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| Re: TA is obsessed with CBTC, and ''New'' tech for no reason. (578637) | |||
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Re: TA is obsessed with CBTC, and ''New'' tech for no reason. |
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Posted by trainsarefun on Fri Feb 29 22:43:03 2008, in response to Re: TA is obsessed with CBTC, and ''New'' tech for no reason., posted by Stephen Bauman on Fri Feb 29 22:21:23 2008. CBTC or any other signal system does not increase terminal or any other capacity. Capacity is determined by acceleration, braking rates and dwell time. None of which has anything to do with the signal system.Thanks for making this crystal clear; I didn't sufficiently qualify my statements, and I should instead express what I was actually supposing. If CBTC enabled trains to operate more to the limit of the characteristics you mention - acceleration, braking rates and dwell time; and a shorter time to traverse the interlocking doesn't hurt either - then it would permit those characteristics to be more useful. Suppose - and I can't say whether this is true or not - that under the former signal system as last employed that in order to prevent a collision with the wall at 8th Av, NYCT in fact set the timers to clear at a speed lower than necessary given the emergency braking characteristic. (Many timed signals in NYCT seem to clear at LESS than the posted speed, anyway, so that really wouldn't be too surprising). In that sense, the full capacity that the train's characteristics would entitle it to aren't being used. Suppose further that with CBTC, trains are allowed to approach the wall at 8th Av up to (and in fact at) the speed limit that would enable an emergency stop short of the wall. In other words, what if CBTC enables more of the characteristic entitlement to be claimed? Of course, I think the objection to this goes something like: but couldn't we have cascading timed signals at decreasing speeds? So first signal approaching interlocking is set at interlocking safe speed, next signal after interlocking 5 mph less than that, next signal 5 mph less than that, etc., until the final signal before the bumper block enforcing the slowest speed/stop. Now maybe CBTC does this better since it can apply the brakes without applying the emergency brakes, but I suppose that, in principle, this could be done with the former system too. But if my thought is wrong, and CBTC doesn't allow any more of what I've called the characteristic entitlement to be used toward terminal capacity, then you're right that, short of strange turnarounds at Union Square pulled off in a way that would be positively miraculous, the effective terminal capacity would remain the terminal capacity. |
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