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How
do digital fixed speed cameras
work?
How do the cameras detect
speed?
The fixed speed cameras detect the
speed of vehicles by using piezo
electronic detectors embedded into the
road surface. These piezo detectors
deflect slightly when a vehicle is
driven over the detectors, which then
triggers an electronic device that
accurately measures the speed of the
vehicle. If the speed of the vehicle
exceeds the legal limit then a digital
picture is taken of the offending
vehicle. Some fixed digital speed
cameras also operate in conjunction
with a measurement device known as a TIRTL which cross-checks vehicles'
speed using a pair of laser beams that
are aimed across the road a few
centimetres above the surface of the
carriageway.
What does the camera
record?
If a vehicle is detected speeding, a
digital image of the vehicle is
recorded onto a disk from which all
details regarding the speeding vehicle
can be extracted. The image usually
shows the colour, type, make and number
plate of the vehicle. Fixed digital
speed cameras have the capacity to
measure speed in both directions.
Digital images also include the
following particulars:
- Date of the offence
- Time of the offence
- Location details of the camera
which took the picture
- Direction of travel of the detected vehicle
- Speed of the detected
vehicle
- Speed limit applying to the road
where the camera is situated
- The lane that the detected vehicle was
travelling in
- Other security and integrity
parameters
How do the fixed speed cameras
work in multi-lane situations?
Fixed speed cameras can monitor one
to four lanes in the same direction. In
the Domain Tunnel for
example, cameras have been installed
and configured to
monitor all lanes simultaneously. This is
achieved by the installation of piezo
detectors for each lane and of a wide
angle lens camera, which monitors all
lanes, and a telephoto lens camera,
targeting each traffic lane. Therefore
it is clear which vehicle has been
detected. Vehicles cannot avoid camera
detection by straddling lanes.
Can the cameras identify a
speeding vehicle in a line of
traffic?
A speeding vehicle can be detected
and photographed even if it is within a
line of vehicles. The angle at which
the cameras are set enables pictures to
be taken even if another vehicle is in
close proximity.
The original recorded images are
stored electronically on a WORM (Write
Once Read Many) disk, which cannot be
overwritten or altered. A security
indicator is also produced when the
file is written to the disk and should
any attempt be made to tamper with the
image at any stage, this is obvious to
the relevant technician viewing the
image.
The original image forms the basis
of the evidence produced in court.
Eastlink fixed speed cameras
Digital fixed speed cameras are mounted under
the bridges at Wellington Road and Dandenong Bypass, as well as in the
Eastlink tunnels. These speed detectors are the Gatsometer Digital Radar Camera System—Parabolic (DRCS-P) which operate on radar, not piezo strips.
These devices can measure and photograph vehicles in each lane on the northbound and southbound carriageways.
There has been a great deal of publicity about
these cameras in the press. No court has ever found that the cameras
are defective. Courts often dismiss speeding charges without ever
make a finding that the speed measuring device is faulty. It is very
unlikely any court will ever make a finding that the Eastlink cameras
are defective. The best that a defendant could hope for is to cast
doubt on the measurement such that the court can not be satisfied
beyond reasonable doubt that the speed measurement is correct.
The threshold of the Eastlink cameras is 108kmh,
which means no photo is taken unless the speed measured is 108kmh or
more. If you collected all the infringement notices issued by the
police in respect of Eastlink and put them in piles corresponding to
the speed detected, you would have a pile for 108, another for 109 and
so on up to 200kmh or more. Without a doubt the biggest pile will be
the the 108kmh pile. I would expect the 112kmh pile to be less than
half the size of the 108kmh pile. Some people claim that the
large number of 108kmh infringements points to the cameras being
faulty. On the contrary, it points to the system working exactly as you
would expect.
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