Efficient Communication of Automated Vehicles and Manually Driven Vehicles Through an External Human-Machine Interface (eHMI): Evaluation at T-Junctions

The absence of a human driver in an automated vehicle (AV) raises new challenges in communication and cooperation between road users, especially for ambiguous situations where road users would like to communicate their intention explicitly. This paper investigates the effect of a novel external human-machine interface (eHMI) which was designed to address this issue by signaling the AV’s intention through a 360° LED light-band mounted outside of the AV. In a simulator study an eHMI interaction strategy was implemented that should convey the message “I am giving way” to a manually driven vehicle operated by participants waiting at a t-junction. The experimental study incorporated three t-junction scenarios where the AV had always the right of way but may yield to a driver waiting at the intersection. The intention of the AV was communicated either implicitly (braking) or implicitly and explicitly (braking and eHMI). It was analyzed whether participants would understand the AV’s intention and accept the gap provided in front of the AV. Through participants’ subjective ratings the understandability, the usability and the acceptance of the eHMI solution were evaluated. The results showed that the majority of participants (85%) understood the meaning of the eHMI signal after two interactions. Initial gap acceptance results showed a positive effect of the eHMI solution. The presence of an eHMI improved participants perceived safety and trust. Subjective ratings for usability and acceptance indicated that participants perceived this eHMI interaction strategy as easy to use and were willing to communicate with an AV in this way. The results of the present study will be used to investigate the beneficial impact of this eHMI interaction strategy further in more complex traffic scenarios