The Right Moment for Braking as Informal Communication Signal Between Automated Vehicles and Pedestrians in Crossing Situations

Automated vehicles must be able to handle situations requiring cooperation with other road users in mixed traffic scenarios. Braking is an important informal vehicle signal for cooperation, indicating e.g. the intention to let a pedestrian cross. The present experimental study assessed the effects of daytime, approaching vehicle speed and participant's age on the last moment of gentle braking initiation from a pedestrian's perspective. Using a Labview-based simulation environment, pre-recorded real videos of approaching cars on a parking area were presented to 42 participants. Independent within-subject-variables were daytime (midday/dusk) and approaching vehicle speed ranging from 10 to 40 km/h in steps of 5 km/h. The between-subjects-factor consisted of two age groups ranging from 20 to 30 years and 50+ years. Results of the mixed ANOVA showed a main effect of daytime, vehicle speed and age as well as an interaction between age and vehicle speed. More conservative time gaps were chosen in the dusk condition. In line with previous studies, accepted time gaps decreased with increasing vehicle speed, indicating more risky crossing decisions. Older participants took more conservative decisions, especially on lower speed levels. Results show that applying one simple time gap for automated cooperative braking does not fit human/pedestrians perception and expectations. A function considering vehicle speed and daylight condition is recommended instead.