Background: As urban development toward smart cities continues in earnest, pedestrians' chances of encountering autonomous mobile robots (AMRs) on the street increase. Although recent studies have discussed how humans avoid collisions with others when passing them, it is still unclear how they would avoid AMRs, which could be common on the streets soon.
Research question: We investigated humans' avoidance strategy against an AMR approaching head-on through an experiment that included recording human-body motions while walking.
Method: The AMR approached from various starting points, including directly from the participants. The participants were asked to circumvent it by moving rightward or leftward while their walking trajectories were tracked.
Result: We found no significant bias on either side, suggesting that the avoidance direction is not simply determined by the participants' attributes, such as the traffic rules followed in their area of living. The probability of rightward avoidance when the AMR approached head-on indicated that the humans had different avoidance strategy when facing other humans and objects. Moreover, the participants' motion analysis revealed that their waists unconsciously twisted in the direction of avoidance before they circumvented.
Significance: The results suggest that the human-waist provides an indicator to predict the avoidance direction. Our findings could be adopted in AMRs' development to fit them more naturally into our lives.