Why is LHCS unfavourable nowadays?

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BuryBlue

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The title is self explanatory. Why are new D/EMUs favoured so strongly over a loco set? Surely it can't just be the acceleration advantage. Considering the shortage of (especially) diesel traction in various regions, I'm surprised there isn't more demand for the spared HSTs/225s, or indeed new locomotives and repurposed Mk3 carriages.

I'd also think they'd be cheaper than a multiple unit set as well. Is it to do with efficiency perhaps?
 
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Philip Phlopp

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The title is self explanatory. Why are new D/EMUs favoured so strongly over a loco set? Surely it can't just be the acceleration advantage. Considering the shortage of (especially) diesel traction in various regions, I'm surprised there isn't more demand for the spared HSTs/225s, or indeed new locomotives and repurposed Mk3 carriages.

I'd also think they'd be cheaper than a multiple unit set as well. Is it to do with efficiency perhaps?

Reliability and track access charges.

Lose an engine on a LHCS set, and it's sat, dead, waiting for assistance, lose an engine on an HST set, and it'll do 100mph at a push, allowing some recovery of service. Lose an engine on a DMU and it'll be anything from a minor inconvenience to a bit of a problem.

EMU stock, particularly the new generation, have duplicate systems - two or three transformers, two pantographs, and form half sets, so one half can still work, the loss of a pantograph isn't an issue, that sort of thing.

Track access charges are a major issue too, because of the sliding scale concerning axle loads, EMUs and DMUs, being only a little heavier than an unpowered coach, are only pennies more per mile than an unpowered coach, when you put all the weight into one locomotive, it becomes significantly more expensive per mile.

Train length is another - adding a locomotive takes up 20m of train length, where you're compromised by signal, platform length and points, you might need that 20m length to fit in a passenger carrying vehicle with 50 seats.

There's also power/braking issues. It's easier to get 4MW down when you've got a dozen powering axles, instead of just four. It's easier to brake and recover energy when you've got a dozen axles with motor generators on them.
 
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NSEFAN

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There's no point in having locos where not needed, as you end up with non-passenger carrying space, as well as a higher weight on the loco axles compared to distributed traction, increasing wear and tear on the infrastructure.

The only reason you would use loco hauled passenger trains nowadays is if there's no other stock available, or for passenger comfort reasons (I.e no underfloor engines).
 

AM9

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The title is self explanatory. Why are new D/EMUs favoured so strongly over a loco set? Surely it can't just be the acceleration advantage. Considering the shortage of (especially) diesel traction in various regions, I'm surprised there isn't more demand for the spared HSTs/225s, or indeed new locomotives and repurposed Mk3 carriages.

I'd also think they'd be cheaper than a multiple unit set as well. Is it to do with efficiency perhaps?

As passenger numbers rise, trains have been extended to limits of the infrastructure. With an MU, platform space is not wasted and no provision for further running around is needed.
 

Philip Phlopp

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That's quite a blanket statement there...

For an equal amount of power and comparable gearing, it's generally true.

To get DMU type acceleration, you need to throw a silly amount of power at the problem, as the Class 68 solution demonstrates.
 

Crossover

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Reliability and track access charges.

Lose an engine on a LHCS set, and it's sat, dead, waiting for assistance, lose an engine on an HST set, and it'll do 100mph at a push, allowing some recovery of service. Lose an engine on a DMU and it'll be anything from a minor inconvenience to a bit of a problem.

Actually, anything from a bit of a problem to no impact. A Voyager pretty much won't suffer from an engine out at all other than a bit more noise from the others
 

221129

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Actually, anything from a bit of a problem to no impact. A Voyager pretty much won't suffer from an engine out at all other than a bit more noise from the others

Given that a lot of voyagers run around with one engine shut off anyway I would have thought it would be 0 impact
 

GatwickDepress

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Multiple units allow much more operational flexibility than loco-hauled stock. Units can attach and divide without requiring additional locomotives or infrastructure (sidings, crossovers, etc). This was taken advantage of by the Southern Railway with their intensive portion workings.
 

LNW-GW Joint

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Locos used to be useful for hauling freight as well as passenger trains.
In fact the Class 91 was designed to work freight/sleepers at night - but hardly ever did.
Nowadays the needs of the two modes are different and a passenger loco has little scope for other work.
Class 67 is typical of a dual-purpose loco that has very little of either work today.
Time will tell if Class 68 will do better, and if a Class 88 electric version is viable on passenger trains.
Sorry to bring it up, but locos also don't fit the DOO trend for passenger trains.
Push-pull operation is also less reliable than MU operation, and you need a special vehicle at the non-loco end.
Reliability of the ATW Class 67+DVT sets is very poor.
I don't think we have ever had a good push-pull solution, hopefully the new CAF vehicles will work well with Class 68 for TPE.
 
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BuryBlue

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Locos used to be useful for hauling freight as well as passenger trains.
In fact the Class 91 was designed to work freight/sleepers at night - but hardly ever did.
Nowadays the needs of the two modes are different and a passenger loco has little scope for other work.
Class 67 is typical of a dual-purpose loco that has very little of either work today.
Time will tell if Class 68 will do better, and if a Class 88 electric version is viable on passenger trains.
Sorry to bring it up, but locos also don't fit the DOO trend for passenger trains.
Push-pull operation is also less reliable than MU operation, and you need a special vehicle at the non-loco end.
Reliability of the ATW Class 67+DVT sets is very poor.
I don't think we have ever had a good push-pull solution, hopefully the new CAF vehicles will work well with Class 68 for TPE.

Why is it not possible to have an effective dual mode loco?

Is it because good acceleration AND overall power is impossible to do with the same gear ratios?

And regarding DOO - I'm fairly sure LHCS on the GEML at least doesn't run with a guard/additional personnel - unless you count the person in the catering car.

And I wasn't aware of the Class 68 previously. Obviously Chiltern saw some use for new locomotives, why is it an exception?
 

221129

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Why is it not possible to have an effective dual mode loco?

Is it because good acceleration AND overall power is impossible to do with the same gear ratios?

And regarding DOO - I'm fairly sure LHCS on the GEML at least doesn't run with a guard/additional personnel - unless you count the person in the catering car.

And I wasn't aware of the Class 68 previously. Obviously Chiltern saw some use for new locomotives, why is it an exception?

No LHCS runs without a guard in passenger service.
 

Harbornite

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It makes you wonder why some operators chose to go against the trend and use LHCS, especially Transpennine. I was also going to add that multiple units don't need to have complicated running around procedures, although this has been negated by the development of DBSOs and DVTs (as mentioned elsewhere in the thread).

With regards to Europe, the picture is similar. New units have replaced loco hauled stock in the likes of Germany and Poland, but some operators like DB Regio and fernverkehr are also sourcing new LHCS.
 
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Arglwydd Golau

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The only reason you would use loco hauled passenger trains nowadays is if there's no other stock available, or for passenger comfort reasons (I.e no underfloor engines).

That says it all really. passenger comfort is not a consideration any more. We have (or at least some of us) become used to the constant noise and vibration of today's diesel units.
I was amused some years ago when the press release by ATW (following the introduction of the WG express) talked about 'increased passenger comfort' of the re-introduced old stock. Clearly I had missed their comments about decreasing passenger comfort when they stopped using LHCS previously.
 

W230

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That's quite a blanket statement there...
Slow, tired Class 319s accerlerate quicker than HST's. This I know, so I think it's fair statement to say multiple units are quicker to accelerate in general.

Philip Plhopp said:
EMU stock, particularly the new generation, have duplicate systems - two or three transformers, two pantographs, and form half sets, so one half can still work, the loss of a pantograph isn't an issue, that sort of thing.
The Class 700's are made up of 2 x 4 car (or 6 car) bolted together but they still only have one transformer per half unit. That said, you are spot on about it not failing in the middle of nowhere as the other half is able to power the dead part.
 

AM9

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Slow, tired Class 319s accerlerate quicker than HST's. This I know, so I think it's fair statement to say multiple units are quicker to accelerate in general.


The Class 700's are made up of 2 x 4 car (or 6 car) bolted together but they still only have one transformer per half unit. That said, you are spot on about it not failing in the middle of nowhere as the other half is able to power the dead part.

Similarly, a failed class 700 can be pushed/towed away by another class 700 unit to clear a route much quicker than getting a rescue loco there when there is a queue of units behind it.
 

GB

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And regarding DOO - I'm fairly sure LHCS on the GEML at least doesn't run with a guard/additional personnel - unless you count the person in the catering car.

All LHCS services on the GEML run with a guard/conductor. No guard/conductor on LHCS = no service.
 

FordFocus

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Class 68s are not slow to accelerate.

They are good locomotives but they are having their issues at Chiltern. Couple of fires, irrecoverable engine shut downs and some software glitches. The coaching stock has it's off days with dragging brakes reported too.

Great trains when they work but as soon as something goes wrong, your stuck there for a bit. Where as with a HST or DMU it will limp or continue on it's journey.
 

najaB

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For an equal amount of power and comparable gearing, it's generally true.
Oh, I agree. But there were no qualifiers on the statement, it just read as *all* units are faster than *all* LHCS. I'd put money on gWr's putative 4+2 HST's being pretty fast off the mark.
 

LNW-GW Joint

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Why is it not possible to have an effective dual mode loco?
Is it because good acceleration AND overall power is impossible to do with the same gear ratios?
And regarding DOO - I'm fairly sure LHCS on the GEML at least doesn't run with a guard/additional personnel - unless you count the person in the catering car.
And I wasn't aware of the Class 68 previously. Obviously Chiltern saw some use for new locomotives, why is it an exception?

It's all about performance really.
Class 67 at 125mph was bought for fast mail and parcels traffic that evaporated more or less the day they arrived.
Heavy freight needs to optimise low-end power up to 75mph.
All LHCS runs with a guard, and the driver is isolated from the train.

Chiltern (and ATW) only use LHCS because of the shortage of DMUs, and redundant Mk3 stock was available (though there are not enough DVTs).
Only TPE has chosen an LHCS solution from new, apparently to get trains in service as quickly as possible.
Then there's the sleepers, which is a niche market (and not high-speed).
VTEC's Class 91+Mk4s are being replaced by IEP (mostly).
AGA's Class 90+Mk3s are still soldiering along, but are expected to be replaced by an EMU solution before long.
 

Harbornite

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VTEC's Class 91+Mk4s are being replaced by IEP (mostly).
AGA's Class 90+Mk3s are still soldiering along, but are expected to be replaced by an EMU solution before long.

It's interesting to note that Bombardier recommended a UK variant of its TRAXX locomotive design for these services, with the existing stock being retained. I also think that there's more chance of EMU's being sourced for the GEML services than the retention of LHCS.
 

LexyBoy

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Ever seen a class 166 accelerate before?

They feel sluggish but they out-accelerate an HST (obviously only at lower speeds). From regular experience I can tell you that a 165/6 leaving Didcot at the same time as an HST won't be overtaken until it's almost stopped at Cholsey - about 5 miles. If it weren't stopping it would be a mile or two further.
 

najaB

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f it weren't stopping it would be a mile or two further.
True. But it will get caught which means that at some point the acceleration curve favours the HST. Hence why I said it was a blanket statement - thenorthern didn't make it clear if we were taking 0-30mph, 0-125mph or even 100 to 125mph.
 

AM9

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That says it all really. passenger comfort is not a consideration any more. We have (or at least some of us) become used to the constant noise and vibration of today's diesel units.
I was amused some years ago when the press release by ATW (following the introduction of the WG express) talked about 'increased passenger comfort' of the re-introduced old stock. Clearly I had missed their comments about decreasing passenger comfort when they stopped using LHCS previously.

That is a misleading response. LHCS, as practiced in the UK now is either about to be replaced with much better performing multiple units (class 800/801s), or (the AGA double enders, the Cumbrian releifs and Chiltern's lipstick on a pig stop-gap effort) as a makeshift exercise to get around the shortage of multiple units. So to compare the interior designs of '70s and '80s long distance coaches with 21st century multiple units for (largely) outer-suburban use is a specious argument. If the UK still ran LHCS on shorter services (as is a dying practice in parts of Europe), there would be designs suitable for the routes and their traffic. This would mean higher density seating with 1/3 2/3 sliding doors and a fair amount of airline seating, rather than the end-doors and sets of four seats with tables that some imagine as necessary for LHCS. Stock like that has been provided there since the UK went over to multiple units.
If you are old enough to remember, there were plenty of outer suburban trains consisting of four or five 57ft non-corridor coaches hauled by medium sized steam locos (2-6-4T and mogul tender types), that had seating no different to the hoards of 2-BILs and 2-HAPs running around in 3rd-rail land. Even after dieselisation, they were still being lugged around by class 31s and 33s until the DMUs appeared.
 

LexyBoy

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True. But it will get caught which means that at some point the acceleration curve favours the HST. Hence why I said it was a blanket statement - thenorthern didn't make it clear if we were taking 0-30mph, 0-125mph or even 100 to 125mph.

True - but I think as Philip implied it was intended as a "all else being equal" type comparison. I was replying to greaterwest's comment about 166s being slow - whilst they are compared to other units, they'll still beat loco-hauled.

Obviously if you compare 0-125 mph performance then a unit limited to 90 will not fare well. I doubt there are many cases where LHCS will out-accelerate a unit to the lower of their maximum speeds.
 

sdrennan

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Just back from Switzerland and the seem to regularly use additional carriages bolted onto an EMU . Seen 4 additional to a 3 car emu. They must have high power emu to cope
Best of both woelds
 

jopsuk

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Just back from Switzerland and the seem to regularly use additional carriages bolted onto an EMU . Seen 4 additional to a 3 car emu. They must have high power emu to cope
Best of both woelds

But what do you mean by that? The train almost certainly runs around like all day- there won't be any demand-responsive lengthening or shortening.

There's a rose-tinted glasses view that it used to be the case that station masters would spy large numbers of passengers wanting to board a service and call up the station pilot to bring in a carriage or two off the nearby sidings to bolster a service. I question how much that happened. Even in the steam days most services had a planned formation and many carriages were arranged in fixed rakes, either full trains or part trains. The "flexibility" didn't exist that much, and required a lot of land and manpower to achieve when it was used.

What's much more of a trend recently is for lengthy fixed-formations MUs. Obviously the Pendolinos were among the first of the modern breed (though the idea stretches back to the Blue Pullman DMUs and was the envisaged concept for the HST and APT), with much of the Super Express Train fleet following that pattern (though not all) and much more the Thameslink and Crossrail fleets.
 
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