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Crash Algorithms for Autonomous Cars: How the Trolley Problem Can Move Us Beyond Harm Minimisation


The prospective introduction of autonomous cars into public traffic raises the question of how such systems should behave when an accident is inevitable. Due to concerns with self-interest and liberal legitimacy that have become paramount in the emerging debate, a contractarian framework seems to provide a particularly attractive means of approaching this problem. We examine one such attempt, which derives a harm minimisation rule from the assumptions of rational self-interest and ignorance of one’s position in a future accident. We contend, however, that both contractarian approaches and harm minimisation standards are flawed, due to a failure to account for the fundamental difference between those ‘involved’ and ‘uninvolved’ in an impending crash. Drawing from classical works on the trolley problem, we show how this notion can be substantiated by reference to either the distinction between negative and positive rights, or to differences in people’s claims. By supplementing harm minimisation with corresponding constraints, we can develop crash algorithms for autonomous cars which are both ethically adequate and promise to overcome certain significant practical barriers to implementation.

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  1. 1.

    In her 1985 work in which she presents the bystander variant of the trolley problem, Thomson frames similar concerns in terms of rights. However, in order to maintain a clear distinction between her and Foot’s views, and because we will primarily draw from the 1976 paper in what follows, we stick to her 1976 usage of the term ‘claims’ in discussing these considerations.

  2. 2.

    Thomson relies on the latter to account for why the surgeon may not distribute the patient’s organs (1976).

  3. 3.

    Unfortunately we cannot, as of yet, point to empirical evidence establishing the actual appeal of this approach, because, as we noted in section 6, existing surveys do not unambiguously differentiate between involved and uninvolved persons. We hope that future research will begin to incorporate and emphasise these factors.


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Many thanks to Markus Ahlers, Sven Nyholm, and two anonymous referees from Ethical Theory and Moral Practice for their useful comments on an earlier draft of this paper.

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Correspondence to Lucie White.

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Hübner, D., White, L. Crash Algorithms for Autonomous Cars: How the Trolley Problem Can Move Us Beyond Harm Minimisation. Ethic Theory Moral Prac 21, 685–698 (2018).

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  • Autonomous cars
  • Self-driving vehicles
  • Crash algorithms
  • Trolley problem
  • Harm minimisation