The Problem with the Trolley Problem

The Problem with the Trolley Problem
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Stop me if you’ve heard about the trolley problem before.

Imagine you’re driving a trolley car. Suddenly the brakes fail, and on the track ahead of you are five workers you’ll run over. Now, you can steer onto another track, but on that track is one person who you will kill instead of the five: It’s the difference between unintentionally killing five people versus intentionally killing one. What should you do?

Philosophers call this the “trolley problem,” and it seems to be getting a lot of attention these days—especially how it relates to autonomous vehicles. A lot of people seem to think that solving this thorny dilemma is necessary before we allow self-driving cars onto our roads. How else will they be able to decide who lives or dies when their algorithms make split-second decisions?

I can see how this happened. The trolley problem is part of almost every introductory course on ethics, and it’s about a vehicle killing people. How could an “ethical” self-driving car not take a view on it, right? 

However, there’s just one problem: The trolley problem doesn’t really have anything to do with the ethics AI—or even driving. 

The original trolley problem came from a paper about the ethics of abortion, written by English philosopher Phillipa Foot. It’s the third of three increasingly complicated thought experiments she offers to help readers assess whether intentionally harming someone (e.g. choosing to hit them) is morally equivalent to merely allowing harm to occur (choosing not to intervene to stop them getting hit). As the trolley driver, you are not responsible for the failure of the brakes or the presence of the workers on the track, so doing nothing means the unintentional death of five people. However, if we choose to intervene and switch tracks, then we intentionally kill one person as a means of saving the other five.

This philosophical issue is irrelevant to self-driving cars because they don’t have intentions. Those who think intentions are morally significant tend to hold strong views about our freedom of will. But machines don’t have free will (at least not yet). Thus, as far back as Isaac Asimov’s three laws of robotics, we’ve recognized that for machines to harm someone—or “through inaction, allow a human being to come to harm”—is morally equivalent.

Without this distinction, the trolley problem has little interest for philosophers, nor should it. Sure, some people have used cases like this to uncover people’s beliefs about how to make trade-offs between human lives. However, such studies merely replicate social prejudices and say little that is deep or significant. (Young lives count for more than the elderly, for example, but thin people also count for more than fat ones.)

On the other hand, the trolley problem specifically disregards just about every aspect of ethical behavior that is relevant to self-driving cars.

For instance, the trolley runs on rails, so its driver knows for certain that they will hit either five people or one person. However, self-driving cars must navigate environments of profound uncertainty, where they must continuously guess how others will react. Any driver knows how important this is and will have come up with their own theories about driver and pedestrian behavior. How can we teach machines this level of understanding and empathy? Psychologists and computer scientists are working on it, but philosophers aren’t that interested.

The trolley also suffers a catastrophic brake failure, so that its driver faces no blame for the deaths that would result from his inaction.