On 24 Jan 2007 07:25:08 -0800, "Neil Williams"
wrote:

On Jan 23, 10:36 pm, "Richard J." wrote:

... the timetable in ruins! It always amazes me that there seems, on
the manually driven lines at any rate, to be little or no automated
assistance to the driver to keep to the timetable.

Is it really necessary to stick strictly to the timetable if you're
running a service as frequent as every 2 minutes? Surely you'd just
feed the trains "into" the system at roughly the right frequency from
each end, and keep them moving as quickly as possible. I'd agree,
though, that if the service is really that frequent holding connections
is probably counter-productive.

Yes it is necessary to run to timetable. As Steve F has explained there
are train crew rostering issues as well as getting trains through
specific junctions in their correct "slot". If we look at the JNP lines
the Northern is most susceptible to very small delays building up and
then becoming minor delays and then potentially severe delays (to use
the standard terminology). This can happen even where there are no train
or signal failures - just little incidents like dwell times taking
longer than planned, a very short passenger incident or a slightly
delayed crew switchover. The line has several complex areas which need
to run like clockwork to ensure a really good service - Finchley
Central, Golders Green, Camden Town, Kennington and Morden.

The Picc Line is generally fine unless things go wrong at Arnos Grove or
Acton Town and then you have the equivalent of a heart attack to the
service. Acton is the worst place as it's very complex, you have the
impact of the District Line service and too depots close by - Ealing
Common and Northfields. You also have crew changes at Acton as well. It
can take the Picc a long time to recover from incidents as the service
is so intensive and busy and there is not very much flexibility on the
core section from Acton to Arnos Grove to allow trains to be turned,
reversed or parked out of the way.

The Jubilee Line has much more by way of sidings, crossovers and bay
platforms and this allows easier access if technicians have to get on
the track to fix things and recovery is generally faster than on the
other JNP lines.

Your "feeding in" comment is perfectly applicable to completely
automatic systems like VAL, Meteor and the Singapore North East line as
there are no staff that have to be rostered to each train. The computer
controlling the line will balance out the service to pre-programmed
parameters or else the controller can intervene and run trains where he
wants them in response to demand. This does require a good initial
system design with turning points and sidings to allow trains to be
shuttled to the busiest points and then placed into service.

--
Paul C


Admits to working for London Underground!