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Red-light Safety Cameras
Road crashes regularly occur at junctions controlled by the traffic signals. Red-light cameras are widely used to identify and prosecute drivers who jump red traffic lights. International studies show that the use of red-light cameras cut down the number of crashes that lead to injuries by as much as 30%.
Red light cameras are placed at traffic light junctions in a position that allows photographs of violating vehicles and the traffic signals available to the offending driver to be captured in the same image. This shows that the red light was visible to the driver.
In addition to the photographic record of the red light illumination, a sensor is placed in the traffic light system that controls the Red Light Camera. Only when illuminating current to the Red Traffic Light is flowing will the Red Light Camera system be commended to capture offences.
The Red Light Camera senses the vehicle position and presence as the vehicle crosses and completes the crossing of the Stop Line at the junction. This is achieved through the presence of inductive loops buried in the road surface. Some camera manufacturers have utilised radar or laser to sense vehicle position at Red Light junctions. However, inductive loops are the most common and more reliable.
An image is taken as the vehicle is crossing the stop line and after the crossing is complete giving a complete record of the offence. The time the lights changed in relation to the offence is also recorded. It is typical to introduce a delay of 0.8s to 1.0s between the light indicating a red stop signal to the Red Light Camera being commended to capture offences to ensure that the drivers have been given enough time to stop before an offence is captured.
Mobile Safety Cameras
The mobile camera technology can be used in a variety of bespoke enforcement vehicles called safety camera vans. They allow practitioners to be reactive with regard to speed complaints and casualty hotspots. On site these special vans create a speed compliance ‘halo’ making most of the drivers to comply with the speed limit. When operated in an effective enforcement strategy, this technology has a dramatic effect on driver behaviour leading to a significant reduction in road casualties over a wider area. The ubiquitous solution in modern mobile enforcement systems is the laser speedmeter coupled with a video or still camera system. Radar solutions, although available, are seldom used or are restricted to specific applications.
The laser speedmeter is operated and aimed by a civilian operator or police officer who aims the device using its built-in sighting system. The laser optics is aligned to the camera optics so the vehicle aimed at by the laser operator is the vehicle that is indicated by visual markers in the photographic or video record. Offence data such as date, time, location, operator ID and vehicle speed and distance at the time of the offence is shown in a data block superimposed on the image.
The laser system typically senses the vehicle distance and performs a statistical calculation that depends only upon the speed of light for accuracy to determine the target vehicle’s speed. Because the speed of light is constant, varies little in any weather condition and is much faster than the target vehicle speed the speed of light reference means that laser speedmeters, used correctly, give the true minimum speed of the target vehicle whenever a speed reading is indicated to the operator. Laser speedmeters require verification of alignment on an annual basis with this being easily verified by the operator whenever it is used.
Average Speed Camera Systems
In recent years, there has been a breakthrough in digital enforcement camera technology with the introduction of the average speed camera. These systems have had a dramatic effect on driver behaviour by monitoring vehicle speeds over a route and encouraging the motorists to drive within the speed limit along an entire stretch of road. The first generation of average speed cameras were point-to-point systems using fibre optic lengths for on-site evidence collection.
The second generation technology, Distributed Average Speed Cameras, is more advanced and even more effective in altering driver behaviour. These cameras offer a multi-point to multi-point solution with almost unlimited cameras allowed within the system. This has a dramatic impact on vehicle speeds over an entire road network. This technology is not restricted by fibre optic lengths and is able to transfer offences via secure Virtual Private Networks (VPNs).
The average speedmeter uses an accurate time reference at each camera point, typically provided by a GPS receiver or a radio distributed atomic clock standard. The subject vehicle passes through a point on the road monitored by a video camera system where the vehicle presence is sensed by a disturbance in the video signal or by loop, laser or radar sensors. The camera system then performs a read of the vehicle registration plate capturing an overview image and an image of the registration plate. InfraRed cameras are used to capture the registration plate images as these give a good degree of contrast with which to make an Automatic Number Plate Read of the registration details. The images at the entry camera are time-stamped and stored with the data of that time stamp and registration. A similar record is made as vehicles pass through the exit camera. Records from entry and exit cameras are compared to match the vehicle details. When a match is found, the time between the records is used with the fixed minimum distance between the cameras to calculate a minimum average speed between the two points. If the speed is above a pre-set threshold, the images and offence data are combined into a record so prosecution of that speed can be made.
In common with unattended devices, two speed calculations must be made and compared and be found to be in agreement before a speeding violation is accepted. The methodology utilised to do this varies between camera systems and is the intellectual property of each of the average speed camera vendors. A matrix of cameras can now be deployed as vendors have developed a way of storing a database of the possible routes between camera locations that can be declared an entry, exit or both an entry and an exit location in the overall average speed installation.
Safety camera effectiveness has been reviewed, researched and analysed world-wide many times over the last three decades. All reach the same conclusion – safety cameras are highly effective and save lives. In 2012, road safety practitioners across Britain are continuing in their battle to reduce deaths and injuries on the roads. By working together and using the various applications of highly effective enforcement technology available to them, they are determined to drive down further the shocking number of unnecessary casualties that occur each year.
Trevor Hall
(A former Police Officer with 30 years’ experience, 26 of which were dedicated to roads policing, Trevor has played a pivotal role in the development and deployment of safety cameras in the UK since 1989. He has been an advisor to the Association of Chief Police Officers’ (ACPO) Traffic Enforcement Technology committee and secretary to its Roads Policing Enforcement Technology Committee. In 1999 he established and managed one of the UK’s first safety camera partnerships. In 2007 Trevor set up and is now the Managing Director of Road Safety Support (RSS). In 2011, he was appointed as a special advisor to the US National Highway Safety Committee).
