Loco & coach combination - why so rare?

[al.currie93]

I don't understand why acceleration could ever be seen as not being a priority. Journey times and all that, especially in the case of Northern.

I never meant to say that it would not be a priority (should have made that clearer sorry!), some routes it should undoubtedly be top priority. But it could well be the case that cost and design simplicity become higher priority on certain routes at least, and I can see how that would come to light and how it may be doing so now.

Say if the 185s and 350s with TPE were set to be transferred to Northern to allow some 142s to be withdrawn - TPE needs new stock. They could go for some brand new DMU trains, but these could prove significantly more costly than some new LHCS trains. Then cost might be a higher priority - fast accelerating trains might be great until the point where they cost the taxpayer/fare-payer an extortion to produce.

Alternatively, in the same situation, TPE might have been getting bad feedback about the engine noise and vibration from customers regarding their 185s, and look to use locomotives next time on the basis they feel that the increased customer satisfaction will be worth it.

These are all quite feasible ways in which advantages posed by LHCS could come to be higher priority than those posed by multiple units.

Units do not always have better acceleration, 168 and 67+6+dvt have the same timings on chiltern and both reach 100 mph at roughly the same point from leaving London. The 68s actually reach 100 about a mile earlier than both the 168 And 67. Also to be noted is that a unit of over 5 coaches in length will use more fuel then a loco hauled set.

That's a good example - I have heard similar things about the 68s do we know if this is just down to timings or not?

 

[CC 72100]

Possibly in the last couple of years before Voyagers took over.

Virgin XC (if that's what we're referring to) was load 7 - 1 half brake, 5 TSOs and then a First class coach containing a buffet.

Only longer trains when West Coast sets were hired in (a semi-regular occurrence on certain Saturday seaside services)

 

[Dent]

You're wrong on one part - the Pacers were not introduced to replace LHCS - they were to replace life-expired 1st generation DMUs that were uneconomic to overhaul mainly due to the presence of asbestos - so classes such as 100, 104, 105.

The DMUs which replaced LHCS were generally the Sprinters - some of the 150s did, but mainly it was the 156, 158, 159s which replaced most LHCS.

Indeed Pacers were not an alternative to hauled stock, they were for local routes where hauled stock would not be suitable because of frequent stops.

 

[87015]

Indeed Pacers were not an alternative to hauled stock, they were for local routes where hauled stock would not be suitable because of frequent stops.

I don't think you can say frequent stops = unsuitable.
A sizeable minority of such routes, S-Bahn's included, around the world are hauled, let alone rural routes that stop at every lampost - look how many RBs are hauled in Germany or Austria and they stop everywhere. Yes its declining, but it far too simple to say its just unsuitable.

The big gap here appears to be BR not developing something along the lines of n-wagen but preferring the lots of doors DMU/VEP etc approach for such services. Imagine how useful some shove rakes which can work with pretty much any EH loco can be...

 

[Dent]

I don't think you can say frequent stops = unsuitable.
A sizeable minority of such routes, S-Bahn's included, around the world are hauled, let alone rural routes that stop at every lampost - look how many RBs are hauled in Germany or Austria and they stop everywhere. Yes its declining, but it far too simple to say its just unsuitable.

Each time a train stops it then has to accelerate again, so the more frequent the stops the more the service will be slowed down by poor acceleration.

Just because something is done badly somewhere else doesn't make it suitable. It is declining for a good reason, that reason being that they are not well suited to their purpose.

 

[ac6000cw]

Possibly in the last couple of years before Voyagers took over.

However, in the 1950s-60s-70s-80s this was a common formation, especially in summer when additional vehicles were diagrammed.

My recollection (from the early/mid 1970s, when I spent a lot of time train-spotting at Birmingham NS) was that 8-10 Mk1s was most common - mixture of compartments and open saloons, with maybe one coach length of brake-van space included in that.

(...and there is no way a 45/46/47 with 10 Mk1's hanging off the drawhook - 250hp per vehicle - could ever match the acceleration of a Voyager - 750hp per vehicle )

 

[87015]

Each time a train stops it then has to accelerate again, so the more frequent the stops the more the service will be slowed down by poor acceleration.

Just because something is done badly somewhere else doesn't make it suitable. It is declining for a good reason, that reason being that they are not well suited to their purpose.

Why is it always slower? Graz is somewhere units and locos interwork to a standard timetable, 2016s keep to Desiro times, the shunter nonsense on the GKB S-Bahn (2010s is it?) runs to Flirt timings... Talk of a 31+4 vs 150 is a different ball game to what can and is done.

It would be interesting to know what say a 90+4 nwagen would do v a 321, or 68+3 v 170 without the drawback of mk2/3 door setup on such services.

 

[RichmondCommu]

I never meant to say that it would not be a priority (should have made that clearer sorry!), some routes it should undoubtedly be top priority. But it could well be the case that cost and design simplicity become higher priority on certain routes at least, and I can see how that would come to light and how it may be doing so now.

Say if the 185s and 350s with TPE were set to be transferred to Northern to allow some 142s to be withdrawn - TPE needs new stock. They could go for some brand new DMU trains, but these could prove significantly more costly than some new LHCS trains. Then cost might be a higher priority - fast accelerating trains might be great until the point where they cost the taxpayer/fare-payer an extortion to produce.

Alternatively, in the same situation, TPE might have been getting bad feedback about the engine noise and vibration from customers regarding their 185s, and look to use locomotives next time on the basis they feel that the increased customer satisfaction will be worth it.

These are all quite feasible ways in which advantages posed by LHCS could come to be higher priority than those posed by multiple units.

Having traveled on class 185's there is no doubt that they get away from stations very quickly. BBC Radio 5's Anna Foster timed her journey from Halifax (where she lives) to Salford Media City to see how the journey compared to the car in terms of journey time. This experiment was carried out after the planned HS3 was announced. I can't remember the exact timings but Anna Foster discovered that it was quicker to drive by some margin. Now if you were to switch from class 185's to slower LCHS (don't forget that route has steep gradients) the journey times will only become slower and rail transport will become less attractive.

In terms of vibration I don't think the class 185's are any worse then say the Voyagers or the Meridians and yet the chances are that the Meridians will move to Cross Country when they are displaced from the MML. In terms of negative feedback for TPE I would imagine over crowding is at the top of the charts. Now in the unlikely event that a class 185 replaces a class 156 a loco and say six carriages would not be able to keep up with a six car DMU built to the same specification as a class 185.

The other point worth making is that if it was indeed more cost effective to order locos and brand new coaches why was this option not chosen over the class 185's? Not only that but if TPE wanted to buy replacement trains, at the very least Siemens can deliver more of the same. However would Siemens be prepared to design and build brand new rolling stock for the British market for a limited order when we already know that FGW are planning to order more distributed traction from Hitachi? The same could be said for Bombardier and Hitachi.

 

[ry34081]

A voyager maybe 750 but this is a 125mph train, most dmus are around 400bhp per car the 170s included. The 3750bhp class 68 would be just as powerfull with 7 coaches plus a dvt if you calculate the combined weight. Bhp per ton. Plus as stated fuel consumption per car is about 1 litre per mile On a unit and 4-5 litre per mile On a loco (250ton Train). Porterbrook etc have the actual Figuers if you look at there brochures for each type of train ( Google will find it)

 

[RichmondCommu]

I don't think you can say frequent stops = unsuitable.
A sizeable minority of such routes, S-Bahn's included, around the world are hauled, let alone rural routes that stop at every lampost - look how many RBs are hauled in Germany or Austria and they stop everywhere. Yes its declining, but it far too simple to say its just unsuitable.

The big gap here appears to be BR not developing something along the lines of n-wagen but preferring the lots of doors DMU/VEP etc approach for such services. Imagine how useful some shove rakes which can work with pretty much any EH loco can be...

The SNCF had a policy of push pull locos and stock for decades for both the Paris suburbs and other areas such as the Côte d'Azur. All of these were frequent stopping services and some services even used diesel locos. However very few examples are now left.

 

[HSTEd]

The reason units tend to use more fuel is they tend to be ridiculously overpowered compared to the loco hauled formation - so you would expect them to use more fuel.

For this reason I would expect something like a 172 stretch formation to do quite well on that metric.
110mph 7-car 172 perhaps? Would have ~3,395hp

 

[RichmondCommu]

A voyager maybe 750 but this is a 125mph train, most dmus are around 400bhp per car the 170s included. The 3750bhp class 68 would be just as powerfull with 7 coaches plus a dvt if you calculate the combined weight. Bhp per ton. Plus as stated fuel consumption per car is about 1 litre per mile On a unit and 4-5 litre per mile On a loco (250ton Train). Porterbrook etc have the actual Figuers if you look at there brochures for each type of train ( Google will find it)

However how would a class 68 compare in terms of tractive effort? Would it get away as quickly as a class 185 with a similar length? And for what its worth, as others have reminded me you wouldn't require a separate DVT with the current safety technology.

 

[TheKnightWho]

A voyager maybe 750 but this is a 125mph train, most dmus are around 400bhp per car the 170s included. The 3750bhp class 68 would be just as powerfull with 7 coaches plus a dvt if you calculate the combined weight. Bhp per ton. Plus as stated fuel consumption per car is about 1 litre per mile On a unit and 4-5 litre per mile On a loco (250ton Train). Porterbrook etc have the actual Figuers if you look at there brochures for each type of train ( Google will find it)

You're forgetting torque. A 68 has far fewer powered axles than a 170, and so even with higher power won't be able to put it down to the rails as effectively. There's more to it than raw hp.

 

[apk55]

A DMU with the simple Voith hydraulic can only deliver the rated motor power output the wheels at a single speed, typicaly maximum speed. At lower speeds much less power is available, due to the engine running at none optimum speed and large torque converter losses. At for example 30MPH I would expect only about half the rated engine power to be available at the wheels. (It is also very ineficient at this speed)

A diesel electric transmision in contrast can deliver the full engine power to the wheels over a wide speed range from maybe 30MPH to maximum speed, particularly a high tractive effort design such as the class 68.

 

[HSTEd]

We don't use simple hydraulic transmissions any more though.

And there is also the fact that DEMUs exist.

 

[ac6000cw]

You're forgetting torque. A 68 has far fewer powered axles than a 170, and so even with higher power won't be able to put it down to the rails as effectively. There's more to it than raw hp.

Has anyone got any figures for the low-speed tractive effort of a modern DMU with hydro-mechanical transmission ?

That way we could make a more scientific comparison of rolling stock acceleration....

(at higher speeds tractive effort becomes power limited so direct power-to-weight ratio comparisons are valid).

 

[ry34081]

http://www.porterbrook.co.uk/downloads/brochures/170 Brochure.pdf
http://www.porterbrook.co.uk/downloads/brochures/172 Brochure.pdf
The acceleration is listed for the 172 with the new type of gearbox but with the old hydraulic type on the 170s it says to inquire for acceleration data.
So as far as i can make out old DMU's 150, 158, 170s etc etc are slower than a loco set but newer types of DMU DEMU will be faster.

 

[Dent]

Why is it always slower?

Because a loco can only apply a limited amount of power before the wheels spin.

Basically the amount of power that can be transmitted before the wheels spin is proportional to the weight being carried by the driving wheels (look up "coefficient of friction"). This means that the (usable) power:weight ratio is optimised when all the weight is carried by driving wheels, and far from optimal when only one vehicle is powered and the rest of the train is dead weight.

Graz is somewhere units and locos interwork to a standard timetable, 2016s keep to Desiro times, the shunter nonsense on the GKB S-Bahn (2010s is it?) runs to Flirt timings...

All that shows is that the units running to those particular timetables are not being pushed to their full advantage.

 

[delt1c]

A good comparison in the 1970's between MkII air con and Mk I was from Edinburgh. there was the 10.00 departure Flying Scotsman from Waverly Delt1c Hauled air con and very comfortable and lovely atmosphere, a walk to the buffet for a coffee and sandwich to eaten when returning to your seat. Then there was the 10.05 Plymouth departure, usually MkI compartment stock but tightly timed with a 47 up front. Bouncy sitting in the compartment , if you were lucky it was 3 a side 2nd class but could eadsily be 4 a side with no arm rests. A visit to the buffet for coffee and sandwich meant sitting in the Buffet otherwise little would remain in the coffee cup upon walking back to your compartment. In winter the corridors were cold and all year long the gangways were noisy .
Yes I enjoyed it and would love to undertake it again, but remember the railways are a business and have to attract custom from the general public.

 

[Rick1984]

Loco hauled trains would be ideal on low density regional services, freeing up DMU's to strengthen existing services where superior acceleration would be useful. Suburban routes with high stopping pattern , congested lines etc.

You could use a mixture of any of existing locos including 67 and 47's, emission compliant new builds like the 68's, remaining Mkii and Mkii carriages, DBSO and DVT's and new build carriagesand driving cars built to a cheap basic standard. You could have mid door and end doors layouts.

These can then have an electric loco slapped on when wires go up or use them as trailers in an EMU

 

[AM9]

A good comparison in the 1970's between MkII air con and Mk I was from Edinburgh. there was the 10.00 departure Flying Scotsman from Waverly Delt1c Hauled air con and very comfortable and lovely atmosphere, a walk to the buffet for a coffee and sandwich to eaten when returning to your seat. Then there was the 10.05 Plymouth departure, usually MkI compartment stock but tightly timed with a 47 up front. Bouncy sitting in the compartment , if you were lucky it was 3 a side 2nd class but could eadsily be 4 a side with no arm rests. A visit to the buffet for coffee and sandwich meant sitting in the Buffet otherwise little would remain in the coffee cup upon walking back to your compartment. In winter the corridors were cold and all year long the gangways were noisy .
Yes I enjoyed it and would love to undertake it again, but remember the railways are a business and have to attract custom from the general public.

Not sure how many people here have had to use MKI LHCS trains as ordinary fare-paying passengers, but there does seem to be a lot of dewey-eyed nostalgia driving claims that these 60-70 year-old wagons would be accepted on the modern railway. It's OK to remenisce about the best of them, tarted-up and fitted with B4 bogies so that they could run on the WCML. It took a lot of regular expensive maintenance to keep them working this way.
Most of the MKIs with their BR1 bogies didn't get anywhere near as much attention, hence their rough ride even on the best CWR. Any slight lateral kinks through pointwork etc. would send them lurching as the slack bolster bearings reached their end of travel. The B4 bogies were much better but for any serious duties, the design had to be beefed-up in the form of the B5 (as or SR EMUs) or given special treatment as with the BGs so that parcels could survive a 110mph ride up the WCML.
The MKIs fulfilled a need back in the '60s and '70s, but they are now only fit for occasional use on the main line carrying nostalgic enthusiasts.
Loco hauling with the types suggested goes completely against operational demands and environmental ethics. Expect MUs to be universal on all trains except specialist duties like sleepers on a modern railway.

 

[CosherB]

Not sure how many people here have had to use MKI LHCS trains as ordinary fare-paying passengers, but there does seem to be a lot of dewey-eyed nostalgia driving claims that these 60-70 year-old wagons would be accepted on the modern railway. It's OK to remenisce about the best of them, tarted-up and fitted with B4 bogies so that they could run on the WCML. It took a lot of regular expensive maintenance to keep them working this way.
Most of the MKIs with their BR1 bogies didn't get anywhere near as much attention, hence their rough ride even on the best CWR. Any slight lateral kinks through pointwork etc. would send them lurching as the slack bolster bearings reached their end of travel. The B4 bogies were much better but for any serious duties, the design had to be beefed-up in the form of the B5 (as or SR EMUs) or given special treatment as with the BGs so that parcels could survive a 110mph ride up the WCML.
The MKIs fulfilled a need back in the '60s and '70s, but they are now only fit for occasional use on the main line carrying nostalgic enthusiasts.
Loco hauling with the types suggested goes completely against operational demands and environmental ethics. Expect MUs to be universal on all trains except specialist duties like sleepers on a modern railway.

the voice of reason!

 

[Western Lord]

Not sure how many people here have had to use MKI LHCS trains as ordinary fare-paying passengers, but there does seem to be a lot of dewey-eyed nostalgia driving claims that these 60-70 year-old wagons would be accepted on the modern railway. It's OK to remenisce about the best of them, tarted-up and fitted with B4 bogies so that they could run on the WCML. It took a lot of regular expensive maintenance to keep them working this way.
Most of the MKIs with their BR1 bogies didn't get anywhere near as much attention, hence their rough ride even on the best CWR. Any slight lateral kinks through pointwork etc. would send them lurching as the slack bolster bearings reached their end of travel. The B4 bogies were much better but for any serious duties, the design had to be beefed-up in the form of the B5 (as or SR EMUs) or given special treatment as with the BGs so that parcels could survive a 110mph ride up the WCML.
The MKIs fulfilled a need back in the '60s and '70s, but they are now only fit for occasional use on the main line carrying nostalgic enthusiasts.
Loco hauling with the types suggested goes completely against operational demands and environmental ethics. Expect MUs to be universal on all trains except specialist duties like sleepers on a modern railway.

Nobody in their right mind would suggest running 70 year old stock. That has nothing to do with an argument about LHCS or MUs. The trend toward MUs is about massively increased stock utilisation. When I started making long distance rail journeys in the early seventies it was still common to see sidings full of carriages that probably only got used a few times a week. It was sensible to separate the motive power from the coaching stock in these circumstances as the more expensive part of the equation (the motive power) had to have greater utilisation than the cheaper part (the coaching stock). Today, stock is intensively utilised so the motive power part can be built in. This brings in other advantages, such as track simplification, easier multi-portion working, one man operation etc. The problem with MUs is that they have to have long service lives and require updating to maintain passenger appeal. Loco hauled stock can just be replaced whilst retaining the same motive power, as happened on the WCML when essentially the same locos went from Mark 1 stock, through the various iterations of Mark 2, to finish up hauling Mark 3s. This was an economic proposition as long as the displaced stock could be cascaded down to lesser services, but that is no longer practical operationally or acceptable politically.

 

[Dent]

Loco hauled trains would be ideal on low density regional services

Hardly "ideal" - they would suffer from the same poor acceleration and inefficient space usage that any hauled sets do.

Journey times are at least as important for regional services as commuter services, in many cases more so when the actual difference is a matter of hours rather than minutes. In addition, most routes either have capacity issues at some places at some times, or share some track with trains that do.