Effect of external HMI for automated vehicles (AVs) on drivers’ ability to infer the AV motion intention: A field experiment

A field experiment was conducted aiming to shed light on how drivers negotiate an ambiguous traffic situation when encountering an autonomous vehicle (AV) in the presence of a yielding intention signal (AV with eHMI) or not (AV without eHMI). A traffic conflict scenario was created with two opposing vehicles instructed to perform a left turn at a four-way junction, at the same point in time. Forty participants were assigned to two groups encountering either an AV with eHMI or an AV without eHMI. To check for equivalence across the two groups, both groups also encountered a conventional vehicle (CV). Results showed that the two groups performed similarly during encounters with a CV. During encounters with AV, however, participants provided with the eHMI maintained higher speed before the AV and finished their maneuver quicker than when they were not provided with eHMI. Additionally participants provided with eHMI rated higher their ability to infer the AV intention before coming to a full-stop than those provided without eHMI. The above findings indicate that the presence of eHMI on AV can accelerate drivers’ inferences about yielding intention of an AV, and have the potential to optimize AV-driver interaction in ambiguous traffic situations.