AUTONOMOUS CARS PROMISE to give us back the time we spend in traffic, improve the flow of traffic, reduce accidents, deaths, and injuries, and make personal car travel possible for everyone regardless of their abilities or condition. But despite impressive demonstrations and technical advances, many obstacles remain on the road to fully autonomous cars.20 Overcoming the challenges to enabling autonomous cars to safely operate in highly complex driving situations may take some time. Manufacturers already produce partially automated cars, and a spirited competition to deliver the most sophisticated ones is under way. Cars that provide high levels of automation in some circumstances (such as highway driving) have already arrived in the marketplace and promise to be in the hands of a large number of car owners in the next few years.