Extrending Park Street Platforms

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Extrending Park Street Platforms

Postby cloudship » Tue Aug 02, 2016 7:18 pm

Most of the stations along the Green Line have only 2 platforms. Park Street, however, has 4. It seems to me that one of the bottlenecks seems to be that section between Park and Government Center, in particular waiting for switches to activate to direct trains to the proper platform. If they extended the platforms south towards Boylston st, and had the trains just use one track on each side, would that cut down on some of the delays?
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Re: Extrending Park Street Platforms

Postby Disney Guy » Tue Aug 02, 2016 9:50 pm

Waiting for switches to throw is not the problem.

The delays are due to congestion further on.

It is not unusual for trains to be held up just after loading and leaving Park St. (in both directions).
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Re: Extrending Park Street Platforms

Postby The EGE » Tue Aug 02, 2016 10:36 pm

Being able to pass at Park is a feature, not a bug. It is the only location on the Green Line where one train can pass another, which makes it immensely valuable for headway control. That will only increase in the future as more advanced control schemes are possible.

It is also valuable to be able to berth four trains simultaneously, both during disruptions, and also for the last-train guaranteed connections.
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Re: Extrending Park Street Platforms

Postby cloudship » Wed Aug 03, 2016 8:11 am

Where is/are the bottlenecks on the green line then?
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Re: Extrending Park Street Platforms

Postby The EGE » Wed Aug 03, 2016 10:15 am

Speed restrictions, grade crossings without transit priority, poor terminal dispatching, and highly variable dwell times (due to front door only boarding, cash and ticket payment, narrow platforms, and a very slow method of boarding passengers with wheelchairs) cause massive bunching on the branch lines. The Central Subway can't work well without reliable branch lines feeding it. Garbage in, garbage out. The new fare system (arriving 2019) will allow all-door boarding and tap-only at all times, which will help. But a substantial investment - combined with political will that simply isn't there - is needed to improve maintenance standards, modernize platforms, and add real signal priority to intersections.

There is no single bottleneck in the Central Subway, other than that 40 trains per hour per direction is approximately the limit for human-driven light rail. Some modifications - allowing through moves from the eastbound fence track at Park, making the North Station turnback less inefficient, computer-controlled priority at Copley Junction - would reduce delays and make operations smoother. While full PTC would likely reduce TPH slightly through the subway (though better branch operations, and possibly converting the D to all triples at rush hour, would wholly mitigate that), some better signalling and control may also help.

Oh, and having enough fleet to actually run service. The Green Line currently has 164 cars active, of which about 152 are available for service on any given day. 146 are needed just to run the schedule, never mind substantial delays: if there's any kind of slowdown, they outright run out of cars.
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Re: Extrending Park Street Platforms

Postby CRail » Sat Aug 06, 2016 1:37 pm

cloudship wrote:Where is/are the bottlenecks on the green line then?

Boylston. Going from 2 tracks to 1 from Park to Boylston combined with westbound trains having to wait until the entire platform is clear before getting the signal to enter (this was implemented after the November 2012 collision between two trains on that platform) and of course the 6mph curve following the station. If anything, Park Street having 4 tracks mitigates delays to its east by allowing backed up trains into the station simultaneously so that people aren't waiting in a tunnel to make their transfers.
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