Converting 3rd Rail to Overhead

[Class73Electro]

Following on from the Diesel vs Electric Thread was thinking - how would it go about converting current 3rd Rail region into overhead? Assuming there would be advantages? Would it be better for something like the Brighton Mainline? What about the current dead spots, such as Marshlink Line or Uckfield Line? with the current rules/guidance/advice, could we get those under the wires easier?

 

[The exile]

Following on from the Diesel vs Electric Thread was thinking - how would it go about converting current 3rd Rail region into overhead? Assuming there would be advantages? Would it be better for something like the Brighton Mainline? What about the current dead spots, such as Marshlink Line or Uckfield Line? with the current rules/guidance/advice, could we get those under the wires easier?

This was of course part of the great empty promise of mass electrification about 15 years ago - though initially for the outer reaches of the SW division (which makes sense as it has more interaction with other “regions”). Non life-expired equipment to be salvaged for reuse elsewhere (in best Southern Railway tradition). I suspect that in a planned “money almost no object” programme the Brighton Line would be one of the last dc survivors.

 

[gg1]

This was of course part of the great empty promise of mass electrification about 15 years ago - though initially for the outer reaches of the SW division (which makes sense as it has more interaction with other “regions”). Non life-expired equipment to be salvaged for reuse elsewhere (in best Southern Railway tradition). I suspect that in a planned “money almost no object” programme the Brighton Line would be one of the last dc survivors.

Ah yes, the 'electric spine', full 25kv AC electrification from Southampton to the WCML at Nuneaton and to Yorkshire/ECML via East West rail and the MML. I recall getting quite excited about that, in conjunction with the original HS2 Y plan.

 

[Sir Felix Pole]

Good luck with the politics - spending billions in London & SE converting already electrified lines, yet not completing the GWML and MMLschemes? There might be a case for the SWML west of Basingstoke if the Reading and Exeter lines ever get 25kV AC.

 

[swt_passenger]

Raising bridge heights and enlarging tunnels all over the DC network, to make room for OHLE? I bet that was never accurately costed. Politically impossible to convert while other areas still need wires for the first time, @Sir Felix Pole just noted.

 

[The exile]

The actual proposal would have only involved converting Weymouth to Basingstoke (Southampton to Basingstoke for the freight spine; Southampton to Weymouth because it would otherwise be isolated (and of course has/had the notorious supply issues).
My “what if” scenario would start there as well, with a second run of conversion out from Ashford. However- it ain’t going to happen!

 

[zwk500]

Following on from the Diesel vs Electric Thread was thinking - how would it go about converting current 3rd Rail region into overhead?

The last back-of-an-envelope figure I saw was several years ago and even then were in several billions. However, you would likely follow a phasing programme that focuses on services which could take advantage of overheads first (operated by Dual-Voltage stock, or extension of existing 25KV services). And then roll out steadily across the region.

One of the key issues with converting from 3rd rail to OLE is that the 3rd rail system is Direct Current, and the OLE system is Alternating Current. Mixing these types is not an easy thing to do. You would also need your signalling to be immunised against both systems for the transition period, and for the rolling stock to also have a conversion or replacement programme alongside.

There are several international examples of converting 3KV DC OLE to 25KV AC OLE, (definitely Belgium and Czechia, possibly more) and it's quite awkward. With multi-system trains generally easier to design nowadays, there's less benefits to harmonising the traction supply infrastructure. Interesting France looked (is looking?) at converting a line from 1.5KV DC OLE to 9KV DC OLE, as voltage upgrades were easier to implement than a change from AC to DC.

Assuming there would be advantages?

OLE is capable of higher speeds, greater efficiency, and is safer for people trackside. There would also be advantages to having only a single system.

Would it be better for something like the Brighton Mainline?

The Brighton Line probably wouldn't benefit that much as uplifting to 100 or 110mph over the 50 miles with the regular stops isn't going to realise much benefit. It would also require changes to the power supply infrastructure and interaction with the grid.

What about the current dead spots, such as Marshlink Line or Uckfield Line? with the current rules/guidance/advice, could we get those under the wires easier?

It would certainly be more feasible to install OLE than 3rd rail, but both those lines are also strong contenders for BEMU operation.

BEMUs change the game quite a lot for the question of what to do about the 3rd rail network. Removing it wholesale is not a viable option, but BEMUs would give the opportunity for power to be turned off with much lower disruption to trains (for incidents, maintenance or conversion works), as well as potentially some judicious pruning of the third rail network. It also gives the option to design a conversion strategy that allows for sections to be converted without needing long-term disruption for traffic.
BEMUs also raise the question of potential for de-electrifying some areas of third rail where there are particular challenges such as small tunnels, AC OLE, or power supply restrictions.

 

[HSTEd]

If you really want to convert from third rail to overhead, I think you'd be better off converting to 3kV DC or the nascent French 9kV standard.

Such an upgrade would avoid the enormous bonding issues inherent in conversion to AC.

But I don't think the benefits of a higher voltage overhead system will ever justify the cost and disruption.

And the ongoing French superconducting 1500V feeder trial at Montparnasse may solve many of third rail's operational downsides at a fraction of the cost.

Even a superconducting 0V return bus would slash energy use and complexity in the system.

 

[JohnElliott]

One of the key issues with converting from 3rd rail to OLE is that the 3rd rail system is Direct Current, and the OLE system is Alternating Current. Mixing these types is not an easy thing to do. You would also need your signalling to be immunised against both systems for the transition period, and for the rolling stock to also have a conversion or replacement programme alongside.

If (as seems likely) the next generation of rolling stock is fitted with traction batteries as standard, then rather than having changeover points with complicated electrical arrangements it would be possible to have nonelectrified gaps between the two systems, or in locations where expensive clearance work would be required.

 

[zwk500]

If (as seems likely) the next generation of rolling stock is fitted with traction batteries as standard, then rather than having changeover points with complicated electrical arrangements it would be possible to have nonelectrified gaps between the two systems,

Agreed. It potentially allows for the very expensive dual-protection arrangements to be omitted, or existing ones simplified. It also provides an opportunity for third rail to be removed from complicated or limited-clearance areas like big junctions or tight tunnels where maintenance access is a serious issue.

 

[35B]

Agreed. It potentially allows for the very expensive dual-protection arrangements to be omitted, or existing ones simplified. It also provides an opportunity for third rail to be removed from complicated or limited-clearance areas like big junctions or tight tunnels where maintenance access is a serious issue.

At the cost of adding complexity and weight to trains, which will manifest in increased wear on infrastructure. It would also have implications on the ability to run electrically hauled freight

 

[zwk500]

At the cost of adding complexity and weight to trains, which will manifest in increased wear on infrastructure.

The complexity and weight of a battery pack are minimal to negligent in terms of noticeable impact on wear and maintenance. I believe @Bald Rick has covered that in quite some detail on other threads. Especially as third rail 377s run round with a big block of concrete underneath in place of a transformer!

And any increased costs would almost certainly be offset by the greater flexibility available, in both normal running and incidents.

It would also have implications on the ability to run electrically hauled freight

Electrically hauled freight would be similarly battery-equipped or bi-mode.

 

[35B]

The complexity and weight of a battery pack are minimal to negligent in terms of noticeable impact on wear and maintenance. I believe @Bald Rick has covered that in quite some detail on other threads. Especially as third rail 377s run round with a big block of concrete underneath in place of a transformer!

And any increased costs would almost certainly be offset by the greater flexibility available, in both normal running and incidents.

Electrically hauled freight would be similarly battery-equipped or bi-mode.

I love the confidence that this will happen - all this effort to avoid infrastructure spend by putting more and more onto the trains.

It takes me back to the bad old days of DfT's attempts to avoid electrification in case of new technologies - the so called "bionic duckweed".

 

[TheGrew]

Whilst I would like to see wires where there is no electrification currently.
If there were to be a conversion of the 3rd rail to 25kv I would have thought it would make most sense to start at the edge and work towards London, as complexity is likely to increase the further in you go. This being said I gather much of the challenge is to do with civil work, raising bridges/lowering tracks to allow the correct clearances. With signalling isolation, I wonder if this could be used as part of the justification to upgrade to ETCS at the same time.

So I would start at Weymouth, working my way up the SWML at least as far as Basingstoke, but ideally Woking. Then I would look to do the Portsmouth Direct Line (as far as Woking), Alton Line, and the North Downs Line.

 

[bluenoxid]

How much of the third rail network today was electrified with OHLE in the early decades of the last century? I appreciate that standards and infrastructure will have changed since the systems were decommissioned.

 

[75A]

Very, very little.

== Doublepost prevention - post automatically merged: 6 Mar 2026 ==

Whilst I would like to see wires where there is no electrification currently.
If there were to be a conversion of the 3rd rail to 25kv I would have thought it would make most sense to start at the edge and work towards London, as complexity is likely to increase the further in you go. This being said I gather much of the challenge is to do with civil work, raising bridges/lowering tracks to allow the correct clearances. With signalling isolation, I wonder if this could be used as part of the justification to upgrade to ETCS at the same time.

So I would start at Weymouth, working my way up the SWML at least as far as Basingstoke, but ideally Woking. Then I would look to do the Portsmouth Direct Line (as far as Woking), Alton Line, and the North Downs Line.

How on earth would you fund this?

 

[Energy]

Overhead conversion seems unlikely, but I'd expect some branch lines to be converted to BEMU operation, e.g. Lewes to Seaford.

 

[TheGrew]

Very, very little.

== Doublepost prevention - post automatically merged: 6 Mar 2026 ==


How on earth would you fund this?

I hoped to make it clear this is a hyperthetical. Electrification of non-electrified lines is priority.

 

[zwk500]

I love the confidence that this will happen - all this effort to avoid infrastructure spend by putting more and more onto the trains.

It takes me back to the bad old days of DfT's attempts to avoid electrification in case of new technologies - the so called "bionic duckweed".

It's quite different to bionic duckweed, because Battery technology is already in widespread deployment internationally and is being introduced in the UK.

The Tyne and Wear metro and Merseyrail fleets are already battery-equipped. And in the case of the 555s (T&W Metro), they run on a 100% electrified route network. Senior people at GWR and SE have already said they're looking very seriously at having battery capability on their new fleets. ROG have a battery equipped freight loco, GBRf and DRS have bi-mode freight locos.

I don't see batteries as a replacement for genuine OHLE proposals. But I do see Batteries as very much a part of the electric railway solution. However for the purposes of this thread it's mostly academic as the 3rd rail network isn't going to be replaced while places like Bristol aren't electrified.

Overhead conversion seems unlikely, but I'd expect some branch lines to be converted to BEMU operation, e.g. Lewes to Seaford.

Lewes to Southerham Jn isn't being de-electrified at all, and I'd be extremely surprised if Southerham Jn to Newhaven was de-electrified, and unless Tide Mills can't be resolved in any other way, fairly surprised if Newhaven to Seaford was. Just politically it'd be very odd.

 

[35B]

It's quite different to bionic duckweed, because Battery technology is already in widespread deployment internationally and is being introduced in the UK.

I'm well aware the technology is a lot more mature - that is not my point. The point is the determination to latch onto anything at all that will avoid having to actually think things through properly. And, given who was in charge of railways at DfT in the bionic duckweed era, I strongly suspect his detestation of engineering constraints has been cascaded down - from experience of a recent Permanent Secretary at DfT, I have no confidence in serious intelligence being applied

The Tyne and Wear metro and Merseyrail fleets are already battery-equipped. And in the case of the 555s (T&W Metro), they run on a 100% electrified route network. Senior people at GWR and SE have already said they're looking very seriously at having battery capability on their new fleets. ROG have a battery equipped freight loco, GBRf and DRS have bi-mode freight locos.

A subset of the Merseyrail 777s are battery-equipped, precisely because of the inability to do small extensions sensibly. I wasn't aware the 555s were fitted, but have some sympathy with limited emergency provision (more so than the single GU in the 800s). As for the various Vossloh/Stadler designs you mention, they have their place. But they are workarounds and a means of sidestepping doing the job properly - if fears about TransPennine come true, it will be impossible to move a Northern EMU between Manchester and Leeds without either a loco or going the (very) long way round. That is no way to run a railway.

I don't see batteries as a replacement for genuine OHLE proposals. But I do see Batteries as very much a part of the electric railway solution. However for the purposes of this thread it's mostly academic as the 3rd rail network isn't going to be replaced while places like Bristol aren't electrified.

The problem is precisely that disingenuous electrification, sorry, discontinuous electrification is being proposed as a way to avoid doing anything.

Lewes to Southerham Jn isn't being de-electrified at all, and I'd be extremely surprised if Southerham Jn to Newhaven was de-electrified, and unless Tide Mills can't be resolved in any other way, fairly surprised if Newhaven to Seaford was. Just politically it'd be very odd.

I agree on this, but the point of discussion about BEMUs is that it makes conversations like this more plausible.

 

[Nicholas Lewis]

How much of the third rail network today was electrified with OHLE in the early decades of the last century? I appreciate that standards and infrastructure will have changed since the systems were decommissioned.

LB&SCR electrified at 6.6kV some parts of its suburban system.

Victoria to London Bridge via Peckham Rye
Victoria to Coulsdon Nth and Sutton (via West Croydon)
Peckham Rye to Norwood Jcn via Tulse hill and Crystal Palace
Balham to Tulse Hill

There other South London services were also in the plan before WW1 but the use of German equipment forced its abandonment and only a few routes got completed before Southern Railway decided to convert the whole lot to 660 V DC to be compatible with LSWR and SECR systems. Given the government had decided that 1500 V DC OLE was to be standard its surprising it was never converted to that but Southern as a private entity could still largely do as it wanted.

Of course in hindsight this wasn't the best decision but to attempt to convert now would be an act of folly given the wider need to decarbonise the rest of the system first.

 

[6Gman]

Good luck with the politics - spending billions in London & SE converting already electrified lines, yet not completing the GWML and MMLschemes? There might be a case for the SWML west of Basingstoke if the Reading and Exeter lines ever get 25kV AC.

The years of disruption would also make it pretty unpopular south of the Thames I suspect.

 

[zwk500]

The problem is precisely that disingenuous electrification, sorry, discontinuous electrification is being proposed as a way to avoid doing anything.

And this is something I join you in strongly opposing.

 

[Bald Rick]

The point is the determination to latch onto anything at all that will avoid having to actually think things through properly.

Or perhaps people have thought things through properly, and come to the conclusion that in many cases battery trains have the potential to bring all the benefits of electric traction at a much lower expenditure up front and in future maintenance and operation costs than full electrification of the infrastructure?

 

[35B]

Or perhaps people have thought things through properly, and come to the conclusion that in many cases battery trains have the potential to bring all the benefits of electric traction at a much lower expenditure up front and in future maintenance and operation costs than full electrification of the infrastructure?

They may have, but I don’t hear that case being made. I do, repeatedly, see actions being taken that seek to avoid short term costs, combined with random assertions of future benefits that assume all possible benefits and pay no heed to downside costs.

I can see a case for BEMUs, but I find it very revealing that this isn’t being made in any structured way, or with any suggestion as to the right place for them.

Meanwhile, we keep seeing attempts to say they’re a good thing in one of the circumstances where they offer least value

 

[martin butler]

The sheer amount of disruption would make it a non-starter, all the main 3rd rail routes are heavily used by commuters it wouldn't even get off the ground, then there's the cost

the most likely change to happen will be BEMUs for some lines, such as Uckfield, Marsh link, and Reading to Redhill, as these are cheaper than electrifying sections of line, and then having to have units with dual power capability, where as BEMU's that can obtain power from 3rd rail, could operate on both electrified as well as un electrified routes, as all the routes I mentioned, do include some 3rd rail sections, but a unit, would still operate other routes if needed as a normal unit.

 

[Bald Rick]

They may have, but I don’t hear that case being made.

Not hearing is not the same as not happening.

 

[Magdalia]

I do, repeatedly, see actions being taken that seek to avoid short term costs

What you are seeing is actions being taken to avoid big up front costs that take a long time to deliver benefits. That matters because of the government's financial position, where long term borrowing costs more than 4.5% in annual interest payments and the existing debt interest costs are already taking up a big chunk of tax revenue.

pay no heed to downside costs.

For projects with big up front costs that take a long time to deliver benefits, one of the biggest downside costs is cost of finance.

 

[Djgr]

A subset of the Merseyrail 777s are battery-equipped,

Very small subset

 

[eldomtom2]

They may have, but I don’t hear that case being made. I do, repeatedly, see actions being taken that seek to avoid short term costs, combined with random assertions of future benefits that assume all possible benefits and pay no heed to downside costs.

I can see a case for BEMUs, but I find it very revealing that this isn’t being made in any structured way, or with any suggestion as to the right place for them.

Meanwhile, we keep seeing attempts to say they’re a good thing in one of the circumstances where they offer least value

I have to agree. Currently there's no public plan for what merits electrification and what can be done with battery units, and LNER still has tri-modes on order and Northern still plans to purchase tri-modes for their new fleet, so clearly at the moment the industry doesn't seem to think that battery units can totally replace diesel.