The problem with self-driving cars: who controls the code?

The Trolley Problem is an ethical brainteaser that's been entertaining philosophers since it was posed by Philippa Foot in 1967: A runaway train will slaughter five innocents tied to its track unless you pull a lever to switch it to a siding on which one man, also innocent and unawares, is standing. Pull the lever, you save the five, but kill the one: what is the ethical course of action? The problem has run many variants over time, including ones in which you have to choose between a trolley killing five innocents or personally shoving a man who is fat enough to stop the train (but not to survive the impact) into its path; a variant in which the fat man is the villain who tied the innocents to the track in the first place, and so on. Now it's found a fresh life in the debate over autonomous vehicles. The new variant goes like this: your self-driving car realizes that it can either divert itself in a way that will kill you and save, say, a busload of children; or it can plow on and save you, but the kids all die.