were costs or disadvantages that make it unattractive.
    - LeafItAlone 1y ago
      >Yes, and those "sensors" have very limited precision. There's only one every several hundred yards. What? There’s one as far apart as you put them. The precision is what you make it.
      - TylerE 1y ago
        And every sensor you add is additional cost, not just upfront, but maintenance for ever.
        LeafItAlone 1y ago
        And not having sensors results in not knowing where the trains might be on your track _forever_. I’m not entirely sure what you are trying to argue. Your original comment said you can’t know where trains are on underground subways because GPS doesn’t work underground, but that’s not the technology they use anyways, so it doesn’t make sense to reference it. The you seemed to argue that what might currently be in place is insufficient, but that wasn’t what this thread was talking about.
        TylerE 1y ago
        You keep putting words in my mouth. I am just pointing out the usual HN tech dork ignorance of how real world mechanical systems actually operate. It's like any time an aviation thread is around here, the rank ignorance is incredibly painful.
        LeafItAlone 1y ago
        I haven’t put any words in your mouth, just summarized what I read. The only one showing ignorance here seems to be you suggesting subways use GPS.

by o11c 1y ago

I mean things like: beyond city scale, you can't assume all the technology has been tested together, you can't assume you actually know where other trains are, etc.

IAmBroom 1y ago

I work in rail. In any automated system, you don't assume anything; you either know it absolutely (fail-safe systems), or you revert to pure manual control at line-of-sight of the operator, which is far slower. And yes, all the technology has been tested together. Before a train can enter a new region of authority, it must have permission from that authority, which means they must prove that the train can work with the local tech.

TylerE 1y ago

You can't assume those things in a subway, either. GPS doesn't work underground.

LeafItAlone 1y ago
The trains ride on a track. The tracks have sensors. The sensor positions are known. Now you know where all of the trains are. GPS satellites could drop out of the sky and you’d still know where the trains are.
- TylerE 1y ago
  Yes, and those "sensors" have very limited precision. There's only one every several hundred yards.
  - kkysen 1y ago
    The latest tech for CBTC uses UWB for train positioning, which has a precision of a few inches.
    - rexpress 1y ago
      New York did some trials with UWB several years ago, which were claimed to have been successful. Since then, there has been very little news of permanent deployment or future developments either in New York or elsewhere. Not sure whether this means that the various signalling suppliers are waiting for a customer to take on the technical risk of being the first to deploy UWB CBTC, or that there were costs or disadvantages that make it unattractive.
  - LeafItAlone 1y ago
    >Yes, and those "sensors" have very limited precision. There's only one every several hundred yards. What? There’s one as far apart as you put them. The precision is what you make it.
    - TylerE 1y ago
      And every sensor you add is additional cost, not just upfront, but maintenance for ever.
      - LeafItAlone 1y ago
        And not having sensors results in not knowing where the trains might be on your track _forever_. I’m not entirely sure what you are trying to argue. Your original comment said you can’t know where trains are on underground subways because GPS doesn’t work underground, but that’s not the technology they use anyways, so it doesn’t make sense to reference it. The you seemed to argue that what might currently be in place is insufficient, but that wasn’t what this thread was talking about.
        TylerE 1y ago
        You keep putting words in my mouth. I am just pointing out the usual HN tech dork ignorance of how real world mechanical systems actually operate. It's like any time an aviation thread is around here, the rank ignorance is incredibly painful.
        LeafItAlone 1y ago
        I haven’t put any words in your mouth, just summarized what I read. The only one showing ignorance here seems to be you suggesting subways use GPS.