On Wed, 29 Sep 2004 09:52:20 +0100, Paul Corfield
wrote:
On Wed, 29 Sep 2004 07:19:39 +0100, Marc Brett
wrote:
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.
[snip]

Not a million miles away... in fact the beacons aren't connected to
anything, they just tell the bus to report its position over the
radio. This information goes to a central system that does the
calculations and the results are sent to the signs by ISDN. This
isn't how you'd do it now, but was pretty advanced for its time.

Details at http://www.symicron.com/corepages/Press1.htm .

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.

If the radio is not logged on, or is out of coverage, there won't be
any location information. I expect that this is another major reason
for buses to not appear on (or disappear from) the displays.

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.

Car navigation systems that I've seen have odometer and gyroscope
input as well as GPS, to maintain accuracy when not enough satellites
are in view - the "urban canyon" effect - I'd expect any bus system to
need these as well. Beacons are not required, though.

Richard.