Final answer:
The traffic control officer is using gestures, a form of nonverbal communication, by raising her hand to stop cars.
Step-by-step explanation:
When a traffic control officer stops a line of cars by holding up her hand instead of shouting "stop," she is utilizing a form of nonverbal communication known as gestures. This kind of communication does not rely on spoken words but on physical movements to convey messages. In this particular instance, the raised hand acts as a universal symbol indicating to the drivers that they need to halt their vehicles. It is an effective means of communication that transcends language barriers and can be quickly understood by drivers from different backgrounds.