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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.
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