How red-light cameras work

red-light cameras

Red light cameras. You have heard about them, but do you know how they work?

It is estimated that drivers running red lights cause nearly twenty-two percent of traffic accidents. Law enforcement officers now have a high tech tool in their arsenal to reduce this percentage. The use of these systems allows law enforcement to deter red light offenders without needing to have an officer present at an intersection.

There are three main components that make up the red light camera system. The first of these is the trigger. Although there are a number of different trigger technologies the basic goal is the same, to detect when a car has moved past a particular point in the road. The most popular type used today is the induction loop trigger.

In this system, a series of wires are placed beneath the pavement. When electrical current is sent through these wires they generate a magnetic field. When a car enters this magnetic field a change in magnetic intensity occurs. The computer controlling the sensor detects this change in intensity and is able to determine the location of the vehicle within the magnetic field.

There is another trigger mechanism that is gaining popularity recently. It is referred to as a video loop system. In this set-up, a camera records a constant video feed from the intersection. The computer then analyzes this footage and searches for any particular changes that signify a car moving through the intersection. This type of trigger sensor system is gaining popularity due to the fact that it can be installed in existing intersections without needing to dig up the pavement.

The next major component to the red light camera is the main computer, or brain, of the system. It is this piece of equipment that analyzes the information provided by the sensors and activates the cameras. This computer is specially programmed to recognize both the timing of a car passing through the trigger and compare it to the exact moment the traffic light changes. Once the computer has determined that a vehicle has ran a red light, a signal is sent to the camera to catch the offender.

Once the system has been activated and a signal sent to the camera, two photographs are taken. The first is taken as the car is approaching the intersection to show that the light is red. The second is taken as the car is going through the intersection to offer proof that the red light was ran. When the pictures are taken, not only do law enforcement officers receive license plate numbers, but several pieces of other information are also recorded. Several important things are superimposed on each picture taken including:

  • The date
  • The time
  • The location of the intersection
  • The rate of speed at which the car was traveling
  • The amount of time that the light was red before the car passed through the intersection

These photographs are then gathered and processed in much the same way as if a traditional law enforcement officer caught an individual. People getting caught by a red light camera can expect to receive a ticket in the mail, typically within one to two months.

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