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Old February 1st, 2013, 11:48 AM   #1
1772
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MISC | 4 tracks (2 in each direction) in subways?

One thing I never got with subways is why there is almost always only one track in each direction.
Since they are used so intensely, they sometimes break down and stop up straffic.
Why not have a second track so broken down wagons can be placed there and let the other subway cars continue, uninterupted?
And then it's more space in case of an accident.
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Old February 1st, 2013, 12:48 PM   #2
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Huge costs.
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Old February 1st, 2013, 02:40 PM   #3
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Exactly, it would be a huge cost for systems that generally are already begging for every penny they can get.

However, there are some systems (New York comes to mind) that have what you are talking about, but they are used for express routes generally rather than spare tracks.
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Old February 1st, 2013, 03:05 PM   #4
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The two main reasons for implementing four track subways in NYC were:
  • Separating local and express services
  • Doubling the capacity of trunk routes

There was ample space below the wide avenues of Manhattan which is why quadrupling tracks was economically viable. At least - until somewhere around 1940. After that time, labour and building costs got increasingly - and eventually prohibitively - expensive and digging a trench in the middle of a busy avenue met with increasing resistance of shop keepers and people living or working in the neighbourhood.

This is why the current SAS is only built as a two-track line using deep-bore tunneling.

The possibility of shifting services between local and express tracks in case of emergencies or track work is an added benefit.
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Old February 1st, 2013, 04:48 PM   #5
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There are a few bits of four-tracking on the London Underground as well though they are defined as separate services:

Between Wembley Park and Baker Street the Jubilee line serves all eight intermediate stations whereas the Metropolitan Line is an express, stopping only at Finchley Road.

Between Acton Town and Earls Court the District Line serves all seven intermediate stations whereas the Piccadilly line only serves two (three in rush hour I think).

I'm not sure to what extent they can exchange rolling stock, but I'd say it's impossible on underground sections due to the larger size of the Met and District trains though these sections of line are mostly above ground. Such arrangements are certainly useful!
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Old February 1st, 2013, 07:32 PM   #6
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Quote:
Originally Posted by CairnsTony View Post
Between Wembley Park and Baker Street the Jubilee line serves all eight intermediate stations whereas the Metropolitan Line is an express, stopping only at Finchley Road.
A quadruple Underground route actually just exist between Finchley Road to Wembley. And then further on to Harrow-on-the-Hill where various lines of the Metropolitan Line runs on four tracks.
Between Baker Street and Finchley Road, however, the lines run in two completely different tunnels.
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Old February 1st, 2013, 11:59 PM   #7
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Quote:
Originally Posted by 1772 View Post
Why not have a second track so broken down wagons can be placed there and let the other subway cars continue, uninterupted?
And then it's more space in case of an accident.
In well-maintained systems, breakdowns and accidents are simply extremely rare. Good train maintenance is probably much cheaper than building redundant tracks.

A redundant signalling system could be useful in some cases, however.

Last edited by micro; February 2nd, 2013 at 12:07 AM.
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Old February 2nd, 2013, 06:25 AM   #8
Winged Robot
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For many of the reasons already listed, most places do fine with a single track in each direction. A (roughly) parallel line can always be built later on to increase service if need be.
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Old February 3rd, 2013, 06:09 PM   #9
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In Melbourne, Australia, there are four tracks: but they all carry uni directional traffic: one track for the north & western suburbs, one for the north east, one for the east, and one for the south-east. Traditionally, these circuits run around the city CBD, & reverse in direction just after noon.
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Old February 4th, 2013, 10:25 PM   #10
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Quote:
Originally Posted by flierfy View Post
A quadruple Underground route actually just exist between Finchley Road to Wembley. And then further on to Harrow-on-the-Hill where various lines of the Metropolitan Line runs on four tracks.
Between Baker Street and Finchley Road, however, the lines run in two completely different tunnels.
Indeed, but like New York that is for fast/slow services. Besides lines like the Metro in London are not what most would consider to be true metro lines. The metro in particular is a suburban railway run by a company that also runs true metro, so metro in name but not in nature.

Guess the bottom line is most metro systems have trains that stop at every station and generally have only one destination in each direction, so have no need for the added expense of additional 'over taking tacks'.
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Old February 7th, 2013, 07:14 AM   #11
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Quote:
Originally Posted by 1772 View Post
One thing I never got with subways is why there is almost always only one track in each direction.
Since they are used so intensely, they sometimes break down and stop up straffic.
Why not have a second track so broken down wagons can be placed there and let the other subway cars continue, uninterupted?
And then it's more space in case of an accident.
In the event of a disabled train, or if they simply need to store a reserve trainset somewhere along the route, most systems do employ pocket tracks or centre sidings which is essentially a third set of tracks that can be accessed from either direction.

If the idea of quad tracking is cost-prohibitive, you could create a 3-track system as is the case along some subway lines in NYC where the third track is used as express service in the peak direction. Of course retrofitting an underground line would still be costly. Surface routes, aside from modifying the stations, could be more manageable.
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Old February 7th, 2013, 05:47 PM   #12
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Parts of Hong Kong's Tung Chung Line and Airport Express run on parallel tracks - 2 in each direction, so an express train doesn't get held up by the slower city train.
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Old February 8th, 2013, 10:47 AM   #13
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Quote:
Originally Posted by hkskyline View Post
Parts of Hong Kong's Tung Chung Line and Airport Express run on parallel tracks - 2 in each direction, so an express train doesn't get held up by the slower city train.
It is hardly a subway operation though is it? Which is what the thread is about. If you want to include non subway operations then you will find 2, 4 6 + tracks in almost any major system.
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