Watch 123Movies. After years of anticipation, autonomous vehicles are now being tested on public roads around the world. As ambitious innovators race to develop what they see as the next high-tech pot of gold, some experts warn there are still daunting challenges ahead, including how to train artificial intelligence to be better than humans at making life-and-death decisions. How do self-driving cars work? How close are we to large-scale deployment of them? And will we ever be able to trust AI with our lives?