Should third rail be considered again for future electrification projects?

[Philip]

In terms of rail electrification projects which are either still in the pipeline without any start on infrastructure, or lines which could/should be electrified in the next 10-15 years, should the option of 3rd rail be considered again in view of the costs and time of work to install overhead wires, particularly with the debt the railway currently has and the need to replace diesel trains with electric promptly?

There is the health and safety issue to considerer; could rails with lower voltages than those used on the London tube, Liverpool and South East rail networks work? The advantages of 3rd rail over wires are fairly clear, but aside from the safety issue, are there other negatives about 3rd rail compared with wires?

 

[Whistler40145]

3rd Rail requires far more substations

 

[O L Leigh]

Before we fall too far down the rabbit hole yet again, this piece of work needs to be completed first.

 

[Tio Terry]

In terms of lower voltages you would need to get below 50V to be considered "Safe", which would not be practical.

Any proposed change would need to be risk assessed in accordance with the Common Safety Method. It would be interesting to see the Risk Assessment for new 3rd rail railway, especially the risk mitigations proposed to minimise the risks to an acceptable level.

 

[swt_passenger]

In terms of rail electrification projects which are either still in the pipeline without any start on infrastructure, or lines which could/should be electrified in the next 10-15 years, should the option of 3rd rail be considered again in view of the costs and time of work to install overhead wires, particularly with the debt the railway currently has and the need to replace diesel trains with electric promptly?

There is the health and safety issue to considerer; could rails with lower voltages than those used on the London tube, Liverpool and South East rail networks work? The advantages of 3rd rail over wires are fairly clear, but aside from the safety issue, are there other negatives about 3rd rail compared with wires?

Reducing voltage causes much increased losses, it’s a complete non starter. It’s why there’s been so many projects over the last few years to actually increase the nominal third rail voltage on both NR and LU existing routes. (Although generally referred to as a 750V system, much of it was only 660V, especially in inner suburban areas.

 

[HSTEd]

There are safety concerns, as previously outlined - however given the repeated failure of the 25kV programme to deliver what was promised, the decarbonisation imperative, and the potential for risk mitigations - I'd say another look is warranted.

A large fraction of the incidents of injuries occur at stations, which are a tiny fraction of the network, and we might be able to do something like gapping the rail in platforms, or having a normally dead portion of rail in stations that is only livened as required.

With advances in power electronics and SCADA systems we have options that were not available historically. For example we could have intrusion alarms that rapidly isolate the rail when tresspassers cross the fence.

To be honest I'd say it might even be worth looking at a novel bottom contact third rail solution given the catastrophic issues plaguing the 25kV programme.

 

[skyhigh]

The advantages of 3rd rail over wires are fairly clear

Are they? 3rd rail needs more substations, is less efficient, is a bigger hazard (in terms of for trespassers, trip hazard for pway staff etc), gets iced up, you get issues with shoe gear probably about as much as panto issues, fried foxes/badgers and I'm not sure new installations would be that much cheaper or faster than overhead wires when you consider new safety technology such as only having rails live when trains are in stations.

Lower voltages are a complete non-starter.

So no, in my opinion, 3rd rail should not be used for new schemes.

 

[O L Leigh]

...given the repeated failure of the 25kV programme to deliver what was promised, the decarbonisation imperative...

I'd say that has more to do with Government failure to drive the programme forward than any failing of the system itself. The clusterf*** that was the GWEP hasn't helped matters in that respect, but again that is no failing of the electrification system.

But then we've had this discussion before.

 

[Ken H]

I think it should be considered for add-ons to existing 3rd rail networks. So Uckfield is an obvious one. Maybe even Marylebone - Aylesbury.
I am sure that we can devise mitigating measures for the dangers.

 

[yorksrob]

Are they? 3rd rail needs more substations, is less efficient, is a bigger hazard (in terms of for trespassers, trip hazard for pway staff etc), gets iced up, you get issues with shoe gear probably about as much as panto issues, fried foxes/badgers and I'm not sure new installations would be that much cheaper or faster than overhead wires when you consider new safety technology such as only having rails live when trains are in stations.

Lower voltages are a complete non-starter.

So no, in my opinion, 3rd rail should not be used for new schemes.

It clearly does make sense for short extensions and infill projects, so yes it should (in specific circumstances).

 

[HSTEd]

I'm not sure new installations would be that much cheaper or faster than overhead wires when you consider new safety technology such as only having rails live when trains are in stations.

Even Network Rail admits that third rail would be cheaper than 25kV these days - as they did in their Kent Route Study

(In 2018 they projected Marshlink at £100-250m for third rail, versus £250m-500m for 25kV.)

 

[O L Leigh]

Even Network Rail admits that third rail would be cheaper than 25kV these days - as they did in their Kent Route Study

(In 2018 they projected Marshlink at £100-250m for third rail, versus £250m-500m for 25kV.)

Hmm. That's a little bit disingenuous.

Having read the document from which those figures came, I feel it important that I should point out that these are specific estimates for a specific scheme, and that they come with a lot of unknowns at present. Both electrification schemes come with an amount of civil engineering and signalling attached (bridge clearances, signalling immunisation, etc) but, as the DC scheme is an in-fill, it does come with a few potential savings built in. For example, the estimate says that power can be fed from either end by upgrading the existing supply whereas an AC scheme would require new feeder stations. This would be a big saving, as would the more modest needs for bridge clearance work.

However, the estimate does make a lot of assumptions that may prove to be false when it comes to designing the project for implementation. These include the number of bridges that may need to be replaced and, indeed, whether or not supplying power to DC electrification from either end is going to be sufficient. The estimate for the AC scheme includes three feeder stations while the DC scheme has none. Power supply requirements and voltage drop through the 3rd rail along the length of the route may mean that feeder stations may be required after all. Indeed, it may be the case that the AC scheme needs fewer than three feeder stations.

What is clear, however, is that comparing in-fill DC electrification on a lightly used line to an AC electrification island does not bolster the argument that 3rd rail is cheaper than OLE. If it was a new electrification scheme (say, to Salisbury) I would expect that the difference between the two would be a lot closer.

To be honest I'd say it might even be worth looking at a novel bottom contact third rail solution given the catastrophic issues plaguing the 25kV programme.

I don't think that we need to be inventing a new system that would make the stock incompatible with existing systems.

 

[Bletchleyite]

I don't think that we need to be inventing a new system that would make the stock incompatible with existing systems.

Depends. It might well be worth considering converting Merseyrail to bottom contact using the standard system the DLR and Hamburg U-Bahn use. Converting Merseyrail to OHLE would be hugely expensive because not all the tunnels are big enough for it, whereas converting to a different type of third rail would be relatively easy - just install it connected to the existing supplies and change the shoegear over. While interoperability is not of relevance because there isn't any, and if there was to be you'd fit pantographs and transformers to a subset of the units for that section - they have passive provision.

Should it be used for any new electrifications? No, other than extensions of that existing system.

What might be worth considering, though, is low voltage OHLE for low speed branch lines that don't run onto the mainline and where you can't just connect it to the mainline like you could at Windermere.

 

[HSTEd]

I don't think that we need to be inventing a new system that would make the stock incompatible with existing systems.

The railway does this all the time with rolling stock and numerous other bits of equipment.

Ultimately it is, in my view, suboptimal, but if it the price of actually getting more electrification, so be it.

It also doesn't help that the RSSB buries all its old technical reports behind a paywall....

 

[Bletchleyite]

The railway does this all the time with rolling stock and numerous other bits of equipment.

Ultimately it is, in my view, suboptimal, but if it the price of actually getting more electrification, so be it.

It also doesn't help that the RSSB buries all its old technical reports behind a paywall....

And it wouldn't be a new system to invent. There is already a standard bottom contact system used on the DLR and all over Germany. Buy the rail, shielding and shoe gear off the shelf and just swap it over using all the existing kit.

 

[HSTEd]

And it wouldn't be a new system to invent. There is already a standard bottom contact system used on the DLR and all over Germany. Buy the rail, shielding and shoe gear off the shelf and just swap it over using all the existing kit.

If we wanted the Hamburg system also uses a higher voltage which partially mitigates against the power limit and losses problems with the conventional third rail.....

(Since given the current rolling stock market realities, electrification will come with new rolling stock anyway)

 

[O L Leigh]

It kills interoperability which reduces efficiency. You'd effectively have to have a captive fleet just for the routes over which this system is installed.

That's fine for networks like Merseyrail where the entire network is captive, but to have islands within an electrified area which have incompatible electrification systems you start to have problems. It's fine to mix AC and DC because the system for dual-voltage EMUs is already well established.

 

[Bletchleyite]

If we wanted the Hamburg system also uses a higher voltage which partially mitigates against the power limit and losses problems with the conventional third rail.....

(Since given the current rolling stock market realities, electrification will come with new rolling stock anyway)

The Hamburg U-Bahn is 750VDC, using exactly the same kit as the DLR. It is the S-Bahn that has the unique side contact system at 1200VDC, which is quite similar to (but not the same as) the long gone Bury line system.

 

[yorksrob]

What is clear, however, is that comparing in-fill DC electrification on a lightly used line to an AC electrification island does not bolster the argument that 3rd rail is cheaper than OLE. If it was a new electrification scheme (say, to Salisbury) I would expect that the difference between the two would be a lot closer.

But it does, perhaps bolster the idea that DC infill third rail electrification should be allowed.

 

[Bletchleyite]

But it does, perhaps bolster the idea that DC infill third rail electrification should be allowed.

Indeed. While battery is an option, really, third rail to Headbolt Lane and then later Skem makes a lot of sense, for example. And so does Oxted-Uckfield and other similar bits of fill in.

You could also certainly argue for fourth rail to Aylesbury and into a couple of Marylebone platforms (unless there is capacity to move those to Baker St), similar to Euston.

 

[skyhigh]

It clearly does make sense for short extensions and infill projects, so yes it should (in specific circumstances).

Sorry - I was using 'new schemes' in the meaning of completely new schemes. I fully agree that extensions and infills are sensible uses of new 3rd rail.

 

[Snow1964]

Clearly a few infills makes sense, especially where one (or both) ends of a current service already have third rail.

Yes there are safety issues, but does adding 1-2% to third rail electrified track mileage make that much extra risk overall, especially when some other risks eg diesel spills would go down.

As for substations, there are a few that need upgrading as they limit the trains power and speed currently, but as most are relatively modular (they use parts that are craned in), it would be relatively cheap to reuse them on the lower capacity infills. I’m assume moving the replaced ones is going to be much cheaper than a 100% new substation.

So with bit of joined up thinking, and the fact there is spare third rail (or dual voltage) electric stock, (and a desperate need for the diesel trains which could be displaced), should be a no brainer

 

[yorksrob]

Sorry - I was using 'new schemes' in the meaning of completely new schemes. I fully agree that extensions and infills are sensible uses of new 3rd rail.

Fair point.

To be honest, I think that that was the previous status quo anyway.

 

[O L Leigh]

But it does, perhaps bolster the idea that DC infill third rail electrification should be allowed.

I'm glad that you used the word "perhaps". I think that the costs would need to be considered on a case-by-case basis and that it would not be the correct approach to simply infer that all schemes would follow the pattern of Marshlink.

It's also worth bearing in mind that the amounts quoted are simply broad estimates reached on a number of assumptions, some of which may prove not to be true. Should any electrification scheme be given the go-ahead we should expect that it would be properly costed, at which point we should get a more accurate picture of the work actually required. It may even be the case that the cost differential between the two electrification options closes somewhat once the engineers get their hands on the scheme.

 

[Gareth]

Sorry - I was using 'new schemes' in the meaning of completely new schemes. I fully agree that extensions and infills are sensible uses of new 3rd rail.

In that case, isolated metro services only and even then, using the bottom contact system.

 

[Ken H]

So what is an add on and what is a 'new scheme'? Uckfield? Marsh Link. Basingstoke - Exeter? Ormskirk - Preston? Kirby - Wigan?

 

[Sm5]

Reading -Redhill, Basingstoke - Exeter (or give it to GWR), Oxted line to me have more common sense.

As for safety, studies reaching conclusion that says its dangerous, despite being surrounded by thousands of miles of track safely operating for nearly 100 years, and likely to continue so for another hundred sounds more academic than substance.

Studies dont always reach the sensible conclusion.. I recall a study on a proposed mainline steam locomotive new build proposing the only safe option for wheels was solid not spoked..

 

[XAM2175]

As for safety, studies reaching conclusion that says its dangerous, despite being surrounded by thousands of miles of track safely operating for nearly 100 years, and likely to continue so for another hundred sounds more academic than substance.

If you introduce a live exposed conductor rail to a place that didn't already have one you've introduced a new risk, which will have a different potential danger compared to track that's had the same risk profile for decades.

 

[Gareth]

Maybe but that would've been the case when the existing third rail was put in. You could argue similar for a new road which didn't previously exist and most roads probably have a worse fatality record than third rail systems do. I do think some of this comes down to squieamishness over the concept of a naked live rail; especially as you can live in much of the country and rarely or never encounter it.

Not that I'd back it for electrifying most of the existing railway, only for extensions. I don't even support it for things like Basingstoke-Exeter considering the long distances involved and its mainline natural. 25kv AC is much more efficient for such lines.

 

[Dr Hoo]

Reading -Redhill, Basingstoke - Exeter (or give it to GWR), Oxted line to me have more common sense.

As for safety, studies reaching conclusion that says its dangerous, despite being surrounded by thousands of miles of track safely operating for nearly 100 years, and likely to continue so for another hundred sounds more academic than substance.

Studies dont always reach the sensible conclusion.. I recall a study on a proposed mainline steam locomotive new build proposing the only safe option for wheels was solid not spoked..

I wasn't 'squeamish' about third rail (having worked with it in North London, Merseyside and on the Southern) until I had to deal with two electrocutions in quick succession. (One an experienced colleague standing next to me, the other a nine-year-old trespasser who got onto the line through a hole cut by rail staff to make a shortcut to a depot.)

Things like that can quite change one's view.