How Should Automated Vehicles Approach Pedestrians? – The Influence of Different Approximation Behaviors & Driver Visibility on Perceived Situation Criticality

Abstract

To ensure acceptance and conformity to society’s expectations for Automated Vehicles (AV), not only objective, but also subjective measures of safety in encounters between AV and Vulnerable Road Users (VRU) must be investigated. Objective safety of a traffic situation can be measured using Inoue et al.’s Safety Cushion Time (SCT) [8], which describes the additional braking distance available due to preventive driver actions. Method. This work describes an online study (within-subject design) with videos of different traffic scenarios with N = 36 participants. This study measured the influence of visibility of a driving person (yes/no) and Safety Cushion Times (1.5 s/ 2 s/ 2.5 s) on pedestrian’s perceived safety. Outcome variables included perceived safety, acceptance, conformity of vehicle behavior to pedestrians’ expectations, and emotional reaction. Results & Conclusion. Low SCT values (= high acceleration combined with late braking) resulted in a low subjective safety assessment of a situation, low acceptance of vehicle behavior and negative emotional reaction of pedestrians. High SCT values (=low acceleration and early braking) resulted in high subjective safety ratings, high acceptance, and high conformity to expectations, thus resulting in a positive emotional reaction. Visibility of a driving person had a lower influence on ratings of subjective safety. Therefore, it is recommended to incorporate our findings into a model for driving behavior for AV if the AV needs to be seen as considerate and subjectively safe.