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Post by philthetube on Dec 28, 2020 12:42:13 GMT
Given todays health and safety considerations I cannot imagine 3rd/4th rail being allowed nowadays, what would the alternatives be, considering the lack of tunnel space available.
<<Rincew1nd: title changed from "powered" to "different">>
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Post by Dstock7080 on Dec 28, 2020 13:11:53 GMT
Given todays health and safety considerations I cannot imagine 3rd/4th rail being allowed nowadays, what would the alternatives be, considering the lack of tunnel space available. If built today the tunnels certainly wouldn’t be as small therefore alleviating the requirements for third and fourth rail, overhead conductor rail (as CrossRail) would be probable. |
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Post by revupminster on Dec 28, 2020 13:42:42 GMT
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rincew1nd
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Post by rincew1nd on Dec 28, 2020 16:08:38 GMT
Copenhagen metro is new, and that is fitted with bottom contact 3rd rail - as per the DLR.
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Post by zbang on Dec 28, 2020 17:59:26 GMT
Overhead rail or wire, probably a somewhat higher voltage (750v? 1000v? higher?). Or a covered 3rd rail (many metro's use them).
But.... even with speculative H&S requirements, I think exposed conductors would be allowed in some controlled circumstances.
Possible a greater question is whether it would be DC or AC. I'd expect DC since the drive electronics would be somewhat easier, but I could be wrong.
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Post by Deleted on Dec 28, 2020 18:18:07 GMT
AC has better transmission over greater lengths thus meaning less sub stations.
Since most trains now have AC traction packages that is my theory
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Post by quex on Dec 28, 2020 18:29:28 GMT
In terms of modern traction systems, it doesn't make a huge difference whether the supply is AC or DC. Trains using AC motors will convert the constant-frequency supply AC to DC anyway, then back to a variable AC using an inverter. Using a DC supply would cut out the rectifiying step but it's not a very big step to remove in the grand scheme of things. Using lower voltages (as on DC) saves on a big transformer on the train, but moves the big transformer to the lineside instead.
It's worth noting that proposal a few years back to use D78s on the Harrogate Line with an underside-contact 750V (?) DC third rail.
As most commenters have said, I reckon if LU was built today it'd probably just use underside-contact third rail or overhead conductor bars. Tunnels would be larger diameter, and so would be more expensive. So half the system as we know it would never be built, and the idea sort of collapses in on itself as we end up with a system that would look very different to LU anyway.
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Post by Chris M on Dec 28, 2020 19:26:12 GMT
The competing routes wouldn't be built today, but then neither would half the complementary routes. Metroland wouldn't exist as the transport would be there solely to "unlock" land for private developers to build houses on so the area would look very different.
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Post by ijmad on Dec 28, 2020 19:33:19 GMT
Can't find much on Google now, but I read that some consideration was given to installing overhead conductor bars on the Victoria Line in the 1990s as part of the early planning phases for the line upgrade that delivered the resignalling and new stock. This seems to be a solution for more 'compact' OHLE. Another possibility for making 3rd rail electrification safer would be to use a digital system that only energises the section where a train is over the top, similar to the Bordeaux tram which uses Alstom APS. One more idea is to add battery or capacitors on to trains. Even if these batteries were small and only lasted for a short time, they would make stations safer (as the train could run on batteries through platforms), pointwork much simpler (no third rail required in these sections), and make depot layouts simpler as well. |
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Post by vincenture on Dec 28, 2020 19:37:13 GMT
I wonder if the Victoria line trains would have 90km/h trains from this overhead conductor addition, which would boost journey times and free up even more capacity especially Finsbury Park to Seven Sisters.
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Post by class411 on Dec 28, 2020 23:24:11 GMT
I wonder if the Victoria line trains would have 90km/h trains from this overhead conductor addition, which would boost journey times and free up even more capacity especially Finsbury Park to Seven Sisters. I the limit on train velocity down to the power transmission interface or the small size of the tunnels? |
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Post by philthetube on Dec 29, 2020 0:17:58 GMT
My thoughts were, when I created this thread were either bottom fed third rail or overhead rail, with on board batteries for stations and other areas where installation may be difficult, however I had not taken into account that new tunnels would have to be bigger, to allow for evacuation and so may as well be overhead wires.
I assume that building oval tunnels is a non starter so there will be spare height available for wires.
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Post by jimbo on Dec 29, 2020 0:42:57 GMT
Can't find much on Google now, but I read that some consideration was given to installing overhead conductor bars on the Victoria Line in the 1990s as part of the early planning phases for the line upgrade that delivered the resignalling and new stock. This seems to be a solution for more 'compact' OHLE. Another possibility for making 3rd rail electrification safer would be to use a digital system that only energises the section where a train is over the top, similar to the Bordeaux tram which uses Alstom APS. One more idea is to add battery or capacitors on to trains. Even if these batteries were small and only lasted for a short time, they would make stations safer (as the train could run on batteries through platforms), pointwork much simpler (no third rail required in these sections), and make depot layouts simpler as well. Original article on Space Train Concept here . With overhead contact raised through stations for safety, despite platform edge doors, I can't get my mind around the transition from tube tunnel contact to higher platform level, and then back again. The talk is of passenger doorways to the ends of the platforms, with the trains being even longer, so end doors would be in the transition zone between contact levels. |
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Post by spsmiler on Dec 29, 2020 13:06:21 GMT
Yes, maglevs, although not if there is a passenger capacity limit - I say this because apparently the Japanese Linimo maglev metro trains have weight limits which prevent severe overcrowding as otherwise they might not be able to float above the track! Can you imagine the uproar if passengers at the height of the evening rush hour at somewhere like Oxford Circus were told to leave the train (return to a packed station platform) because it is too severely overcrowded? As for power supply systems, I recall the failed proposals for the new Victoria line trains to use an overhead rail, and for D Stock trains between Leeds and York via Harrogate & Knaresborough which would be converted to receive electricity using a DLR style third rail power supply system. Whilst neither of these came to fruition we do now have battery powered D Stock trains (albeit on a different route and yet to enter service). As others have said, if London was only starting out today the Underground would be very different, possibly powered via overhead rails energised at 750v or 1500v DC. I also wonder if its trains would be Standard gauge - for a self-contained system there would be no logical need for this, wider trains could possible make greater sense than ultra long trains. For the future I can foresee a transition away from externally powered trains - all overhead wires and electric rails will become redundant, everywhere except transport museums. Instead the trains will be powered via something that uses powerful magnets. I expect this to start happening within my lifetime, although not for a few years. So, the new tube trains currently being planned for London could be the last new trains which rely on electric rails. I am not an engineer but have heard other people discussing this... if a normal car engine was converted to magnetism it should be possible to replace polluting fuels creating sparks to get the pistons to move with powerful electromagnets that work on the 'like' / 'repel' feature to create the movement. Once going it could even be possible to use a small generator to recharge the battery, so that the vehicle rarely needs an external top-up charge. I am aware of several other technologies which are under development, but it is a waiting game as to how soon before they are ready to reach the demonstration prototype stage. |
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Post by Chris M on Dec 29, 2020 13:49:32 GMT
also wonder if its trains would be Standard gauge - for a self-contained system there would be no logical need for this, wider trains could possible make greater sense than ultra long trains. A wider gauge railway would have no scope for interoperability, increased costs of rolling stock due to being non-standard, issues with delivery and disposal of stock, etc. It would also necessitate tunnels with a larger diameter still, and tunnelling costs increase significantly with diameter (iirc the amount of spoil to be dealt with increases with the cube of the diameter). A larger loading gauge on standard gauge track has fewer of these issues, but it still not a panacea. The BART system in San Francisco uses a broad gauge (5'6") but this has not been regarded as a success and any new lines are likely to be standard gauge. |
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Post by class411 on Dec 29, 2020 13:53:46 GMT
For the future I can foresee a transition away from externally powered trains - all overhead wires and electric rails will become redundant, everywhere except transport museums. Instead the trains will be powered via something that uses powerful magnets. I expect this to start happening within my lifetime, although not for a few years. So, the new tube trains currently being planned for London could be the last new trains which rely on electric rails. You can't 'power' a train with magnets. A magnet does not provide an energy; it provides a force. (Obviously, powerful magnets are used in powerful motors, but they are not an energy source.) The only (relatively) non polluting technology that exists at the moment that is even close to being practical for a self contained power source for a train is a small nuclear reactor. And it's very unlikely that anyone is going to sanction the use of those to power trains. As above. More powerful magnets might enhance the efficiency of the motor (and make it smaller), but they would do little to vary the kw (kilowatts) needed per mile. By a few percent, maybe, whereas the fictional system you allude to would appear to reduce energy requirements to a few percent. |
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Post by quex on Dec 29, 2020 14:00:11 GMT
You can have very, very big trains on standard gauge - as Chris M suggests loading gauge is the limiting factor. The trains on Hong Kong's Mass-Transit Railway are as big as (if not bigger than) those of SF's BART, but the former are standard gauge (give or take a few mm). But if you used trains as big as that, you'd demolish the coping stones on the first Network Rail platform you encountered. It's for problems like these that almost all new-built metro systems globally are entirely self-contained operations. Many still use standard gauge to allow "off-the-shelf" equipment to be used (e.g. standard rolling stock types used internationally) and reduce costs. However to apply the same kind of self-contained principle to London would change the shape of the network dramatically. No District to Richmond, Chiltern would be booted off the top end of the Met, and the Bakerloo would be a lot shorter...
I should add the BART's gauge is a special case, chosen to allow for greater stability due to very high winds in the valleys around San Francisco. There's also an old story that the system was designed by aerospace engineers (as opposed to railway engineers), who were less likely to adopt old railway standards.
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Post by revupminster on Dec 29, 2020 18:58:41 GMT
The first underground trains were broad gauge to Farringdon and Hammersmith although not for long as Brunel's system fell out of favour. If it had survived then the underground could never have expanded over so many BR tracks and the Central Line would have been a lot shorter.
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Post by brigham on Dec 30, 2020 8:39:04 GMT
If Brunel's gauge had prevailed, there would have been no break-of-gauge between the Underground and the other British lines.
Initial construction costs would have been somewhat higher...
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Post by billbedford on Dec 30, 2020 10:45:43 GMT
If the Underground had not been build in the late 19th century, would we not be living in a Steam Punk type world, so electrical traction would not be possible?
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Post by croxleyn on Dec 30, 2020 10:57:17 GMT
One advantage of AC over DC, especially for a catenary, is that an arc fed by AC will tend to self-extinguish, whereas DC will continue for ever. If the pantograph power collector is graphite, it will burn very effectively.
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Post by ijmad on Dec 30, 2020 15:25:09 GMT
If Brunel's gauge had prevailed, there would have been no break-of-gauge between the Underground and the other British lines. Initial construction costs would have been somewhat higher... There is no break of track gauge, only a break of loading gauge between tube lines and mainline (which aren't much different in size to the subsurface lines). Brunel's gauge was a broad track gauge wasn't it? So I'm not sure I get what you're saying. |
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Post by ijmad on Dec 30, 2020 15:26:59 GMT
If the Underground had not been build in the late 19th century, would we not be living in a Steam Punk type world, so electrical traction would not be possible? The C&SLR was originally expected to use cable hauled trains before a late switch to electric traction which was considered quite experimental at the time! |
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Post by norbitonflyer on Dec 31, 2020 6:30:55 GMT
If Brunel's gauge had prevailed, there would have been no break-of-gauge between the Underground and the other British lines. Initial construction costs would have been somewhat higher... There is no break of track gauge, only a break of loading gauge between tube lines and mainline (which aren't much different in size to the subsurface lines). Brunel's gauge was a broad track gauge wasn't it? So I'm not sure I get what you're saying. I assumed he meant if the Gauge Commission had decided to standardise on Brunel Gauge rather than Stephenson Gauge for railways in Great Britain |
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Post by norbitonflyer on Dec 31, 2020 6:37:40 GMT
(iirc the amount of spoil to be dealt with increases with the cube of the diameter). The square of the diameter, not the cube. The volume of spoil is the length of the tunnel x its cross sectional area. The area is pi/4 x d squared. |
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Post by brigham on Dec 31, 2020 9:35:09 GMT
I'e always been an advocate of the Adkins-Lewis propulsion system, even as a kid.
The Waterloo and City line would be an ideal test-bed.
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Post by 35b on Dec 31, 2020 10:29:56 GMT
I'e always been an advocate of the Adkins-Lewis propulsion system, even as a kid. The Waterloo and City line would be an ideal test-bed. Wiki doesn’t help - what is that? |
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Post by croxleyn on Dec 31, 2020 11:37:35 GMT
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Post by 35b on Dec 31, 2020 11:42:29 GMT
Many thanks - an interesting concept, though I'm not convinced about it's practicality. |
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Post by quex on Dec 31, 2020 11:46:05 GMT
The basic idea behind the Never-Stop Railway - continuously moving carriages - raises many accessiblity concerns for the boarding of less mobile passengers at stations in modern times. It was a good idea back in the day, but wouldn't be acceptable now. Sure, you could (like the London Eye or cable car systems) temporarily pause the whole system to allow someone to board a stationary car. But as the size of the system increases, this becomes more and more disruptive. That's why the Adkins-Lewis/Never-Stop idea is/was best suited to small-scale "people-mover"-type installations.
More to the point, with modern technology we have far more efficient methods of achieving the same end result that the screw-drive system did.
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