Vivarail D-Train Diesels?

D Stock
There has been much publicity recently about a company called Vivarail that has been set up to buy redundant London Underground (LU) electric rolling stock and convert it to diesel-electric operation. The idea is to use the converted stock on various routes currently suffering from rolling stock shortages or where the outmoded and much-hated, bus-style "Pacers" are still used.

The LU trains are officially referred to as "D78 Stock"; the D being the District line where they are used and 78, the year of their order. Everyone calls them "D Stock". Your author is quite familiar with them, having written much of the original instruction material for the stock and then doing much of the original training of its maintenance staff.

Fleet Size
The Underground's D Stock fleet consists of 75 x 6-car trains, with each train made up of two 3-car units. The standard formation is arranged so that driving cabs are only provided at the ends of the train, so each of the units is "single-ended". The inner end of the unit couples to the inner end of another unit facing the other way round.  This means that you need an even number of units of each type to make up complete sets of trains. Some units are "double-ended", i.e they have a cab at each end so that, in the event of a shortage of either type of single-ended unit, a double-ended unit can be used to replace it.

There are 65 west facing single-ended 3-car units and 65 east facing 3-car units. There are 20 double-ended 3-car units. The publicity says that Vivarail have purchased enough cars to make up 75 units in 2-car or 3-car formation. Vivarail themselves suggest 4-car units are possible.

D-Train
Vivarail are calling their converted trains "D-Train". The D-Train concept proposes using the original car body (suitably modified) and the existing bogies and their traction motors. Each driving car will be equipped with two 200 h.p. 3.2 litre diesel engines. Each engine will drive an alternator to provide electric power for the two traction motors on each bogie. Presumably, the auxiliary power will be derived in the same way. Of course, there aren't many details at this stage, but there are lots of unanswered questions. Here are some to whet your appetite.

Top Speed
This is set at 60mph. A Pacer can do 75mph and Class 170 will do 100mph. The modelling results published so far suggest a 4% increase in timings as a result. Not too bad but it could get worse for a heavily loaded train with long station stops. Only two of the existing doorways per car side will be used so the dwell times will be similar to the existing.

Weight
A D Stock car weighs 30t. A pair of diesel engines and their alternators will be heavier than the existing PCM traction equipment. I expect the weight of the motor car to go up by 5-7 tonnes. How a weight increase of over 20% will affect the bogie and ride performance is anyone's guess. Both suspension systems are solid rubber. Speaking of weight, I'm wondering where they will put the batteries. They are currently under the passenger seats but they will need a better spec for the D-Train.

Vibration
This is a big concern. Two underfloor diesel engines, operating independently will generate a lot of vibration and noise and this will require serious research and substantial mitigation. There is also the question of the car body harmonics and how these will be affected.

Air Conditioning
There is no mention of air conditioning. It will be a passenger expectation that modern or upgraded trains will have it. Not to will be a significant omission. To fit this to the D Stock passenger saloon would require significant modification to the roof. The space along the ceiling would quickly get filled up with ducting and fan units.

Toilets
The 3-car trains will have a trailer car between two motor cars and this is where the toilet will have to go. There is no room for the waste retention tank under the motor cars. Two-car units will not be able to have toilets. My own feeling is that all the trains should be 3-car sets. This offers flexibility and consistent performance. Also, these cars are 15% shorter than a Pacer, so they wouldn't have much capacity in 2-car format.

Cab Controls
The LU cab is completely different from what's seen on main line trains and it will be necessary to strip out the existing console and replace it with a new one. The LU driver's safety device (DSD) is in the controller handle, so there is no DSD pedal. That will have to be added. The desk displays and controls are completely different and there are no CCTV or computer screens in the cab so these will have to be added for Driver Only Operation (DOO).

Cab Doors
The cab has four doors. These are a nightmare for draughts. I would expect to see the front door (M Door) sealed closed and some serious draught proofing put in for the side doors. There are no drop-down windows. Fitting them might give problems for the door opening pocket. It will increase the draught proofing requirements.

DOO
I can't imagine these trains being accepted without DOO already fitted. For a modern train, you need bodyside cameras and in-cab CCTV. The LU system for DOO (they call it One Person Operation (OPO)) is based on platform-mounted equipment so the D-Trains will need the on-board systems added. This is not as simple as it sounds and it needs to be integrated with the cab console design.

Couplers
It would be silly not to equip the outer ends of units with automatic couplers but I suspect the LU type would not be suitable. It will be desirable to have longer trains on some routes and flexibility should be maximised. However, auto-couplers are not cheap and there maybe some difficult engineering to do to the ends of units to enable them to be fitted.

Cost?
Always a difficult issue. In 2013, Angel Trains re-engineered a 4-car Class 317 EMU with a new traction system and quoted a cost of £7million; that's £1.75million per car but it's a prototype, so there's lots of development costs in there too. Let's say Vivarail can get orders for 70 x 3-car units. This is 210 cars, a reasonable production run so, allowing for development and financing costs, there is probably a good business case if the cost per vehicle can be kept below £1million for a 20-year life. As always, the big risks are the technical unknown unknowns.

Finally
There's lots of other detailed stuff but this article gives a flavour for what's involved. I am sure that the Vivarail team, led by the very experienced railway manager Adrian Shooter, are familiar with all the pitfalls of train refurbishment but for those readers who aren't, I wrote about it a couple of years ago:
http://railway-technical.blogspot.co.uk/2012/05/train-refurbishment.html
It is based on real life experience.