Toward a Holistic Communication Approach to an Automated Vehicle's Communication With Pedestrians: Combining Vehicle Kinematics With External Human-Machine Interfaces for Differently Sized Automated Vehicles

Abstract

Future automated vehicles (AVs) of different sizes will share the same space with other road users, e. g., pedestrians. For a safe interaction, successful communication needs to be ensured, in particular, with vulnerable road users, such as pedestrians. Two possible communication means exist for AVs: vehicle kinematics for implicit communication and external human-machine interfaces (eHMIs) for explicit communication. However, the exact interplay is not sufficiently studied yet for pedestrians' interactions with AVs. Additionally, very few other studies focused on the interplay of vehicle kinematics and eHMI for pedestrians' interaction with differently sized AVs, although the precise coordination is decisive to support the communication with pedestrians. Therefore, this study focused on how the interplay of vehicle kinematics and eHMI affects pedestrians' willingness to cross, trust and perceived safety for the interaction with two differently sized AVs (smaller AV vs. larger AV). In this experimental online study (N = 149), the participants interacted with the AVs in a shared space. Both AVs were equipped with a 360° LED light-band eHMI attached to the outer vehicle body. Three eHMI statuses (no eHMI, static eHMI, and dynamic eHMI) were displayed. The vehicle kinematics were varied at two levels (non-yielding vs. yielding). Moreover, “non-matching” conditions were included for both AVs in which the dynamic eHMI falsely communicated a yielding intent although the vehicle did not yield. Overall, results showed that pedestrians' willingness to cross was significantly higher for the smaller AV compared to the larger AV. Regarding the interplay of vehicle kinematics and eHMI, results indicated that a dynamic eHMI increased pedestrians' perceived safety when the vehicle yielded. When the vehicle did not yield, pedestrians' perceived safety still increased for the dynamic eHMI compared to the static eHMI and no eHMI. The findings of this study demonstrated possible negative effects of eHMIs when they did not match the vehicle kinematics. Further implications for a holistic communication strategy for differently sized AVs will be discussed.

Effect of vehicle external acceleration signal light on pedestrian-vehicle interaction

“…Most previous studies observed that front signal light only convey implicit signals when vehicles slow down 30 . In reality, however, many drivers do not slow down in front of zebra crossings under unsignalized roadways or even pass at a constant speed or accelerate to indicate that they are not yielding.…”

“…The results showed that the overall communication effect had great potential when the signal expression of the eHMI was aligned with the vehicle’s kinematic state. However, the findings also highlighted that when the signaling of the eHMI contradicted the behavior of the vehicle, the consequences could be fatal 30 . Moreover, when a vehicle has an eHMI, humans may ignore the actual movement state of the vehicle and focus instead on the signals presented by the eHMI 29 .…”

"It Must Be Gesturing Towards Me": Gesture-Based Interaction between Autonomous Vehicles and Pedestrians

“…Werner et al [71] identified turquoise as the best color for AV external lighting, emphasizing visibility and uniqueness. Lau et al [40] showed that dynamic eHMI enhances safety in yielding AVs but warned against mismatches between eHMI signals and vehicle actions. Dey et al [18] discovered cyan with flashing or pulsing animations as effective for eHMIs in AVs, aiding pedestrian interaction.…”

Principles for External Human–Machine Interfaces

“…References: [22,[33][34][35]. Rationale: The communication of the CAV must be consistent and shall not send any contradicting messages to avoid a feeling of uncertainty.…”

“…References: [6,17,18,22,[36][37][38][39][40]. Rationale: According to §1 of the German Road Traffic Act (StVO), all road users should behave in such a way that no one is endangered, harmed, hindered, or disturbed.…”