On Jan 6, 10:57*am, Patrick Osborne wrote:
Whilst I don't want to encourage Boltar's constant negativity about
everything, it is amazing how on the tube the minute one small thing
goes wrong, everything screws up totally.

Let's take a look at the above scenario. *A train is stalled at
Cockfosters, right at the extreme end of the line. *There's a turning
point at Arnos Grove. *Why can't they just switch the signalling to
immediately turn all trains around at Arnos Grove, so the only
disruption is between Arnos Grove and Cockfosters? *In this situation,
passengers south of Arnos Grove shouldn't have noticed a thing.

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.

Compare this to the excellent action taken by First Great Western this
morning (I'm not making this up!) on my trip to Bristol. *There was a
major signal failure between Swindon and Bristol. *They immediately
rerouted my train to run via Bristol Parkway and we arrived at Bristol
on time. *They managed it despite having to deal with intersecting
lines and having to find paths between other trains; why can't the
tube do it on a single line with no junctions when the disruption is
at an extreme end?

The excellent action will have been taken by Network Rail, although
FGW may have been involved in the planning process for What To Do If
There's A Failure.

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).

--
John Band
john at johnband dot org
www.johnband.org