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Old May 3rd, 2008, 12:32 PM   #2501
lasdun
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I think by arches you mean the cable crossovers - the signalling and other cables run on racks down the side of the track, free standing or attached to tunnel or cutting wall. Where they need to cross over to the other side to allow for a junction, station etc then you get these arches over the line.

There is an explanation of the four rail system here: http://en.wikipedia.org/wiki/Railway...em#Fourth_rail

It's used to earth the current to prevent damage to the tunnel lining and nearby conductive water mains and gas pipes.

LIRR Jamaica and Stratford are similar in purpose as suburban hubs where rail, metro and light rail meet, but that's about it so far as I can tell.
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Old May 3rd, 2008, 12:43 PM   #2502
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i know but look at the differences of LIRR jamacia station and Stratford Regional.



this is the LIRR Jamacia station it does serves the LIRR lines while the subway is on the street not within the station note though it was recently renovated in recent years



and this is London's Stratford regional station to me it seems similar the difference could be the london underground and the overhead wires and also there is a lower level of railways as well.

because the london underground central serves this station by the upper level and the lower level is the Jubliee line, also this station was also renovated in recent years and its going thru more rennovations.
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Old May 4th, 2008, 11:10 AM   #2503
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wow where is everybody?
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Old May 4th, 2008, 12:53 PM   #2504
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According to what I have read about Jamaica Station is that it was renovated after the new Stratford Regional station was built. The building was constructed to cover the Jubilee and NLL services when the NLL station which is closer to Stratford High Road was closed (this is going to be reopened and used as passrt of the Stratford International DLR services), whilst the older part on the higher is currently undergoing refurbishment and extension.

This weekend is a public holiday in the UK so people may not be around.
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Old May 5th, 2008, 08:06 AM   #2505
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oh right how stupid of me and also tubeman is in vietnam as well.
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Old May 5th, 2008, 08:54 PM   #2506
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Quote:
Originally Posted by lasdun View Post
the four rail system here: [/url]

It's used to earth the current to prevent damage to the tunnel lining and nearby conductive water mains and gas pipes.
Neat, while all along I`d read in a book (or more) that the central live rail was set at a minor voltage for train accessories while the outside major one was just for its traction....
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Old May 6th, 2008, 12:44 AM   #2507
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yeah but still odd why most metro systems don't use 4 rail systems and why only london uses this? is it the advancements of the technology?
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Old May 6th, 2008, 05:11 PM   #2508
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London had bored tubes made out of metal, with electric traction before 1900. There was nothing else like it at the time.

Originally LU had several different electrification systems and eventually went for 4-rail, mostly due to Yerkes going with that. IIRC 4th rail was actually the CSLR's traction system, and thus the oldest electric one.

It's a by product of history and politics (the CLR was originally electrified differently, but changed not long afterwards).

It's not only an return route for current, but also, due to the split voltage (+420V and -210V) a way of making the potential difference between the tunnel's edge and the rails less, reducing current leakage which still providing enough voltage to get the trains moving.
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Old May 6th, 2008, 05:41 PM   #2509
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Quote:
Originally Posted by sotonsi View Post
London had bored tubes made out of metal, with electric traction before 1900. There was nothing else like it at the time.
The Moscow Metro has deep level metal lined tunnels, and they use a bottom contact third rail system...

I think the Washington Metro also uses metal lined tunnels, and i'm pretty sure they don't use four rail electrification.
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Old May 6th, 2008, 07:56 PM   #2510
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Quote:
Originally Posted by Songoten2554 View Post
why only london uses this? is it the advancements of the technology?
Me, I reckon their network must`ve become too large to retrofit all its tracks . . .



Quote:
Originally Posted by sotonsi View Post
It's not only an return route for current, but also, due to the split voltage (+420V and -210V) a way of making the potential difference between the tunnel's edge and the rails less, reducing current leakage which still providing enough voltage to get the trains moving.
Interesting -- thanks.
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Old May 7th, 2008, 01:34 AM   #2511
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Quote:
Originally Posted by sotonsi View Post
London had bored tubes made out of metal, with electric traction before 1900. There was nothing else like it at the time.
Quote:
Originally Posted by iampuking View Post
The Moscow Metro has deep level metal lined tunnels, and they use a bottom contact third rail system...

I think the Washington Metro also uses metal lined tunnels, and i'm pretty sure they don't use four rail electrification.
Clear enough for you?

It's a matter of the age of the tunnels - over 100 years ago, the best system was, it seems, 4 rail, whereas later, when Moscow made its Metro, and even later when Washington made its, technology had advanced enough that 4 rail wasn't the best system and so these Metros don't use 4 rail.
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Old May 7th, 2008, 01:41 AM   #2512
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Quote:
Originally Posted by sotonsi View Post
Clear enough for you?

It's a matter of the age of the tunnels - over 100 years ago, the best system was, it seems, 4 rail, whereas later, when Moscow made its Metro, and even later when Washington made its, technology had advanced enough that 4 rail wasn't the best system and so these Metros don't use 4 rail.
By saying "London had bored tubes made out of metal" specifically, you imply that it has nothing to do with age but the tunnel construction.

Anyway, what "technology advancements" were there between the first tube tunnels in 1890 and the construction of the Moscow Metro in 1935?
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Old May 7th, 2008, 03:06 PM   #2513
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Quote:
Originally Posted by iampuking View Post
By saying "London had bored tubes made out of metal" specifically, you imply that it has nothing to do with age but the tunnel construction.
That's a bit unfair, the sentence did go on after that...
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Old May 7th, 2008, 03:48 PM   #2514
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I think it's a bit unfair that he is trying to make out my question was stupid!
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Old May 7th, 2008, 10:51 PM   #2515
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Quote:
Originally Posted by elfabyanos View Post
That's a bit unfair, the sentence did go on after that...
yes, he ignored that section before, so I emboldened it, and he ignored it again in the sentence that you are commenting on, but then dealt with the it in the sentence afterwards, making himself look rather stupid all by himself.
Quote:
Originally Posted by iampuking View Post
Anyway, what "technology advancements" were there between the first tube tunnels in 1890 and the construction of the Moscow Metro in 1935?
mostly on the electric front, as well as size of bore - a bigger bore could have bigger insulators between tunnel and track, as well as the possibility of things like bottom contact - on the early tubes, any electric collection system that was bigger than the wheels, or in a different place to the wheels cost vital headroom space. A shoe touching a rail underneath the train allowed for small size in an existing place.

Electric technology was relatively new 100 years ago, especially for trains (the CSLR was one of the first electric railways). There was lots of room for the technology relating to conductors and insulators to develop more so in the intervening 30+ years - just as it has in the last 30 - I don't know the specifics in this case, but it surely doesn't require a great intellect to work out.
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Old May 8th, 2008, 12:40 AM   #2516
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Quote:
Originally Posted by sotonsi View Post
yes, he ignored that section before, so I emboldened it, and he ignored it again in the sentence that you are commenting on, but then dealt with the it in the sentence afterwards, making himself look rather stupid all by himself.
I still see it as a failure on your part, you should've said in your original post that subsequent technological advancements in electrical insulation meant that a deep level metal lined tunnel could run with three rails. Your original post implied that it had nothing to do with the age of the tunnel, but with the construction material, which is the same as in the Moscow Metro. Anyway, I don't see what difference the age the tunnel was built makes, LU still uses a four rail system today, if you think it has never changed because of the narrowness of the tunnels (which is hard to tell since your post is so badly written and unclear) then using the C&SLR as an example is stupid, as it had it's tunnels widened in the twenties.
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Old May 8th, 2008, 11:53 AM   #2517
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On this subject of electrification, I recently went to the Covent Garden Transport Museum and was mystified by one of the exhibits. It was a glass floor with a representation of the four rails of the tube lines, which lit up if you stood on a rail that was electrified. All four rails apparently could electrocute people who were to come in contact with them.

That seemed strange to me. The outer rail I understand is the high voltage conductor, the centre rail the return conductor and the two running rails I would have thought would have been at the same potential as the train so that anyone coming in contact with the metalwork of the train could therefore become electrocuted. Perhaps the intention of the exhibit was to warn people against trespassing on the railway.

In a third rail system, such as is used in the London area and on Merseyrail, the conductor rail is at 750v and the running rails, which are the return conductors, are ostensibly at earth potential. However, as there is not a clear path to earth from the running rails, leakage can occur through metallic objects such as the cast-iron lining of a tunnel, or signalling equipment, which can promote corrosion or signalling problems. The idea of the fourth rail is that it will act as a return conductor by being at a potential significantly below local earth potential so that it is the natural path for the return current.

Have to say though that before I knew much about how these trains operated, the four rails on the London Underground always fascinated me. I used to wonder which rails the trains actually ran on or whether they had four sets of wheels that ran on each rail.
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Old May 8th, 2008, 04:24 PM   #2518
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Quote:
Originally Posted by iampuking View Post
Anyway, I don't see what difference the age the tunnel was built makes,
it seems everyone else does, the problem lies with you - the age affected the size and also the technology available at the time. If the C&SLR was built 15 years later, it would have been standard tube tunnel size, and also may have had a different electrification system.
Quote:
LU still uses a four rail system today, if you think it has never changed because of the narrowness of the tunnels (which is hard to tell since your post is so badly written and unclear)
no it never changed as change is difficult - it was like that originally because the tunnels were narrow. I'll remember to spell it out really clearly for you, from first principles and taking into account that you don't hold such common sense positions as 'if it ain't broke, don't fix it, especially if everything uses it and it would cost a lot of money"
Quote:
then using the C&SLR as an example is stupid, as it had it's tunnels widened in the twenties.
indeed, to the standard tube size, which all used 4 rail system anyway, because it's what Yerkes chose as best in the early 1900s (which is what I have said before as a main reason and you went "well Moscow and DC didn't go with it"). It was a system designed to cope with the problems of very small tunnels that spread to tunnels that were bigger (though are still small). It was an excellent example to use, as it was the first example. IIRC the CLR changed to 4 rail fairly quickly after it's different system wasn't as good. It was invented to cope with the small tunnels of the C&SLR and then was used on other railways that didn't have the problems of small tunnels as much as the C&SLR (though still did).

The electrification system could have been changed at anytime since 1926, but changing it from 4 rail would have been like changing the gauge of railways to broad gauge, rather than changing broad gauge to standard gauge. Broad gauge was better, however far more of the network had standard gauge, and it worked well enough. In this case, it was 100% of the Underground Network that had electrification, had 4 rail electrification (also the NLR/DC lines between Broad Street and Richmond/Watford, which shared track with LU)

There's also the problems of changing - when the Jubilee went to 7-car trains it closed for a week so that all the trains could be coupled up before they sent any into service. How much longer would a line need to be closed to change the electrification system? You'd need to modify rolling stock as well as the static infrastructure (and the static infrastructure wouldn't be as easy as widening the C&SLR which was done overnight, as you changing the equipment needed to run trains, rather than just being able to add bigger trains). And the new and old would very likely be incompatible. What normally happens when you bring in new rolling stock is you bring it in gradually, running at the same time as old stock. It's very hard to change, and frankly, there's little point.

Here's a summary to make this all really clear
  • The 4 rail system was developed to deal with the problems due to the C&SLR's small tunnel size and the poor electrical technology available in 1890
  • Tunnel size improved, but Yerkes decided to go with 4 rail electrification anyway, perhaps because the technology still wasn't good enough in 1905 to not need 4 rail, despite the bigger (though still fairly small) tunnels, perhaps just to keep the electrification system the same across his network.
  • The C&SLR was expanded in diameter, and also the electrical technology continued to improve. Yet, even if it was possible to have a different system in 1926, it remained 4 rail, as changing the ENTIRE tube system's electrification was too expensive, both in financial and hassle terms, for the benefit that would have been gained.
  • Moscow and Washington, because they started their systems later, from scratch, had the better technology and the ability not to have to go through the hassle of change (as there was nothing to change), so could use different systems.
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Old May 8th, 2008, 05:45 PM   #2519
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Quote:
Originally Posted by sotonsi View Post
it seems everyone else does, the problem lies with you - the age affected the size and also the technology available at the time. If the C&SLR was built 15 years later, it would have been standard tube tunnel size, and also may have had a different electrification system.no it never changed as change is difficult - it was like that originally because the tunnels were narrow. I'll remember to spell it out really clearly for you, from first principles and taking into account that you don't hold such common sense positions as 'if it ain't broke, don't fix it, especially if everything uses it and it would cost a lot of money"indeed, to the standard tube size, which all used 4 rail system anyway, because it's what Yerkes chose as best in the early 1900s (which is what I have said before as a main reason and you went "well Moscow and DC didn't go with it"). It was a system designed to cope with the problems of very small tunnels that spread to tunnels that were bigger (though are still small). It was an excellent example to use, as it was the first example. IIRC the CLR changed to 4 rail fairly quickly after it's different system wasn't as good. It was invented to cope with the small tunnels of the C&SLR and then was used on other railways that didn't have the problems of small tunnels as much as the C&SLR (though still did).

The electrification system could have been changed at anytime since 1926, but changing it from 4 rail would have been like changing the gauge of railways to broad gauge, rather than changing broad gauge to standard gauge. Broad gauge was better, however far more of the network had standard gauge, and it worked well enough. In this case, it was 100% of the Underground Network that had electrification, had 4 rail electrification (also the NLR/DC lines between Broad Street and Richmond/Watford, which shared track with LU)

There's also the problems of changing - when the Jubilee went to 7-car trains it closed for a week so that all the trains could be coupled up before they sent any into service. How much longer would a line need to be closed to change the electrification system? You'd need to modify rolling stock as well as the static infrastructure (and the static infrastructure wouldn't be as easy as widening the C&SLR which was done overnight, as you changing the equipment needed to run trains, rather than just being able to add bigger trains). And the new and old would very likely be incompatible. What normally happens when you bring in new rolling stock is you bring it in gradually, running at the same time as old stock. It's very hard to change, and frankly, there's little point.

Here's a summary to make this all really clear
  • The 4 rail system was developed to deal with the problems due to the C&SLR's small tunnel size and the poor electrical technology available in 1890
  • Tunnel size improved, but Yerkes decided to go with 4 rail electrification anyway, perhaps because the technology still wasn't good enough in 1905 to not need 4 rail, despite the bigger (though still fairly small) tunnels, perhaps just to keep the electrification system the same across his network.
  • The C&SLR was expanded in diameter, and also the electrical technology continued to improve. Yet, even if it was possible to have a different system in 1926, it remained 4 rail, as changing the ENTIRE tube system's electrification was too expensive, both in financial and hassle terms, for the benefit that would have been gained.
  • Moscow and Washington, because they started their systems later, from scratch, had the better technology and the ability not to have to go through the hassle of change (as there was nothing to change), so could use different systems.
Great, now that i've got your essay writing in tune could you explain to all of us why AirTrack is not allowed to have three rail electrification despite the fact that it'll be using 21st century technology (probably with concrete tunnels), and full size loading guage? No malice intended.
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Old May 8th, 2008, 07:17 PM   #2520
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No one knows why Air Track is not allowed to have 3 rail electrification - except BAA - it's all rather odd. I can speculate that it's to push HEx to Staines without their TOC not need to adapt it's trains to dual voltage. ie maximising profit for them.

The H&S rules of extending the network apply, so it's not in case people tread on the rail (and seeing as it's just the tunnel that 'has to be' OHLE, it's rather difficult for them to tread on it).
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