London DLR third rail system - forever segregated?

[ijmad]

Hey folks,

As I'm sure many of you know, the DLR has something of a unique third rail system with lightweight, small cross section bottom contact power rails rather than the traditional NR/Tube heavy top contact third rail.

Was wondering, does this arrangement completely preclude the possibility of ever running mixed services on the same track? I'm imagining that the DLR trains might foul a normal third rail, and vice versa, but I'm not sure, there might just be room?

Are there also additional loading gauge constraints on the DLR that would stop a normal sized NR stock from running on its lines?

I know it's unlikely we'd ever see this for real, but just a thought experiment really, also looking for further details on the DLR's system and whether it's used anywhere else.

 

[AM9]

Hey folks,

As I'm sure many of you know, the DLR has something of a unique third rail system with lightweight, small cross section bottom contact power rails rather than the traditional NR/Tube heavy top contact third rail.

Was wondering, does this arrangement completely preclude the possibility of ever running mixed services on the same track? I'm imagining that the DLR trains might foul a normal third rail, and vice versa, but I'm not sure, there might just be room?

Are there also additional loading gauge constraints on the DLR that would stop a normal sized NR stock from running on its lines?

I know it's unlikely we'd ever see this for real, but just a thought experiment really, also looking for further details on the DLR's system and whether it's used anywhere else.

It would be totally unworkable to have both top and bottom 3rd rail on the same tracks. Bottom contact systems are not uncommon on modern metro and light rail networks across the world because there is less of a passenger/staff risk of electrocution and the system is not really affected by ice and snow.
As far as the infrastructure goes, the DLR is more like a tramway system with quite small radius curves and sharp gradients. Then there's the issue of a fully automated train control with no visible signals.
The DLR wouild be a very hostile environment to any non-resident rolling stock.

 

[edwin_m]

Nearly all totally new Metros within the last few decades (ie not extending an older system) will use a bottom contact third rail. At least one heavy rail network (the Metro North in New York) uses something similar.

 

[Bald Rick]

Leaving aside the Con rail gauging issues, there are some rather more weighty issues, literally.

The middle initial of the DLR is the key one. Every part of the network is designed for lightness, the rails, the sleepers, and the bridges.

Then there is the gauge. There are some corners that national rail rolling stock would struggle to get round, not least because of some very severe overhang. And that’s before we get to any platforms.

Of interest, some of the older DLR units were sold, I think to a German light rail system.

Also, when Manchester Metrolonk was in the planning stages, a DLR unit was taken up there and had a pantograph attached. They will be a picture of it somewhere.

 

[ijmad]

The DLR wouild be a very hostile environment to any non-resident rolling stock.

Then there is the gauge. There are some corners that national rail rolling stock would struggle to get round, not least because of some very severe overhang. And that’s before we get to any platforms.

I was actually thinking about the inverse, e.g. if we could run DLR stock down to Hayes or Bromley North via a suitable connection at Lewisham. Again, without any regard to real concerns, purely as a thought experiment: would the existing third rail need to be torn up and replaced with the DLR's system, or could both systems just squeeze in without fouling each other.

The DLR's conductor rail seems further away from the running rails, but this could just be an optical illusion. Could you place the DLR's system on one side of the track and NR third rail on the other? Would the conductor shoes from DLR trains foul the NR live rail and vice versa?

 

[4-SUB 4732]

 

[mmh]

I was actually thinking about the inverse, e.g. if we could run DLR stock down to Hayes or Bromley North via a suitable connection at Lewisham. Again, without any regard to real concerns, purely as a thought experiment: would the existing third rail need to be torn up and replaced with the DLR's system, or could both systems just squeeze in without fouling each other.

The DLR's conductor rail seems further away from the running rails, but this could just be an optical illusion. Could you place the DLR's system on one side of the track and NR third rail on the other? Would the conductor shoes from DLR trains foul the NR live rail and vice versa?

As someone who lives on the Hayes line I really wish people would stop suggesting it as an easy expansion to the TFL empire. We'd much rather not have our 10 and occasionally 12 car full size trains replaced with the Bakerloo line, no matter how often those who've never heard of West Wickham think it's a good idea. Sadly TFL encourage this nonsense with their repeated meaningless proposals and "consultations". Tube stock would be an enormous reduction in capacity and journey option convenience, DLR even more so to the point it'd be unusable.

I'll freely admit to being biased here. If all the new residents of Lewisham and Catford are so annoyed by not being on the tube map, they shouldn't have moved there. Leave the rest of us alone.

 

[ijmad]

As someone who lives on the Hayes line I really wish people would stop suggesting it as an easy expansion to the TFL empire. We'd much rather not have our 10 and occasionally 12 car full size trains replaced with the Bakerloo line, no matter how often those who've never heard of West Wickham think it's a good idea. Sadly TFL encourage this nonsense with their repeated meaningless proposals and "consultations". Tube stock would be an enormous reduction in capacity and journey option convenience, DLR even more so to the point it'd be unusable.

I'll freely admit to being biased here. If all the new residents of Lewisham and Catford are so annoyed by not being on the tube map, they shouldn't have moved there. Leave the rest of us alone.

I actually don't know or care if the DLR to Hayes would be a good idea or not. It was just the closest near-connection I could think of! Was purely interested in whether it'd even be possible on a technical level, not whether it should actually be done.

The only other places where the two systems come close to connecting would be the lines between Shadwell and Limehouse with LTSR, and around Stratford International with the North London Line (although that's OHLE, whether the DLR could run under wires seems like a whole other kettle of fish).

 

[edwin_m]

In principle it could be done, probably with some kind of retractable alternative shoegear. In practice you'd need the same signalling modifications as tram-train schemes to offset the risk of reduced structural strength of the DLR units, plus no doubt a whole load of heartache over EMC. Not to mention getting a safety case for driverless operation...

 

[NorthKent1989]

As someone who lives on the Hayes line I really wish people would stop suggesting it as an easy expansion to the TFL empire. We'd much rather not have our 10 and occasionally 12 car full size trains replaced with the Bakerloo line, no matter how often those who've never heard of West Wickham think it's a good idea. Sadly TFL encourage this nonsense with their repeated meaningless proposals and "consultations". Tube stock would be an enormous reduction in capacity and journey option convenience, DLR even more so to the point it'd be unusable.

I'll freely admit to being biased here. If all the new residents of Lewisham and Catford are so annoyed by not being on the tube map, they shouldn't have moved there. Leave the rest of us alone.

I don’t think the Bakerloo or DLR line for that matter will ever reach the Hayes line, the closest the Hayes line will ever get to being a “tube” line will be once LO takes over the SE metro routes to Hayes,
Bromley North, Sevenoaks & Dartford which is an entirely different mode.

I do agree with you on your points however

 

[NorthKent1989]

Since the DLR went 3 cars, I have a hard time defining it as a light rail or tram like system

 

[Journeyman]

Since the DLR went 3 cars, I have a hard time defining it as a light rail or tram like system

It has many of the characteristics of light rail, but I agree it's somewhat "heavier" than it was when it opened. It's much more of a metro-type operation now, and will be more so when new trains are introduced in the future. The intention is to use articulated units the length of a current three-unit train.

 

[4-SUB 4732]

Doubt London Overground will get the Metro routes on SE - they’re about to issue yet another whole franchise for it. The political willpower doesn’t exist for it and, much like the SW and Central, there’s too much crossover of stock and staff to split it easily. It would require years of building up extra stock but more importantly more drivers for the change.

And yes, I can imagine Hayes passengers would have a deep sense of frustration about being linked to the Bakerloo line extension HOWEVER a quick check on arrivals at London Bridge between 07:45 and 09:15 shows just 8 arrivals - an average of just 5-5.5 trains per hour. Not all are 12 coaches; but that is roughly 55 coaches of capacity per hour. The Bakerloo line would only need 8 trains per hour with 7 coaches a piece to satisfy demand. 12 trains per hour, for example, of which 8 come from Hayes and a further 4 perhaps come round from Beckenham would result in a vast uplift in overall capacity.

The point I would make is that whilst I know the Hayes line folk like their incumbent service, sometimes we have to make sacrifices. What I mean here is that there is a finite capacity into London Bridge and we will have to sacrifice something: Hayes is the best one for it. Heavy rail locally includes Kent House, Catford and of course Hither Green and Lewisham; and if the correct routing is followed there will also be interchange at New Cross Gate, the Elephant and so on.

Definitely worth extending the Bakerloo and using all the freed-up capacity for the other Metro and even Main Line routes.

 

[NorthKent1989]

Doubt London Overground will get the Metro routes on SE - they’re about to issue yet another whole franchise for it. The political willpower doesn’t exist for it and, much like the SW and Central, there’s too much crossover of stock and staff to split it easily. It would require years of building up extra stock but more importantly more drivers for the change.

And yes, I can imagine Hayes passengers would have a deep sense of frustration about being linked to the Bakerloo line extension HOWEVER a quick check on arrivals at London Bridge between 07:45 and 09:15 shows just 8 arrivals - an average of just 5-5.5 trains per hour. Not all are 12 coaches; but that is roughly 55 coaches of capacity per hour. The Bakerloo line would only need 8 trains per hour with 7 coaches a piece to satisfy demand. 12 trains per hour, for example, of which 8 come from Hayes and a further 4 perhaps come round from Beckenham would result in a vast uplift in overall capacity.

The point I would make is that whilst I know the Hayes line folk like their incumbent service, sometimes we have to make sacrifices. What I mean here is that there is a finite capacity into London Bridge and we will have to sacrifice something: Hayes is the best one for it. Heavy rail locally includes Kent House, Catford and of course Hither Green and Lewisham; and if the correct routing is followed there will also be interchange at New Cross Gate, the Elephant and so on.

Definitely worth extending the Bakerloo and using all the freed-up capacity for the other Metro and even Main Line routes.

It’s easy to say Hayes line folk have to make sacrifices if I lived on that line I’d be hard pushed to accept the fact that a small, claustrophobic tube will replace the networkers which aren’t perfect I know but still.

Won’t half the Hayes trains be diverted to Victoria in a few years anyway?

 

[4-SUB 4732]

It’s easy to say Hayes line folk have to make sacrifices if I lived on that line I’d be hard pushed to accept the fact that a small, claustrophobic tube will replace the networkers which aren’t perfect I know but still.

Won’t half the Hayes trains be diverted to Victoria in a few years anyway?

Two will, the other two will continue to go to Charing Cross. I can’t remember exactly what TSR2 said on the Hayes line in respect of whether it got a Cannon Street service in peak or not at all; it certainly doesn’t during the off-peak period.

And let’s be honest, the Hayes line will need to make sacrifices. It’s proximity to direct trains in other key areas that will go to the ‘City’ (Blackfriars) such as Kent House and Catford mean it’s ripe for the chop and so it should.

 

[LLivery]

Wouldn't it just cause havoc/a headache with the signaling?

As someone who lives on the Hayes line I really wish people would stop suggesting it as an easy expansion to the TFL empire. We'd much rather not have our 10 and occasionally 12 car full size trains replaced with the Bakerloo line, no matter how often those who've never heard of West Wickham think it's a good idea. Sadly TFL encourage this nonsense with their repeated meaningless proposals and "consultations". Tube stock would be an enormous reduction in capacity and journey option convenience, DLR even more so to the point it'd be unusable.

I'll freely admit to being biased here. If all the new residents of Lewisham and Catford are so annoyed by not being on the tube map, they shouldn't have moved there. Leave the rest of us alone.

I couldn't have said it better myself. Some are obsessed with being on the Tube Map and will take anything given to them even if it means longer journey times. There's no way a Bakerloo line train could get into Charing X within the same time as currently. Fortunately, they'll never get the money to spend the insane amount of money it'll cost to convert.

Two will, the other two will continue to go to Charing Cross. I can’t remember exactly what TSR2 said on the Hayes line in respect of whether it got a Cannon Street service in peak or not at all; it certainly doesn’t during the off-peak period.

And let’s be honest, the Hayes line will need to make sacrifices. It’s proximity to direct trains in other key areas that will go to the ‘City’ (Blackfriars) such as Kent House and Catford mean it’s ripe for the chop and so it should.

As a very frequent user of it, I respectfully disagree. Also, I suspect like the Victoria line at Brixton, the Bakerloo will struggle to handle anything beyond Lewisham, especially with the developments in the area and the Bakerloo line stock being one car less than the Victoria.

 

[4-SUB 4732]

Wouldn't it just cause havoc/a headache with the signaling?



I couldn't have said it better myself. Some are obsessed with being on the Tube Map and will take anything given to them even if it means longer journey times. There's no way a Bakerloo line train could get into Charing X within the same time as currently. Fortunately, they'll never get the money to spend the insane amount of money it'll cost to convert.



As a very frequent user of it, I respectfully disagree. Also, I suspect like the Victoria line at Brixton, the Bakerloo will struggle to handle anything beyond Lewisham, especially with the developments in the area and the Bakerloo line stock being one car less than the Victoria.

Incorrect. Modelling of it all has shown that the Bakerloo has a plentiful supply of capacity (particularly even post upgrade with a few extra trains an hour - I think it’s going up from 24 to 28?) to support this. Most importantly perhaps because unlike the Victoria which in effect serves a ‘captive’ and extremely busy London terminal, this will not. People from Lewisham will probably use the Bakerloo to get to Charing Cross and the West End; but will change at the likes of Lewisham from Hayes etc to get to London Bridge and Cannon Street. The inclusion of New Cross Gate will also help distribute East London passengers so they don’t all go to Canada Water and fill the Jubilee; and people will naturally in the Sydenham and Catford areas make changes to their journeys into Thameslink and Southeastern to get themselves to places like Blackfriars if they don’t want the Bakerloo line.

In short, even if it is a big change, people naturally re-jig themselves and find new ways of doing things. Out of all the Metro routes radiating from Charing Cross and Cannon St it’s the Hayes line that makes the most sense for the chop and conversion. It’s also a good kick-starter for a more frequent service on the Beckenham spur to Lewisham and will open up new journeys from Beckenham to parts of South London and the West End.

 

[DynamicSpirit]

Two will, the other two will continue to go to Charing Cross. I can’t remember exactly what TSR2 said on the Hayes line in respect of whether it got a Cannon Street service in peak or not at all; it certainly doesn’t during the off-peak period.

My memory accords with yours. In the franchise spec, Hayes line gets 2tph to Victoria and 2tph to Charing Cross (not calling at Lewisham). To be honest, I think the Hayes line has been rather shafted in the franchise, since when returning from London, they get a choice between half hourly at Victoria and half hourly at Charing Cross, with few interchange possibilities. (I also can't recall if there are any extra trains in the peaks). A complete loss of any sense of turn-up-and-go when you're trying to get home. I think that's regrettable, and it may mean that Hayes line commuters become more favourable to the idea of having a Bakerloo line train about every 2 minutes instead.

 

[ijmad]

So anyway, back on topic, I never intended this thread to suggest the DLR should go to Hayes or Bromley or anywhere, I simply wanted to know whether track sharing was possible between the DLR and NR.

Certainly interesting that a DLR P86 was used as a demonstrator for the Manchester Metrolink, with a pantograph! Presumably then, it'd be possible to fit future DLR stock with pantographs so they could share tracks with NR stock fitted for OHLE.

However, still not sure about third rail. I found this document that shows the position of the conductor rail in UK 3rd rail systems.

If I could find something similar for the DLR it'd answer my question. Maybe I'll do an FOI if it's not already in the public domain.

 

[swt_passenger]

Scaled off photos DLR third rail is significantly further away from the running rail than mainline top contact third rail. I’d estimate it to be about 150-200 mm further out.

 

[ijmad]

Scaled off photos DLR third rail is significantly further away from the running rail than mainline top contact third rail. I’d estimate it to be about 150-200 mm further out.

Yeah, it also looks higher. Hence I wonder if the DLR's upside down shoegear would foul the NR third rail or not.

 

[swt_passenger]

Yeah, it also looks higher. Hence I wonder if the DLR's upside down shoegear would foul the NR third rail or not.

I’m 99.9% certain it must, the DLR pickup arm must be positioned slightly lower than its own rail, and would therefore have to extend straight through the position of the ‘normal’ third rail and its insulators.

 

[ijmad]

I’m 99.9% certain it must, the DLR pickup arm must be positioned slightly lower than its own rail, and would therefore have to extend straight through the position of the ‘normal’ third rail and its insulators.

Aaaaaand confirmed, I found this in an existing FOI.

Judging by the diagram the arm of the DLR shoegear can ride as low as 35 to 60cm above wheel base level. This is well below the 76cm headroom the NR third rail occupies above the level of the top of the running rails.

So, as I expected, the two systems are incompatible, including ruling out any option of placing the two systems on alternate sides of the running rails, as the DLR's shoegear in the offhand side still wouldn't clear the NR third rail.

Of course this doesn't preclude permanent conversions of routes from NR heavy rail to DLR or a DLR-like system, but that's a discussion for another thread IMHO.

My question is answered.

 

[AM9]

So anyway, back on topic, I never intended this thread to suggest the DLR should go to Hayes or Bromley or anywhere, I simply wanted to know whether track sharing was possible between the DLR and NR.

Certainly interesting that a DLR P86 was used as a demonstrator for the Manchester Metrolink, with a pantograph! Presumably then, it'd be possible to fit future DLR stock with pantographs so they could share tracks with NR stock fitted for OHLE. ...

There might be anough hardpoints to mount a lightweight pantograph, but there certainly isn't the soace for a 25kV installation including switchgear and a large transformer without significant rebuilding. The metyrolink is wired with 750VDC OLE.Take a look at the built from new tram/trains like will soon be introduced in the Sheffield area.

 

[ijmad]

There might be anough hardpoints to mount a lightweight pantograph, but there certainly isn't the soace for a 25kV installation including switchgear and a large transformer without significant rebuilding. The metyrolink is wired with 750VDC OLE.Take a look at the built from new tram/trains like will soon be introduced in the Sheffield area.

Yeah, I was more thinking about hypothetical future trains rather than today's models. I doubt that such a capability would ever be needed but as I said, this was just a thought experiment rather than a practical plan.

Interesting to note the Metrolink is 750V, I didn't realise that, thanks for the info.

 

[AM9]

... Interesting to note the Metrolink is 750V, I didn't realise that, thanks for the info.

I think that it general practice to keep on-street OLE below peak voltages* of 1000V, especially as there isn't usually a problem feeding the system every kilometer or so. All of the six modern tram networks in the UK have nominal 750V systems.

* Due to surges and transients, line voltages can rise above the nominal values so all components need to operate safely with those voltages present. Above about 1KV, traction motor design requires more attention to provide long-term reliability.

 

[edwin_m]

There's a standard for the variation in voltage that's permitted to occur at any particular nominal voltage - I don't have details but I recall the maximum for nominal 750V is somewhere around 1000V.

Another good reason to allow variation in voltage is regeneration. When a train regenerates, current flows away from it and the resulting voltage drop increases the line voltage close to the train. If the voltage gets close to the maximum the train must stop regenerating, as this is an indication that the line is not "receptive" to the energy being fed into it. The higher the permitted maximum voltage, the more the train can regenerate.

 

[mark-h]

Judging by the diagram the arm of the DLR shoegear can ride as low as 35 to 60cm above wheel base level. This is well below the 76cm headroom the NR third rail occupies above the level of the top of the running rails.

So, as I expected, the two systems are incompatible, including ruling out any option of placing the two systems on alternate sides of the running rails, as the DLR's shoegear in the offhand side still wouldn't clear the NR third rail.

It may be possible to design a train with retractable shoegear giving the option of using both top and bottom contact third rail.

 

[Jass]

It’s easy to say Hayes line folk have to make sacrifices if I lived on that line I’d be hard pushed to accept the fact that a small, claustrophobic tube will replace the networkers which aren’t perfect I know but still.

Won’t half the Hayes trains be diverted to Victoria in a few years anyway?

As a hayes line commuter, southeastern are utter ****e, the trains are just as packed as tube trains, no aircon, the tube would definitely benefit me as there will likely be around 25tph running from catford bridge if it is ever extended compared to the current 4tph