"Too Crowded for a Robot?": Modeling Human Acceptance Criteria for Elevator-Riding Robots

Robots are increasingly expected to share elevators with people, yet little is known about the conditions shaping acceptance. We introduce the Robot Boarding Area (RBA)—a designated entry zone for robots—and examine how its availability and congestion affect user evaluations. In an online survey, acceptance sharply decreased once the RBA was occupied by any person or large object, even under moderate crowding. A VR experiment confirmed this pattern and further showed that participants preferred when robots refrained from boarding in crowded conditions compared to forcing entry. By formalizing the RBA as an acceptance criterion and demonstrating the value of adaptive skip strategies, this work identifies spatial availability and boarding behavior as central to socially acceptable robot deployment in elevators.