Are some trains too long?

[Krokodil]

I remember (but may be misremembering) reading years ago about British Rail research which had concluded that for loco haulage was more economical for trains of more than five coaches. I suspect it referred to inter-city rather than suburban operations. Does anyone else recall that, and when it was done? And if my recollection of the research is correct, what are the key things that have changed such that we now have 10-coach inter-city EMUs, and even 12-coach ones for long-distance "suburban" services (e.g. Cambridge-Brighton)?

It's mostly down to fuel and engine maintenance - so mostly a concern for DMUs rather than EMUs. How many long pure-DMUs can you think of? A handful of 222s are the only things I can think of with seven engines in a single unit.

 

[Nottingham59]

I remember (but may be misremembering) reading years ago about British Rail research which had concluded that for loco haulage was more economical for trains of more than five coaches. I suspect it referred to inter-city rather than suburban operations. Does anyone else recall that, and when it was done? And if my recollection of the research is correct, what are the key things that have changed such that we now have 10-coach inter-city EMUs, and even 12-coach ones for long-distance "suburban" services (e.g. Cambridge-Brighton)?

That sounds about right. When the HSTs were originally developed, it was expected that each rake of mk3 coaches would be more or less permanently associated with a given pair of Class 43s.

But after introduction into service, BR found that maintenance was needed on the locomotives far more than on the coaches, and it ended up that the HST sets were treated more like loco-hauled stock, with locomotives frequently being swapped between rakes.

 

[NCT]

Much of the tube runs pretty empty outside of the peaks. Even on the Victoria line you can have a whole carriage to yourself in some hours of the day.

When service level gets to a certain point it becomes unfeasible to divide trains.

 

[AM9]

I remember (but may be misremembering) reading years ago about British Rail research which had concluded that for loco haulage was more economical for trains of more than five coaches. I suspect it referred to inter-city rather than suburban operations. Does anyone else recall that, and when it was done? And if my recollection of the research is correct, what are the key things that have changed such that we now have 10-coach inter-city EMUs, and even 12-coach ones for long-distance "suburban" services (e.g. Cambridge-Brighton)?

Modern EMUs provide optimised and consistent dwell times, a key requirement for a high density mainline (whether IC, Regional or outer suburban). A class 700/1 can disgorge over 500 passengers in less than 30 seconds, - just fast enough to clear the section for the next service.

 

[fwsmVor]

Modern EMUs provide optimised and consistent dwell times, a key requirement for a high density mainline (whether IC, Regional or outer suburban). A class 700/1 can disgorge over 500 passengers in less than 30 seconds, - just fast enough to clear the section for the next service.

Would that be any slower if the 700 had its motors removed and a loco of equivalent power at the front?

 

[Seehof]

I wish Cross Country trains were too long!

 

[AM9]

Would that be any slower if the 700 had its motors removed and a loco of equivalent power at the front?

Yes:
the stations that the class 700s call at are mostly just as large as they need, (c. 245m +) so wasting good space beneath the floors of the coaches means reducing the overall capacity, (or stopping twice). That's why EMUs are prevalent. The class 700/0 and 700/1 have power to weight ratios of around 12hp /tonne. It is also distributed along the train giving far better traction within a lower maximum axle loading.
So:

What gains would there be in changing from multiple units to loco hauled?​

What provision would you suggest for changing the ends of locos?​

How much would extending most of the platforms along the routes that they cover cost?​

​

Can you say what would be any advantages of loco hauled trains on Thameslink?

 

[Tetchytyke]

Chiltern say that it’s 6 cars plus - but that’s for diesels. Electrics are a different matter.

Diesels make sense. One large capacity diesel engine will be more efficient than several small capacity diesel engines. And the only way to have a large capacity diesel engine is in its own space, so either in a loco or in a power car as with the 755s.

 

[Hadders]

Would that be any slower if the 700 had its motors removed and a loco of equivalent power at the front?

How much time and capacity is lost running the loco round?

 

[800301]

Yes as been mentioned above but also because the driver wouldn’t be able to release doors and the service wouldn’t be able to operate DOO

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Would that be any slower if the 700 had its motors removed and a loco of equivalent power at the front?

 

[Trainbike46]

How much time and capacity is lost running the loco round?

For a theoretical new train, why would you run the loco around instead of having a DVT at one end and a loco at the the other? Or even more sensibly, just get an EMU!

Can you say what would be any advantages of loco hauled trains on Thameslink?

I can't think of any

 

[Krokodil]

Diesels make sense. One large capacity diesel engine will be more efficient than several small capacity diesel engines. And the only way to have a large capacity diesel engine is in its own space, so either in a loco or in a power car as with the 755s.

Or above solebar behind the cab as per the SR DEMUs

Yes as been mentioned above but also because the driver wouldn’t be able to release doors and the service wouldn’t be able to operate DOO

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No reason that they couldn't, but this deviation in to the realms of fantasy is nuts.

 

[Bald Rick]

Would that be any slower if the 700 had its motors removed and a loco of equivalent power at the front?

Yes, because the 500 people are aloghting / boarding from 22 doors rather than 24. 8.33% less door openings means 8.33% longer for the passenger movement.

I’m also not confident that a loco of any power would be capable of hauling the 400+ tonnes itself plus 220 metres of coaches up the bank south of City TL on a wet November morning.

I’m also reasonably confident that a single loco drawing 4MW on DC would cause some rather unpleasant return currents that the signalling really wouldnt like

 

[Zomboid]

Yes, because the 500 people are aloghting / boarding from 22 doors rather than 24. 8.33% less door openings means 8.33% longer for the passenger movement.

I would expect that the fact that no matter how long a train is, everyone is trying to get on through the two doors next to the platform entrance would offset that.

 

[Bald Rick]

I would expect that the fact that no matter how long a train is, everyone is trying to get on through the two doors next to the platform entrance would offset that.

Us Thameslink commuters are rather better trained in that respect

 

[norbitonflyer]

Diesels make sense. One large capacity diesel engine will be more efficient than several small capacity diesel engines. And the only way to have a large capacity diesel engine is in its own space, so either in a loco or in a power car as with the 755s.

A loco has the disadvantage that part of the length of the train is not available for payload. This is important if platform space is at a premium. (Think of the 159s at Waterloo)

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Would that be any slower if the 700 had its motors removed and a loco of equivalent power at the front?

less traction with only 4 or six axles powered

== Doublepost prevention - post automatically merged: 3 Jul 2025 ==

It's mostly down to fuel and engine maintenance - so mostly a concern for DMUs rather than EMUs. How many long pure-DMUs can you think of? A handful of 222s are the only things I can think of with seven engines in a single unit.

1st generation DMus often ran in eights (eg 2xclass 115 or 127 on the Chiltern and Midland Main lines). Or 2x6car on the Charing Cross - Hastings line - admittedly that was only four engines

Even today, Class 159s run in formations of nine or even ten cars.

 

[pokemonsuper9]

1st generation DMus often ran in eights (eg 2xclass 115 or 127 on the Chiltern and Midland Main lines). Or 2x6car on the Charing Cross - Hastings line - admittedly that was only four engines

The question was single unit, not pairs of.

If pairs counted then 222 pairs or 221 pairs would count at 10 carriages (I don't think 7+5 222 has been done in passenger service since it wouldn't fit at Kings Cross)

 

[Krokodil]

The question was single unit, not pairs of.

If pairs counted then 222 pairs or 221 pairs would count at 10 carriages (I don't think 7+5 222 has been done in passenger service since it wouldn't fit at Kings Cross)

Indeed.

And I'd like to bet that the cost of running a double Voyager exceeded the cost of running an equivalent capacity HST.

 

[Zomboid]

Indeed.

And I'd like to bet that the cost of running a double Voyager exceeded the cost of running an equivalent capacity HST.

To be fair though, you'd probably need about 4 HST power cars to achieve voyager level performance for that capacity.

 

[Magdalia]

1st generation DMus often ran in eights (eg 2xclass 115 or 127 on the Chiltern and Midland Main lines).

1st generation DMMUs could run with up to 6 power cars in multiple.

 

[The exile]

Yes as been mentioned above but also because the driver wouldn’t be able to release doors and the service wouldn’t be able to operate DOO

== Doublepost prevention - post automatically merged: 3 Jul 2025 ==

There’s no intrinsic reason why not - German S-Bahn services ran like that for years. Working agreements, legal frameworks etc are of course a different matter.
Sorry - realise I was beaten to it.

 

[saismee]

Diesels make sense. One large capacity diesel engine will be more efficient than several small capacity diesel engines. And the only way to have a large capacity diesel engine is in its own space, so either in a loco or in a power car as with the 755s.

755s have two (/3) or four (/4) smaller diesel engines as there needs to be enough space to fit a corridor down the middle of the coach. The separation is likely just for passenger comfort and the low-floor design, as there's no space to put engines under the floor.

 

[in_the_west]

I wish Cross Country trains were too long!

A few days ago I was on a Cross Country train that became too long.

It started off from Penzance with just 4 carriages and became full and standing as it called at stations towards Plymouth. The train manager kept announcing that 5 additional carriages would be added at Plymouth.

However, just before the train reached Plymouth the train manager came into the end carriage where I was seated and told everyone that because the train would be too long once the additional 5 carriages had been added, the end carriage would be locked out of use between Plymouth and Exeter. The reason for this was that the platform at Totnes could only accommodate 8 carriages.

This resulted in lots of unhappy passengers, especially those with luggage and elderly folk who needed special assistance. Once the train reached Plymouth, the station staff worked with the on-board train staff to help move everyone from the rear carriage to one of the front 8 carriages.

I was able to change onto a 9 carriage GWR train starting from Plymouth to continue my journey to Exeter. Seems a bit odd that 9 carriage GWR trains can be accommodated at Totnes whereas 9 carriage Cross-Country trains cannot!

 

[saismee]

I was able to change onto a 9 carriage GWR train starting from Plymouth to continue my journey to Exeter. Seems a bit odd that 9 carriage GWR trains can be accommodated at Totnes whereas 9 carriage Cross-Country trains cannot!

If my math is correct, a 9-coach class 800 is 19.95m longer than a 9 coach 220+221 combo... maybe a different platform?

 

[Zomboid]

IETs have SDO, don't they?

 

[physics34]

It's Stansted Express.

The back four will be full and standing most likely because people suffer from an allergy to walking with luggage.

I've been on many Stansted Express trains where the train loading diagram shows the back 5-6 carriages as full and people tweeting about it dangerously overcrowded whilst my carriage is at best 30% full.

Also loads are not totally predictable, flight delays, passport queues mean that the load is not as predictable as your average train.

Same on the Gatwick Express..
Move along a bit!

 

[Krokodil]

Seems a bit odd that 9 carriage GWR trains can be accommodated at Totnes whereas 9 carriage Cross-Country trains cannot!

Voyagers have no Selective Door Operation (SDO), IETs do.

 

[allbarbarry]

The Class 700s on Thameslink cart nothing but fresh air in many of their 12 carriages between Horsham and Peterborough, during the middle of the day (particular on weekdays, I find weekends tend to be busier) - although this is a fixed formation..

 

[Class 170101]

I would expect that the fact that no matter how long a train is, everyone is trying to get on through the two doors next to the platform entrance would offset that.

Us Thameslink commuters are rather better trained in that respect

That depends on the weather. If its too hot or especially if its snowing forget it. People will 'hide' under the canopy and get on the nearest door, in my experience.

 

[AM9]

That depends on the weather. If its too hot or especially if its snowing forget it. People will 'hide' under the canopy and get on the nearest door, in my experience.

Such conditions are relatively rare and given the frequency of peak services, passengers generally spread along the platform to board quicker as the waits are shorter. In addition, there isn't that much room at some of the busiest stations, (e.g. St Albans City P3) as EMR trains pass through at 95-100mph.