What are the cameras on traffic lights for?

Some are the so called "red light" cameras, that will record those vehicles that go thru the intersection on a non green signal light; others are for monitoring the flow of traffic and / or crime controlWhat are the cameras on traffic lights for?
They are set up to catch anyone who passes the light when it is on red that way they get the license plate and mail them a ticket.What are the cameras on traffic lights for?
If you answer a question you need to have the answer. The are NO Weight sensor in the road to change lights. Look and you see the back line that shapes the retangle. They cut the tar and then run wire around that rectange many times which creates a magnetic field when electric is run throught it. When a large metal item, car, is in that area the magnetic induction is altered and that is the sensor that tells the traffic controller there is a vehical there. Now we use cameras to sence cars. Its cheaper and much easier to maintain. The sensor in this question, above the light itself is for Emergency Vehicals allowing them to have better access to the intersection. One person answered this correcly already and one completely wrong and that answer has a vote. Go with facts not guesses. Dave, Tx. DOT.