On-vehicle displays and on-ground projection for automated vehicle communication - test track study results

In this article, we present findings from test track studies investigating external Human Machine Interfaces (eHMIs) designed to facilitate communication between automated vehicles and other road users. Firstly, four eHMIs, ranging from simple patterns to complex pictograms, were implemented on an automated car and tested with pedestrians in a road crossing and a car parking use case, during daytime or nighttime. Secondly, two rear-oriented eHMIs were tested on drivers overtaking a stationary robotaxi in a passenger drop-off use case. Overall, a positive users' acceptance was found for all the eHMIs, with three of them showing potential for real world application: (1) a waiting state pictogram at the front of the car, displayed when the automated car was yielding to a pedestrian, (2) a ground projected turn indicator when the automated car was leaving a parking spot, and (3) a pictogram indicating passenger descent to a following driver. Moreover, we highlighted the link between the understanding and the use of the waiting state pictogram and the behaviour of the automated vehicle.