External HMI for self-driving vehicles: Which information shall be displayed?

•Analysis of pedestrians’ informational needs towards self-driving cars.•Information on automated driving status explains absence of a driver.•Additional information on vehicle’s perception is perceived as obvious gimmick.•Additional information on vehicle’s intent leads to subsequent improvements.•...

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Bibliographic Details
Published in:Transportation research. Part F, Traffic psychology and behaviour Traffic psychology and behaviour, 2020-01, Vol.68, p.171-186
Main Authors: Faas, Stefanie M., Mathis, Lesley-Ann, Baumann, Martin
Format: Article
Language:English
Subjects:
Automobile driving
Autonomous cars
Autonomous vehicles
Design factors
Drivers
External human-machine interface
Human-computer interaction
Informational need
Man-machine interfaces
Pedestrians
Perception
Self-driving vehicles
Steering
Traffic accidents & safety
Traffic flow
Traffic information
Traffic safety
User interfaces
Vehicle-to-pedestrian communication
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Summary:•Analysis of pedestrians’ informational needs towards self-driving cars.•Information on automated driving status explains absence of a driver.•Additional information on vehicle’s perception is perceived as obvious gimmick.•Additional information on vehicle’s intent leads to subsequent improvements.•Pedestrians show highly individual crossing and clearing strategies. The objective of this study was to investigate pedestrians’ informational needs towards self-driving vehicles (SDVs). Previous research has shown that external human-machine interfaces (eHMIs) compensate for pedestrian-driver communication when SDVs are integrated into traffic. However, detailed insights on which information the eHMI shall provide lack so far. In a mixed design study, N = 59 participants encountered a simulated driverless vehicle in different traffic scenarios (a. unsignalized intersection vs. b. parking lot; between-subject factor). We investigated the effect of no eHMI (baseline) vs. eHMIs displaying the automated driving system (ADS) status, and informing subsequently about its perception of the pedestrian and/or its intent for the next maneuver ((1) no eHMI, (2) status eHMI, (3) status + perception eHMI, (4) status + intent eHMI, (5) status + perception + intent eHMI; within-subject factor). A mixed-methods design was used to explore participants’ subjective feelings, traffic behavior, and underlying attitudes. The findings reveal that any eHMI contributes to a more positive feeling towards SDVs compared to the baseline condition without eHMI, consistent among traffic scenarios: participants felt significantly safer, reflected greater trust and user experience ratings, and perceived the SDV as more intelligent and transparent. The status indicator mainly drives these beneficial effects on subjective measures. Participants reported that the status information explains the absence of a driver steering the vehicle. Compared to the status eHMI, the status + perception eHMI reflects no further benefit regarding subjective feelings and even has a negative impact on traffic flow. Moreover, participants regarded the additional information on the vehicle’s perception as an obvious gimmick. On the contrary, the status + intent eHMI increases user experience, perceived intelligence, and transparency for pedestrians more than the mere status eHMI. Participants reported that additionally informing about the vehicle’s intent adds a further sense of safety. The present study failed to sho
ISSN:1369-8478
1873-5517
DOI:10.1016/j.trf.2019.12.009