Pbs Learning Media: Traffic Jam Part 2: Straight to the Source

Students visit their city's traffic management center, tour the traffic signal control room and meet with Nick Van Gunst, a traffic engineer who shows them that the city's traffic light system is controlled by computers. They learn that a stoplight queue, which is a line of waiting cars, is caused when the cars waiting at a red light don't get a long enough green light to get through the intersection. [1:53]