The preferred placement of the external Human Machine Interface for the safety communication between automated vehicles and vulnerable road users

This paper explores the preferred placement for an external Human Machine Interface (eHMI) on automated vehicles (AVs) to enhance the safety of communication with vulnerable road users (VRUs) in six scenarios: VRUs crossings at crosswalks in front of two types of vehicles, a passenger car and a van, with the distance difference at three conditions, 50m, 25m, 0~5m. For the selected scenarios, potential eHMI positions include the front grille (including the headlamp position), front windscreen, engine cover, side windows, side doors, and the upper space of the wheels for effective communication under three different distance scenarios for each type of vehicle. With this research survey and post-processing of the collected data, the top two rated areas are the upper middle of the front grille (max 46.51%) and the upper middle of the front windscreen (max 44.19%) for both vehicles, the passenger car and the van. These placements aim to provide intuitive visual cues to convey AV intentions, such as yielding or proceeding with caution. Feedback based on user experiences will be used to guide the development of eHMIs with better performance. Regarding to the application of the eHMI module on self-driving vehicles, it seems that more efforts should be put on the regulation aspects, so that people would not be confused by the different exterior maker lights in the near future.