Here's a question: how does a self-driving car reveal its intentions to you without an audio cue? Humans can gesture when they let you cross the street, but autonomous vehicles don't have that luxury. Ford and Virginia Tech think they have the answer. They're testing a communication method that uses light signals from dedicated strips to indicate what self-driving cars are doing. If a driverless machine is yielding, for example, it could flash two white lights side to side. Ford has also developed cues for launching from a stop (a rapidly blinking white light) and an autonomous mode (a solid white light).