Coupled coaches vs permanently coupled trainsets

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Joanna

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Hej guys,

I am struggling with writing my report for academic course which concerns coupled trans/trainsets (long distance and freight trains).

I guess in the future passengers trains will consist of permanently coupled trainsets, which is connected to (potential) implementation of ETCS level 3 and getting rid off axle counters. But what about freight trains?

If we are operating on ETCS level 2 then what is the benefit of using trainsets over coupled coaches?
 
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Domh245

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The first thought that comes to mind with a trainset as opposed to wagons coupled together, is that you could move to a distributed traction system, which would help when the weather conditions aren't ideal. However, you are then stuck at the capacity you've gone with, if the train is underloaded, you've got to take those extra cars with you anyway, but if the train is very popular, you'd have to turn away customers or try and put them on a different train, which isn't ideal.
 

jopsuk

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there's an almost mythical past where trains were lengthened because of demand at source using carriages from adjacent sidings- the reality is this barely happened and the majority of trains, even in the steam age, ran in planned formations or even fixed sets. There were actually a fair number of articulated sets in use too, using shared bogies.

With the modern multiple units, any splitting or joining is done according to diagrams, not responsive to flow.

Freight trains tend to run around in rakes too, the same wagons staying togther to avoid a surplus building up at any point. some are in semi-fixed sets any, four or five wagons with bar couplings between them and buffers/coupling gear at each end
 

HSTEd

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Manifest [ie. Wagonload] freight is dying even in the US, let alone in the UK where it died many years ago at privatisation - as I recall because it was losing the horrifying sum of £50m per annum.....

With containers you can "shunt" the wagonload freight using a pair of sidings and a straddle crane, much cheaper than a giant hump yard or similar.
It also means all the trains stay in fixed formations - which means you can potentially move to distributed traction even on them - the fabled return of the freight multiple unit.
 

Joanna

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Thank you guys :))

But even though containers are widely use in freight transport there are still a lot of things that cannot be fit into containers, as timber or gravel. Thus the train will still consist of coupled wagons.
Do you have any ideas how these trains will operate on lines equipped with ETCS level 3? They will not? It will be computer controlled?
 

swt_passenger

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Thank you guys :))

But even though containers are widely use in freight transport there are still a lot of things that cannot be fit into containers, as timber or gravel. Thus the train will still consist of coupled wagons.
Do you have any ideas how these trains will operate on lines equipped with ETCS level 3? They will not? It will be computer controlled?

Container trains are still coupled wagons in the normal manner. I can't see any connection between type of train in use and ETCS level 3.

Have you got something you can quote?
 

Joanna

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Yeah, you are right, they are still coupled trains...

As I was taught in ETCS level 3 we want to get rid of axle counters thus there is a need for train integrity. If the line is equipped with ETCS level 3 how the integrity of freight trains will be detected?
 

headshot119

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One simple method is an electrical wire running the length of the formation, and back. If the train divides the wire brakes, on come the brakes and ETCS detects there is an issue.

This is how the brakes work on stock like 141s/142s.
 

Johncleesefan

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One simple method is an electrical wire running the length of the formation, and back. If the train divides the wire brakes, on come the brakes and ETCS detects there is an issue.

This is how the brakes work on stock like 141s/142s.

And most trains today I believe. If train wire 4 breaks an emergency brake application applies
 

HSTEd

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Thank you guys :))

But even though containers are widely use in freight transport there are still a lot of things that cannot be fit into containers, as timber or gravel. Thus the train will still consist of coupled wagons.

Timber and gravel can and is sometimes carried in containers - either in 'half height' containers like those which are occasionally used for the shipping of coal or simply by adopting the enormous SECU containers.

There is no real reason you can't carry anything that can physically fit in a container sized box.
 

apk55

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Problem with carrying minerals in containers is dead weight. A dedicated mineral wagon can be quite light with structural strength coming coming from wagon sides. In contrast a container wagon is quite heavy plus the extra weight of the container. Therefore the same weight of train can have a higher percentage of payload if wagons are used, which is why they are used for high capacity routes such as port to power station.
 

ChiefPlanner

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Problem with carrying minerals in containers is dead weight. A dedicated mineral wagon can be quite light with structural strength coming coming from wagon sides. In contrast a container wagon is quite heavy plus the extra weight of the container. Therefore the same weight of train can have a higher percentage of payload if wagons are used, which is why they are used for high capacity routes such as port to power station.

Very well explained - which explains why a good number of high capacity bulk wagons were / are built with lightweight bogies and aluminium (or similar) bodies. Tare + payload = around 100 tons.

Container flats tended to be around 20 tons tare weight and allowing for "container" weight (say 2 tons for a standard shipping box) - give a payload of about 82 tons for a 60ft wagon (am old school so forgive me) - equating to 20 tons wagon weight + 82 tons carrying capacity (minus ety container weight)..

Pretty much the "golden rule" was axle weight of about 25 tons.

Of course - certain loaders would disregard these conditions and overload - but compressed wagon springs is what you looked for when giving a train a final check over before departure.
 

MarkyT

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I can't see infrastructure based train detection technology disappearing entirely in the foreseeable future under ETCS L3 or any other moving block system. Train length determination is easy to do for a metro type operation with fixed train lengths, but is much more challenging on a multi-traffic railway which may have to cater for single car passenger units as well as variable length freights. Even on London's LUL and DLR, where train lengths are fixed, The Seltrac moving block system employs axle counter deadlocking through junctions for additional security, as there is little worse in in the rail-verse than a set of points moving under a speeding train whose length has been incorrectly determined, and operators have to cater for all scenarios, including partial failures, unfitted engineering vehicles etc. Those deadlock zones are in fact fully fledged conventional interlockings with detection boundaries split for parallel running of multiple trains through a junction (where safe), sectional route locking to release parts of more complex junctions earlier, and flank protection rules applied as with any conventionally signalled railway. Because they very accurately determine precisely when a train clears a conflict zone, a fixed train detection system can release a junction for another conflicting train far quicker than a calculated offset from the front cab position because of the cycle time in communicating and processing and the uncertainty in train position leads to a generous added tolerance value being neccessary, even with fixed or known train length. On TfL the same wheel counting sensors are also employed for plain line axle counter sections between junctions and stations for degraded mode working with fixed blocks, if train or track equipment fails (albeit with severely reduced capacity). TfL also plans to use Seltrac on the resignalled subsurface network (Circle / District / Hammersmith & City / Metropolitan Lines) in a similar configuration. A new development which may come about in this latest application is to replace the unloved continuous 'wiggly wire' feature (used for position determination) with passive beacons (balises) installed wherever a wire transposition would occur and overlay a full coverage radio system based on COTS (commercial off the shelf) wi-fi technology.

https://www.thalesgroup.com/sites/default/files/asset/document/SelTracBrochure_CBTCSolutions_eng.pdf

A simple single line of railway equipped with a notional moving block system has to be set for a particular 'current of direction' just like a conventionally signalled line with multiple headway signals, then can admit a number of following trains in the same direction whose separation is controlled by other means. At it's simplest such other means could be the drive on sight rules used on light railways such as Manchester Metrolink, but could equally be a sophisticated system of train to train or track to train communication to safely separate faster or more diverse traffic such as ETCS L3. Either way the section needs to be proved clear of vehicles before it's direction can be reversed, just like a conventionally signalled fixed block line.

One idea I had for variable length determination exploits those short deadlocking train detection sections that are likely to remain through junctions. If the sections only admitted one train at a time (not overly restrictive as they are usually short compared to braking distance), then at the moment of their clearing at a particular extremity, the system could compare the known position of the active front cab with the fixed position of the deadlocking sensor and thus determine the train length accurately. This measured value could then be used for following train separation throughout the subsequent moving block section.
 
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