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| Re: Latest updates: R-179 order saga, R-160 CBTC for (L) line & special reports ... (1135096) | |||
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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 Thu Jan 26 18:03:30 2012, in response to Re: Latest updates: R-179 order saga, R-160 CBTC for (L) line & special reports ..., posted by Stephen Bauman on Thu Jan 26 14:46:07 2012. There were two moving block systems in operation in NYC more than a century ago. Both were on the Brooklyn Bridge at different times.After 1908,fixed length blocks of 100 feet each were built. So in the first paragraph, you say that it was a fixed block system! I understand what you're getting at, but at the end of the day, even though it was an extremely robust fixed block system, it was just that: fixed blocks. Additionally, examining this system shows why CBTC becomes appealing: you can get signal protection as robust as the system you described for a fraction of the cost. But more on that later. The predecessor cable provided even better performance. It kept trains a fixed distance between one another regardless of their position on the bridge. The precision and accuracy of that train control system has not been equalled by newer technologies. It even provided rudimentary ATO. All without electricity. Pardon my ignorance, but what system is this you're speaking of? A cable car? You left out one important detail. Block length is determined by both desired headway (which you mentioned) and also by the expected distance between trains where the block is. When trains are operating at 30 mph at 40 tph,the expected distance between trains is approximately 4000 feet... Block system designers have the luxury of placing shorter length blocks only where they will be needed. They can use longer length blocks where they are not needed. That's the exact issue that makes CBTC attractive. You don't need to increase the amount of equipment to facilitate shorter blocks as you get closer to the areas where you will need shorter blocks. The benefit is even greater on some commuter or freight roads where the existing signalling might only allow for a much lower frequency, and transponders don't have to be placed so frequently. I honestly don't know how far CBTC technology is, or can be pushed, but you could really save a lot of money if you can get away with limiting the number of transponders on above surface RRs. |
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