The Trolley Problem: An Interactive Ethical Dilemma

Tracks

People on Track A (straight) 5

People on Track B (side branch) 1

Trolley speed 6 m/s

Live Readout

Set both group sizes, then run the trolley. You can pull the lever any time before it reaches the switch.

Distance to switch

— m

Active track

People at risk now

Net lives saved

How it works

Philippa Foot's 1967 thought experiment: a runaway trolley is heading down Track A toward n_A people tied to the rails. You stand at a lever. Pulling it diverts the trolley onto Track B, where n_B people stand instead. You cannot stop the trolley and cannot warn either group in time.

Utilitarian rule:  choose the action that minimizes deaths
                   pull lever  iff  n_B < n_A
Net lives saved =  n_A − n_active_track   (0 if you never switch)

Two ethical frameworks disagree about what matters once you can see this number:

Consequentialism / utilitarianism — only the outcome counts. If n_B < n_A, pulling the lever is not just permitted but obligatory, because it produces strictly fewer deaths.
Deontology (act/omission distinction) — pulling the lever makes you the proximate cause of Track B's deaths, a new act, whereas staying still lets an existing threat run its course. Many deontologists judge the two as morally different even when the death count is identical, which is why the "trolley problem" and its footbridge variant (pushing one person off a bridge to physically block the trolley — same math, most people refuse) are used to probe exactly where that line sits.

This simulator only implements the switch variant: the lever is thrown before the fork, the trolley's path bends smoothly onto the chosen branch, and the group standing on the branch the trolley actually reaches is the one at risk — the other group is always safe. Once the trolley passes the switch point the lever locks; you cannot change the outcome after committing.

Trolley Safe group At-risk group

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