Two Questions on the Green Lines

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Re: Two Questions on the Green Lines

Postby diburning » Fri Aug 09, 2013 9:53 pm

I'm talking about the outbound platform, not the inbound one.
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Re: Two Questions on the Green Lines

Postby Disney Guy » Sun Aug 11, 2013 8:07 am

I have noticed that on all rapid transit lines, the trains enter stations at a somewhat reduced speed compared with in decades past, presumably to provide additional although not perfect safety if someone should fall onto the track suddenly.

It is possible to come up with different standards for each station regarding where trains stop. This would take into account ergonomic factors such as where people congregate or should congregate. This would probably not work on the MBTA since some people will continue to stand or go where they think they can get on the train and perhaps find a seat more quickly.

The Green Line signal system is for the most part a standard three aspect color light system. A (single) yellow has the standard meaning of "proceed prepared to stop at next signal." Double yellow at the station entrance is wired more or less like a (single) red; the preceding signal shows yellow, not green. When a train leaves a station leaving the station vacant, the double yellow at the station entrance changes to single yellow.

When a signal shows red (and the preceding signal is yellow if no train is in the block approaching the red) the rear of a train may be just a few feet past the red signal. If automatic trips to activate the brakes on trains in the event of red light running were installed in the Green Line subway, they would not act fast enough to prevent a collision. There exist variations of 3 aspect signal systems where a red aspect does not change (to yellow) unless not only the block ahead is clear but all or a significant portion of the next block protected by the next, red, signal is also vacant. Due to tne necessity of spacing trains closely on the Green Line between Kenmore and North Station, such variations would not be practical.

Portions of the Green Line (I think Science Park to Lechmere is one portion) use "two aspect color light signaling," also a traditional railroad signalling standard except that here the signal indications are yellow for proceed (and red for stop). Two aspect systems using green and red must use some means, such as a variation described in the preceding paragraph, to ensure that the engineer (or motorman) upon seeing a red indication can stop the train before colliding with a train up ahead.
(To the theater stage manager) Quit twiddling the knob and flickering the lights while the audience is entering and being seated. (To the subway motorman) Quit twiddling the knob and dinging the doors while passengers are getting off and others are waiting to board.
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Re: Two Questions on the Green Lines

Postby Gerry6309 » Mon Aug 12, 2013 2:58 pm

BostonUrbEx wrote:
Usually, GC terminating trains will only pull up to the escalator, so everyone can filter out easily. Trains going to North Station or Lechmere pull all the way to the end.

At Government, most eastbound trains pull all the way down, regardless of their destination. The Eastbound Platform, though longer than back in 1963, is still shorter than the Westbound. On the westbound side, there used to be two stopping places, the further one for C & D trains and 1/2 (PCC) car length back for the B. (E trains never visited there in those days) In more recent times Bs and Es sometimes stop one spot further back as people still expect it that way.
Gerry. STM/BSRA

The next stop is Washington. Change for Forest Hills Trains on the Winter St. Platform, and Everett Trains on the Summer St. Platform. This is an Ashmont train, change for Braintree at Columbia.
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