HST: DMU or LHCS

[SamYeager]

Mod Note: Posts #1 - #6 originally in this thread.

Advocates of the new DMUs

I believe that you can accurately describe the HSTs as DMUs as diesel was their only mode of propulsion. The IETs might be better described as DEMUs as their mode of propulsion can be either diesel or electric depending on NR's progress or lack of such in commissioning the OLE infrastructure.

 

[The_Engineer]

I believe that you can accurately describe the HSTs as DMUs as diesel was their only mode of propulsion. The IETs might be better described as DEMUs as their mode of propulsion can be either diesel or electric depending on NR's progress or lack of such in commissioning the OLE infrastructure.

No..... The HST is a locomotive-hauled diesel train (Class 43 locomotives). It is not a multiple unit.
A DEMU is a multiple unit with diesel-electric rather than mechanical transmission (e.g. Class 201 - 210).
The IET is an electro-diesel train, in the same way Class 73 locomotives are electro-diesel - their primary mode is electric with a supporting diesel-electric capability.

 

[najaB]

The HST is a locomotive-hauled diesel train (Class 43 locomotives). It is not a multiple unit.

Ermm... BR Class 253/254 - still referenced to as such in SA's and similar.

 

[The_Engineer]

Ermm... BR Class 253/254 - still referenced to as such in SA's and similar.

There was an intention to treat them as a unit train originally, this was quickly dropped as the locomotives are frequently changed around and not part of a fixed set. The coaches do have rake numbers but are maintained as coaches and are swapped too. And the train does not multiple with anything, so cannot be a MULTIPLE unit.....

 

[najaB]

And the train does not multiple with anything, so cannot be a MULTIPLE unit.

Class 390s don't multiple with anything either. They're still EMUs.

 

[Bletchleyite]

Class 390s don't multiple with anything either. They're still EMUs.

They don't in normal service, but they can - including Voyagers, which is why the latter have an Alstom rather than Bombardier TMS.

 

[najaB]

They don't in normal service, but they can - including Voyagers, which is why the latter have an Alstom rather than Bombardier TMS.

IIRC, when a Voyager and Pendolino are coupled, only one provides traction.

 

[Bletchleyite]

I believe that you can accurately describe the HSTs as DMUs as diesel was their only mode of propulsion. The IETs might be better described as DEMUs as their mode of propulsion can be either diesel or electric depending on NR's progress or lack of such in commissioning the OLE infrastructure.

HSTs are DEMUs as they have electric transmission. Using that notation a Class 800 is an electro-diesel multiple unit, i.e. an EDMU, as per the Class 73.

 

[DarloRich]

Class 43 = Locomotive

 

[rebmcr]

HST = LMU (Locomotive Multiple Unit)

 

[87015]

There was an intention to treat them as a unit train originally, this was quickly dropped as the locomotives are frequently changed around and not part of a fixed set. The coaches do have rake numbers but are maintained as coaches and are swapped too. And the train does not multiple with anything, so cannot be a MULTIPLE unit.....

The power cars are always in multi with each other - no different to two power cars of a three car 117 or whatever being in multi with each other.

 

[TwistedMentat]

Got to side with the locomotive hauled group. The HST clearly wasn't designed to operate in multiple in revenue service so doesn't fall into that grouping to me.

Now trains that are designed to couple together and run at full line speed but do not in regular service are still multiple units to me because it was a serious feature put into them. So the Class 345 is an EMU even though it'll never do a revenue service as a coupled pair. Same with the Pendolinos.

 

[USRailFan]

The HST clearly wasn't designed to operate in multiple in revenue service so doesn't fall into that grouping to me.

That's not what "multiple unit" means...

 

[najaB]

The HST clearly wasn't designed to operate in multiple in revenue service so doesn't fall into that grouping to me.

Semi-fixed formations with multiple traction motors controlled from a single desk at either end. Sounds like a MU to me.

 

[nlogax]

The more I read into this the more confused I become. I always considered HSTs to be a pair of locos hauling unpowered trailer stock. Is there any difference between an HST and some non-HST Mk 3s sandwiched between a pair of 68s if those Mk3s are through-wired for AAR? Other than the HST being a semi-fixed formation of course.

 

[pdeaves]

Even within BR there was confusion. Officially, the HST was originally deemed a DEMU and later deemed two locos with coaches between. In all honesty, it is probably the case that the HST will always fall into some grey area that doesn't suit any given definition other than what officialdom says it must be.

 

[Doomotron]

Even within BR there was confusion. Officially, the HST was originally deemed a DEMU and later deemed two locos with coaches between. In all honesty, it is probably the case that the HST will always fall into some grey area that doesn't suit any given definition other than what officialdom says it must be.

Exactly. In fact I'd say they're both loco-hauled stock and a multiple unit because the Class 43s work like multiple units when they have Mark 3s between them but they can uncouple from them and become locos.

Actually, forget that example. Think of them like TGVs (coaches with power cars) but the power cars are locos.

 

[swt_passenger]

Even within BR there was confusion. Officially, the HST was originally deemed a DEMU and later deemed two locos with coaches between. In all honesty, it is probably the case that the HST will always fall into some grey area that doesn't suit any given definition other than what officialdom says it must be.

I wonder if this regularly repeated debate might die after they’re all scrapped?

 

[43096]

Oh dear. Train spotters who have to put everything into boxes can’t cope with anything different.

HSTs are HSTs.

 

[nlogax]

I wonder if this regularly repeated debate might die after they’re all scrapped?

Probably. No-one's asking 'Blue Pullmans: DMU or LHCS?' anymore, so..

 

[cactustwirly]

What about LHCS that works in multiple?

DSC_0051 by litecactus, on Flickr

It's an Austrian RJ, which is doubled up between Salzburg and Vienna.

A HST is no more a DMU than the Norfolk 'short set' TnT 37s!

 

[DelW]

That's not what "multiple unit" means...

Semi-fixed formations with multiple traction motors controlled from a single desk at either end. Sounds like a MU to me.

As I understood it when DMUs were introduced in the 1950s, the word "multiple" signified that several (usually) 2-, 3- or 4-car units could be coupled together to make up a train and worked in multiple, i.e. all the train's engines could be controlled from the leading cab. This was a big change from steam locos where if there were more than one loco on a train, each had to have its own engine crew.
Thus thumpers and tadpoles were considered as multiple units (DEMUs in their case) despite the fact that the engine and traction motors were all located in a single vehicle at one end of the set.
These days we have trains like Pendolinos and Thameslink units which are certainly not locos and hauled coaches (as the traction motors are spread throughout the train), but are not multiple units either, as they're not intended ever to work as more than single sets (and AIUI can only be coupled using special equipment if at all?).
As nlogax commented, I can't see any difference in principle between an HST and a topped and tailed loco-hauled set with remote control of the rear loco. HSTs aren't intended to work in pairs (or more), so for me they're closer to being locos & hauled stock than they are to being multiple units.

 

[Doomotron]

These days we have trains like Pendolinos and Thameslink units which are certainly not locos and hauled coaches (as the traction motors are spread throughout the train), but are not multiple units either, as they're not intended ever to work as more than single sets (and AIUI can only be coupled using special equipment if at all?).

I think that now the definition of multiple unit has slowly gone from what you said to being more of a train 'without separate carriages'. The Class 345 will never work in multiple but it doesn't have separate carriages.

Even if MU still did mean that the trains could work in multiple, I think that it would just be easier to call the modern MUs multiple units instead of making a new classification.

 

[Journeyman]

Semi-fixed formations with multiple traction motors controlled from a single desk at either end. Sounds like a MU to me.

Well, the power cars are sort-of locos, but can't easily work singly, and the trailers are sort-of loco-hauled, but are wired very differently to Mark 3 coaches and have multiple working cables.

 

[sprinterguy]

These days we have trains like Pendolinos and Thameslink units which are certainly not locos and hauled coaches (as the traction motors are spread throughout the train), but are not multiple units either, as they're not intended ever to work as more than single sets (and AIUI can only be coupled using special equipment if at all?).

Both Pendolinos and Crossrail stock are fitted with fully functional Dellner couplers and are fully capable of working in multiple with other class members if required.

 

[43096]

Well, the power cars are sort-of locos, but can't easily work singly, and the trailers are sort-of loco-hauled, but are wired very differently to Mark 3 coaches and have multiple working cables.

The trailers are Mark 3s......

LHCS has multi-working cables too - TDM signals pass down the RCH cables.

 

[Mag_seven]

I describe the HSTs as well err HSTs - in many ways they are unique so much so that they are almost a type of train on their own.

(As an aside I am sitting on one now)

 

[DelW]

Both Pendolinos and Crossrail stock are fitted with fully functional Dellner couplers and are fully capable of working in multiple with other class members if required.

Thanks for the correction, I'd had a quick look for photos of couplers but I hadn't found any.

 

[Domh245]

Cast your minds back to the most recent discussion on this topic (that I can remember)

I had a look in RIS-2453-RST (Vehicle Registration, Marking and Numbering) - and came across the following:

A.1.2 High speed train (HST) power cars (Class 43) are covered by the multiple unit set and fixed formation rail vehicle number ranges as set out in Table 4.

Admittedly, the reference to HST vehicles comes under Table 6, but the first 2 digits of their EVN are 95, as is the case for DMUs whilst a diesel locomotive would have 92.

So there you go, definitive proof that as far as anyone important is concerned, they are officially a type of DMU, even if they don't have the usual hallmarks of a DMU with regards to formation and multiple working.

But.......

According to R2 (the rolling stock database set up by RSSB) the first two digits of their EVN are 92. That means the database set up by RSSB is in direct contravention of the document issued by RSSB. So even RSSB can’t decide, much like BR couldn’t!

Nominally a multiple unit by several metrics, but if the industry itself can't even decide, what chance does the forum have? As so eloquently put:

Why does all this have to be so 'either/or'..?

Thing is, conceptually they were conceived to be a distinct concept in rolling stock provision... a combination of elements of push-pull loco-haulage and multiple-unit set formation... and helpfully a distinct new nomenclature was adopted to describe the concept.. namely HSTs, comprising power cars and trailers, in their own distinct numbering series within the BR coaching stock series.

Turns out in the event the concept proved to be more flexible in practical operational terms, and it made practical operational sense to use them more flexibly than was originally conceived..

But the concept is still recognisably what it always was, even though it was flexible enough to evolve and adapt through time, as it continues to be..

And none of that undermines the nomenclature that has always been used for them, in terms both of vehicles and concept.

So it's difficult to work out why anyone would be so insistant on re-defining them at this stage, and trying to force them into narrow, prescriptive, pre-existing, limiting, 'either/or' boxes.. when a perfectly adequate, accurate and suitably flexible descriptor has existed for them for half a century..!

It all seems a bit pointlessly obsessive/trainspottery/OCD..? (Disclaimer.. no gratuitous trivialisation of mental health issues intended)

Maybe everyone could agree that what they actually are is HSTs, comprising power cars and trailers, and in everyday practical terms (wiring and control systems, drawgear, day-to-day operation), that's what they always were and what they continue to be..

 

[nlogax]

Wouldn't the 'ultimate' definition be Network Rail's variable usage charges? From what I can see they determine Class 43s as locos (so - loco-hauled stock). This is currently the case for CP5 and is proposed again for CP6.

I do tend to agree with the points raised above..as HSTs and for practical purposes a little from column A and a little from column B. From everything I read on these forums trying to neatly categorise anything railway-related for the sake of sanity and order is destined to lead to disappointment and frustration