Strategies & Installation Criteria for Gatso Cameras
Criteria
for Site Selection / Possible Criteria for Camera Enforcement
Sites
Speed Cameras
1. |
Site = 400
metres length |
2. |
Number of
injury accidents in 3 years = 8 or more |
3. |
(a) Number
of Fatal/Serious accidents = 5 or more |
|
(b) Number
of loss of control accidents = 3 or more |
|
(c) Number
of excessive speed w.r.t. conditions or limit
accidents = 3 or more. |
4. |
85%of speed
greater than limits plus 10 m.p.h. |
5. |
Site conditions
are suitable. |
6. |
No other engineering
measures appropriate. |
|
|
Red signal Cameras
1. |
Number
of failure to comply with signal accidents
= 3 or more. |
2. |
Number of
failure to comply with signal accidents
in at least 1 direction = 2 or more. |
3. |
Site condition
suitable |
4. |
No other engineering
measures more appropriate |
5. |
85 %of speed
(free flow through junction)
greater than limits plus 10 m.p.h. |
Note: for
Pelican/Puffin/Toucan crossings, sites with 6 or more pedestrian
casualties may be considered providing there is some evidence
(from accidents or Police)
that red running is taking place.
Traffic Camera Office Objectives
To maintain traffic camera availability at a sufficient
level to dramatically increase the likelihood of speed, red light
and bus lane offence detection, thus creating a real deterrent
to dangerous road behaviour, and establishing a base for long
term modification in driver behaviour and attitudes.
With the likelihood of being caught increased to
a level of real deterrence, to further reduce excessive travel
speeds and red light non observance across the community and thus
reduce the number and severity of road traffic collisions.
The Speed Camera
The speed cameras used by the police are supplied
by Gatsometer BV in Holland. The Gatsometer MRC System operated
by trained members of the Police Traffic Operations Group. Before
operating the cameras, police members complete a training course
in which they are examined in both theory and practical aspects
of the speed camera.
Cameras are operated in areas which have been identified
as having speed related problems, areas identified as high risk
roads based on validated speed complaints, or in traffic accident
blackspots. They can be used anywhere however at any time of the
day or night.
Radar Speed Camera Setup
The radar unit may be set up on a tripod, Fixed
Installation Post or mounted in an unmarked police vehicle positioned
at the side of the road, not very common in the UK. The radar
beam is transmitted at an angle across the road.
The Camera Control Unit is set up by programming
certain information such as the time, date, film magazine number,
speed zone, film type, the direction of the traffic to be covered,
and the threshold speed, and connecting it to the camera. The
35mm camera operates as an ordinary camera, but it is controlled
by the Camera Control Unit and Radar Control Unit, and can photograph
2 speeding vehicles per second.
How the Gatso Type 24 MRC Operates
The radar unit transmits a radar beam, at a frequency
of 24.125 GHz, which is 5 degrees wide, 20 degrees high and slanted
at an angle of 20 degrees across the road. As a vehicle travels
through the beam, the reflected radar frequency is changed (Doppler
effect) and the beam is reflected back to the radar antenna. The
antenna receives any signals which arrive from the same 5 degrees
by 20 degrees and converts this into the speed of the vehicle.
If the vehicles speed is greater than the threshold speed set
by the operator, a photograph is automatically taken of the vehicle.
A camera is capable of taking two photographs every second, and
detects the speed of vehicles travelling in either direction.
Determining the Speed and Travel Direction of
the Vehicle
Determining vehicle travel direction using the Doppler
Principle
The radar unit emits a continuous wave at a frequency
of 24.125 GHz at a 20 degree angle across the roadway. When a
vehicle enters the radar beam, the reflected frequency changes
due to relative motion between the radar and the vehicle.
If the relative motion brings the target closer
to the radar, the reflected frequency will be increased. If the
relative motion takes the target further away from the radar,
the reflected frequency will be decreased.
Conceptually, if the vehicle is travelling towards
the radar unit, the returning beam will be compressed. If the
vehicle is travelling away, the returning beam will be expanded.
How much the frequency is increased or decreased
is directly proportional to the speed of that relative motion.
What is most important about the Doppler effect is that the frequency
change happens only when there is relative motion between the
objects. If both objects are standing still (e.g.. Parked vehicles)
there is no relative motion, and the reflected signal has the
same frequency as the transmitted signal (i.e.. No change in frequency
= no speed reading). Police traffic radar merely measures this
change in frequency and converts it to a speed reading.
The Gatso Type 24 has the capability to determine
in which direction a vehicle is travelling. Basically, this works
by the radar unit determining increase or decrease in reflected
frequency determines direction of travel, and the size of the
increase or decrease determines the speed of the target.
Calculating the Speed of a Vehicle
Trigonometry can be used to calculate the speed
of a vehicle travelling along a road, detected by a radar beam
transmitted across a road.
Because the radar beam of the Gatso Type 24 Unit
is slanted across the road at 20 degrees, the Doppler frequency
shift recorded will indicate a speed that is slower than the targets
true speed. In the radar unit there is an automatic calculation
for the slant angle so that the true speed in the direction of
travel is determined. |