In message , Ian Jelf
writes

Presumably to protect against a situation where the JLE doors "think" it's
a long train, but it isn't.

Can't they just add the extra car but leave it permanently locked and
out of use until all train have been so equipped? Or am I missing
something here? (I realise I must be but I'm sure someone will spell
it out!)

No. The internal doors in the train would still allow access to the
locked out car and can't be secured for safety reasons. Can you imagine
the fuss when someone managed to get into the 'unused' car, as they
would, and then couldn't get out because the doors didn't open.

This is a similar reason to why a train is taken out of service if one
car is unavailable for any reason - the out of service car can't be
secured.
--
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