The Anonymous Widower

The Aventra Car Length Puzzle

I think that Bombardier have a very flexible nature to how long a car can be in the new Aventra. This flexible length, could be enabled in part, by the way the trains are built, which I believe used aluminium exclusions and a lot of specialist weldimg. I wouldn’t be surprised that if you wanted a 40 metre long car, then Bombardier would be able to build it.

They now have three orders for the train and they can be summarised as follows.

The information has been gleaned from  Wikipedia, Modern Railways and other sources.

Crossrail Class 345 Trains

The Class 345 trains for Crossrail have the following characteristics.

  • 9 cars – Wiki
  • articulated trains
  • 200 metres long – Wiki
  • Around 23 metres long cars – MR
  • 3 pairs of doors per car – MR

Seating will be a mixture of Metro-style and some groups of four.

This article in Rail Technology Magazine says a lot about the design of the trains. This is said about seating.

“The layout of the seats is also different per different carriage, so where people will crowd there’s more space, and at the end of the trains, where people might not be crowding on, there’s more seats. So a lot of thought has gone into the ergonomics of this train.

“But generally, the average journey on this train will be 15 minutes – so what people want is to be safe, comfortable, and air conditioned, but they really want to get on. Capacity is one of the big drivers – but 450 seats if a really good ratio.”

So perhaps the old Tube rule will apply – If you want a seat go to the front or back of a train.

Dividing nine-cars into a 200 m. long train, gives a car-length of 22.22 m, which is probably good enough for around 23 metres.

But if you assume that the two driving cars are identical and the trailer-cars between them are 23 metres long, you get two 19.5 metre driving cars at either end. Given that the train is articulated and there is a need for a Crash-worthiness crumple zone at both ends of the train, it could be that so that the middle trailer cars are identical as they are in the Class 378 train, that the end driving cars are slightly shorter, which could be structurally stronger.

If the two driving cars are 20 metres, then you get a trailer car length of 22.85 metres.

Could it be too that all different facilities like wheelchair spaces and transverse seating are in the driving car?

I also have this feeling, if I remember correctly, that if you can cantilever a heavy weight forward in the nose, that this helps dissipate the kinetic energy in a crash. It’s why car engines are often placed as far forward as the design will allow.

This statement can be found a couple of times on the Internet including in this article on Railway Gazette.

There will be a mixture of ‘metro-style’ and bay seating, with four wheelchair spaces and a number of multi-use spaces with tip-up seating to accommodate prams or luggage.

Only a detailed look inside a finished train will find out what they are really like.

London Overground Class 710 Trains

The Class 710 trains for London Overground have the following characteristics.

  • 4 cars – Wiki
  • articulated trains (?)
  • Around 20 metres long cars – MR – Similar to Class 378 trains
  • 2 pairs of doors per car – MR

Seating will depend on where the trains are deployed and will be Metro or traditional, although the September 2016 edition of Modern Railways says its all longitudinal. Passengers won’t like that between Liverpool Street and Cheshunt.

Abellio East Anglia Trains

These trains haven’t been allocated a class yet and this is the best description from this article in Rail Magazine describes the trains.

The Bombardier units will be based on the Class 345 Aventras being delivered for Crossrail, but with the focus on seating capacity rather than standing space. The trains will come in two versions: ten-car and 240 metres long; and five-car and 110 metres long. All will be electric.

Note, if these train and car lengths are correct, the cars are longer than for the Class 360 trains and a ten-car Aventra is as long as a twelve-car Class 360 train.

I think it would be reasonable to assume, that the driving and trailer cars for both length of trains are identical, as this would give the operator various advantages.

  • Having only one type of driving car must ease driver training and rostering.
  • Servicing will surely be easier to organise.
  • If say a route needed a six-car train, then an extra car could be easily added.

Three different ways of calculating the car lengths can be used.

Method 1 – If d is the length of the driving car and t is the length of the trailer car, you get two simultaneous equations.

2d+8d = 240

2d+3t = 110

These give a trailer car length of 26 metres and a driving car length of 16 metres.

I don’t think that sixteen metres is too feasible, even if Bombardier could build one.

Method 2 – The driving cars are 20 metres long.

This car length would be a compromise driving car length that would work with both Class 345 and Class 710 trains, to give identical driving cars across all trains.

The length of a trailer car will be as follows.

  • 10-car – 25 metres.
  • 5-car – 23.3 metres.

What is intriguing is that if 25 metre trailer cars were used in a five-car train, this would give a train length of 115 metres. So two five-car train running as a pair, would fit any platform able to take a ten-car train.

Method 3 – The trailer cars are a fixed length.

  • 20 metre trailer cars would give 40 and 25 metre driving cars for 10-car and 5-car trains respectively.
  • 23 metre trailer cars would give 28 and 20 metre driving cars for 10-car and 5-car trains respectively.
  • 24 metre trailer cars would give 24 and 19 metre driving cars for 10-car and 5-car trains respectively.
  • 26 metre trailer cars would give 16 and 16 metre driving cars for 10-car and 5-car trains respectively.

I suspect there’s a compromise in there somewhere, that will allow both types of car to be all of the same length.

I suspect that it could be 20 metre driving cars and 25 metre training cars, as indicated by Method 2.


  • Both train layouts, allow two five-car trains to fit a ten-car platform and if they can, work as a pair.
  • As with the Crossrail trains, I wonder if the driving cars will have all the specials like disabled toilets, wheelchair and bicycle spaces and First Class seating.
  • You could even  have different versions of the driving cars. First Class, bicycle, accessible toilet etc.
  • Perhaps only one First Class seating area is needed per train.
  • Would all routes need bicycle spaces?
  • If the trailer cars were longer, then this would mean there could be a more relaxed interior with more space for tables.

Again as with the Crossrail trains, only a detailed look inside a real train, will show the car lengths and the interiors.


It all leads me to the conclusion that Bombardier have a very flexible design.

  • Pictures show the driver’s cab to be generously-sized.
  • Pictures show that the driver’s cab might be cantilevered outwards from the train, which would increase crash-worthiness.
  • I’m tending to believe that driving-cars will all be the same for the driver, but the space behind the cab will be used for special parts of the train like disabled toilets, bicycle spaces and First Class seating. The latter is traditionally placed at one end of many EMUs, anyway.
  • Trailer cars might be of a flexible length between 20 and 26 metres long.
  • Saying you could only have one length of trailer and dtiving cars would be so Henry Ford
  • The number of doors in each car can be two or three pairs.

Bombardier have attempted to allow the customer to procure a train to their precise needs.

But overall, I’m still puzzled.




August 28, 2016 - Posted by | Transport/Travel | , , , ,


  1. […] In The Aventra Car Length Puzzle, I talked about the flexibility of Bombardier’s new Aventra trains.  The first of these; Crossrail’s Class 345 trains, will hit the tracks in May 2017, when according to the September 2016 Edition of Modern Railways, they will enter service between Liverpool Street and Shenfield. […]

    Pingback by Siemens And South West Trains Unviel The Class 707 Train « The Anonymous Widower | August 30, 2016 | Reply

  2. […] In The Aventra Car Length Puzzle, I came to the following conclusions. […]

    Pingback by Bombardier’s Plug-and-Play Train « The Anonymous Widower | September 2, 2016 | Reply

  3. […] In The Aventra Car Length Puzzle, I said that the Class 710 trains for the Overground would have twenty metre long cars, which is similar to the 20.4 metres of the Class 378 trains. […]

    Pingback by Will The New Class 710 Trains Use Selective Door Opening At Gospel Oak Station? « The Anonymous Widower | November 26, 2017 | Reply

  4. The mystery is over. An FoI request eventually revealed the dimensions. See the PDF suppied by TfL here:

    Comment by Ian | June 30, 2018 | Reply

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