In message
,
John B writes

Not missed, perhaps misinterpreted - I'd assumed that if Connect was
down then the OPO alarm would most likely also be down. If not, then
it's less of an issue.

Usually the case although they do use different parts of the kit and
thus it's possible to have one without the other - just depends on the
defect.

But I still don't quite understand why these precautions (ie no empty,
single-manned trains if the Connect radio and the OPO alarm aren't
working) are necessary, given that the safety issues with OPO compared
to double-manning are passenger-related rather than train-related.

The OPO alarm is there in case the driver collapses; it sends an alarm
to the Control room if the TBC (deadman) is not depressed within 1.5
minutes of being released.

Assuming a radio fault situation, how long would it take to get someone
down there to see if the driver's OK, bearing in mind you have no
contact to know if the driver's OK and might have just attended to a
defect and drive his/her train out of the tunnel at any time? At least
with an OPO alarm, they have an idea what might be happening and can
scramble the train behind to move forward and investigate quickly.
--
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