Yeah, that makes sense, especially with the object permanence issues for cruise. I've worked on similar systems with vision data and figuring out how an object leaves frame is significantly easier said than done. My big qualm with that video is the degree it minimized the danger of human drivers. The advantage of autonomous vehicles isn't traffic reduction or price or any of the topics he mentioned; rather it's that machines don't get drunk or high or tired or angry. Autonomous vehicles aren't a permanent solution, however, as a concept they serve as harm reduction by being significantly safer than humans when comparing mileage.