Automatic license plate readers from companies like Flock have made many drivers wary of roadway cameras, prompting interest in where they are and how to avoid them. Not every camera above the road serves the same purpose, however. Most cameras on roadways are not used to track individual drivers but to monitor traffic conditions.
Cameras meant to catch drivers running red lights are also controversial. They are banned in many states and are rare even where they are allowed. Far more common are cameras that monitor traffic in real time or automatically control traffic lights. Distinct from enforcement cameras, these traffic cameras are not designed to capture evidence for law enforcement. Instead, they are meant to be watched live to track the current state of traffic and spot accidents.
Local transportation departments can use this real-time data to keep traffic moving, in some cases by overriding automatic light timings, or to alert first responders when needed. The systems can also track traffic patterns over time, helping engineers decide when roadways or signals need changes to control congestion.
In many cases, cameras mounted on traffic lights feed automatic signaling systems rather than a live video feed. Engineers designate a section of the video frame for the camera to monitor for cars. When a car enters that space, it triggers the light to change on a pre-programmed timing sequence. These systems often combine video with radar, infrared cameras and electromagnetic detectors built into roads. What cameras are used for varies widely by location, based on local laws and the needs of each intersection. When you see a camera above a traffic light, it is most likely there to keep things moving.
Source: Engadget · Summarized by HeadlinesBriefing