White cameras above traffic lights serve a purpose few people know
Most cameras mounted above traffic lights in the US are meant to monitor traffic and control signals, not to track drivers. Unlike license plate readers, they are not designed to collect evidence.
Cameras mounted above intersections and traffic lights are often confused with automatic license plate readers (ALPRs), such as those made by the company Flock. Reported abuses of the latter have made American drivers wary, and some want to learn where those cameras are so they can avoid them. Yet not every camera above a road does the same job.
Cameras that watch traffic, not people
Most roadway cameras are not used to track individual drivers. They monitor traffic conditions. Cameras that catch red-light runners are also controversial: they are banned in many states and rare even where permitted. Far more common are cameras that watch traffic in real time or control signals automatically.
These cameras differ from those that catch speeding or red-light violations, and they are not built to gather evidence for law enforcement. Their live images can be used by local transportation departments to keep traffic moving, in some cases by overriding automatic light timings, or to alert first responders. Data collected over time helps engineers decide when roads or signals need changes to ease congestion.
How a camera runs a traffic light
In many cases, the cameras are linked to automatic signaling systems rather than a live video feed. Engineers can mark a section of the video frame where the camera should look for cars. When a vehicle enters it, the light changes according to a timing sequence pre-programmed for that road. Besides video cameras, such systems often use radar, infrared cameras and electromagnetic detectors built into the road.
Uses vary widely by location. Local laws determine which camera types may be installed, and how they are used depends on the needs of a given intersection. Despite justified concern about Flock cameras and other ALPRs, a camera above a traffic light is most likely there simply to keep traffic moving.
