On Fri, 11 Apr 2008, MIG wrote:

On Apr 11, 5:48*pm, Mizter T wrote:
On 11 Apr, 17:20, MarkVarley - MVP
wrote:

I have no idea what they're called, the LED signs in some bus stops
that tell you how long the busses are supposed to be, my question is,
how do they work? how do they update?

The system is called Countdown, and as part of the iBus project it is
set to become much more reliable and accurate.

I wonder if it means more reliable in terms of whether it breaks down
or reliable in terms of the content, which must be down to where the
locations of the bus-detectors rather than the system that passes
information to the punters.

The new system won't use bus detectors, it'll have a GPS unit on each bus
which radios its position back to base (by GPRS?). That gives it higher
resolution, and makes it impossible for a bus to fall off the system, as
they can now.

Provided that the bus can get good GPS and GPRS signals. GPS is
notoriously inaccurate in built-up areas, as buildings block lines of
sight to the satellites, and introduce reflections which confuse the
receiver (like ghosting on the telly). I wonder what they're doing to deal
with this? Maybe just having the receiver on the top of the bus will be
enough. Newer GPS chipsets are also getting better at operating in urban
environments - for instance, i hear that the SirfStar III is much better
than older kit:

http://wiki.openstreetmap.org/index.php/SiRF_III

I suspect that the information is very accurate, but that it doesn't
necessarily relate to the location of the bus stop.

That is, some stops will display information about buses that have
already gone past (and therefore seem to disappear) and others
disappear the information off long before the bus has turned up.

Neither of those should happen. The main failure mode will probably be the
display (or its communication link) breaking down altogether.

Another plus of iBus is that it will let the bus operators and TfL track
all buses all the time, which will give them a much, much better ability
to (a) regulate the service and (b) monitor performance. Operators will
find it much harder to get away with providing a substandard service,
particularly at night, when i understand tfL's inspectors don't operate.

tom

--
Ed editor textorum probatissimus est -- Cicero, De officiis IV.7