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Four-track subways, like the ones in New
York, allow both express and local service
to run side-by-side, increasing capacity
and speed, but the locations of express
stops are fixed. Stations which are not
served by express trains simply have no
platforms adjacent to the express tracks,
so
express trains cannot stop at them. It is
difficult or impossible to refrofit express
platforms to an existing station where
express service is now justified, e.g.
because of new development. An example
of this is 14th Street-6th Avenue station
on the New York Subway - on the 6th
Avenue Line, it has no express platforms,
but all other north-south stations on 14th
Street in Manhattan are served by express
service. Express service is never run on the
local tracks, since it is dangerous for
trains to run at high speed beside an
occupied platform. Another problem
occurs at night, when only local service is
usually run - during track maintenance on
the local tracks, it is sometimes necessary
to run trains non-stop on the express
tracks.
The solution to this problem is to
construct a central platform between the
local and the express tracks at every
station, and to install platform screen
doors throughout. These doors only open
when a train is stopped at a station, and
are closed at all other times. They protect
passengers from moving trains, whether
they are stopping at a station or not,
prevent passengers from touching the
third rail, and allow subway stations to be
heated and air conditioned. As a result,
express trains can dynamically change
their stopping patterns based on time of
day, and new express service can be
added at stations which previously only
had local service. Furthermore, either track
in one direction can be used for local
service while track maintenance is
performed on the other track (at night, on
weekends, etc.) allowing 24-hour service.
Baked
http://en.wikipedia...atform_screen_doors [jhomrighaus, May 29 2007]
slightly over baked
http://www.railway-...ghouse_brakes3.html [jhomrighaus, May 29 2007]
Way Overbaked
http://www.platform...s.com/psd/services/ [jhomrighaus, May 29 2007]
Burned
http://www.cnim.com...nsport_palieres.htm [jhomrighaus, May 29 2007]
[link]
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I remember 8-track subways. The music never stopped (+). |
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Haven't we got these platform doors on certain London Underground lines? The train stops fairly precisely (!) so that the platform doors line up with the train doors. |
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//it is sometimes necessary to run trains non-stop on the express tracks.// Isn't that the definition of "express" ? |
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Bun, for normzone's comment. |
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I'm pretty sure this is baked both with and without the doors. |
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