A runaway trolley is approaching a fork in the tracks. if the trolley runs on its current track, it will kill a work crew of five. If the driver steers the train down the other branch, the trolley will kill a lone worker. If you were driving the trolley, what would you do? What would a computer or robot do? Trolley cases, first introduced by philosopher Philippa Foot in 1967[1] and now a staple of introductory ethics courses, have multiplied in the past four decades. What if it's a bystander, rather than the driver, who has the power to switch the trolley's course? What if preventing the five deaths requires pushing another spectator off a bridge onto the tracks? These variants evoke different intuitive responses.

Given the advent of modern “driverless” train systems, which are now common at airports and are beginning to appear in more complicated rail networks such as the London Underground and the Paris and Copenhagen metro systems, could trolley cases be one of the first frontiers for machine ethics? Machine ethics (also known as machine morality, artificial morality, or computational ethics) is an emerging field that seeks to implement moral decision-making faculties in computers and robots. Is it too soon to be broaching this topic? We don't think so.