Paul Corfield wrote:
On Wed, 29 Sep 2004 07:19:39 +0100, Marc Brett
wrote:


On Tue, 28 Sep 2004 23:16:04 +0100, "John Rowland"
wrote:


"Paul Corfield" wrote in message
...

there are well known problems with the Countdown system
which means that the displays cannot always be relied upon.
I understand a new system is being procured by TfL (it was
certainly in the EU OJEC process) - whether it's still in the
budget and when it will be implemented I cannot say.

I hope it will be specified better than the current system, which uses a
relatively expensive display but doesn't tell people what they really want
to know. A much more useful system could be produced a lot more cheaply. Who
can I write to about this?

How DOES it work anyway? I've looked for technical info on the system but have
found nothing.


Well I think it works like this.

There are roadside beacons that detect the passage of buses.
The buses have a version of an axle counter (on the rear axle) to
determine where they are between beacons and how fast they are moving.
I think, but am not sure, that the relevant info is transmitted from the
bus to the beacon via radio. The beacons then transmit to the displays
and given the position of the next stop then determine a time of
arrival. There is also some form of central data capture.

The key issues that cause problems are the axle unit on the buses - if
they fail the bus has to be taken off the road. This is not an
attractive option if the operator can otherwise run the bus so it does
not incur performance penalties for a cancelled bus. I don't know about
the relative reliability of the rest of the system but it is entirely
plausible that other aspects of the system fail thus resulting in blank
screens.

ISTR that Bob Kiley made comment on the new system being GPS based which
would remove the need for beacons and axle units. It would also be
closer to common technology used for a lot of other purposes and
therefore cheaper and easier to maintain and upgrade. We shall see.
Metroline have trialled a GPS type system for service control which
seems to have worked well.

Apparently (according to a friend of mine who used to post here some
years ago), the beacons run on batteries and therefore inevitably run
down. The problem is they're left in a run down state for some time so
it causes the displays to show false information as they're not getting
the right location of the bus.

This is just information given to me during general conversation, but
this combined with what you were saying above would explain either the
lack of, or false information.

I'd also like to introduce myself to the group as I'm new to it. I ended
up here from various websites about disused tube stations etc. and other
tube related sites (I've somehow got a sudden interest in this). I've
only been living in London for a month and a half, moved down from
Edinburgh and I'm staying at W. Ealing.

--
Robert Gordon
http://m33p.be