Re: Connected cars 'promise safer roads' - BBC News article

On Mon, 9 Jul 2007 7:27:46 +0100, Dogpoop wrote
(in message <Czkki.24916$nE2.15568@xxxxxxxxxxxxxxxxxxxx>):

GPS is not used because it is not good enough for safety
applications in cars.

Ahem, from the article the OP referenced .. "The Car-2-Car Consortium's
system, which includes GM's Vehicle-to-Vehicle project, combines three
technologies - a Global Positioning Satellite (GPS) antenna, a wireless data
system and a computer that interprets the information it receives. "

It is true that GPS alone would not be reliable or accurate enough. High end
navigation systems take inputs from wheel rotation and steering sensors which
they use as the primary positioning system (ie X pulses from the wheel
counter = Y metres travelled along the road) but also use GPS (particularly
for the initial position estimate). Such systems would be essential for any
system like this, as would a VERY accurate road model*. Since retrofitting
such a system to existing vehicles is much more than just sticking a GPS on
top of the dash and wiring it up, it's going to be a 'significant cost' and
will prevent it's widespread adoption**.

To a point you can design a system where the two vehicles will exchange
messages and work out their distance and relative bearing by determining
signal timing and bearing - but these are not accurate enough (IMO) for such
collision avoidance. It's notable that in aviation, collision avoidance
systems do NOT use horizontal movements because the data is not accurate
enough - they use vertical movements (one aircraft climbs, the other decends)
because altitude as measured by calibrated barometers is more accurate.
Obviously, use of the Z axis is not generally available to road users :-(



* The current road models would be woefully inadequate - I've only had TomTom
for a short while, not used it outside my local area, and already found at
least 6 significant database errors (none of which could be considered due to
'recent' changes). That brings up another factor - unless use is mandated AND
regular updates are mandated, then the update process has to be free if a
significant number of users aren't going to be using old maps.

** If it isn't fitted to everything, then as has already been pointed out,
it's in some ways worse than no system at all. And what about foreign
visitors ?

.

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