What self-driving cars want, and what people want from them, varies widely. Often these desires are at odds with each other. For instance, carmakers—and the designers of the software that will run autonomous vehicles—know that it’s safest if cars stay far away from each other. But traffic engineers know that if every car operated to ensure lots of surrounding space, local roads and highways alike would be clogged for miles, and nobody would get anywhere.

Another inherent conflict involves how cars handle crises. No consumer wants to buy a self-driving car that’s programmed, even in the most remote of circumstances, to kill its driver instead of someone else (even if it would save a class of kindergarteners or a group of Nobel Prize winners). However, if every car is programmed always to save its occupants at any cost, pedestrians and cyclists are at risk.

 …