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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
shows that the cameras are
faulty. On the contrary, it indicates
that the system is working exactly as
you would expect.
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