What moral code should your self-driving car follow?

Imagine you are driving down the street when two people -- one child and one adult -- step onto the road. Hitting one of them is unavoidable. You have a terrible choice. Now imagine that the car is driverless. Until now, no one believed that autonomous cars -- robotic vehicles that operate without human control-- could make moral and ethical choices, an issue that has been central to the ongoing debate about their use.