Why does it matter, for a deontologist, that the classic trolley case fixes who will be sacrificed?

Because deontology protects individuals against being sacrificed for others — and that objection has its full force exactly when the person to be sacrificed is already identifiable.

In the classic trolley case the actor faces the possibility of sacrificing a specific human being to save several others. The identity of the endangered persons is fixed, and so is the identity of those who would benefit.

• For a consequentialist this fixedness may carry no special significance: on that view the interests of different people can be offset against each other in any case.
• From a deontological point of view it is of considerable importance. The focus on the rights and freedoms of the individual, and the associated rejection of sacrificing one person for the benefit of others, is one of the most fundamental elements of deontological ethics.

The underlying commitment, stated as a principle: in democratic states under the rule of law, securing individual rights and freedoms should take precedence over maximising the intersubjective utility sum. A violation of fundamental rights cannot be outweighed by advantages to third parties, however large those advantages may be.

That is the objection the injury-minimising proposal has to answer. And the answer the paper develops turns on noticing that this feature — a known victim, a known beneficiary — is precisely what the autonomous-car case lacks.

Go deeper:

• Stanford Encyclopedia: Deontological Ethics — agent-centred constraints: why a right that yields whenever the sums favour yielding is not a right.
• Wikipedia: Dignity — the constitutional concept that does the blocking work in European legal orders.