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| Re: R211a sets (1633697) | |||
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Re: R211a sets |
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Posted by Stephen Bauman on Fri Jul 5 08:34:52 2024, in response to Re: R211a sets, posted by randyo on Fri Jul 5 00:46:52 2024. The way it was presented was that CBTC IS supposed to increase capacity...There were numerous discussions on SubTalk, when CBTC was proposed and being installed on the "Canary Sea" line. (There had been a translation from a Japanese technical article that translated Canarsie to "Canary Sea.") For the record: service level capacity is determined by: rolling stock operating characteristics (length, acceleration, service braking and emergency braking); station dwell time; and reaction time (the interval between when a dangerous situation exists to when emergency brakes are applied). The reaction time component includes the signal system. This is the smallest component of minimum headway. The reaction times for conventional block systems (basically the uncertainty due to block lengths) and CBTC (permitted communication delay before emergency brakes are applied ~ design is 2 seconds) are about the same. There is also an optimum operating speed to minimize headway, based on emergency braking rate and train length. If I remember correctly, it's about 30 mph for NYCT's 600 ft trains and 3.0 mph/sec emergency braking rate. The idea that CBTC would permit faster operation is also a myth. it was a waste of money to go to the expense of installing such a system It is a much bigger waste, when NYCT's retrofit per track-mile cost is compared to that of London and Paris. an upgraded version of the existing signal system would have sufficed. That depends on NYCT's definition of upgraded. Railway signaling had the misfortune of coming before digital circuit theory and design was understood. The railroad industry never upgraded their standards to make use of the technical and analytical advances in the second half of the 20th century. The FRA has cast the early 20th century digital circuit design techniques in stone. Railroad signaling may be the only application left for digital circuitry implemented with relays. It certainly is the only application for vital relays. The result is that signal system replacement is prohibitively expensive, if existing designs are followed. Digital circuitry is used in factories. Factory floor digital circuitry is implemented by special purpose computers called Programmable Logic Controllers (PLC). Their programming language is the ladder logic diagrams for the relay circuits they replace. PLC's are rugged, reliable, commodities and inexpensive. They require no (or minimal) programming because they use the existing circuit diagrams for the relay networks. Because they can be a 1-to-1 replacement for a relay network, they could be replaced piecemeal - as needed. At one of Andy Byford's early public meetings to sell CBTC, I asked him, "how much CBTC would increase existing service level capacity". He dodged the question. |
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