What comes after the HST?

[HSTEd]

I agree but I think you'd need to cut the length down. For example I think a 2+8 HST is probably going to be a bit much for a Liverpool - Norwich service. You also have to consider platform lengths, even a cut down 2+4 HST is going to be significantly longer than a 4-car 158 (sticking with Liverpool - Norwich) so would there be issues with platform lengths?

Well Liverpool, Stockport, Sheffield, Chesterfield, Nottingham< Grantham and Peterborough all take HST length trains on the platforms used by the Norwich-liverpool services.
Thanks to Pendolinos on the WCML, HSTs on the Midland and the fact that I have been on a 225 from Platform 4 at Grantham.

I'm not sure about some of the other places but Ely surely can because it takes London commuter trains and Norwich takes eight carriage plus DVT and loco formations all the time.

So only the minor stations (and the two Manchester stops) might have issues and that can be solved with SDO (which would probably be fitted during the power door refit if it hasn't been already)

 

[Nym]

I agree but I think you'd need to cut the length down. For example I think a 2+8 HST is probably going to be a bit much for a Liverpool - Norwich service. You also have to consider platform lengths, even a cut down 2+4 HST is going to be significantly longer than a 4-car 158 (sticking with Liverpool - Norwich) so would there be issues with platform lengths?

I'm thinking 4, 5 or 6 and the following kind of services....

NOTE: I'm assuming a re-build of Oxford Road station here...

Manchester - Cardiff - Swansea - Random Welsh Village
Manchester - Llandudno
Edinburgh - Aberdeen & Inverness

Liverpool Lime Street - Warrington Central - Manchester Piccadilly - Stockport - Sheffeild: - Cleethorpes and - Nottingham - Norwich

Might not be long enough for this, because they're currently 9 or 10 cars long.
But Waterloo - Exeter & Bristol?

 

[ainsworth74]

Manchester - Cardiff - Swansea - Random Welsh Village
Manchester - Llandudno
Edinburgh - Aberdeen & Inverness

Liverpool Lime Street - Warrington Central - Manchester Piccadilly - Stockport - Sheffeild: - Cleethorpes and - Nottingham - Norwich

Those sound like reasonable routes to be using them on and would free up a number of 158s and 175s (and perhaps even some 185s). How about Cardiff - Holyhead as another option?

 

[Nym]

Yup, also fits...

 

[AndyLandy]

Might not be long enough for this, because they're currently 9 or 10 cars long.
But Waterloo - Exeter & Bristol?

I had wondered if the Pennine Desiros that are displaced with the TPE electrification might be suitable stock for this line. Not sure if you'd actually gain much by that cascade, but it would give SWT a more uniform fleet, if there's enough 185s.

 

[TGV]

My experiences of this forum is that many people have differing opinions on what's best and aren't overly disposed to entertaining other people's suggestions. This may be in part to there being an awful lot of uninformed suggestions that are completely unfeasible.

That said, I'd certainly be interested in hearing interesting ideas of people who actually understand what might work.

There is a wide range of people here Andy (assuming that is in fact your name!). Speaking myself, I have coming up for 9 years of high speed rail engineering experience. Before that a mixture of some workshop and minor operational roles starting in 1993 when I started as a teenage volunteer rebuilding an 08 shunter. In between I have done a stint at designing and being a maintenance engineer on depot as well as acceptance of new rolling stock and first article inspections of new builds.

There are many people here who have been on the railways longer than I have - at least I presume that is the case anyway - and you'll note that the more cynical opinions tend to be those who have done this for a living for many years. Not because we are negative, but we have first hand experience of what the reality of it all is like. So don't be offended if it seems we are putting ideas down to be awkward or obstructive - it's just that there are hidden pieces of legislation, standards, financial constraints or engineering details (Where as the saying goes, the devil resides) that will kill off many an idea before it becomes something that'll roll on rails.

On your question, I see Nym has come up with many answers that should get you thinking. I'm not sure if Nym is a railway engineer (although I feel like I should - we have both been on this site for many years), but regardless of whether he has ever done fault-finding on an AC loco or night shifts servicing trains, he seems to know one end of a ciruit diagram from the other and has clearly been thinking about the HST replacement a fair bit.

My original musings of just having 2 fleets (one electric and one diesel) are mainly because of history (both mine and the railways in general). I don't think it would be a deal breaker to phase in new, proven AC stock when the lines have been electrified, but retain a fleet of known diesel units for the longer or more convuted routes. That said, the idea of having diesel locos with auto couplers ready and waiting for an arriving AC train where the wires run out is worthy further study.

I'm afraid that all my experience and instict is telling me that bi-modes/hybrids are a risky waste of money - especially when billions will have already been spent putting wires up in the first place. That said, it may well still happen. Remember that someone somewhere once thought APT was the right solution for the problem at that time.

 

[AndyLandy]

There is a wide range of people here Andy (assuming that is in fact your name!). Speaking myself, I have coming up for 9 years of high speed rail engineering experience. Before that a mixture of some workshop and minor operational roles starting in 1993 when I started as a teenage volunteer rebuilding an 08 shunter. In between I have done a stint at designing and being a maintenance engineer on depot as well as acceptance of new rolling stock and first article inspections of new builds.

Yep, Andy is my real name (although I assume 'TGV' may not be yours)
Sounds like you've done a fair bit of work in the field.

There are many people here who have been on the railways longer than I have - at least I presume that is the case anyway - and you'll note that the more cynical opinions tend to be those who have done this for a living for many years. Not because we are negative, but we have first hand experience of what the reality of it all is like. So don't be offended if it seems we are putting ideas down to be awkward or obstructive - it's just that there are hidden pieces of legislation, standards, financial constraints or engineering details (Where as the saying goes, the devil resides) that will kill off many an idea before it becomes something that'll roll on rails.

Well, quite. My earlier post was intended as tongue-in-cheek (and I hope that came across, but you can never tell with the Internet.) Being on other forums where I'm an expert in the field, I know how frustrating it can be to deal with people who come out with 'smart' ideas that just won't float because they're missing some crucial bit of understanding.

On your question, I see Nym has come up with many answers that should get you thinking. I'm not sure if Nym is a railway engineer (although I feel like I should - we have both been on this site for many years), but regardless of whether he has ever done fault-finding on an AC loco or night shifts servicing trains, he seems to know one end of a ciruit diagram from the other and has clearly been thinking about the HST replacement a fair bit.

There are certainly some very interesting ideas being floated. That's chiefly the reason why I hang around here at all. I do like to see insightful and well-thought-out suggestions for where we should be going with our railways.

My original musings of just having 2 fleets (one electric and one diesel) are mainly because of history (both mine and the railways in general). I don't think it would be a deal breaker to phase in new, proven AC stock when the lines have been electrified, but retain a fleet of known diesel units for the longer or more convuted routes. That said, the idea of having diesel locos with auto couplers ready and waiting for an arriving AC train where the wires run out is worthy further study.

That was always my first thought as well, as we have with Pendolino/Super Voyager on WCML and HST/IC225 on the ECML. But as has been pointed out, if we're investing in electrification, buying more diesel trains might not be such a wise idea.

I'm afraid that all my experience and instict is telling me that bi-modes/hybrids are a risky waste of money - especially when billions will have already been spent putting wires up in the first place. That said, it may well still happen. Remember that someone somewhere once thought APT was the right solution for the problem at that time.

So, from my naïve viewpoint, the idea of an IC fleet composed entirely of hybrids would provide a single type of traction for a TOC's drivers to sign off on. It could run electric under the wires for as far as the wires will stretch, whilst still being able to go to all the long-distance destinations where the decision has been taken to not (yet) electrify. Couple that with the ability to run under its own motive power should there be an OHLE failure or a diversion via a route that's not wired and you have a remarkably versatile train. But as you say, I'm not privy to enough details to know where the pitfalls are with this.

On the other hand, someone somewhere has to be designing new trains. Would Pendolino have ever happened if APT didn't? That's not to say that bi-mode is something they should be looking at, but that at some stage, there has to be innovation and taking steps into the unknown. If they didn't, we'd still be hauling wooden coaches with steam engines. (Although I daresay there are a few here who wouldn't mind were that the case!)

But yes, once again, many thanks for your replies. I'm finding the discussion quite fascinating.

 

[TGV]

Absolutely - innovation has to happen and all too often the railways change much slower than, for example, the automotive industry, but their rules, culture and products are vastly different.

Would Pendolino have happened had it not been for APT - possibly yes as the theory of tilting trains has been long known. They would have got there somehow. That's not to say that APT was a bad idea - the key words in that were "at that time" - it was rushed through because of political pressure, it was in fact too complex for it's own good (and the budget and technology available then) and these are the lessons I want transferred to whatever replaces HST.

I worked with a guy who was involved with the hydrokinetic braking system on the APT and we have talked about it at length. It was a fascinating project and he is an outstanding engineer, however none of that could prevent the final product being a failure - and a well publicised one too. We can't afford that again, especially when replacing something as important (and it must be said, iconic) as the HST.

Yes, the advantage of a one train solution would be that drivers only need sign one traction. Also spare parts would be common, depots could share more work between them and you needn't have to haul a specific train back to a specific depot to have work done to it, should it fail in service. There are many advantages operationally too (seat booking systems, depot layouts, etc...). I'm speaking purely as an engineer though when I say I'm not convinced by it though. I want to provide the passengers with a reliable, good value and comfortable train for service and I am still not sold on a bi-mode as the solution to that. I'm open to being changed on that though and will be keeping an eye on what develops.

 

[Nym]

But at the moment I think that the DfT are being swept up in some eastern stupidity á la Prius if they think that the likes of widespread EDMUs are a good idea with the current stock available in the UK and current electrification strategy. End of next week I'll put the numbers together for you on the front of LDPE Diesel Stock requirements if you're interested.

Basically, refurbishing HSTs to live until 2025 and having the new EMU stock as Loco Haulable sees us right until around about 2035, and by then, 20 years from now, who knows what state we'll be in even with the choice of fuel for self powered units.

We could have moved on from Diesel to something different...

All too often perfectly good solutions are swept under the carpet in favour of 'innovation' that isn't necessary and provides a less optimal solution than what is already available.

Eg.

Toyota Prius (Realistically; 50mpg)
BMW 320d ED (Realistically; 75 - 80mpg)

About the same price, but the 320d ED is much more recyclable and environmentally friendly for what I see most prius drivers using as their work cycles (long mileages). And they're also about the same price, and the beemer can be run on bio-fuels with ease.

Before we go too far off topic, I'm not against hybrids, the new generation of hybrid buses are a brilliant idea, either way they're implemented but I prefer the full shaft disconnect ones, simply because I can see a return to Trolley Buses as a result when these become more widespread.

 

[HSTEd]

Toyota Prius (Realistically; 50mpg)
BMW 320d ED (Realistically; 75 - 80mpg)

About the same price, but the 320d ED is much more recyclable and environmentally friendly for what I see most prius drivers using as their work cycles (long mileages). And they're also about the same price, and the beemer can be run on bio-fuels with ease.

Before we go too far off topic, I'm not against hybrids, the new generation of hybrid buses are a brilliant idea, either way they're implemented but I prefer the full shaft disconnect ones, simply because I can see a return to Trolley Buses as a result when these become more widespread.

Hybrid engines do have benefits beyond simple fuel consumption however, the increased control over the engine power bands and so on accorded to them allows them to produce 90% less particulates per unit of fuel burned.

And you are comparing a petrol hybrid with a diesel, a better comparison would be that new Citreon diesel hybrid in my opinion.

 

[Rhydgaled]

The reason I support bi-mode 22x units but not bi-mode IEP is simple. A class 22x unit is a DMU, and bi-mode is better than a DMU. However, an EMU is better than a bi-mode, and if (and this is the biggest problem with trying to avoid IEP bi-mode I think) you order around 20 more Pendos for ICWC to release their 221s, IEP needn't be anything other than an EMU. Hence, making IEP (which should be an EMU) into a bi-mode is making the IEP worse, whereas making 22xs bi-mode is making them better.

what do you guys think IEP should be?

I think it should be an 'Intercity-ed' (use plug doors, move them to end of coaches and stick them in vestibles, ensure an Intercity-spec interior with decent legroom, make them 9 coaches long with a buffet car) class 395 EMU, no diesel engines anywhere near it, with vehicles that are similar dimensions to a mark3 coach (so fit the same loading guage and can go anywhere IC125s can without guage clearance works). It should have a 125mph top speed and accelerate rapidly. These would work the shorter-distance IC services, eg. Kings Cross - Leeds/Hull/Harrogate/Lincon (class 67 locos (there are enough around) dragging to Harrogate and Lincon, Hull too if the wiring proposals fall through) and Paddington - Oxford/Cheltenham/Cardiff and most Paddington - Bristol trains. These routes would also have more of the intermediate stops in. Cheltenham might need diesel haulage too, but not buying diesel engines and not having to guage clear for 26-metre coaches should save enough to wire Swindon - Cheltenham and Swansea - Cardiff (the problem, as I say, is the cost of the extra 390s to release 221s to start a cascade that puts bi-mode Voyagers on Paddington - Cotswolds and the Paddington - Westbury semi-fasts).

The longer-distance trains would be worked by 140mph Intercity 225s and have fewer stops (the extra 15mph and fewer stops would help these keep up with the new EMUs). This would be Paddington - Swansea (Reading being the only calling point in England), and one of the 4 Paddington - Bristol services (calling at Bath and Chippenham (perhaps Reading at a push) only) each hour, and Kings Cross to all East Coast's Scottish destonations (1tph max though, the 2nd, slower, Edinbrough services in some hours would be an IEP EMU). Might need a few new 125mph electric locos working with mark3s to cover all those services though. West of Swansea the electric loco would be taken off and a massivly refurbished (or new-build) 100mph TDM-fitted class 47 put on (that's the only way west of Swansea would work I think, unless the EMU can drive a diesel loco that pushing, due to reversal at both Swansea and Carmarthen on Pembroke/Tenby services). North of Edinbrough, the logical thing is to use 67s as you can share locos with the sleepers, but they don't have TDM so you'd probablly have to drag the electric loco with you and have the 67 run-round at Aberdeen and Inverness or drag an IEP EMU instead of a LHCS set.

That leaves the extensions of the Westbury semi-fast to Exeter, which I suggest GW's 5 180s are used for, and Paddington - Plymouth/Penzance services which I suggest are all routed via Westbury to cut down under-wires mileage (put a few more IC125s on XC's Penzance/Plymouth services to compensate) remain in the capable hands of IC125s until 2030-2035. Then, I'd electrify at least to Plymouth and order a fleet of 140mph electric locos and new (mark 5) coaches and passenger-carrying DVTs to replace all the sleeper vehicles and the remaining day-stock mark 3s, followed by the Intercity 225 fleet.

 

[Nym]

Hybrid engines do have benefits beyond simple fuel consumption however, the increased control over the engine power bands and so on accorded to them allows them to produce 90% less particulates per unit of fuel burned.

And you are comparing a petrol hybrid with a diesel, a better comparison would be that new Citreon diesel hybrid in my opinion.

Either way, they both make use of batteries and provide little benefit over simply switching to a more economical model without hybrid drive. And I'm not a fan of using batteries in anything like this, they're simply too complicated to make to see any environmental benefit, the same as I'm against the scrappage scheme because of production costs to the environment, that no-one seems to consider.

 

[tbtc]

I'm afraid that all my experience and instict is telling me that bi-modes/hybrids are a risky waste of money - especially when billions will have already been spent putting wires up in the first place

Part of the problem when dealing with British railways is politics.

For example, the population of Penzance is only 20,000. That's around the same size as Truro/ Falmouth/ St Austall/ Newquay and around double that of St Ives/ Bude.

So there's nowhere beyond Plymouth of any real size (I'm sure there are a few places in the UK with well over 20,000 people but no train station).

However, whilst extending electrification of the GWML beyond Bristol to serve Exeter (120,000) and Plymouth (250,000) should be justified on economic grounds (both are big places, you'd also reach the 60,000 in Taunton and around double that number around Torbay), there's no real economic case to electrify to Cornwall.

At the moment, Cornwall gets a decent number of trains to London and to Birmingham (and other XC destinations), so there'd be an outrage if you chopped all of these when you electrified to Plymouth...

..but then there'd be complaints if you ran Cornish diesel trains under the wires for 200 miles to London (or much further for XC services) - and wiring these routes whilst continuing to run a significant number of diesel services would undermine the case for electrification in the first place.

(the same could be said of routes like Holyhead/ West Wales/ Inverness etc)

So, the only two real options are to bring diesel haulage for the last section of some long distance routes (meaning something like a 67 dedicated to pulling these Intercity services). From an enthusiast viewpoint that'd be great because I grew up with loco-hauled/ shunting etc. However, whilst it'd be fun, there are problems with this.

Whilst a bi-mode train has drawbacks, it'd allow services to continue running to small places like Penzance. It'd also allow these units to be cascaded to other routes once lines are wired (e.g. if you use bi-mode on London - Hull trains then the line gets fully wired then you can use the bi-mode trains on London - Sunderland trains). You'd also be able to deal with diversions much easier (no need for drags).

It's not perfect, but I can see why they are doing it. I know that this goes against the view of the majority on here, but the logic of technology doesn't always match with the logic of "politics" in the UK. All the expert stuff about batteries/ transformers/ circuits is great but doesn't deal with how our railways work.

For example, based on a previous thread, the number of people travelling from Inverness to London each day could fit into a Pacer. But the Highland Mainline route "needs" a direct London service because people see it as being important to have (even though there are other places with no London link that may justify one more).

(and, no, we aren't going to wire *enough* up to avoid this problem before HSTs will need scrapping - much as I'd like it!)

 

[Failed Unit]

I had wondered if the Pennine Desiros that are displaced with the TPE electrification might be suitable stock for this line. Not sure if you'd actually gain much by that cascade, but it would give SWT a more uniform fleet, if there's enough 185s.

SWT don't like non-corridor connected trains, but really this line should be electrified. If it has 9 coach trains at times then EMUs are the way forward.

 

[Aictos]

I'm not sure about some of the other places but Ely surely can because it takes London commuter trains and Norwich takes eight carriage plus DVT and loco formations all the time.

Ely and Norwich can easily take HSTs, I should know as I travelled on a East Midlands Trains one last year from St Pancras International to Peterborough via the Mid Norfolk Railway and Norwich

 

[hst2cornwall]

Some really good ideas here, and I'm glad I started this topic. Good points made about the population of cornwall and places such as st austell, penzance etc only being small but the population grows by a massive amount in the summer period and many travel by train meaning surely the need for something more substantial than 3/4 coach trains such as the voyagers. This is where the hst comes in, so any replacement for this area would have to be 8/9 coach. I like the idea of an emu halled by diesel traction but would this really work on paddington penzance type services when I can't see anyway of increasing the line speed between penzance and plymouth due to te geography in part part of the world. I just think any opperater will hold on to the simplest option for as song as posible, and in the case of london penzance this will be diesel all the way. From a passenger/enthusiast's point of view, travelling long distances such as this in a voyager/180 is a nightmare. I know what an important part polotics play in this game, its just a shame that that seems the only factor that drives these descisions.

 

[HSTEd]

How much would it even cost to extend from Plymouth to Penzance (assuming the wires do eventually reach plymouth after a post-upgrade consolidation of services onto the route via Bristol)?

It might be cheaper to simply pay the upfront costs to run them all the way, especially if you can get away with single end feeding from Plymouth (the fact that the line is so quiet would help that surely?).

The low speed would also enable the use of the simpler equipment people like TramPower and Furrer and Frey are pushing for secondary route electrifications.

 

[Nym]

The problem with single end feeding though is that you only use up two of the three phases, but if you can feed with three conductors going down the line from Plymouth, also handling all the branches (why not electrify them) to Penzance, then single feeder could well work.

But if the EMUs running the majority of the route are designed to have locomotives attached as I would have them designed as such, then I really don't see why we would NEED the wires to go all the way into Cornwall. I can see either Exeter or Plymouth being the limit of wires, with haulage beyond here.

The same as wires reaching Swansea and haulage beyond there, and Haulage beyond Edinburgh to Inverness, Woucster I can see being done as part of XC so it's a matter of infill to Swindon via Kemble.

 

[Zoe]

I can see either Exeter or Plymouth being the limit of wires, with haulage beyond here.

Would there be any benefit in ending the wires at Exeter unless you are going to cut back the current Plymouth terminating services to Exeter?

 

[HSTEd]

Would there be any benefit in ending the wires at Exeter unless you are going to cut back the current Plymouth terminating services to Exeter?

Ofcourse the case immediately west of Exeter is likely better than the one immediately east of Exeter if we consider the possibility of through traffic from the WEML.

Which in an ideal world would be electrified as well at some point. (Atleast to salisbury and likely beyond there for operational reasons).

 

[tbtc]

Some really good ideas here, and I'm glad I started this topic. Good points made about the population of cornwall and places such as st austell, penzance etc only being small but the population grows by a massive amount in the summer period and many travel by train meaning surely the need for something more substantial than 3/4 coach trains such as the voyagers

Looking back, I wasn't intending my comments to look anti-Cornish, just using it as an example of a long running London service that wouldn't justify *full* electrification.

The ECML and WCML both lost a lot of London links at/near electrification (e.g. Middlesbrough), but there are lots of places off the GWML that have direct London services that can't all justify wiring (Newquay, Pembroke, Hereford etc). For that reason I can see bi-mode being used to maintain a link (without running diesels all the way to the capital).

 

[Zoe]

Ofcourse the case immediately west of Exeter is likely better than the one immediately east of Exeter if we consider the possibility of through traffic from the WEML.

Which in an ideal world would be electrified as well at some point. (Atleast to salisbury and likely beyond there for operational reasons).

But if not all of the Basingstoke and Exeter Line is electrified then any through service wouldn't be able to benefit from any electrification west of Exeter unless bi-mode was used. Also don't forget that all services from Waterloo were cut back to Exeter in 2009. That said if Exeter to Exmouth and Newton Abbot to Paignton were to also be electrified then this service could go over to EMU operation and there are plans for this to increase to 2 trains per hour between Exeter and Paignton.

 

[AndyLandy]

Don't forget that large portions of Salisbury-Exeter line are still single track, courtesy of Dr. Beeching. I'd assume no electrification would happen unless it includes line redoubling. I'd be surprised if someone decided to invest in electrification of that route otherwise.

 

[TGV]

Don't forget that large portions of Salisbury-Exeter line are still single track, courtesy of Dr. Beeching. I'd assume no electrification would happen unless it includes line redoubling. I'd be surprised if someone decided to invest in electrification of that route otherwise.

Agreed. I would be surprised if electrification reached Exeter via that route. More likely from Bristol, but I doubt very much that it would go further west than Exeter. If it even got there in the first place.

 

[Zoe]

Agreed. I would be surprised if electrification reached Exeter via that route. More likely from Bristol, but I doubt very much that it would go further west than Exeter. If it even got there in the first place.

As I say though, there isn't much point in electrifying to Exeter with the current service pattern. It could be an option though to change this though and starting terminating a lot more services at Exeter, leaving Plymouth to be served by the Penzance intercity trains and a DMU shuttle from Exeter but I doubt this will be popular.

 

[tbtc]

There isn't much point in electrifying west of Bristol if it only goes as far as Exeter. Only a handful of services start from or terminate at Exeter although in theory you could change this to have Exeter the principle terminus for South West services and reduce Plymouth to just the Penzance service.

One benefit of bi-mode trains is that you could electrify in small sections and still get some benefit (rather than full EMU operation, where you'd have to wait until the line was completed before getting the real benefit).

If wiring to Bristol works then extend the wires to Exeter (and bi-mode the Plymouth/Cornwall trains). If wiring to Exeter works then wire to Plymouth (and retain bi-mode for the Cornish services). It becomes a virtuous circle.

 

[Zoe]

One benefit of bi-mode trains is that you could electrify in small sections and still get some benefit (rather than full EMU operation, where you'd have to wait until the line was completed before getting the real benefit).

If wiring to Bristol works then extend the wires to Exeter (and bi-mode the Plymouth/Cornwall trains). If wiring to Exeter works then wire to Plymouth (and retain bi-mode for the Cornish services). It becomes a virtuous circle.

The difference is that west of Plymouth the service level is reduced to only 1 tph and not all of these are intercity trains. The service level west of Exeter isn't significantly different to east of Exeter.

 

[Nym]

Or don't have bi-mode and use Exeter because it has a large enough layout to attach and detach locomotives and is far away enough from the Bristol Commuter towns, unlike Weston, Yatton etc.

One could also attach a loco at Bristol but Weston would benefit from electrification quite a lot as it sees significant commuter services. Taunton would be a pain for loco attach and detach so the next major point is Exeter.

 

[Zoe]

Or don't have bi-mode and use Exeter because it has a large enough layout to attach and detach locomotives and is far away enough from the Bristol Commuter towns, unlike Weston, Yatton etc.

Why do this at Exeter though when you could wire though to Plymouth and not need the locos at all other than the Penzance services? There's nothing to suggest that Plymouth wouldn't be able to cope with attaching locomotives.
--- old post above --- --- new post below ---

Taunton would be a pain for loco attach and detach so the next major point is Exeter.

Taunton has four through lines, only one less than Exeter. Platforms 1 and 3 though at Exeter are often busy with Exmouth/Paignton services.

 

[Nym]

Theres also the point of Exeter being the last major point in the national grid that can take a big single phase hit to the supply, spanning much further into Cornwall is going to be a pain on the National Grid, and the chances are that Exeter would be fed from Bristol where the phases can be much better balanced than on a limb of the grid down at Exeter or Plymouth. (It's not just the cost or difficulty of throwing up some wires!)

Exeter also has some handy loops and sidings...