Abstract
Automated vehicles do not yet have clearly defined signaling methods towards other road users, which could complement natural communication practices with human drivers, such as eye contact or hand gestures. In order to establish trust, external human–machine interfaces (eHMIs) have been proposed, but so far, these have not been widely evaluated in natural traffic contexts. This paper presents a user study where 30 participants interacted with a functional display-based visual eHMI for an automated shuttle in mixed urban traffic. Two distinct features were investigated: the communication of (1) its awareness of different obstacles on the road ahead and (2) of its intention to start or to brake. The results indicate that the majority of participants in general regarded eHMIs as necessary for automated vehicles. When reflecting their experience with the eHMIs, about half of the participants experienced an increased comprehension and safety. The combined presentation of obstacle awareness and vehicle intentions helped more participants to understand the shuttle’s behavior than the presentation of obstacle awareness only, but fewer participants regarded this combination of awareness and intent to be safe. The strength of the found effects on subjective responses varied with regard to age and gender.
Highlights
Driving vehicles (AVs) are neither an idea from science fiction, nor are they a vision for our far future anymore
In order to address our research questions, we evaluated two different designs of external human–machine interfaces (eHMIs)—one only with iconic awareness communication (TCA) and another with both iconic awareness communication and textual intent communication (TCA-I) with regard to the factors of trust, sense of safety, comprehensibility, and predictability
I know that it brakes for me and that I can go” [P03]. Participants explained this by having received more information on the shuttle’s behavior and some feedback on their subjective impressions and predictions. Participants stated that they felt noticed by the shuttle due to the external communication, which made it easier for them to establish the connection between the displayed information and their behavior
Summary
Driving vehicles (AVs) are neither an idea from science fiction, nor are they a vision for our far future anymore. Previous research has recommended that automated vehicles should continually communicate the state and awareness of a vehicle, such that other traffic participants can develop an understanding on a case-by-case basis on when to rely on their behavior and when to remain more cautious [4,5]. If this form of trust calibration in different traffic situations can be established over a longer period of time, this is expected to result in overall trust in a system [6]
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