How do red lights “see” your car and know to turn green?

How does a traffic signal knows when to turn green? Especially late at night when you are the only driver on the road. In this video, I chat with two traffic signal experts: Mohammed Bendelhoum, an engineer with the California Dept. of Transportation (Caltrans) and Brian Girardo (Iteris) explore the history of vehicle detection (induction loops and video/camera detection) to explore which method is better.