On 6 Jan, 12:31, John B wrote:
1) the depot is at Cockfosters. Not sure what time this incident took
place, but if the train died in a place where it blocked or
significantly impaired depot access, then that's going to have an
obvious knock-on effect on the line

2) normal line operation is based on turning some trains at Arnos
(6ish) and some at Cockfosters (18ish). There are three reversing
platforms at Cockfosters; there is one at Arnos. If suddenly 24 trains
have to be reversed in the one platform, this is going to create some
fairly obvious bottlenecks.

Anyway... while junctions make life more complicated, they also
provide diversions and alternative routes. Whereas when you've got a
railway that's fundamentally two tracks with trains separated by only
a couple of minutes, any disruption is going to have instant and rapid
knock-ons - and the only way you can deal with that is to add
extremely expensive redundancy (in this case, adding signalling and
track work at Arnos so that it can be used as a full-capacity terminus
mirroring Cockfosters, or turning one of the stations north of Arnos
into an alternative reversing point - in either case, these will only
be useful for the few hours a month when access to Cockfosters has
completely failed).

I take your point about the depot and the smaller turning capacity of
Arnos Grove; I'd not considered these.

However, I really do think Boltar has a point here. It was mid-
afternoon, so most trains should have been out of the depot and
theoretically distributed evenly across the length of the line, thus
only a few would have been unavailable due to being trapped north of
Arnos Grove.

There is an additional turning point at Oakwood, apparently, so could
this not have been utilised? And although without having been there
at the time it's impossible to know for certain, but Boltar's claim of
trains sitting at Arnos Grove for AGES before turning around certainly
has the ring of truth to it, in my experience of the tube when things
go wrong. Why would they make trains wait for ages rather than
turning them around urgently? Does the signalling not permit it? If
not, why not? And how does it cope with the scheduled turnarounds at
Arnos Grove?

I'm really not a tube-basher and I think that on balance the tube does
pretty well at providing a service. However, I do think that they are
very unprepared for when things go wrong and seem incapable of dealing
with incidents quickly to stop them becoming major headaches.
Although of course it's easy to say that they could run things better
when we don't know all the constraints, but it does seem to me that
they could have done better in this instance, based of course on what
I've read here!

Patrick