Why can't future train orders be for double deck trains?

[RobShipway]

This is a point that my Dad keeps bringing up, which is why is it that any new UK trains orders are for longer trains rather than double deck trains as they have in Europe?

I have explained to my Dad many times that I do not think that the UK rail infrastructure would be able to take double deck trains with the heights of bridges, tunnels etc.... Plus also the height that we have overhead wires in this country I believe from discussing it the one time with a Network Rail engineer would be too low.

 

[greatvoyager]

Low bridges would probably be the biggest problem.
Also, would they fit in stations like Birmingham New Street, even if it didn’t have overhead wires?

 

[Bletchleyite]

Yep, very costly to change the infrastructure for relatively little benefit (you only get about 1.3-1.5 times the amount of seating in a single deck vehicle).

It'd be worth it if the infrastructure was already up to it but it's not.

 

[SynthD]

Ask him to find a route that has enough passengers, no bridges, no tunnels, no third rail.

 

[dm1]

The fundamental problem is something called loading guage. This is, to put it simply, how much space a train is allowed to take up (how tall, how wide etc) without hitting anything (bridges, tunnels, platforms, etc)

Loading gauge - Wikipedia

en.m.wikipedia.org

The railways in Great Britain were generally built much earlier than most railways in Europe and for various reasons were built to much smaller loading guages. One reason is for example the difficulties of building large tunnels before tunneling technology developed to where it is today. The most extreme example of this is the tube lines in London.

These smaller loading guages are not large enough for double decker trains to fit without serious design compromises that make them fairly impractical (there have been some examples in the past, where this can be seen). Therefore they cannot be used anywhere on the GB rail network, with the single exception of HS1 which was built to a European loading guage.

When HS2 is built, its loading guage will also allow double decker trains in theory, but since its trains will have to leave HS2 to serve stations on the conventional network, this won't be possible at the very least for the first generation of trains until the high speed network is extended further.

 

[zwk500]

Obligatory mention for the 4DD whenever Double-Deck trains are mentioned: https://en.wikipedia.org/wiki/SR_Class_4DD

On a serious note, the other key point about Double-Deck trains is that you often end up needing longer dwells at stations with high churn, as the extra people have no extra doors to pass through. Imagine 12 cars worth of people through 8 cars of doors at East Croydon and you can quickly see why longer trains would be preferred in any event.
Double Deck might work quite well for routes like Birmingham-Northampton-MK-London where the intermediate stops have reasonable turnover but lots of people are heading right through. Not a cat in hell's chance of the infrastructure being modified to take it though.

 

[stuu]

Ask him to find a route that has enough passengers, no bridges, no tunnels, no third rail.

In the unlikely event anyone would do it, the Fenchurch St-Southend route would be the most appropriate as it has no tunnels and is (almost) self-contained, and busy enough to justify it. Won't happen though.

The design of UK platforms and structures below the floor level, especially girders for underbridges, are at least as big a problem as the roof height too

 

[Grumbler]

This is a point that my Dad keeps bringing up, which is why is it that any new UK trains orders are for longer trains rather than double deck trains as they have in Europe?

I have explained to my Dad many times that I do not think that the UK rail infrastructure would be able to take double deck trains with the heights of bridges, tunnels etc.... Plus also the height that we have overhead wires in this country I believe from discussing it the one time with a Network Rail engineer would be too low.

We could if we were hobbits.

 

[swt_passenger]

There’s a detailed Network Rail report explaining exactly why this is incredibly difficult, it must have been linked to and discussed numerous times since I’ve been a member of these forums.

https://webarchive.nationalarchives...whitepapersupportingdocs/provevalddtrains.pdf

 

[Paul Jones 88]

How would a modern version of the Bullied 4DD go down?
I don't see why it can't be done but with sliding doors and all PRM bases covered.
I've always thought that the original 4DD was a great idea and that if the government was a bit more ambitious towards the railway they or at least versions of them could have appeared on suburban lines all around the country, by now we would have had a 3rd generation version like I described at the top of this post.

 

[JonathanH]

How would a modern version of the Bullied 4DD go down?
I don't see why it can't be done but with sliding doors and all PRM bases covered.
I've always thought that the original 4DD was a great idea and that if the government was a bit more ambitious towards the railway they or at least versions of them could have appeared on suburban lines all around the country, by now we would have had a 3rd generation version like I described at the top of this post.

We can't build stock with closed compartments now, even with sliding doors. It wasn't acceptable 30 years ago, let alone now.

It wouldn't be acceptable to build a train where there is no visibility down the carriage. It isn't really possible to have the seating arrangement of the DD in an 'open' layout. There is a clear movement in recent years to have units on suburban services with very open layouts.

 

[NoRoute]

Obligatory mention for the 4DD whenever Double-Deck trains are mentioned: https://en.wikipedia.org/wiki/SR_Class_4DD

On a serious note, the other key point about Double-Deck trains is that you often end up needing longer dwells at stations with high churn, as the extra people have no extra doors to pass through. Imagine 12 cars worth of people through 8 cars of doors at East Croydon and you can quickly see why longer trains would be preferred in any event.
Double Deck might work quite well for routes like Birmingham-Northampton-MK-London where the intermediate stops have reasonable turnover but lots of people are heading right through. Not a cat in hell's chance of the infrastructure being modified to take it though.

Isn't it about using the correct tool for the task, or rather the correct carriage for the service?

The double deck trains I have travelled on were regional expresses where the churn at each station was low and most passengers were travelling through. Local stopping services with high churn used trains like a 321, single deck with lots of doors. The double decks had more unobstructed standing space around the doors for passengers to wait prior to leaving, or to accommodate people boarding the train, than you find on many British designs. There's also some human factors and passenger learning which goes on, you notice passengers get up and move to the door area well before the train arrives in the station because there's fewer doors and a longer walk, people are also still heading to find seats as the train moves off.

So in practice, used in the right application, I wonder how much of the potential extra dwell time is mitigated by using them on high through capacity, low churn type services.

Can HS2 accommodate double-deck trains?

 

[zwk500]

Isn't it about using the correct tool for the task, or rather the correct carriage for the service?

Exactly this

So in practice, used in the right application, I wonder how much of the potential extra dwell time is mitigated by using them on high through capacity, low churn type services.

But this makes them unsuitable as a replacement for conventional lengthening schemes in London commuter land, which is where they are most frequently proposed, because of the very high churn at intermediate stations approaching London, such as Stratford, East Croydon and Ealing Broadway.

Can HS2 accommodate double-deck trains?

It will be able to, yes. And HS1 currently can. However, for reference, the UIC Universal gauge has a maximum height for rolling stock of 4.28m clearance above rail level. The UK has 3.965m maximum height for rolling stock, with the differences between W6a and W12 largely being about how 'boxy' the profile is, less relevant to passenger trains (but still important for upper deck comfort). 33cm doesn't sound like a lot, but if you've got to lift every bridge it'll quickly add up. So DD trains would be captive to either HS line for the foreseeable future.
Also relevant to this is that UK standards are for 2.82m vehicle body width, whereas UIC standards are for 3.15m vehicle width. Again, 33 cm doesn't sound like a lot but it makes a difference to the circulating areas and the width of seats/gangways. If you've got DD stock you'll want wide circulating areas and gangways to facilitate the circulation of passengers. And I haven't even got on to the platform height differences and lower sector.

 

[NoRoute]

How would a modern version of the Bullied 4DD go down?
I don't see why it can't be done but with sliding doors and all PRM bases covered.
I've always thought that the original 4DD was a great idea and that if the government was a bit more ambitious towards the railway they or at least versions of them could have appeared on suburban lines all around the country, by now we would have had a 3rd generation version like I described at the top of this post.

If you look at the pictures and cross-section diagrams of the 4DD, it looks like the height of the base of the carriage is either the same or very similar to conventional single deck trains, at platform level, so it doesn't use the extra space available by lowering the carriage floor closer to the track.

If you get onto an double decker train in Europe, the doors and entrance area are at the normal platform level, but the lower deck is below this, you access it by going down a small set of stairs. By lowering the position of the lower deck, this releases space above it, to allow for the second deck, accessed from the door area via stairs up to it, so by using this extra space you get two long, open seating areas like a conventional train.

Granted, the European rail networks have more space to play with, but if you took some inspiration from airplane designers, having full height walk-ways combined with seating with reduced head height, then positioning the seating and walk-ways of the two decks, such that the walk-ways were not inline, I wonder if you could have two decks of this. This would remove the need to accommodate two full height walk-ways, directly above each other within the loading gauge.

 

[2192]

"Granted, the European rail networks have more space to play with, but if you took some inspiration from airplane designers..."

1. Airplane designers are not used to bridges and tunnels, so don't have a headroom restriction.
2. At the time HS2 rolling stock was being discussed, a european firm produced a double deck design and Modern Railways printed a cross sectional drawing, but in the end the order was for stock capable of running on the whole of the network, not just HS2.
3. I went on a 4DD as a child from London Bridge to Charing Cross and back off peak and found it quite claustrophobic. IN rush hurs it would have been slow to load/unload. The tiny windows were no good for engine spotting.

 

[JonathanH]

Granted, the European rail networks have more space to play with, but if you took some inspiration from airplane designers, having full height walk-ways combined with seating with reduced head height, then positioning the seating and walk-ways of the two decks, such that the walk-ways were not inline, I wonder if you could have two decks of this. This would remove the need to accommodate two full height walk-ways, directly above each other within the loading gauge.

It would be totally unacceptable (and frankly unnecessary) to have such a closed layout on modern rolling stock.

 

[swt_passenger]

All that stuff below the sole bar such as transformers, traction converters, batteries, switchgear, toilet tanks etc etc all has to go elsewhere in the train if it can’t go between the bogies. The bogies can’t go further apart, so in a typical length suburban coach the theoretical lower floor volume is very small anyway, and it’s so narrow because of the lower structure gauge 2+1 would be a push. As they said in the report, with 2+2 seating, an increase in seating capacity of only about 8% was achievable. You can get that on a typical current 12 car train by using fixed formation rather than 3 x 4 car. So double decker ends up being a costly way of making a trivial improvement.

 

[gordonthemoron]

In the unlikely event anyone would do it, the Fenchurch St-Southend route would be the most appropriate as it has no tunnels and is (almost) self-contained, and busy enough to justify it. Won't happen though.

The design of UK platforms and structures below the floor level, especially girders for underbridges, are at least as big a problem as the roof height too

maybe no tunnels, but it does have over bridges, at least in Southend

 

[zwk500]

maybe no tunnels, but it does have over bridges, at least in Southend

And the small matter of an over-site development on the end of Fenchurch Street platforms. It's hard to tell if it'd be high enough from pictures though.

 

[Well Hall]

3. I went on a 4DD as a child from London Bridge to Charing Cross and back off peak and found it quite claustrophobic. IN rush hurs it would have been slow to load/unload. The tiny windows were no good for engine spotting.

Thinking about the unloading times that would be the reason for the two 4DD units ran fast from London to Eltham Well Hall. They were cramped and if tall you wouldn't to use the stifling upper deck. The ventilators never worked. I used to travel in the front unit to be near the peak time exit stairs on to Well Hall Road by the florests shop.

 

[Ken H]

All that stuff below the sole bar such as transformers, traction converters, batteries, switchgear, toilet tanks etc etc all has to go elsewhere in the train if it can’t go between the bogies. The bogies can’t go further apart, so in a typical length suburban coach the theoretical lower floor volume is very small anyway, and it’s so narrow because of the lower structure gauge 2+1 would be a push. As they said in the report, with 2+2 seating, an increase in seating capacity of only about 8% was achievable. You can get that on a typical current 12 car train by using fixed formation rather than 3 x 4 car. So double decker ends up being a costly way of making a trivial improvement.

The double deck trains I have used around Berlin are not MU's but a rake of trailers, with a DVT at one end, with a loco at the other. So less underfloor equipment.

 

[zwk500]

The double deck trains I have used around Berlin are not MU's but a rake of trailers, with a DVT at one end, with a loco at the other. So less underfloor equipment.

Are there many lines in the UK that would require double-deck trains and suit a push-pull arrangement? Although that being said, you could do something where a part of one car is a psuedo-loco, but the traction motors are still distributed along the train (FLIRT-Style).

 

[swt_passenger]

The double deck trains I have used around Berlin are not MU's but a rake of trailers, with a DVT at one end, with a loco at the other. So less underfloor equipment.

And 2 coaches less in the platform at the terminus, which is already mostly constrained to 12 car in the busiest suburban areas. So that doesn’t help much at all.

 

[RobShipway]

The double deck trains I have used around Berlin are not MU's but a rake of trailers, with a DVT at one end, with a loco at the other. So less underfloor equipment.

Not sure if they have changed, but the trains in and around Zurich where the same back in the 1990's.

 

[stuu]

And the small matter of an over-site development on the end of Fenchurch Street platforms. It's hard to tell if it'd be high enough from pictures though.

Somewhat moot as it isn't going to happen, but there is quite a lot of height over the platforms at Fenchurch Street

 

[6Gman]

If you look at the pictures and cross-section diagrams of the 4DD, it looks like the height of the base of the carriage is either the same or very similar to conventional single deck trains, at platform level, so it doesn't use the extra space available by lowering the carriage floor closer to the track.

If you get onto an double decker train in Europe, the doors and entrance area are at the normal platform level, but the lower deck is below this, you access it by going down a small set of stairs. By lowering the position of the lower deck, this releases space above it, to allow for the second deck, accessed from the door area via stairs up to it, so by using this extra space you get two long, open seating areas like a conventional train.

Granted, the European rail networks have more space to play with, but if you took some inspiration from airplane designers, having full height walk-ways combined with seating with reduced head height, then positioning the seating and walk-ways of the two decks, such that the walk-ways were not inline, I wonder if you could have two decks of this. This would remove the need to accommodate two full height walk-ways, directly above each other within the loading gauge.

Disability Discrimination Act (and successors).

"Slips, trips and falls".

 

[OldNick]

I think the German DD example I went on had a ramp to the lower level for accessibility and bicycles.

 

[ainsworth74]

And 2 coaches less in the platform at the terminus, which is already mostly constrained to 12 car in the busiest suburban areas. So that doesn’t help much at all.

It's not a DVT it's more akin to a DBSO in our parlance as it is mostly passenger accommodation with just a cab on the end.

 

[swt_passenger]

It's not a DVT it's more akin to a DBSO in our parlance as it is mostly passenger accommodation with just a cab on the end.

Oh ok. Still not going to happen here though, I suggest

 

[ainsworth74]

Oh ok. Still not going to happen here though, I suggest

Oh blimey no. Making them fit the physical infrastructure kills that stone dead before we worry about terminal capacity or loading/unloading times.