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| Re: The Return Of ''Rapid'' Transit ? (1500008) | |||
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Re: The Return Of ''Rapid'' Transit ? |
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Posted by Stephen Bauman on Mon Jan 14 22:31:56 2019, in response to Re: The Return Of ''Rapid'' Transit ?, posted by Michael549 on Mon Jan 14 12:41:03 2019. The current signal system is a kind of analog computerIt's digital. One must separate the algorithms from how they are implemented. Current systems use track circuits to determine train location. The train locations determined by these track circuits are then processed by a distributed digital network to prevent collisions and many other possible functions. CBTC stands for Communications Based Train Control. The train has an independent means of knowing its position. The train then communicates its position to the control system. The control system responds by issuing a speed command to the train. That's the algorithmic difference between CBTC and existing block systems. There's no difference in service level capacity, between the two systems. Service level capacity is determined by the operating characteristics of the rolling stock: braking and acceleration rates. The control for CBTC tends to be implemented by computers because CBTC is newer. Block systems, being older, tend to be implemented by hard wired relay logic. However, there's nothing to prevent block system control to be implemented by computers nor CBTC control to be implemented by hard wired relay logic. One big problem for both computer and relay based systems is the availability of spare parts. The railroad industry uses a special type of relay which they call a vital relay. It's used only within the railroad industry. Vital relays are difficult to find because the railroad industry is too tiny to make it worth manufacturing them. There's an equally difficult problem in finding exact replacement parts for computers. The technology turnover is so rapid that products rarely last 3 years before something better replaces them. Finding an exact replacement on a scale required for NYCT after 5 or 10 years becomes nearly impossible. (The latest embedded computer is something called the Raspberry Pi 3. It came out within the last few months. Its manufacturers are promising to continue production until 2022.) There are strategies for managing technological innovation. Most companies, including the MTA, are not following them. |
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