There is another method used by NR» in Scotland to run 25kV OLE▸ through low over bridges and that is to use an earthed section of contact wire; the train VCB▸ is tripped and reset by an APC the same way as a neutral section, the train just coasts through the earthed section.
If for some reason a train was gapped in such a section - after, say, emergency braking, etc. - is there a way to move it under power using shed leads for instance, or must it wait for a shove from behind?
The standard way of changing over between overhead voltages is to coast across an insulated (and perhaps earthed) section. This may seem surprising, and of course it's rare here, but pretty common elsewhere - e.g. France with 25kV/1500VDC and Germany or France with tram-trains.
While (as usual) almost every way of doing this has been tried somewhere sometime, the consensus now is that you provide one pantograph per unit, tell it what to expect and switch it over, but provide fast-acting switchgear so it will change automatically and not be destroyed by the wrong voltage (which could be more difficult than snow!).
EMUs▸ up to four cars usually have 1 pan (e.g. 387s), and tram-trains do too - they are even shorter. Five-cars seem to be 1-pan too if suburban (e.g. 707s - yes they are
DC▸ , but they have a bit of flat roof for a pan), but
IEPs▸ have two. Above eight cars two is usual, and sixes and sevens are too rare to really say.
While designs vary, a lot now put the electronics and motors on one self-contained vehicle, and about half of a train made up of those motor cars. The pantograph goes on a trailer of its own, due to the weight of the transformer (mainly) and switchgear. Power is then fed to the motor cars at some suitable "low" voltage, such as 750V up to 3kV - most likely as DC.
So longer trains, or multiple units, can rescue themselves from stranding with another pantograph. Short ones can't, and have to wait for the next train to come along, and do whatever the rules demand about giving another train a shove. OK for trams, otherwise I suspect it's going to be a slow procedure. Obviously the trick is to make sure it's very rare.
It does occur to me that one of the few things that's likely to strand a train is stopping to push another one at just that point ... so I guess you'd be best to couple them first.
I read somewhere that for 25kV OLE it is usual to put manual isolating switches between the tracks of a line, so each track can be disconnected individually, and that means there is an isolating gap there too. While you'd never intend to stop part-way across such a crossover, you could well be going very slowly - so is that a potential issue?
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