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| Re: Canarsie CBTC (97406) | |||
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Re: Canarsie CBTC |
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Posted by Stephen Bauman on Sat Jun 11 07:28:18 2005, in response to Re: Canarsie CBTC, posted by Jeff H. on Sat Jun 11 01:27:16 2005. The more recent design philosophy of centralzing everything leads to a higher likelihood of catastrophic failure.One can design a centralized control system with great reliability and uptime. Tandem has been doing that for a quarter century. It is an expensive solution and there are now less expensive distributed alternatives. The philopsophy of distributed, localized control points tends to isolate the failures to specific places on the railroad. You are assuming that the railroad topology lends itself to isolating failures. This isn't very practical on the Canarsie Line during rush hour. Any single failure anywhere on the line is likely to propagate to its entire length. There are some pretty heavy failure modes in CBTC. What happens when a zone controller crashes, for example. Something akin to an AC power failure at 33rd St on the Lex. Much of the operating cost savings of CBTC amounts to transferring operating budget to capital budget, which, guess what, eventually comes back into the operating budget as debt service! A lot depends on how much the system costs. The recent contracts for retrofitting the Paris Metro are approximately 30% the cost of the Canarsie Line on a per track-mile basis. That places its cost at or below a conventional block system. Of course, there are many ways to reduce the cost of conventional block systems but we've gone down that path before. I'm sure TA CBTC will eventually work, but right now first base (being able to reliably measure train speed and position) is still 90 feet away. I thought the TA's problems were related to the RF-DCS, not to measuring position and speed. Did they require the vendor to get the speed reading off their mickey mouse speedometers instead of from the propulsion system tachometer? |
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