Legibility and Predictability of Protocol-Constrained Motion : Evaluating Human-Robot Ship Interactions Under COLREGS Collision Avoidance Requirements

Human ship drivers use protocol-constrained motion to signal their intent to comply with collision avoidance rules when other means of communication are not readily available. By limiting allowable motions using the protocol constraints of the sea-going Rules of the Road (COLREGS), legibility criteria are well defined by existing human practice, regulation, and case law. Motion requirements of the COLREGS collision avoidance rules require vehicle action from a limited set of acceptable maneuvers when certain states of geometry and collision risk exist, thus promoting predictability. In this paper, predictable motion was realized using on-water experiments under the protocol constraints of COLREGS using several autonomous vessels and one human-operated vessel. By observing other vessels’ states and motion during on-water experiments, the autonomous vehicles successfully performed both legible and predictable protocol-constrained maneuvers as observed by a neutral third party evaluation tool. On-water experimentation demonstrated the ability of a field of autonomous surface vehicles to successfully interact with a human-operated surface craft in accordance with COLREGS. Open questions are posed to the community for advancing human-robot interaction in protocol-constrained collision avoidance scenarios across all physical domains. The results presented in this paper demonstrate successful humanrobot interaction to avoid collision during multi-contact on-water encounters under the protocol constraints of COLREGS using only the vehicles’ motions for communication.