Could multiple unit trains be split up outside of a station?

[signed]

This is purely for my curiosity.

I'm wondering whether you could detach a multiple unit from a set at speed (reduced, like 10-20kph) to allow the unit to go onto another platform?

The example I had in mind was :

Rennes station in France is the centerpoint of a trident of destinations served from Paris

All TGVs stop there, and 99% of the seen rolling stock run 2 units for the Paris leg and then split at the platform for their final destinations.

I was wondering whether, technically, you could (stock capability outside of the question) run a 3 units set to cater for the core, split the last one out (because there is no way you could install a 600m platform) while at reduced speed before the station so that it can then go into another platform or would that be way too dangerous in anyway?

 

[150219]

I'm not qualified on French traction, but in the UK it wouldn't be possible with most traction; especially newer traction.

Unintended divisions in traffic tend to result in one or more parts not being able to 'talk/find' eachother electrically and then come to a stand.

 

[hexagon789]

This is purely for my curiosity.

I'm wondering whether you could detach a multiple unit from a set at speed (reduced, like 10-20kph) to allow the unit to go onto another platform?

The example I had in mind was :

Rennes station in France is the centerpoint of a trident of destinations served from Paris

All TGVs stop there, and 99% of the seen rolling stock run 2 units for the Paris leg and then split at the platform for their final destinations.

I was wondering whether, technically, you could (stock capability outside of the question) run a 3 units set to cater for the core, split the last one out (because there is no way you could install a 600m platform) while at reduced speed before the station so that it can then go into another platform or would that be way too dangerous in anyway?

Brake continuity would usually prevent it for one thing...

 

[MotCO]

There used to be a system of 'slip trains' where carriages used to be cut adrift in motion, and brought to a stand in a platform by a guard in the carriage. It then required a shunter to move it out of the way. It died out probably in the 1950s.

See this Wikipaedia article: https://en.wikipedia.org/wiki/Slip_coach

Edit - link added

 

[hexagon789]

There used to be a system of 'slip trains' where carriages used to be cut adrift in motion, and brought to a stand in a platform by a guard in the carriage. It then required a shunter to move it out of the way. It died out probably in the 1950s.

See this Wikipaedia article: https://en.wikipedia.org/wiki/Slip_coach

Edit - link added

September 1960 was the final slip coach operation in the UK.

 

[Belperpete]

I can see some safety issues with changing the points between the two halves of the split train! What happens if the points fail halfway? For it to be done safely, it would have to be done a long way before the station, such that the second half of the train fell back significantly far behind the first part, giving adequate time for the points to motor to the other platform, plus braking distance in case they didn't and you need to stop the train before the points.

It would also raise some interesting issues as to how the track circuits or axle counters would see it as two separate trains, rather than one train that was getting progressively longer!

Signalling systems are generally designed so that you always have at least braking distance between two trains, so that should the first train stop instantaneously, you can stop the second train before it ploughs into the back of the first. If you split two trains on the move, then inherently the moment they split you end up in a dangerous situation where the second half has no chance of stopping should the first half stop suddenly. Bad enough when the second half is an unpowered slip coach already braking, but if the second half is a powered train that could potentially be accelerating!

Interestingly, ETCS included some theoretical provisions not just for trains dividing on the move, but also joining on the fly! I don't think the functionality was ever developed.

 

[D7666]

Actually either late SR or early BR SR did experiment with exactly this. It was tried with 1930s express stock; I can't remember if it was Cor type stock or Pan/Pul, empty test trains of course. Nor can I remember where I read about this, vaguely recall the idea was wanted to do it with Cor stock for one or other of the Portsmouth lines, but the tests were done with Pul/Pan without end gangways on the 'test one step at a time' principle but are in the way for basic functional tests. Before anyone asks, I have absolutely no idea how they were to have uncoupled either the coupling itself, a screw t a buckeye, or split the jumpers, which 1930s express stock had 630 V power jumpers as well as control cables. I don't think they advanced very far with this..............................


On a modern day 21C technology train neither brake continuity or on board control systems would block it - because to split a train in this way would be a known function of the train and accordingly allowed for and be programmed into the TMS and anything else in order to recognise it as a legitimate split. This is not 'unintended' split - but exactly the opposite. It is not really rocket science to do any of it if it were wanted. Likewise a contemporary signalling system only needs to have some additional logic in it to recognise the situation. How you deal with stopping the once seperated portions from recombining in an uncontrolled manner might be tricky if trying to misalign all the swiss cheese holes.