The Original Trolley Problem
Philippa Foot introduced the trolley problem in 1967 to illustrate the doctrine of double effect. A runaway trolley is heading toward five people tied to the tracks. You stand next to a lever that can divert the trolley onto a side track where only one person is tied. Do you pull the lever? Most people say yes — saving five at the cost of one seems like simple arithmetic. But the moral calculus is far more complex than it appears.
Why It Matters
The trolley problem isn't just an abstract puzzle — it has real-world implications for autonomous vehicle programming, medical triage, and military decision-making. When a self-driving car must choose between hitting a pedestrian or swerving into a wall, it faces a trolley problem in milliseconds. The simulation above lets you explore how different configurations change the moral landscape.
The Utilitarian Calculation
From a strictly utilitarian perspective, the answer is straightforward: pull the lever whenever the main track has more people than the spur. The simulation calculates net utility across thousands of randomized scenarios to show how often action produces better outcomes than inaction. But utilitarianism struggles with the footbridge variant, where most people refuse to push one person to their death — even though the math is identical.
Beyond Numbers
The trolley problem reveals that human moral reasoning is not purely computational. We care about the difference between doing and allowing, between intended and foreseen consequences, between personal force and impersonal switches. These distinctions may not survive logical scrutiny, but they are deeply embedded in our moral psychology — and any ethical theory must account for them.