Most of us would sacrifice one person to save five. It’s a pretty straightforward bit of moral math. But if we have to actually kill that person ourselves, the math gets fuzzy.

That’s the lesson of the classic Trolley Problem, a moral puzzle that fried our brains in an episode we did about 11 years ago. Luckily, the Trolley Problem has always been little more than a thought experiment, mostly confined to conversations at a certain kind of cocktail party. That is until now. New technologies are forcing that moral quandry out of our philosophy departments and onto our streets. So today we revisit the Trolley Problem and wonder how a two-ton hunk of speeding metal will make moral calculations about life and death that we can’t even figure out ourselves.

This story was reported and produced by Amanda Aronczyk and Bethel Habte.

Thanks to Iyad Rahwan, Edmond Awad and Sydney Levine from the Moral Machine group at MIT. Also thanks to Fiery Cushman, Matthew DeBord, Sertac Karaman, Martine Powers, Xin Xiang, and Roborace for all of their help. Thanks to the CUNY Graduate School of Journalism students who collected the vox: Chelsea Donohue, Ivan Flores, David Gentile, Maite Hernandez, Claudia Irizarry-Aponte, Comice Johnson, Richard Loria, Nivian Malik, Avery Miles, Alexandra Semenova, Kalah Siegel, Mark Suleymanov, Andee Tagle, Shaydanay Urbani, Isvett Verde and Reece Williams.

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