> Not necessarily. There is an Australian design which has superior
> filtration without much sacrifice to the sensitivity. This one is
> capable of detecting up to 1km away, and with low-power radar (used
> primarily for photo-radar systems due to their close proximity nature of
> operation), up to 300m as you approach the authority's vehicle from
> behind, depending on how many other cars out there you can get a
> reflection from.

>In a worst case scenario, you would get about 100m
> warning which is still enough time to slow from say 90km/h to 50km/h

Anyone who NEEDS to slow from 90 kph to 50 kph rightly deserves to meet an
"authority's vehicle" armed with something very substantially more harmful
than a radar unit. It continually amazes me that people are so in contempt
of the "social contract" implicit in a 50 kph speed limit, and therefore the
lives of their fellow citizens,  that they will unblushingly talk about
travelling at (probably in excess of) 90 kph in such an area, obviously with
no concern at all for the dangers they would be imposing on others they are
contracting with. At 90 kph your vehicle has over 3 times the energy it does
at 50 kph, proportionally greater stopping distance and a near certainty of
killing anyone it hits (whether you have started braking or not). [[
Probability of death for a pedestrian struck by a car is very very roughly

    Death probability = (V^2/50)%
                                                                V in kph.

For %ages above 100% you just get overkill :-(

The speed you will be doing when the car doing 50 kph would have stopped if
you both hit the brake pedal together is about sqrt(V^2-2500) or more
generally if the car doing V2 can JUST stop in time then the car doing V1
will still be travelling at sqrt(V1^2-V2^2) when it hits the
social-contractee.
In this case a car doing 90 kph at the start of braking will still be doing
around 75 kph when it hits a pedestrian that a driver doing 50 kph would
have just managed to stop for.
[[This is based on energy considerations and assumes that brakes are devices
that remove energy at a constant rate and that your high speed driver's
brakes do not fade and also does not allow for any reaction times which
makes the results even worse.]]

Anyone who countenances driving at 90 kph (+) in an area where people
(including, often enough, children) reasonably expect them to be driving at
somewhere around 50 kph and who uses instrumentation to allow them to
continue to do so deserves to have their social-contract-document (you may
call it a "licence") revoked for a long long time. Anyone who so values
making a personal profit and supporting the other guys freedom to attempt to
commit murder by making and selling him such instruments deserves a mix of
pity and contempt. Both deserve to spend considerable periods helping clean
up the carnage caused by idiots who think their "rights" to get where they
are going a truly insignificant time sooner, so over-ride the rights of
others in their community.

Lay on, "gentlemen".



        Russell McMahon

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