Top and tailing. Is it really necessary?

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Okay, I get the reasons for top and tailing, and I understand why it's needed for freight, but surely in the medium to long term, it'd be more economical for the hire companies to convert some mk3 TS's into DTS's? Scotrail did it back in the 90's with the 47/7's and their mk2 DBSO's, so why not save on the unnecessary cost of two locomotives?
 
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Darandio

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Isn't it now all to do with safety, and the relatively low weight of a driving cab in a DTSO type vehicle, versus the weight being pushed/pulled?
 

LE Greys

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Considering most loco-haulage happens on the short-term and that there are still a few MkIII DVTs about, like the ones operating with Chiltern, then it probably isn't. My mechanism for it though would be to design a cab based on the 442s and see if it's possible to attach one of those to the end of a MkIII. If not, then a DVT with seats would be an option if it is possible to cut a few windows.
 

12CSVT

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One reason why top & tailing is often done these days (especially with charters) is that since the vast majority of passenger workings have become DMU or EMU operated, many terminus stations no longer have run round loops, or have a resident class 08 / 09 shunter. Another factor is that as the number of passenger trains have increased, there are far fewer paths for locos to do shunt movements within stations.
 

Eng274

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Several reasons:

- The Polmont crash of 1984, in which a DBSO derailed after hitting a cow, put paid to coaches being used as driving vehicles (DVTs don't count as they are better designed for object strikes, and are ballasted)
- Redundancy. Having two locomotives provides a back up when one locomotive fails (see HST)
- Traction; having the power spread over more axles improves traction and performance; more relevant to MUs though (see 390s, 220s, 221s, 222s v HSTs, cl 91+mk4s).

Distributed traction is becoming the preferred setup for modern stock, due to improvements in reliable traction technology. The spread of the traction equipment along the train reduces axle weight compared to having a heavy loco at one end, which means lower wear to the rails, which means lower track access costs to the operator.

For freight, it's all about cost - two medium-power locomotives cost more to run in a freight train than one super powerful loco; and there's the issue of controlling the rear loco, without wiring every wagon with multiplex capability. If one loco (or sometimes two) can do the business from the front, there's no need for a rear loco.

Edit: except the steepest gradients - I believe DB Schenker have a small number of 66s which deputise as banking locos that latch onto the rear for steep hills, which have an automatic un-coupling capability.
 
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Yew

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Dont forget that a lot of top and tail is done in heritage situations, where having an extra motor to work as a backup incase the kettle/deltic/whatever at the front goes kaput
 

jopsuk

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Okay, I get the reasons for top and tailing, and I understand why it's needed for freight, but surely in the medium to long term, it'd be more economical for the hire companies to convert some mk3 TS's into DTS's? Scotrail did it back in the 90's with the 47/7's and their mk2 DBSO's, so why not save on the unnecessary cost of two locomotives?
The 47/DBSO operation started in 80s, being replaced in the early 90s with 158s. Key part here though was that the vehicles converted to DBSOs were already Brake vehicles, with a handbrake. As I understand it, on trains being top and tailed, the additional loco can replace the need for a brake vehicle? DVTs, all specially built, perform this function.

There are, as far as I know, only three passenger carrying Mark 3 Brake vehicles, all part of the Night Riviera fleet at the moment. Converting non-brake vehicles would be far more extensive.
 

Eng274

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The 47/DBSO operation started in 80s, being replaced in the early 90s with 158s. Key part here though was that the vehicles converted to DBSOs were already Brake vehicles, with a handbrake. As I understand it, on trains being top and tailed, the additional loco can replace the need for a brake vehicle? DVTs, all specially built, perform this function.

There are, as far as I know, only three passenger carrying Mark 3 Brake vehicles, all part of the Night Riviera fleet at the moment. Converting non-brake vehicles would be far more extensive.
I believe that is the case, each portion of the Caledonian Sleeper needs a mk2 BUO/BFO as part of the rake as they are fitted with handbrakes.

On that note, is it the case that DVTs are fitted with a compressor to supply brake pressure?
 

sprinterguy

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Edit: except the steepest gradients - I believe DB Schenker have a small number of 66s which deputise as banking locos that latch onto the rear for steep hills, which have an automatic un-coupling capability.
Yep, there's five modified 66s that can be used for banking duties on the Lickey incline, although they do perform other work as well.
 

jopsuk

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Several reasons:

- The Polmont crash of 1984, in which a DBSO derailed after hitting a cow, put paid to coaches being used as driving vehicles (DVTs don't count as they are better designed for object strikes, and are ballasted)
No it didn't. The DBSOs were returned to duty following some modifications, and were furthered modified to work with electric locomotives and sent to the Great Eastern mainline where they worked up to 2004.

True, BR did get did get touchy about passengers in the lead cars of high speed trains (thus the mrk3 and mrk4 DVTs), but as you'll have noticed, modern 100mph+ units have passengers in end vehicles, even within the front 3rd despite a belief that this is forbidden...
 

Eng274

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No it didn't. The DBSOs were returned to duty following some modifications, and were furthered modified to work with electric locomotives and sent to the Great Eastern mainline where they worked up to 2004.

True, BR did get did get touchy about passengers in the lead cars of high speed trains (thus the mrk3 and mrk4 DVTs), but as you'll have noticed, modern 100mph+ units have passengers in end vehicles, even within the front 3rd despite a belief that this is forbidden...
I was under the impression they were promptly withdrawn, my mistake.

I wouldn't really compare a Pendolino or Voyager with a mk2 coach, even if newer stock does have passengers near the front, the improved crashworthiness standards would improve safety over a mk2. I know its not forbidden to have passengers near the front in 100mph+ units, but there is a big difference between a sturdy, purpose-designed front end and a retrofitted coach.
 

jopsuk

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Very true. Didn't stop them being used for a further 20 years in passenger service without incident- there was even an additional one built to replace the destroyed one. There's even a number of them in departmental service with Network Rail, and NI railways have one (re-gauged) as part of a "reserve" set.
 
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