How should autonomous vehicles drive? Policy, methodological, and social considerations for designing a driver

Autonomous vehicles (AVs) are being developed, tested, and commercialized around the world. While skilled human drivers can rely on their experience and common sense to navigate complex driving situations that involve trade-offs between competing objectives, AVs are engineered systems, which may handle complex scenarios based on driving principles articulated at the time of system design. This raises the question of what constitutes proper driving behavior in a complex driving scenario. Many jurisdictions point to existing rules of the road as a description of good driving and, by requiring AVs to follow such rules, hope to improve the safety and efficiency of the transportation system. This paper discusses the desirability of a comprehensive definition of AV behavior, reviews subnational, national, and international regulatory developments that seek to define how AVs might drive, and discusses the tensions between safe, lawful, and efficient driving. Locally defined rules of the road can serve as a guide to a comprehensive driving behavior specification. However, translating rules of the road, which are legal documents written in natural language, to formal rules for use by computers deployed on AVs is a challenging task. In particular, the pervasive appeals to judgment that are present in many rules of the road do not easily lend themselves to the precise formalization of conditions and quantification of values that computers use to make decisions. This work also considers the effect that formalizing behavior for adoption by AVs might have on the general driving culture, and especially on the relationship between existing classes of road users. To highlight the challenges associated with formalizing the rules of the road, this work reports on an experiment where two teams independently translated two rules of the road into formal rules to instruct AVs or to verify the correctness of AV behavior. The study results emphasize the desirability of new technical and political structures to mediate a shared understanding of the rules of the road. The harmonization of behavioral expectations has the potential to improve the safety and efficiency of AV deployments, as well as the broader transportation system.