Victim or injurer, small car or SUV: Tort liability rules under role-type uncertainty

In this paper we modify the standard tort model by introducing role-type uncertainty. That is, we assume that neither party knows in advance whether she will be the victim or the injurer when an accident occurs. When the standards of care of the two parties are set at the socially optimal levels, only pure comparative negligence and the equal division rule guarantee efficiency, while the rules of simple negligence, contributory negligence, and comparative negligence with fixed division (other than a 50:50 split) may produce inefficient equilibria. Since pure comparative negligence splits liability between negligent parties according to each party's degree of fault, it makes the accident loss division independent of one's role-type. This produces its efficiency advantage.We extend the model to the choice of vehicle size, as a factor determining who will be the injurer and who the victim in motor vehicle collisions. In the extension we analyze various standard negligence-based liability rules, and tax rules, as instruments to mitigate inefficiency resulting from the vehicle size “arms race.” We also examine two strict liability rules, one of which incorporates a comparative negligence feature; this rule prevents inefficiency from both role-type uncertainty and from the “arms race.”