The video shows the car approaching the intersection and stopping when it doesn’t detect any light coming from the stoplight. It then identifies a police officer out in the middle of the intersection directing traffic and monitors their hand movements until it detects the signal to go. Easy as that.
Waymo first began working on hand-signal recognition technology so that its autonomous vehicles would be able to interact safely with bicyclists on the road. But if recent events are any indication, it looks like the technology could have a much broader application.