by Jim Kerr

Whether you agree or disagree with the use of red light cameras, they are used in many parts of the U.S. and Canada. The concept is really very simple: take a picture of cars that do not stop for a red light and send the ticket to the registered owner of the vehicle. This type of traffic enforcement has proven it does reduce the number of side impact collisions and those are the types of collisions that cause the majority of occupant injuries. It also frees up valuable police time so more time can be spent protecting the public in other ways.

A red light camera system typically consists of three groups of components. The cameras are mounted on poles at the corners of the monitored intersection. Triggers are used to monitor traffic movement and position, and a computer is used to operate the system.

Currently, there are three types of red light cameras in use. Film type was first used, but as technology improves, digital still cameras are now used on many systems. Video camera monitoring is now being used in some areas. All three have advantages and disadvantages. Film camera technology produces a physical piece of evidence that can be presented in court, but these systems require the film to be developed and new film loaded into the cameras frequently.

Digital cameras eliminate developing and film costs but digital pictures can easily be manipulated with a computer. Therefore, a back up copy must be created that has not been opened by anyone so that if a problem arises, the courts can see an original file graphic.

Video cameras provide action that can be easier to use in case of a collision but also have the same file security problems as digital cameras. Video camera technology also requires sophisticated software when used as a red light camera.

Trigger mechanisms are what monitor the position of the car in the intersection. Laser, radar, and software vehicle position recognition are sometimes used, but the induction loop trigger is the most common choice for traffic engineers. Induction loops are two loops of wire placed under the surface of the road in the crosswalk area. As the body of the vehicle passes over these loops, the capacitance of the loop changes and this signal is sent to the red light computer. Many traffic lights also use induction loop triggers placed before the crosswalk to sense vehicles waiting for a light so the light sequence can be changed. You often see cuts in the pavement where these induction loop sensors have been installed.

Red light cameras only take pictures of vehicles that travel through a red light. The computer program monitors the lights and when one turns red, it then monitors the trigger. If a vehicle passes through the trigger after the light is red, two pictures are taken. One picture is of the vehicle entering the intersection. The second is of the vehicle in the middle of the intersection. Typically, the date, time, and length of time the light was red are digitally recorded on the picture too.

A specialist views each picture and those that clearly show a traffic infraction has occurred are used to identify the vehicle’s owner and a ticket is issued. Some tickets are treated similar to parking tickets. Others are charged to the owner of the vehicle, and some systems actually take a picture of the driver so that individual can be ticketed.

Not all cars that enter the crosswalk area will trigger the system. Vehicle speed is also calculated, so if a vehicle brakes quickly to a stop over the crosswalk, the system usually doesn’t trigger. Vehicles that proceed slowly through the intersection such as making a “right turn on red” are ignored, and those that are trapped in the intersection by other traffic when the light turns red are also not recorded.

Studies have shown that some busy intersections have as many as 20 vehicles an hour running a red light. This is a dangerous situation that is reduced by the use of red light cameras. Studies also show that while side impact collisions are reduced, rear end collision rates actually increased. Fortunately, these cause fewer injuries, so stop for those red lights, but watch for that vehicle behind you.

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