 Automated speed enforcement systems have been used by authorities for many years and have now become a prevalent part of society. The two major technologies used today are RADAR (Radio Detection and Ranging) and LIDAR (Light Detection and Ranging)
Expanding infrastructure and an increasing number of vehicles on the roads mean that measuring devices are a valuable aid for police forces. Since the concept was first developed major technological advances have been made. The two major technologies used today are RADAR (Radio Detection and Ranging) and LIDAR (Light Detection and Ranging).
Multi-lane enforcement
Conventional doppler RADAR systems measure ‘on-the-spot’ speed. A single radio signal is directed at a point on the road and reflected back: a change in frequency indicates movement. In many cases RADAR systems cannot attribute the movement to a moving vehicle or another object in the field of view. Reflections from stationary objects such as parked vehicles, roadside barriers and street signs can lead to a ‘falsification’ of the RADAR measurement. Additionally if two or more vehicles are in the field of view it is not possible to ascertain to which vehicle the measurement belongs unless costly secondary evidence (e.g. video surveillance, multiple violation images etc.) is provided. Mobile RADAR speed enforcement requires a patrol officer to constantly attend to the system to check whether the correct vehicle has been captured.
Using LIDAR technology to track and detect moving objects is the most modern method of speed enforcement. The PoliScanspeed system from VITRONIC sends a ‘fan’ of laser beams across an entire stretch of road and, as they hit a target, the light is reflected back. The time taken for the light to reach the object and travel back to the LIDAR unit can determine the distance and angle to the target. These ‘time-of-flight’ measurements are carried out continually which enables the system to build up a 3D simulation of the current traffic situation. As a vehicle moves, its distance to the sensor changes and its precise speed can be calculated. Even vehicles traveling parallel, tailgating or changing lanes are captured.
Reflections from stationary objects are automatically discarded as their distance and angle to the laser unit never changes, so a LIDAR system can be used in challenging traffic situations such as dense urban areas, tunnels, bends and road works. The high LIDAR accuracy, and the ability to single-out vehicles traveling within a pack, means that the system has been certified for unattended use. Traffic statistics can also be collected.
Differential speed limits
In many countries the law sets separate speed limits for trucks and cars. A speed enforcement system has to be able to distinguish between the two. To prevent large amounts of manual processing in the back office the vehicle first needs to be classified (i.e. the size of the vehicle determined) and then the speed measurement taken. Due to the ‘on-the-spot’ measurement RADAR systems can only enforce differential speed limits from the rear because the vehicle has to drive past the unit to be classified. In several municipalities driver identification is mandatory therefore the vehicle has to be photographed from the front. For this to happen the vehicle has to be classified before it passes the unit. The LIDAR system detects and tracks vehicles from distances of up to 75m and by creating a 3D measurement of the scene the vehicle size can be determined and the speed calculated simultaneously.
An advantage brought by PoliScanspeed is the lack of in-road equipment such as light barriers or induction loops. These sensors have to be installed into the road surface and, for lane-specific speed enforcement, a separate sensor inserted into each lane. The section of road has to be partially blocked for installation to take place and the traffic flow disrupted. The sensors also have to be installed under a level road surface otherwise their ability to detect passing vehicles may be unreliable.
As a result the entire road may have to be leveled-off and resurfaced. After the equipment has been installed it has to be regularly maintained for reliability. They are also considered unsuitable for countries with extremely varied climates. Constant temperature changes cause the road surface to expand and contract, causing movement underneath the surface which can make the in-road equipment shift and become unreliable. Such sensors have to be replaced regularly
The installation and maintenance of such equipment requires intensive time and cost investments which can be avoided with LIDAR systems.
Time of flight victorious
Owing to these substantial advantages manufacturers of doppler RADARs are now introducing systems based on the LIDAR time-of-flight measurements. VITRONIC has focused on such technology from its inception and has unparalleled experience in the field. As with the previous adaptation from analog to digital camera technology, the change from RADAR to LIDAR is inevitable.
For more information
For more information on VITRONIC’s next-generation speed enforcement solution PoliScanspeed, contact Malcolm Smith (
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), Adrian Wilkinson (
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) or see the VITRONIC website: www.vitronic.com. |
