As Philippa Foot original framed the thought experiment in "The Problem of Abortion and the Doctrine of the Double Effect" (in her "Virtues and Vices"), a runaway trolley will kill five trackworkers unless you switch it to a siding where it will only kill one hapless victim. There will inevitably be a death, but whether it is just the one or five is up to you. Should you flip the switch?
Studies show most say "yes".
In her 1976 Monist article "Killing, Letting Die, and the Trolley Problem", Judith Jarvis Thompson suggested an alternative to Foot's original thought experiment. Suppose that there is no siding and no switch. Instead, you are standing on a footbridge over the tracks and see the runaway trolley at the same time as a very fat man leaning over the side next to you.
Should you push the fat man over onto the tracks to stop the trolley from killing the five? (He's fat enough to stop the trolley, but he will surely be killed as a result.)
Studies show most say they should not push the fat man onto the tracks, which suggests a problem with our moral consistency. To test your moral consistency, take this short experiment.
Wired Magazine has a terrific article, "Kill Whitey. It’s the Right Thing to Do.", about psychologist David Pizaro's clever experiments extending so-called Trolley Cases to include racial scenarios. (They also link to an Edge video of Pizarro discussing his research.) From Wired,