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| Re: W train returning when Phase I of the 2nd Av subway opens in December 2016?. (1386794) | |||
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Re: W train returning when Phase I of the 2nd Av subway opens in December 2016?. |
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Posted by Stephen Bauman on Wed Feb 24 16:04:47 2016, in response to Re: W train returning when Phase I of the 2nd Av subway opens in December 2016?., posted by randyo on Wed Feb 24 15:07:22 2016. I don't know exactly what this measures. It definitely does not measure the minimum headway.Here's how one should go about measuring the 3 components. N.B. these measurements are made on a clear track (green aspects showing). 1. braking time - the interval from when the front of a train enters the station and the doors open. 2. dwell time - the interval from when the doors open until the train starts moving to leave the station. 3. acceleration time - the interval from when the train starts leaving the station until first signal within the station changes from red to yellow. N.B. this signal usually has only red and yellow aspects. Let me explain this with the minimum number of signals (3) that control the train's passage through the station. There's a 3-aspect signal that is located just before the station entrance. Call this signal 1. There's a 2-aspect signal located somewhere on the station platform. This is signal 2. There's a 3-aspect signal located at the station exit. This is signal 3. Braking measurements are taken only when signal 2 shows a yellow aspect. This means signal 1 shows a green aspect. As the train enters the station signal 1 changes from green to red. As the train passes the insulated joint (IJ) associated with signal 2 it changes from yellow to red. When the entire train is within the station, the tripper for signal 1 will go up. Acceleration measurements are taken only when signal 3 shows a green aspect. As the train leaves the station, signal 3 changes from green to red. As the rear of the train passes the IJ associated with signal 2, its tripper goes up. The train completely leaves the station. Some time later the tripper on signal 3 goes up. Some time later signal 2 changes from red to yellow. This is the end of the acceleration time. The action of the signal 3's tripper going up, changes signal 1's aspect from red to yellow. The action of signal 2 changing from red to yellow, changes signal 1 from yellow to green. At this instant any following train will see a green aspect on entering the station and the cycle can repeat. Moreover, that following train will have seen nothing but green signals from leaving the previous station to its approach to signal 1. The nominal times for braking, acceleration and dwell times as defined above is roughly 30 seconds. |
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