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| Re: Wouldn't 67-foot cars make more sense? (1251809) | |||
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Re: Wouldn't 67-foot cars make more sense? |
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Posted by WillD on Fri Oct 4 18:15:06 2013, in response to Re: Wouldn't 67-foot cars make more sense?, posted by randyo on Fri Oct 4 17:26:08 2013. It depends on the method by which CBTC is being implemented. I believe NYCT's Trainguard MT system from Siemens as installed on the R188s uses an unbraked idler odometer on one or two axles of the train to provide more precise distance within a given track block specified by wayside beacons. Each train of a given length would need to have one axle dedicated to providing odometer data so a married pair would lose one eighth of its power and braking. Clearly it is preferable to increase the length of the fixed trainset so as to have the smallest ratio of unbraked axles to powered and brake equipped axles.Unbraked idler axles are also used by the Seltrac system. BBD's ICTS, like JFK's Airtrain is a notable local example. And somehow Seltrac is related to the Trainguard MT system being used by NYC. But Seltrac uses an inductive loop that is crossed below the train every few hundred feet to provide coarse positioning data that corrects for errors in the fine positioning data from the odometer axle. As I understand it the R143s were equipped with a system which imaged either the wheel tread or railhead to provide that same fine grain distance information without requiring an unbraked idler axle. But from what has been said here the system was not particularly successful. That's unfortunate as it could provide a viable means by which to provide CBTC to a train of an arbitrary length without worrying about train lengths. There are other CBTC systems which manage to operate without either arrangement (I think). SEPTA installed Bombardier's CityFlo 650 CBTC train management and control system on the Subway Surface lines as part of a settlement over the installation of cab signals on the Market Frankford line. It would be quite impossible to provide an odometer axle on a trolley car, so they must be using some other means to provide fine positioning data, but unfortunately I don't know what it is. Really at this point the Europeans are churning ETCS balises or beacons out by the thousands. The marginal cost of even tripling the number of beacons on a project is likely to be relatively small compared to the fixed costs associated with refitting the rolling stock and providing the processing capabilities in the wayside. It might end up being best to just go with a tremendous number of beacons establishing a virtual fixed block network with very small blocks as an alternative to CBTC. That way the on-car equipment need not convert analog measurements into digital data (as with an odometer axle), and yet we can still achieve much closer train spacing than is possible with (fairly expensive) fixed block signalling. |
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