Re: Latest updates: R-179 order saga, R-160 CBTC for (L) line & special reports ... (1135306) | |||
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Re: Latest updates: R-179 order saga, R-160 CBTC for (L) line & special reports ... |
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Posted by J trainloco on Fri Jan 27 19:01:09 2012, in response to Re: Latest updates: R-179 order saga, R-160 CBTC for (L) line & special reports ..., posted by Stephen Bauman on Fri Jan 27 16:28:55 2012. No, it's a moving block system. A fixed block system to guarantee 700 foot spacing between trains would have had 700 foot blocks across the bridge.No, it's a fixed block system. It doesn't matter if there were 20 blocks behind the train. Each signal block is in a fixed location. That location doesn't move. The amount of signals set to DANGER behind defined an area that trains could not enter. As a train vacated a block 6 blocks away, the first one would clear. The advantage here is that unlike the 700' long block you mentioned, where the tail of that train could be anywhere within that 700', we can now pinpoint that train to a 100' distance. Whatever the CBTC system used, the blocks are not fixed in nature. Even if it's using integer block lengths, and those blocks are defined by the locations of the beacons, the area that a train cannot enter is not fixed. Where as a signal aspect will always be encountered at 135+50, along some line, on a CBTC line, the point a train cannot enter moves, based upon the location of the train. There are no fixed locations that will stop a train. A preceding train is allowed to get to a certain distance from its leader, based upon a certain allowance for the system's deficiencies. CBTC is also more sophisticated than fixed blocks, because it allows trains to have their speed governed based on distance to the leader, which fixed block systems can only do but so well (and that adds cost to the fixed block installations). Don't knock the New York And Brooklyn Bridge Railway. The cars were 10 feet wide. The trains were longer than those on the El's on the Brooklyn and Manhattan sides. They also averaged 90 second headways over a continuous 24 hours with 80+ tph peak service after 1893. The cable was not only a partial ATO propulsion system but also ultimate moving block system for traffic control. As we used to say when I worked on the Apollo program, "if it works it's not sophisticated." Not knocking it, but how does such a system provide signal protection for stopped trains that have released the cable? The CBTC equipment must be capable of handling maximum demand at all locations. Whether this is cost effective depends on the percentage of track is in or near stations and the CBTC equipment cost. An installation like the 14th Street Line should have favoured CBTC costwise because its large number of stations and short route length. That has not been the case. Has more to do with the chosen implementation than the system. The way to handle long distance freight lines is to use GPS for determining the train's position. Yes, I agree! And what if PTC were implemented through those same GPS satellites? It would be a train system with no fixed blocks, and where train control was through a wireless communications system... |
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