Making top-contact third rail safer

[Mojo]

What I don't understand about third rail is why nobody has developed an affordable and safe means of shielding it. You can't shield the top, but U shaped fibreglass troughs do exist and significantly reduce the risk of it being stepped on/caught by accident.

In my experience at locations with kickboards (I’m not sure if this is the correct term but I’ve always called them that and people seem to understand what I’m talking about), the likelihood of fires seems much more prevalent. Arcing on the conductor rail can set the older wooden boards alight in its own right, but also items such as litter and dried vegetation getting caught in the gap between the rail and board.

 

[HSTEd]

Would kickboards truly be the way to go if we are doing it now?

With modern polymer insulator technology we could probably pultrude (fancy extrusion) a polymeric insulator directly onto the rail, leaving only the top surface exposed, along with periodic gaps on the sides for jointing on cables.
If the connectors took the form of bolts, the boltholes could be filled with pultruded plugs when not in use.

 

[alloverplace]

The numbers in this thread made me want to do some basic risk assessment to get a feel for what might be considered reasonable.

In general, health and safety law allows you to decide what safety measures are needed based on cost benefit analysis. According to this Modern Railways article, third rail generates 0.47 FWIs (fatalities and weighted injuries) per thousand track km year. That’s considered to be worth spending at least £1 million to prevent – £1000 / km / year, or about £60k / km over a 60 year assessment period (give or take some discounting).

To me, this raises two points:

• £60k / km is absolutely nothing in the context of electrification costs. So, unless swapping from third rail to OHLE is virtually free, it’s really hard to justify a third rail ban on cost/benefit grounds. It's interesting to see that the ORR policy doesn't mention cost/benefit - I wonder whether they considered it, and if so whether they got the same answer I did.
• £60k / km sounds like it should buy quite a lot of “warning high voltage” signs and maybe even some fiberglass troughing at high-risk locations (like stations).

This is pretty crude first pass analysis – I hope someone in the industry’s done it more thoroughly. But it fits with my first impression that the rail industry is very harsh on new schemes and perhaps a little too relaxed about existing ones.

 

[HSTEd]

In general, health and safety law allows you to decide what safety measures are needed based on cost benefit analysis. According to this Modern Railways article, third rail generates 0.47 FWIs (fatalities and weighted injuries) per thousand track km year. That’s considered to be worth spending at least £1 million to prevent – £1000 / km / year, or about £60k / km over a 60 year assessment period (give or take some discounting).

At least in the nuclear industry, a 1:1 Cost Benefit is not enough to justify a "So Far As Is Reasonably Practicable" (SFAIRP) defence.
The cost being more than ten times the benefit would be more likely to meet with the regulators approval.

So probably more like ~£600k than £60k.
With 25kV installations running several million per single track kilometre (£4m supposedly in recent projects) this is still a small portion of the cost of a 25kV scheme.

Of course the FWI can probably be avoided with far cheaper innovations which would reduce the SFAIRP driver for using 25kV instead. Given that something like 3/4 of FWI appears to be tresspassers, the obvious move is to improve fencing or walling to prevent them getting near the track in the first place. On lines that do not operate at night, killing the power (or reducing the voltage to below the ~100V limit set for DC touch potentials) would probably slash trespasser fatalities.

 

[Taunton]

The cheapest way to change the system to be safe enough (for any sensible person) would be to switch to bottom-contact, but the problem is that (unlike the wires) that can't coexist with top-contact, so you'd need lengthy closures to do it.

The issue with bottom contact is that the train collector shoes, all being connected, are live, now pointing upwards and unshielded, just beneath the platform edge at stations, even though the actual conductor rail is over on the other side. In conventional 3rd rail the shoebeam covers them.

The DLR has worked through multiple versions of shielding over time to try to overcome this.

== Doublepost prevention - post automatically merged: 10 Jun 2024 ==

On lines that do not operate at night, killing the power (or reducing the voltage to below the ~100V limit set for DC touch potentials) would probably slash trespasser fatalities.

Some years ago this was done on Christmas Day when there were no trains. Come Boxing Day major amounts of the copper power supply cabling had been stolen. Keeping it powered up is the best protection against theft.

 

[Falcon1200]

I have to say the number of fatalities for members of the public took me by surprise. I would not have anticipated it being quite so high! 132 fatalities in twenty years feels like quite a high number of fatalities. It's perhaps also interesting that it was, seemingly, trending down from the early 00s before spiking over the last five years, which includes the pandemic years of course.

Thanks (and to the NR staff of course) for obtaining the figures, they are of concern, but perhaps the number of fatalities from third rail contact should be put in context against the number of deaths on the railway overall; From the ORR for 2022/23;

]https://dataportal.orr.gov.uk/statistics/health-and-safety/rail-safety/

• There were 11 people who died in accidents while trespassing in the year April 2022 to March 2023. They involved ten trespass fatalities on the mainline and one on the non-mainline. There were six fatalities at level crossings which involved four pedestrians and one motorcyclist on the mainline and a member of the public on a scooter at a footpath crossing on the non-mainline network. There were 300 suicide or suspected suicide attempts on the mainline, of which 236 were fatalities.

Disregarding the level crossing incidents, 246 trespasser fatalities, in one year, compared to (caused by the third rail) 31 for the 5+ years from 2019 to now, an average of 6 per year.

Here are these really dangerous, exposed electrical conductors running along at ground level and yet to the non-trained person, there's no clear and obvious difference, no indications or warnings to distinguish them from the other rails and the serious threat to life they pose to anyone getting near them.

Members of the public could also be people on level crossings, people at stations, etc.

Is there anywhere on any of the third rail systems where the public can come into contact with the third rail without trespassing? Being on the track without proper authority and knowledge is dangerous everywhere.

There is no doubt that the third rail can be dangerous to both staff and the public, more so than overhead wires (although I have been involved in tragic incidents to both staff and the public from the overheads as well), but so dangerous that it cannot be extended ever again? That is the question (which I, thankfully, do not have to answer).

 

[Trainbike46]

Thanks (and to the NR staff of course) for obtaining the figures, they are of concern, but perhaps the number of fatalities from third rail contact should be put in context against the number of deaths on the railway overall; From the ORR for 2022/23;

]https://dataportal.orr.gov.uk/statistics/health-and-safety/rail-safety/



Disregarding the level crossing incidents, 246 trespasser fatalities, in one year, compared to (caused by the third rail) 31 for the 5+ years from 2019 to now, an average of 6 per year.

Fortunately, some of the mitigations suggested above, especially better fencing, would help against both 3rd rail and tresppasser fatalities.

Is there anywhere on any of the third rail systems where the public can come into contact with the third rail without trespassing? Being on the track without proper authority and knowledge is dangerous everywhere.

The main point I was making is that someone who falls of a platform and gets hurt by third rail after, may technically be tresspassing (in that they are somewhere they shouldn't be), but is clearly not the same as someone going for a dander along the railway right of way.

There is no doubt that the third rail can be dangerous to both staff and the public, more so than overhead wires (although I have been involved in tragic incidents to both staff and the public from the overheads as well), but so dangerous that it cannot be extended ever again?

That is the question (which I, thankfully, do not have to answer).

Same for me, fortunately!

 

[MarkyT]

Fortunately, some of the mitigations suggested above, especially better fencing, would help against both 3rd rail and tresppasser fatalities.

I read some other material recently from ORR that stated platform falls have become the no.1 cause of passenger fatalities today, whether or not there is a train about at the time and regardless of electrification status or type.

The main point I was making is that someone who falls of a platform and gets hurt by third rail after, may technically be tresspassing (in that they are somewhere they shouldn't be), but is clearly not the same as someone going for a dander along the railway right of way.

A platform fall is usually accidental, possibly with some carelessness on the part of the individual, but might be health related or due to actions of someone else on a platform, possibly with recklessness or deliberate malice on their part. Crowding might be contributory if not controlled adequately by an operator, and platform surface conditions including temporary contaminants like snow and ice. There are many ways someone might end up on the track at a station where it's not intentional and thus not their (entire) responsibility.

I'm becoming more supportive of removing conductor rail from most station platform areas and around level crossings, common points of incursion. That would have been unthinkable 20 years ago, but the concept of having a moderately sized battery installed on all new DC units is finding favour for various reasons. The new South Eastern metro fleet procurement is investigating the option. The measure provides capabilities to:

• Power through short planned or unplanned isolations.
• Always reach the next station in the event of more widespread and serious power outages, and have plenty of 'hotel power' in reserve for extended waits there for onward transportation.
• Shunt around depots and sidings without widespread and complex conductor provision in the yard (employee hazard).
• Simplify or eliminate complex conductor arrangements through junction areas with no risk of gapping.

It seems a good moment to revisit the design concept for 3rd rail if trains were to have such abilities. The concern here in the forums seems to be mainly about authorising new provision in the light of recent ORR policy, but 'grandfather rights' on existing systems are also not an eternal license to retain the entire 1930s concept unchanged forever, just a recognition of 'reasonable practicability' constraints for long-lasting major assets. I suggest the industry should embark on a robust long-term programme to get the casualties on existing 3rd rail right down, then we'll talk about system extensions. Part of that programme might include a small extension as a pilot for new techniques.

 

[HSTEd]

It seems a good moment to revisit the design concept for 3rd rail if trains were to have such abilities. The concern here in the forums seems to be mainly about authorising new provision in the light of recent ORR policy, but 'grandfather rights' on existing systems are also not an eternal license to retain the entire 1930s concept unchanged forever, just a recognition of 'reasonable practicability' constraints for long-lasting major assets. I suggest the industry should embark on a robust long-term programme to get the casualties on existing 3rd rail right down, then we'll talk about system extensions. Part of that programme might include a small extension as a pilot for new techniques.

Well doing that depends on whether we believe, not without reason, that the regulator will take a mile if given an inch.

Once the idea of using batteries somewhere has been given to the ORR, they are likely to demand it be used everywhere with an ever-widening field of application.
The ORR did, after all, blow up an already in progress electrification scheme (Glasgow-Edinburgh) as part of its bid to abolish British overhead wiring clearance standards in favour of European ones.

== Doublepost prevention - post automatically merged: 10 Jun 2024 ==

Some years ago this was done on Christmas Day when there were no trains. Come Boxing Day major amounts of the copper power supply cabling had been stolen. Keeping it powered up is the best protection against theft.

Well modern installations could be built with no copper in them at all. Aluminium cables could be used which have a far lower theft value.

In the medium term the work on superconducting DC rail feeders in France is likely to reduce the amount of conductive metal in an installation by orders of magnitude. It will depend on how the current trial installation at Montparnasse goes.

But I'd rather suffer losses to theft than not have any rail electrification installed at all.

EDIT:
Clarifying language.

 

[Trainbike46]

Once the idea of using batteries somewhere has been given to the ORR, they are likely to demand it be used everywhere with an ever-widening field of application.
The ORR did, after all, blow up an already in progress electrification scheme as part of its bid to abolish British overhead wiring clearance standards in favour of European ones.

That is something that should have been pushed back on much harder, at least for any bridge that met the old standards, or for which design work (or beyond) was complete.

 

[HSTEd]

That is something that should have been pushed back on much harder, at least for any bridge that met the old standards, or for which design work (or beyond) was complete.

In my view, the major flaw of the current system is that the ORR's word is de-facto law and there is little or no recourse to appeal against it.

It, like other similar bodies, likes the idea of risk-assessed derogations from its rules making them more reasonable. However, in the nuclear industry at least, risk assessments have a reputation for being massive time and effort sinks. Consequently people end up doing whatever the regulator demands to escape them, no matter how outrageous in engineering terms.

 

[Taunton]

That is something that should have been pushed back on much harder, at least for any bridge that met the old standards, or for which design work (or beyond) was complete.

As I understood it (I think this refers to the Glasgow-Edinburgh electrification) it was indeed seen as a nonsense, but quick discussion showed that arguing the toss and all that entailed would take such time out of the project schedule, and require countless meetings and reviews, that redesigning and incurring substantial extra engineering cost was still seen as the most effective way to get something done.

 

[Trainbike46]

In my view, the major flaw of the current system is that the ORR's word is de-facto law and there is little or no recourse to appeal against it.

It, like other similar bodies, likes the idea of risk-assessed derogations from its rules making them more reasonable. However, in the nuclear industry at least, risk assessments have a reputation for being massive time and effort sinks. Consequently people end up doing whatever the regulator demands to escape them, no matter how outrageous in engineering terms.

As I understood it (I think this refers to the Glasgow-Edinburgh electrification) it was indeed seen as a nonsense, but quick discussion showed that arguing the toss and all that entailed would take such time out of the project schedule, and require countless meetings and reviews, that redesigning and incurring substantial extra engineering cost was still seen as the most effective way to get something done.

Sounds like, in this at least, the nuclear industry and the railway industry are similar

 

[MarkyT]

The problem is probably that many in the industry, not without reason, believe that the regulator will take a mile if given an inch.

Once the idea of using batteries somewhere has been given to the ORR, they are likely to demand it be used everywhere with an ever-widening field of application.
The ORR did, after all, blow up an already in progress electrification scheme as part of its bid to abolish British overhead wiring clearance standards in favour of European ones.

ORR is partly an economic regulator as well as overseeing rail safety, so I'm sure they could be persuaded to see the provision of ever larger batteries for ever greater range without conductors is a diminishing returns game, especially if smaller batteries might allow NR to remove much of the risk at the critical locations on DC. This is where the sweetspot of discontinuous electrification can come in. South Wales Metro is the most important project in the UK for demonstrating this concept on rail, albeit using 25kV OHLE for the electrified bits, but it's also becoming a popular method to extend lower voltage trolley bus networks further afield, and a tramway closer to home in Birmingham (although primarily for aesthetic reasons in that case). Similar principles could apply to a 3rd rail DC network allowing conductor rail to be removed from certain areas where it represents most risk or a high cost of maintenance and renewal.

 

[Nottingham59]

This is where the sweetspot of discontinuous electrification can come in.

Of course it is. Battery trains can easily do 100 miles off the wires. That's plenty to cover Uckfield, Rye, North Downs. And out to Salisbury. I can't see anywhere that needs extension to third rail.

 

[Falcon1200]

I'm becoming more supportive of removing conductor rail from most station platform areas and around level crossings, common points of incursion.

The platform area idea is interesting, but there are a lot of stations! And in most cases the third rail is on the side away from the platform, thus reducing the risk to someone falling. Maybe more useful at the few stations where there is a platform both sides of a single track. Level crossings should certainly have cattle grid style guards to prevent people accessing the track there.

 

[MarkyT]

Of course it is. Battery trains can easily do 100 miles off the wires. That's plenty to cover Uckfield, Rye, North Downs. And out to Salisbury. I can't see anywhere that needs extension to third rail.

If you had a toolkit of measures to extend or fill in a little in selected places that might allow smaller, cheaper, and lighter batteries and increased range, to Exeter and back perhaps.

 

[zwk500]

If you had a toolkit of measures to extend or fill in a little in selected places that might allow smaller, cheaper, and lighter batteries and increased range, to Exeter and back perhaps.

Extending conventional third rail c.1km past the junction at Hurst Green, Ashford, North Camp, Shalford Jn, etc would be fine. Exeter suits OLE much better than third rail, especially if it can be part of electrifying Redbridge/Chandler's Ford to Westbury and Bath with OLE as well for a Dual-Voltage Solent-Severn service.

 

[MarkyT]

Extending conventional third rail c.1km past the junction at Hurst Green, Ashford, North Camp, Shalford Jn, etc would be fine. Exeter suits OLE much better than third rail, especially if it can be part of electrifying Redbridge/Chandler's Ford to Westbury and Bath with OLE as well for a Dual-Voltage Solent-Severn service.

I think that's a better West of England Line concept with Exeter - Waterloo trains able to run on either system. I'm no great supporter of 3rd rail in principle, the main reason being the high transmission losses in the 'final mile' conductor and return regardless of how losslesly you can feed the substations. It has its uses for short extensions, maybe a little further than you suggest, if it makes sense for battery range beyond.

 

[HSTEd]

Extending conventional third rail c.1km past the junction at Hurst Green, Ashford, North Camp, Shalford Jn, etc would be fine. Exeter suits OLE much better than third rail, especially if it can be part of electrifying Redbridge/Chandler's Ford to Westbury and Bath with OLE as well for a Dual-Voltage Solent-Severn service.

I doubt that Redbridge to Westbury and Bath is going to get done any time soon though however.

I think we have to face things as they are, not as we wish they were, in economic terms.
If the 25kV programme gets back on track it will still be a very long way down the list. As far as I can tell the Wessex Main Line is two short trains per hour and a smattering of freight services (at least that is the situation at Dean station, which I selected at random).

Given the trend in recent 25kV projects, I think it is likely that the alternative to a modern third rail installation is likely to be battery operation without end. I don't think its reasonable to assume that affordable 25kV installations will definitely be available - we need a contingency for failure.

 

[zwk500]

I doubt that Redbridge to Westbury and Bath is going to get done any time soon though however.

I think we have to face things as they are, not as we wish they were, in economic terms.
If the 25kV programme gets back on track it will still be a very long way down the list. As far as I can tell the Wessex Main Line is two short trains per hour and a smattering of freight services (at least that is the situation at Dean station, which I selected at random).

Salisbury-Exeter is likely further down the list than Southampton-Bristol! And on third rail it'd be even further down the list. But I agree OLE won't get south of Westbury for a long time, in fact it'll be a long time before it gets near Westbury at all!

The remaining third rail gaps are relatively short. Extensions 'around the corner' at the boundary junctions make sense to prevent strandings and give acceleration away from the junctions but batteries can easily cover the intermediate distances, especially if you put a top-up charger at Uckfield and Rye. Reigate-Shalford and North Camp - Wokingham are pretty short sections.
The other remaining diesel-over-juice services are heading out of the network, although the 'Romsey Rounder' services could probably go third-rail/battery with a charger at Salisbury. Freight and Crosscountry aren't converting any time soon, and GWR would need OLE at least Bath-Bristol-Patchway to transition to Dual Voltage + Battery units, so it's only the Waterloo-Exeters that remain as a problem. Of the potential solutions, Bi-Mode or Battery with Fast-charge top-up is the most likely medium-term solution.

Given the trend in recent 25kV projects, I think it is likely that the alternative to a modern third rail installation is likely to be battery operation without end. I don't think its reasonable to assume that affordable 25kV installations will definitely be available - we need a contingency for failure.

I genuinely think that moving forwards all EMUs will have a secondary battery on board to allow them to get to a sensible place in the event of an emergency switch-off, or to manage temporarily disruptive events such as response to an incident. It wouldn't need to be big or powerful, but if everything has it as standard then a sub-fleet with beefier batteries would be relatively simple to provide.

 

[MarkyT]

Salisbury-Exeter is likely further down the list than Southampton-Bristol! And on third rail it'd be even further down the list. But I agree OLE won't get south of Westbury for a long time, in fact it'll be a long time before it gets near Westbury at all!

The remaining third rail gaps are relatively short. Extensions 'around the corner' at the boundary junctions make sense to prevent strandings and give acceleration away from the junctions but batteries can easily cover the intermediate distances, especially if you put a top-up charger at Uckfield and Rye. Reigate-Shalford and North Camp - Wokingham are pretty short sections.

It might be worth looking at the alternative of an isolated 3rd rail section of a few miles for in motion charging on the Uckfield for example, in a fully segregated area well clear of stations and crossings. The short switched platform section at the terminus could still be provided for a top up in emergency but you wouldn't want to rely on having time to charge if you wanted to do a swift bounceback due to late running incoming.

The other remaining diesel-over-juice services are heading out of the network, although the 'Romsey Rounder' services could probably go third-rail/battery with a charger at Salisbury. Freight and Crosscountry aren't converting any time soon, and GWR would need OLE at least Bath-Bristol-Patchway to transition to Dual Voltage + Battery units, so it's only the Waterloo-Exeters that remain as a problem. Of the potential solutions, Bi-Mode or Battery with Fast-charge top-up is the most likely medium-term solution.

It's likely Exeter will be a 25kV area eventually, so to avoid the need for a diesel generator onboard or supersized batteries, a handful of isolated OHLE stretches on the single line might be worth considering. A single line on a former double track formation should be able to accommodate wiring with minimal structural alterations, and each section might be supplied by a local DNO feeder, easier and quicker to arrange than a traditional big National Grid feeder connection. West of Tisbury signalling is axle counter based so there should be little problem with compatibility and traction return and earth bonding. The feeder might have a quantity of local storage built in to help manage peak loading as necessary, like fast charging stations. Onboard battery sizing would aim to allow a train to reach the following charging opportunity if such a section was encountered de-energised.

I genuinely think that moving forwards all EMUs will have a secondary battery on board to allow them to get to a sensible place in the event of an emergency switch-off, or to manage temporarily disruptive events such as response to an incident. It wouldn't need to be big or powerful, but if everything has it as standard then a sub-fleet with beefier batteries would be relatively simple to provide.

I agree and it would be reasonable to use that capability to have some routine scheduled battery operation over short unsparked route extensions like Headbolt Lane. The same battery probably wouldn't take a Merseyrail unit out to Warrington and back along the CLC however, hence that might be another good infill project using the discontinuous 3rd rail techniques I outlined upthread. It's a mostly urban railway, fully segregated with no level crossings. Fencing refurbishment and improvements would be very wise anyway if service levels were planned to improve over today's frequency in a notional Merseyrail takeover.

 

[Nottingham59]

It might be worth looking at the alternative of an isolated 3rd rail section of a few miles for in motion charging on the Uckfield for example, in a fully segregated area well clear of stations and crossings.

It's really not that far. Flixbus are running battery coaches from London to Newport without intermediate charging. A battery train should be able to get to Uckfield and back.

 

[zwk500]

It might be worth looking at the alternative of an isolated 3rd rail section of a few miles for in motion charging on the Uckfield for example, in a fully segregated area well clear of stations and crossings. The short switched platform section at the terminus could still be provided for a top up in emergency but you wouldn't want to rely on having time to charge if you wanted to do a swift bounceback due to late running incoming.

It's 26 miles from Hurst Green to Uckfield, if you're putting any 3rd rail halfway down you may as well do the whole thing. A top-up charger and you just eat the delay is far more cost-effective for disrupted working, remembering that the units will be able to take charge from Hurst Green to London Bridge/Victoria and back.

It's likely Exeter will be a 25kV area eventually, so to avoid the need for a diesel generator onboard or supersized batteries, a handful of isolated OHLE stretches on the single line might be worth considering. A single line on a former double track formation should be able to accommodate wiring with minimal structural alterations, and each section might be supplied by a local DNO feeder, easier and quicker to arrange than a traditional big National Grid feeder connection. West of Tisbury signalling is axle counter based so there should be little problem with compatibility and traction return and earth bonding. The feeder might have a quantity of local storage built in to help manage peak loading as necessary, like fast charging stations. Onboard battery sizing would aim to allow a train to reach the following charging opportunity if such a section was encountered de-energised.

Honestly I can't see the advantage of islands in this situation over just squeezing the feed as far east from Exeter as possible.

I agree and it would be reasonable to use that capability to have some routine scheduled battery operation over short unsparked route extensions like Headbolt Lane. The same battery probably wouldn't take a Merseyrail unit out to Warrington and back along the CLC however, hence that might be another good infill project using the discontinuous 3rd rail techniques I outlined upthread. It's a mostly urban railway, fully segregated with no level crossings. Fencing refurbishment and improvements would be very wise anyway if service levels were planned to improve over today's frequency in a notional Merseyrail takeover.

For me, Merseyrail is where providing continuous third rail has a far better case against batteries. It's a heavy metro in all but ownership.

 

[MarkyT]

It's really not that far. Flixbus are running battery coaches from London to Newport without intermediate charging. A battery train should be able to get to Uckfield and back.

I'm sure the coach operation has some contingency plan for the unexpected insufficient charge scenario. Probably rustling up a backup diesel bus. Whatever it is, such an occurrence will not delay all traffic on the motorway. If a train made it to Uckfield late with less charge than expected, it might have to depart late to give time for a top-up causing knock on delays over the single line possibly propagating for hours. A short in-motion section on approach to the terminus could mitigate this scenario as it would allow you to always be able to pick up enough to return immediately without any waiting at the turnround. Batteries don't need to be as large as possible. They might be more optimised in size, weight, and cost if some further infrastructure work was contemplated. Fast charging is great and the tech is getting better, but in most chemistries, slower charging is almost always better for battery charge cycle life, so for long life it's best to minimise it unless its the best value option on a self-contained branch, or for emergency top ups at termini.

 

[zwk500]

I'm sure the coach operation has some contingency plan for the unexpected insufficient charge scenario. Probably rustling up a backup diesel bus. Whatever it is, such an occurrence will not delay all traffic on the motorway. If a train made it to Uckfield late with less charge than expected, it might have to depart late to give time for a top-up causing knock on delays over the single line possibly propagating for hours. A short in-motion section on approach to the terminus could mitigate this scenario as it would allow you to always be able to pick up enough to return immediately without any waiting at the turnround. Batteries don't need to be as large as possible. They might be more optimised in size, weight, and cost if some further infrastructure work was contemplated. Fast charging is great and the tech is getting better, but in most chemistries, slower charging is almost always better for battery charge cycle life, so for long life it's best to minimise it unless its the best value option on a self-contained branch, or for emergency top ups at termini.

How often is the delay likely to be sufficient that the train would not be able to do the return journey in the charge available from the top-up time available? It seems rather cost-ineffective to provide infrastructure against that occasion instead of using an operational strategy such as turning short, cancelling a return trip or cutting the branch to an Oxted shuttle.

 

[MarkyT]

Honestly I can't see the advantage of islands in this situation over just squeezing the feed as far east from Exeter as possible.

That would require the major feeder for the area to be in place which can take many years to arrange. Alternatively, perhaps you could build out an isolated OHLE installation from that end but put in a temporary DNO feeder just for that line in the shorter term, tapping it into the new grid feeder later when its provided for the GWR route wiring.

For me, Merseyrail is where providing continuous third rail has a far better case against batteries. It's a heavy metro in all but ownership.

Definitely a Metro. Some of the class 777 fleet have bigger batteries already which is a good thing for all the emergency reasons we agree on as well as the ability to get to Headbolt Lane. While this is a good test location for the battery tech, I'd have thought that a very short extension of the 3rd rail could be justified there in the longer term. I expect the end substation can handle the power requirements and the extension doesn't actually add any additional simultaneous train movements at peak load. I recall the manufacturer stated the train design could support line haul batteries OR a 25kV transformer for dual system operation but not both due to space and weight constraints. All 777s have a depot movement-sized battery already.

== Doublepost prevention - post automatically merged: 12 Jun 2024 ==

How often is the delay likely to be sufficient that the train would not be able to do the return journey in the charge available from the top-up time available? It seems rather cost-ineffective to provide infrastructure against that occasion instead of using an operational strategy such as turning short, cancelling a return trip or cutting the branch to an Oxted shuttle.

On such a line a peak short turn or cancellation could lead to frustrating long waits and subsequent overcrowding for many disappointed customers on a line with a fairly low frequency to begin with. Finding a substitute bus at short notice to ship people over to the higher frequency Brighton line would also be next to impossible in the peaks, especially in school term time. An alternative resilience measure might be to provide a 'range extender' gen set, that wouldn't be scheduled to be used routinely but might be fired up when necessary in a 'range crisis' scenario. The emergency range extender might equally be a hydrogen fuel cell. It's all more complexity of course and both technologies require a source of fuel to be carried around. Not sure if hydrogen is suitable to be stored for long periods for occasional use. Pretty much all forms of hydrogen are either dirty under the hood in course of their production or in the case of hydrolysis simply very inefficient compared to using the same electricity to charge a battery. Another solution is to provide larger batteries so the likelihood of being stranded and needing to take a fast charge at the terminus is significantly reduced.