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| Re: Old LIRR Rockaway Beach Branch (1252647) | |||
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Re: Old LIRR Rockaway Beach Branch |
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Posted by Stephen Bauman on Wed Oct 9 18:09:00 2013, in response to Re: Old LIRR Rockaway Beach Branch, posted by Joe V on Wed Oct 9 13:16:45 2013. You are forgetting key-by went away.Not at all. Key-by is not necessary to achieve the capacities shown on the TA document. You can verify that for yourself. The block after a station is 600 ft long. You want the leader to pass this block before the follower enters the station. The 600 ft leader must travel 1200 ft to fulfill the first condition. It will take 12 seconds for the leader to accelerate to 30 mph at an acceleration of 2.5 mph/sec. The leader will have travelled 264 ft during the acceleration. The leader still needs to travel 936 ft at 30 mph. This will take an additional 21 seconds. This brings total time to 33 seconds. At this instant the follower is about to enter the station. The follower will see: a green aspect outside the station; a yellow aspect within the station and a red aspect at the station exit. The follower is travelling at 30 mph. The follower's service brakes decelerate at 2.5 mph/sec. The follower will apply the service brakes 264 feet from the station's end taking 12 seconds to do it. Prior to this the follower will have continued into the station at 30 mph for a distance of 336 ft. It will have taken the follower 8 seconds to travel this distance. The follower will have taken 20 seconds to enter the station and come to a complete stop. This allows 37 seconds of dwell time for the follower to maintain 90 second headways. The follower and his follower will never encounter anything but green aspects. You may also verify these leader's exit time and the follower's entry time with a stop watch. For the leader it's the time he starts moving to the time the tripper at the station exit goes up. Alternatively you may measure the time form when the leader starts moving to the time the signal at the station entrance turns green. For the follower's time you should measure the time from when the follower enters the station until he stops. You are going to have to take several measurements because there is great variablity among T/O's. If you are not mathematically challenged, you may see the effect increasing the acceleration and service braking rates to 4.0 mph/sec (like the Multi's, Bluebirds and PCC trolleys.) |
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