When the car approaches a pedestrian crossing, it can warn those waiting to cross in advance that it has spotted them. It then stops and displays green arrows, for example, to tell them it’s safe to cross. Once they have crossed, and the car is about to set off, it can display a different signal to warn pedestrians that the car is moving. In more extreme examples, a car approaching the crossing that is unable to stop can send out a clear signal to pedestrians not to cross.