DMU v Loco Hauled

[mike57]

I can understand the reasons for using DMU's for short (say up to 3 carriage) trains, but once one gets to 5 or 6 carriages surely the costs of maintaining 5 or 6 engines, transmissions etc is higher than using a single, or even 2 locomotives with un-powered carriages

Also what about purchase costs, are 6 smaller engines cheaper than one big engine assuming similar overall power to weight ratio?

The fact that unpowered carriages can be refreshed and a newer (or different energy source) loco is swapped during their life if they are displaced onto other services or electrification takes place is another consideration.

Also passenger comfort on longer journeys, no noisy engines under the floor

TPE are partially going this route with the Mk5's.

So why the proliferation of 'long' DMU's, 7 car 222's, 4/5 car 220/1 5 car 180...

Is it just short-termism or are there other benefits in using DMU's on longer units. I am not thinking of 2 x 3 car units coupled together, unless they were nearly always run in 6 car formation from purchase.

On a personal level I think the HST sets still provide the most comfortable (diesel powered) journeys on the east coast mainline, and the 180's used by Hull Trains and Grand Central are the worst.

I can understand having longer EMU's as there are less mechanical components per 'engine', its longer DMU's with the extra complexity it brings that I cant see

 

[RichmondCommu]

I can understand the reasons for using DMU's for short (say up to 3 carriage) trains, but once one gets to 5 or 6 carriages surely the costs of maintaining 5 or 6 engines, transmissions etc is higher than using a single, or even 2 locomotives with un-powered carriages

Also what about purchase costs, are 6 smaller engines cheaper than one big engine assuming similar overall power to weight ratio?

The fact that unpowered carriages can be refreshed and a newer (or different energy source) loco is swapped during their life if they are displaced onto other services or electrification takes place is another consideration.

Also passenger comfort on longer journeys, no noisy engines under the floor

TPE are partially going this route with the Mk5's.

So why the proliferation of 'long' DMU's, 7 car 222's, 4/5 car 220/1 5 car 180...

Is it just short-termism or are there other benefits in using DMU's on longer units. I am not thinking of 2 x 3 car units coupled together, unless they were nearly always run in 6 car formation from purchase.

On a personal level I think the HST sets still provide the most comfortable (diesel powered) journeys on the east coast mainline, and the 180's used by Hull Trains and Grand Central are the worst.

I can understand having longer EMU's as there are less mechanical components per 'engine', its longer DMU's with the extra complexity it brings that I cant see

I regularly use class 222 Meridians to travel from London to the East Midlands and I have no issues with them whatsoever. I barely notice the engine and they are very quick off the mark.

With loco haulage if the loco fails you are knackered with up to several hours delay. Lose an engine, maybe even two and the Meridian will still get you home.

 

[NotATrainspott]

Distributing the mass of the engines over the carriages means lower track wear and better acceleration, which are key for high performance on a modern railway. Modern operating practices also favour multiple units which can be joined together at peak times but run separately to reduce costs when demand is lower. The 7-car Meridian sets are the longest DMUs in use in Britain but they're understandable given that they were built and are maintained alongside their 4 and 5-car classmates.

If you want a fixed-formation long diesel train then the HST is hard to beat. It gives you the best of both worlds, such as the lower track wear (dividing total engine mass by the two powercars makes a big difference versus a single locomotive) and ability to be run in either direction. Originally, before GWML electrification was proposed, the HST2/IEP train was going to be able to operate that way too.

The TPE sets are a bit of an aberration. It seems like CAF were able to build them quickly and cheaply enough that the inherent costs of loco haulage weren't an issue. Had Hitachi been able to churn out a dozen more AT300s in the same timeframe I think we would have seen some more of them instead.

 

[yorkie]

I regularly use class 222 Meridians to travel from London to the East Midlands and I have no issues with them whatsoever. I barely notice the engine and they are very quick off the mark.

I can really notice the engine on these units. I regularly use loco hauled trains and have no issues with them whatsoever.

As for Meridians, they are costly and difficult to maintain (that's a lot of engines!) and have high running costs. They also create a poor station environment, with so many engines running, when idling.

With loco haulage if the loco fails you are knackered with up to several hours delay. Lose an engine, maybe even two and the Meridian will still get you home.

That's a simplistic way of looking at it that only describes one particular scenario. In practice a failure of one vehicle can result in the whole train failing. A modern reliable Class 68 very rarely fails, so it doesn't make sense to have a less efficient train that is harder to maintain just because of one particular set of unlikely circumstances. Also when a DMU failure does occur, it can be harder to rescue it, depending on the compatibility of other units in the area.

 

[yorkie]

Distributing the mass of the engines over the carriages means lower track wear ...

Is, say, a 6-car class 185 really more friendly to track than a 68 and 5 coaches? I am not convinced.

... the HST is hard to beat....

I'll agree with you on this though!

 

[mike57]

I regularly use class 222 Meridians to travel from London to the East Midlands and I have no issues with them whatsoever. I barely notice the engine and they are very quick off the mark.

With loco haulage if the loco fails you are knackered with up to several hours delay. Lose an engine, maybe even two and the Meridian will still get you home.

I haven't been on a 222, but I am assuming its going to be similar to a 220/1, in which case I would rate them as better than 180's. (Which IMO are the worst units on long distance services that I have travelled on, anywhere, ever)

As for the one loco, I would assume at 6-7 cars you would go for the smaller loco x2 like the HST, redundancy and reduced loco weight without having 6 or 7 engines under the floor.

I have to say that until initial problems were solved, I had a few 80mph one engine journeys from London to York in the early 80's. HST's are an excellent design, which is no doubt why they have lasted 40 years in front line service albeit with some major updates over the years.

 

[RichmondCommu]

That's a simplistic way of looking at it that only describes one particular scenario. In practice a failure of one vehicle can result in the whole train failing. A modern reliable Class 68 very rarely fails, so it doesn't make sense to have a less efficient train that is harder to maintain just because of one particular set of unlikely circumstances. Also when a DMU failure does occur, it can be harder to rescue it, depending on the compatibility of other units in the area.

It may well be simplistic but if it happens its catastrophic. The Meridian and the class 68 are both modern reliable trains but I would be very surprised if the class 68 is 100% reliable with no failures in service. I don't see why a class 222 cannot rescue another class 222 but on the trans-pennine route could a unit rescue a class 68 in Standedge Tunnel?

 

[yorkie]

It may well be simplistic but if it happens its catastrophic. The Meridian and the class 68 are both modern reliable trains but I would be very surprised if the class 68 is 100% reliable with no failures in service.

Class 68s are very reliable. No train is 100% reliable.

I don't see why a class 222 cannot rescue another class 222 but on the trans-pennine route could a unit rescue a class 68 in Standedge Tunnel?

I don't understand what point you are trying to make. I said "Also when a DMU failure does occur, it can be harder to rescue it, depending on the compatibility of other units in the area" and all you've come up with is stating that a DMU can be rescued by a unit of the same type, so I assume you are not disagreeing with me?

If you are making a direct comparison, I think a 9-car class 222 rescuing a 9-car class 222 would be more problematical than a loco rescuing a loco hauled train. In practice many modern DMUs are not compatible with many other types of DMUs and the proliferation of many different designs of DMUs is not a good thing in this respect.

 

[Starmill]

The argument about reliability is a moot point really. Everyone wants and expects reliable rolling stock. There is no reason why such expectations might not be met with new trains.

Locomotives are clearly easier to maintain but again that's not likely to be the reason they've become more popular recently.

The main reason for the increasing popularity of locomotive hauled stock is that it's the only thing that is available. Both in terms of what can be hired on the ground right now and what can be produced in a short time frame from manufacturers.

I also think the driving force behind locomotive hauled diesel trains with 7, 8, 9, 10 carriages etc is that fundamentally they'll use less energy per passenger kilometre than an equivalent DMU. I very much doubt that applies to electric locomotives.

The main downside is that the loco takes up space.

 

[RichmondCommu]

Class 68s are very reliable. No train is 100% reliable.

I don't understand what point you are trying to make. I said "Also when a DMU failure does occur, it can be harder to rescue it, depending on the compatibility of other units in the area" and all you've come up with is stating that a DMU can be rescued by a unit of the same type, so I assume you are not disagreeing with me?

If you take the MML as an example, south of Derby / Nottingham there are only two types of Intercity stock used with the Meridians used in much greater numbers. On the trans-pennine route what are the chances of a class 68 hauled train being followed by another class 68? The chances are the next train will be a unit and I'm not certain that a unit could rescue a class 68.

 

[RichmondCommu]

If you are making a direct comparison, I think a 9-car class 222 rescuing a 9-car class 222 would be more problematical than a loco rescuing a loco hauled train.

Why do you say that?

 

[broadgage]

I suspect that some in the rail industry consider loco hauled to be "old fashioned" and that DMUs are now the default choice for most new trains, without serious consideration of alternatives.

Two generations ago the mantra was "all will be good when we get rid of steam" I suspect that one generation ago this was replaced with "all will be good when we get rid of loco haulage"

For long distance services I certainly prefer HSTs to DMUs, and feel that more of these should have been built. Not of course an exact copy of a 40 year old train, but similar in basic design.

A locomotive or power car at each end to spread the weight, first class at one end, standard class at the other, with a buffet in between.
Retention toilets and power operated doors would be the main change over the 40 year old trains.

Indeed the original proposed new trains for the West country were have been somewhat similar there was even talk of calling them HST2.

The design has gradually morphed into a fleet of mainly shorter DMUs, progress I suppose.

 

[jopsuk]

Is, say, a 6-car class 185 really more friendly to track than a 68 and 5 coaches? I am not convinced.

I'll agree with you on this though!

I'm not sure about rail, but with road it's estimated that damage due to impact forces increases with the fourth power of pressure (weight divided by tyre contact area) - to the extent that a car does approximately 10,000 times the damage to road surface that a bicycle does. If the same holds true for rail, even roughly, then that 3 extra tonnes per axle of a 68 (21 tonnes per axle) versus a 185 (18 tonnes per axle) (which is an extreme example of a DMU as you well know) makes a heck of a difference. With something such as a class 220 at 11.5 tonnes (a 222 is similar) and the likes of Turbostars even lighter the differences becomes stark. The lighter coaches won't make up for the sheer pounding of the loco.

 

[RichmondCommu]

In practice many modern DMUs are not compatible with many other types of DMUs and the proliferation of many different designs of DMUs is not a good thing in this respect.

Are the railways not moving towards unification of train design? Hitachi seem to be building trains of the same design for various different operators including the East Coast and Transpennine franchises. So if a Transpennine Hitachi built train fails on the ECML one of Virgins new trains can help it out. Could a Hitachi built train rescue a class 68?

 

[mike57]

snip

I also think the driving force behind locomotive hauled diesel trains with 7, 8, 9, 10 carriages etc is that fundamentally they'll use less energy per passenger kilometre than an equivalent DMU. I very much doubt that applies to electric locomotives.

The main downside is that the loco takes up space.

Interesting 3 x 185's gives 504 seats and weighs in at just over 500t and an 8 carriage HST, as far as I can work out would weight in at (70*2 + 8*34 = 412t) and assuming 2 first class and 6 second class would seat 540. I wonder what the comparative fuel consumption of these two would be.

 

[Mugby]

Presumably a 7-car Meridian has seven fuel tanks which need to be filled. Does anyone know what the total volume of fuel is when all tanks are freshly topped up?
Also, how would the said amount compare with one or two locomotives similarly topped up?

 

[fowler9]

snip

Interesting 3 x 185's gives 504 seats and weighs in at just over 500t and an 8 carriage HST, as far as I can work out would weight in at (70*2 + 8*34 = 412t) and assuming 2 first class and 6 second class would seat 540. I wonder what the comparative fuel consumption of these two would be.

I would guess, and it is just a guess, that 3x185's would be more fuel efficient being a more modern design. Loads of wasted space though and in my opinion a far less comfortable journey. That said the 185's are not operated that way.

 

[RichmondCommu]

I would guess, and it is just a guess, that 3x185's would be more fuel efficient being a more modern design. Loads of wasted space though and in my opinion a far less comfortable journey. That said the 185's are not operated that way.

How much space does a loco take up?

 

[robbeech]

I'm not sure really, I think real world figures would be the only way to tell.
Don't forget that the HST has newer engines than when first introduced. The first MTU engines went in in 2005, incidentally this is when the 185 was introduced.

 

[Driverme10]

At Chiltern loco hauled is roughly the same cost to run as a 5car 168 as you go over 5 the loco is cheaper. There also quicker to reach 75/100 compared to 165 168. Only the 172s are about the same.

 

[RichmondCommu]

At Chiltern loco hauled is roughly the same cost to run as a 5car 168 as you go over 5 the loco is cheaper. There also quicker to reach 75/100 compared to 165 168. Only the 172s are about the same.

Are the class 68s consuming much more fuel than the class 172s?

 

[Driverme10]

I know that a 5 car 168 would be similar to a loco and 5coaches and that a 172 is more thirsty than a 168 or 165 mainly because they don't coast thus you have to take power to keep speed even on a down hill gradient.

 

[Bornin1980s]

Why can't a 172 coast?

 

[yorkie]

I would guess, and it is just a guess, that 3x185's would be more fuel efficient being a more modern design....

Not true; the (modern) MTUs in HST power cars are far more efficient than the 'lardbutt' 185s if you were hauling a HSTs worth of passengers.

 

[fowler9]

How much space does a loco take up?

3x185 would have way more disabled access space than would ever normally be used. That is a fair bit of space. Plus all the driving cabs in the consist not being used. At the same time if it encouraged more wheelchair users to take the train it wouldn't be a bad thing.

 

[fowler9]

Not true; the (modern) MTUs in HST power cars are far more efficient than the 'lardbutt' 185s if you were hauling a HSTs worth of passengers.

Ha ha, I had forgotten about that. Good point.

 

[Driverme10]

Why can't a 172 coast?

It's because of the gearbox, it basically means the engine stays connected to the drive so you get the effect of engine braking. For example if you shut off between Beaconsfield and seer green at 100 in a 168 you could coast into London (roughly 25mile) in a 172 you would be nearly at a stand by Gerrards cross (roughly 4mile) hence why they use alot more fuel.

 

[tbtc]

why the proliferation of 'long' DMU's, 7 car 222's, 4/5 car 220/1 5 car 180...

Is it just short-termism or are there other benefits in using DMU's on longer units. I am not thinking of 2 x 3 car units coupled together, unless they were nearly always run in 6 car formation from purchase

The four/five coach Voyagers/ Meridians do daily portion work, so being able to split/join easily is a big help. Loco hauled would presumably mean an end to services like Wrexham - London (which portion work off other services).

There's also the issue of how much space you can afford to give over to two "locomotives", if you want to go down the HST route - is there scope to sacrifice a coach or two at St Pancras etc?

The 180s on the ECML (generally) don't double up or interwork but I guess that the only realistic alternative at the time was trying to get a 67 to run at 125mph with five coaches, assuming that you had the unpowered coaches to use - the 180s were at least available and "known entities" on the second hand market (not particularly reliable, I know, but possibly easier to lease second hand than getting new locos built for?). Would the loss making Grand Central have been able to order brand new trains for their Open Access services (when TOCs can't justify that investment)?

If you want to blame anyone, blame National Express for ordering seven 9 coach 222s for their proposed London - Leeds service (later reduced to seven coaches so that some of the four coach trains could become five coaches) - but I guess their logic was that it made sense to have these nine trains compatible with the sixteen 4 coach units that they were ordering to replace 170s.

Some things would be a lot easier if we had around six hundred 125mph capable unpowered coaches instead of all of the 180/ 220/ 221/ 222s - it'd be much easier to alter formation lengths, it'd be much easier to swap coaches between TOCs (compared to the saga of the "spare" Voyager power cars at Virgin). All of the small fleets of DMU can become awkward - see also 175s etc. But, since we are where we are, any fleet of unpowered coaches (like the TPE ones) is going to be another micro fleet which doesn't necessarily solve things.

 

[robbeech]

Do they have a lock up solenoid on them so they become effectively direct drive at higher speed or is it just the fluid coupling keeping the engine spinning and they don't have a neutral position? The former would be more efficient under load, but less efficient on overrun, or rather wouldn't coast as you say thus meaning more fuel used. The latter would give a potentially smoother ride at higher speeds particularly in situations where it is difficult to maintain a constant speed and there is frequent changing of power levels.

 

[Richard_B]

It's because of the gearbox, it basically means the engine stays connected to the drive so you get the effect of engine braking. For example if you shut off between Beaconsfield and seer green at 100 in a 168 you could coast into London (roughly 25mile) in a 172 you would be nearly at a stand by Gerrards cross (roughly 4mile) hence why they use alot more fuel.

I assume it is downhill but that still seems phenomenal from the 168.

To the original question, better acceleration to squeeze more paths in seems to becoming a more and more important factor, but as others posters have pointed out this doesn't necessarily mean automatically selecting a DMU option but usually makes it more likely