What are the advantages of permanently coupled coaches, e/dmus etc?

[poshbakerloo]

What are the advantages of permanently coupled coaches, e/dmus etc?

All modern trains are permanently coupled...No more "Ooh this train will be busy, lets add an extra coach"...

...All I can see is that it makes trains less flexible, but I'm guessing its done for a reason?

 

[ukrob]

No offence meant, but before we answer, is it a serious question or an attempt to cause arguments (as you know it likely will)?

You don't strike me as the type who doesn't know the pros and cons of each.

 

[poshbakerloo]

No offence meant, but before we answer, is it a serious question or an attempt to cause arguments (as you know it likely will)?

You don't strike me as the type who doesn't know the pros and cons of each.

"You don't strike me as the type who doesn't know the pros and cons of each"

I don't know the pros and cons, I've just seen it mucho times and wanna know why its done like that, crash safety? Why would it cause arguments...?

 

[devon_metro]

Saves time in depots, and due the reduction in the number of loco hauled trains we have its not very practical.

 

[MCR247]

And you'd need a DVT or to be able to run around the train, almost 2 coaches worth of space gone. IMO MUs should be used on regional services, with LHCS on InterCity

 

[poshbakerloo]

Saves time in depots, and due the reduction in the number of loco hauled trains we have its not very practical.

couldn't you have multiple units that can be swapped around easily? Isn't this the case with the sprinters? I know you can couple the whole units up, but can you just add as many middle coaches from 159s together?

 

[WillPS]

Not 'on the fly'.

 

[starrymarkb]

There are some big pros to fixed formation.

Firstly everything is on the same maintenance cycle. This makes things a lot easier as it saves having to remarshall rakes if a coach needs exams and the rest don't

Secondly a big cause of failures is the coupling of vehicles, sockets get worn and loose, if you can minimise the amount of it the better. Also permanent jumpers can be more substantial then autocouplers. There is lot less to go wrong if vehicles are bolted together with pipes/jumpers. On a similar point some of the inter unit connections are very high voltage. There isn't a suitable design of socket to handle a Pendo's 25kV bus

Finally it makes it easier for passengers, if their train is in the same formation they can make a guess at where to stand on the platforms etc. It also means you can provide information to that effect too

 

[Oswyntail]

couldn't you have multiple units that can be swapped around easily? Isn't this the case with the sprinters? I know you can couple the whole units up, but can you just add as many middle coaches from 159s together?

Ok, just visualise it. Lead coach with driver decouples from "base" unit; moves to siding with "spare" coaches in; (are they coupled up?); if coupled, then has to couple up, then uncouple "unneeded" coaches test and draw off; if uncoupled, then has to couple and test each "neede" coach; then toddles back to couple up with remainder of "base" unit. Somewhat complicated, eh? With lots of things to go wrong, movements, coupling etc. Much easier to have pre-formed sets, to minimise movements and coupling. Add to that (with MUs) platform space saved and no DVT required, and we are into no-brainer territory.

 

[royaloak]

If you have a bolted bar coupling between coaches on a unit, there are different rules if the brakes are isolated on the front or back coach compared to a "normal" coupling.

 

[truckman060473]

same thing has happened with some freight. EWS Thrall coal hoppers have bars coupling them together in fixed formation style

 

[Waddon]

I'm not an expert, but modern stock seems to have a lot more cables and wiring between each coach, so I'm assuming its not just a simple matter of disconnect/reconnect. Also, whichever unit disconnected would (i guess) have to have a cab at each end, or similar, if moving around on its own steam to shunt?

 

[jopsuk]

The class 158 based units that went to Thailand are double cabbed, but usually run in formations of two or three- this then allows flexibility. On the other hand, it reduces passenger accomodation space- if you took it to the extreme (say a 12-car commuter service in and out of London) having a cab at every car end would lose you about one or two carriages worth of accomodation.

Why MUs, and not loco hauled, well as said there's binifits in terms of platform space (not having to have space for locos). going away from "flexible" formation loco hauled services has also meant the elimination at terminals of loco release points at the "city" end, run around loops between platform roads and carriage sidings immediatly outside stations. The lack of loco release and run around allows more space for more, longer, wider platforms (or as at Kings Cross now) a bit more concourse space.

It's hardly a new idea, either, certainly as far as commuter trains down south go.

 

[gordonthemoron]

starrymarkb, is that wagenstandanzeiger from Berlin Hauptbahnhof?

 

[Drsatan]

MUs usually accelerate more quickly than LHCS, which means that more trains per hour can be run on busy routes, and journey times can be reduced. I've read that the quickest Waterloo-Exeter journey time with around 14 stops is less than using a class 50 and eight Mark 2s, or even a 42 and a rake of Mark 1s.

On Mark 1 based units (such as the 101, 307, 421), if there was a problem with one of the coaches it was a simple affair to remove one and replace it. On units like the 377 and 444 that use computers far more extensively it's not possible just to swap a coach. That means even if a door fails the unit has to be taken out of service, which results in a cancelled train.

Remember, LHCS tend to be quieter than MUs because of the lack of underfloor engines or traction motors. The voyagers for instance are bloody noisy because of the cummins engine underneath the floor. Combined with the other faults inherent to a voyager (air conditioning stinks, too few seats, lack of luggage space), myself, and a lot of ordinary passengers I guess, would rather use an HST than a Voyager.

 

[ailsa]

All modern trains are permanently coupled...No more "Ooh this train will be busy, lets add an extra coach"...

That ability hasn't been lost with the advent of DMUs. Locally the trains to Weymouth are usually 2 car class 150/2s. When it's going to be busy you will sometimes get a 150 + 153 (one extra coach) or two 150s (two extra coaches). So nothing has really changed, it just that that with DMUs you tend to be adding 2 or 3 coaches at a time.

An advantage of this is that as all carriages are powered, the power to weight ratio stays constant as the train is made longer. So the addition of carriages doesn't result in a train which accelerates more slowly, affecting the ability to keep to time.

Of course DMUs can range from really nice to travel on (159) to miserable (voyagers). I think this reflects the quality of the design and how well it's maintained, rather than any essential distinction between LHCS and DMU.

Of course some people say that HSTs are DMUs but that is a whole different can of worms

 

[bluebottle]

They are permanently coupled though.

 

[ukrob]

They are permanently coupled though.

How is a 150+153 combination 'permanently coupled'?

 

[bluebottle]

Oops! Forgot to quote the post I was replying to. Didn't notice the thread had gone to page 2 either. I was answering this

MUs usually accelerate more quickly than LHCS, which means that more trains per hour can be run on busy routes, and journey times can be reduced. I've read that the quickest Waterloo-Exeter journey time with around 14 stops is less than using a class 50 and eight Mark 2s, or even a 42 and a rake of Mark 1s.

On Mark 1 based units (such as the 101, 307, 421), if there was a problem with one of the coaches it was a simple affair to remove one and replace it. On units like the 377 and 444 that use computers far more extensively it's not possible just to swap a coach. That means even if a door fails the unit has to be taken out of service, which results in a cancelled train.

Remember, LHCS tend to be quieter than MUs because of the lack of underfloor engines or traction motors. The voyagers for instance are bloody noisy because of the cummins engine underneath the floor. Combined with the other faults inherent to a voyager (air conditioning stinks, too few seats, lack of luggage space), myself, and a lot of ordinary passengers I guess, would rather use an HST than a Voyager.

and was referring to HSTs.

 

[90019]

HSTs are semi-permanently coupled. They can be split, but can't work with any other trains without prior modifications.

 

[Drsatan]

HST trailers are, in theory, interchangable though.

 

[asylumxl]

HST trailers are, in theory, interchangable though.

So can coaches from say 165s and 166s etc and many earlier MUs.

 

[jopsuk]

Crikey. We've been through the HST thing plenty. BR envisaged them as MUs, but found that operationally power cars were swapped between sets much more often than intended, so sets ended up with different numbers on each end. So the power cars (which were already numbered 43xxx as coaching stock) became Class 43. They're still reffered to as class 253/254 in some internal uses, and day-to-day are essentially MUs, as the formations are only changed in cases of carriage problems. East coast Mark 4/DVT rakes and the Great Eastern, Pretendolino and WSMR Mark 3/DVT rakes are pretty much operationally MUs as well, with formations rarely altered (though locos change on these even more than HST power cars).

Am I near enough right?

 

[ralphwedgewood]

Permanently coupled sets are nothing new: the GWR 'B' sets had bar couplings "inside". A lot of London area 4 wheel sets were permanently coupled i.e SE&CR 'Z' sets. (and no heating).

 

[Aictos]

HST trailers are, in theory, interchangable though.

Yes staying within HST operation they certainly are but they're not interchangeable when it comes to being loco hauled.

Hence why the ex Virgin LHCS MK3s needed to be converted before they could be used in the Grand Central HST Sets as the wiring is different.