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I write this from the comfort of a train speeding from Brussels to Bruges for the weekend. The train is a double decker similar to other European trains.
I was just wondering, seeing as how the network is full and the platforms too short, as to why we only have single decked carriages?
Thanks

The British system (bridges, tunnels, etc) has a much smaller cross-section so it's quite hard to get a second storey on to a train.   It was tried (somewhat) in South East London with two 4 car units about 60 years ago, with compartments offset above each other - cross seating with (in effect) a compartment above in the luggage racks.  But there were far more seats per door, and station dwell times suffered.

https://www.flickr.com/photos/rw3-497alh/5330944631/

http://en.wikipedia.org/wiki/SR_Class_4DD

I believe the reasons stated by Graham, essentially gauge clearance issues, are, at least in part, a relic of WW2, in that our rail system was relatively lightly damaged (and largely continued to operate "normally") in comparison to that of our continental neighbours, whose rail systems were pretty much rebuilt from scratch post-war. So, we're stuck with Victorian spec railway, whereas France, Belgium, the Netherlands, Germany etc all have mid 20th century specification rail systems that allowed more sustainable growth, particularly with double deck trains & electrification. I understand it is also less of an issue to carry the larger sized shipping containers on Euro rail systems as opposed to ours.

I always through the gauge difference went back to the beginning, and places that got railways even 20-30 years after Britain saw the advantage of bigger loads. According to this (http://www.railway-technical.com/berne.shtml) that's true for the German sphere of influence, but not the French (perhaps too early). However, they made the effort to upgrade main lines before the WWII, so post-war reconstruction would not have had much effect  - especially given the small amount of damage in Paris and much of the rest of the country.

I've seen an analysis (no idea where) of the gains from an upstairs, given that it can only fit between bogies and you need stairs. That showed the gain is pretty small, especially for fast-loading commuter trains. That's because moving up and down stairs is slow, so you need more standing space to hold a whole station's joiners and leavers (or to try to). The gain is even smaller for 2-storey RER trains, as they have three doors per carriage, hence three stairways.

You might be thinking of this:

http://webarchive.nationalarchives.gov.uk/20100513020716/http://www.dft.gov.uk/about/strategy/whitepapers/whitepapercm7176/railwhitepapersupportingdocs/provevalddtrains

Basically it isn't just the height of vehicles, the GB network usually has less space to deepen carriages between the bogies as well.

Coincidentally the possibility of using double deck trains on discrete parts of the SWML (e.g. Waterloo to Basingstoke) has just resurfaced in the Wessex route study draft - though NR still appear lukewarm about it, with only a 50% capacity increase being assumed.

Paul

This is the critical part. British trains evolved with high platforms with the result that the width of the coach below floor level is narrower than the body. In central Europe, and much of France, low level platforms were the order of the day so the coach maintained its width down to rail level.

Although higher platforms are now common in parts of central Europe they are spaced far enough from the rails that there is no interference fit between the train and the platform. ;)

It would be very expensive to enlarge the UK structure gauge on existing lines - not only the platforms would need to be moved but potentially hundreds of under bridges with longitudinal girders between the rails would have to be rebuilt.

While there is little detail in the study, it is clear that they are considering clearing a specific route (Waterloo-Basingstoke, and perhaps to Southampton) for these trains which will not (indeed cannot) run anywhere else. That suggests greater height, and/or perhaps greater below-platform width (within the restrictions of third rail stock). They would also only be used for peak service, so potentially one up and one down per day. That, plus being a small-volume custom design, is all going the weight the BCR heavily against it.

Interestingly, the 1930s French Voitures ^tage ^tat were also used as peak-busters - though that was not the first double-decker design; that was the Bidel back in 1882 (and very quaint it looks (http://fr.wikipedia.org/wiki/Voiture_Bidel)).

Fascination - From that link, which is in French, via Google Translate:

Hmm - not one of Google Translate's best - for "network of former French West" read "the old Paris East network" - in fact from the gare de Paris-Bastille to Vincennes. Also, ^ imp^riale ("to imperial", excusably) means double-deck, as applied to buses too (and imp^riale refers to the upper deck itself).

An excellent Pathe Newreel video via
http://www.ianvisits.co.uk/blog/2014/11/22/double-deck-trains-proposed-for-waterloo-station-lines/?

showing how the seating was going to work on the prototype

An old video - introduction of double decker trains from Charing Cross.   I wonder how this will differ from first run of a 387 out of Paddington

https://youtu.be/22GWR3MmBIg

Perhaps we won't have double decker trains for fears of bridge strikes where road over rail
 ;) ;)

If the use of rail continues to grow, then someone will have to decide what to do with busy terminal stations, such as those in London.

A typical station with ten platforms, a train turnaround of 2ph (with unloading, cleaning and loading) and 6 primary routes has a limited capacity. With a further growth of 40%(guess) over the next 10-20 years quite likely, are we going to add extra decks of platforms, or deploy double deck trains.

The current Paddington plan of adding two new Crossrail platforms (underground), re-allocate some local platforms to intercity and longer trains makes the current situation more tolerable.

Perhaps someone has ... with Thameslink, Elizabeth Line, Crossrail 2 so far, and HS1 relieving some pressure inbound from Kent.  Could there be more in the series? 

That might be more plausible than perhaps you'd think.

That 2007 Network Rail study into two-storey trains (referred to in this forum before) looked at adapting just one route into London, e.g. Southampton-Waterloo. Just raising the height to French gauge (same width as ours) was costed at the thick end of 1 G£. Doing the same for 16-car trains cost a little less, but gave more extra seats, so would always be a better bet - and you could go on to look at longer trains still.

The real killer for that extra deck is the narrow UK gauge below platform level. Continental gauges go right down at almost the same width, while our trains don't, and can't due to all the stuff down there. The NR study didn't even look at clearing that - dismissed as far too expensive (especially all those bridge girders). If downstairs can only hold 2+1 seating, its benefit is pretty limited.

Raising the height is familiar from electrification, hence much easier to cost. But if you got a few taller trains, you would have to very careful where you drove them. CTRL and your cleared route (and maybe a short link between) would be OK, but any routeing or signalling brain fade and that hugely embarrassing bridge strike is all too possible.

As has been repeated frequently (including in this thread), not only are double-deck trains difficult in terms of loading gauge, but they significantly increase dwell times, are difficult to make accessible, you lose significant area with the stairs and the upstairs/downstairs split makes the train less secure compared with modern full-width gangway designs where effectively the whole train is an open cylinder with few hidden corners where anything untoward can go on etc.

Far better to spend money on increasing the length of trains and service frequency (which has the further benefit that a more frequent service is more attractive to users).

As Graeme says, Thameslink and Crossrail (1 and 2) have the dual benefits that they reduce the number of services turning around at the London Terminii (hence the rebuild of London Bridge to have more through platforms and fewer terminating platforms), and also that they relieve pressure on the tube network (Central line for Crossrail, Victoria line for Crossrail 2). There's also the proposed Bakerloo line extension which should provide an alternative to heavy rail in SE London.

As for Crossrail 3, it's unlikely to be built for another 10 years at least, and who knows how London's geography will have changed by then. There's a whole thread on Skyscraper City (http://www.skyscrapercity.com/showthread.php?s=ff6f228432d711905417057aee9ddd38&t=1381717 (http://www.skyscrapercity.com/showthread.php?s=ff6f228432d711905417057aee9ddd38&t=1381717)), but NW to SE would fill a gap in the map, and if you wanted to be radical, you could even take over the Metropolitan line re-electrify it at 25kV together with Chiltern and send it through the City to connect up with the Fenchurch Street lines. 

Should this thread really be in The Wider Picture... or The Higher Picture?  :D

Other's have answered this question in general terms.  There does remain however the question of why HS1 doesn't have double decker trains.  The first generation Eurostars were build to GB loading gauge so that is your answer, but the new e320 trains are only single decker.

My understanding that there is room for double deckers here (and with few stops that arguments about increased dwell times does not apply).  The only reason I can think of is what might seem like a perverse desire to keep the trains long so as to comply with Chunnel safety regs. 

or the extra cost in building deeper/bigger tunnels? And what about the London terminal? isn't that into/out of a tunnel too?

As I understand it the whole route into St Pancreas is built to the GB+ gauge used in France where there are TGV duplex trains. 

A load of new Paris RER trains have been ordered (by STIF). The design is based on Alstom's X'trapolate series though for some reason (probably devious and political) Bomardier are helping them.

These are double-decker trains, not unusual on the RER, but this time also open throughout (car-width gangways) and with a very high standing capacity. They quote 1860 passengers in a 130 m length - compare that with Crossrail's 1950 (min) in 205 m (max).

Alstom's announcement (http://www.alstom.com/press-centre/2017/832228/new-generation-trains-ordered-for-lines-d-and-e-of-the-sncf-network-in-ile-de-france/) has a cut-away picture in it, which shows large vestibules with only tip-up seats, and that area is marked "5 minutes". Then there's downstairs, with 30 seats in 3+0, but several of these are tip-ups, marked "20 minutes". Then upstairs is 18 seats in 2+0, again with some of them tip-ups, and marked "50 minutes".

Now that pictures has ambiguities: upstairs could be 2+2 with the nearside cut away, and downstairs might have single seats along the nearside. But then some seats shown down might flip up - or even all of them! Cramming so many people into the length is not going to be easy.

I can't explain, in terms of vehicle lengths and numbers, how trains are made in 112 m and 130 m lengths. Despite being Alstom the bogies are not shared. The inner vehicle length does look short, though, presumably to optimise the vestibule and double-deck lengths in relation to the number of doors). 

You might well call them sheep trucks (they are better then cattle at climbing the stairs). To compare with here, the furthest terminals are Malesherbes at 60 km on RER D, and will be similar for Mantes-la-Jolie on RER E once extended. Those are straight-line from the city centre, on which basis Reading is also 60 km. Thameslink of course goes a lot further.

[This seems as good a place as any ... for now, anyway.]

Having travelled on the final journey in passenger service of the 4DD, I have read about its story before and after with interest.

A new website on the subject - coming right up to date with the efforts to preserve / conserve / pass on to heritage the remaining two carriages has been lauched .. https://www.bulleid4dd.org.uk