Exploring the Impact of Interconnected External Interfaces in Autonomous Vehicleson Pedestrian Safety and Experience

TL;DR

This study explores ‘interconnected eHMIs,’ where multiple AV interfaces are interconnected to provide pedestrians with clear and unified information and assessed the effectiveness of this concept in improving pedestrian safety and their crossing experience.

Abstract

Policymakers advocate for the use of external Human-Machine Interfaces (eHMIs) to allow autonomous vehicles (AVs) to communicate their intentions or status. Nonetheless, scalability concerns in complex traffic scenarios arise, such as potentially increasing pedestrian cognitive load or conveying contradictory signals. Building upon precursory works, our study explores 'interconnected eHMIs,' where multiple AV interfaces are interconnected to provide pedestrians with clear and unified information. In a virtual reality study (N=32), we assessed the effectiveness of this concept in improving pedestrian safety and their crossing experience. We compared these results against two conditions: no eHMIs and unconnected eHMIs. Results indicated interconnected eHMIs enhanced safety feelings and encouraged cautious crossings. However, certain design elements, such as the use of the colour red, led to confusion and discomfort. Prior knowledge slightly influenced perceptions of interconnected eHMIs, underscoring the need for refined user education. We conclude with practical implications and future eHMI design research directions.

Figures (7)

• Figure 1: Sketches illustrating eHMI visuals in three distinct AV states: Cruising, Yield to pedestrians, and Full stop. In the unconnected eHMI design (top), a green crossing is projected upon full stop, irrespective of the second lane's conditions. Conversely, in the interconnected eHMI design (bottom), a red crosswalk is displayed when the second lane poses risks, while a green crosswalk appears when both lanes are deemed safe.
• Figure 2: A participant walking with a VR headset on (left). The same participant using a Touch controller to navigate to the next scenario (right).
• Figure 3: From a bird's-eye view, the simulated environment presents a bus stop opposite the pedestrian's starting point. Dotted lines highlight three groups of background people. The view captures a moment when the AV's eHMI signals to the pedestrian it has stopped, but cautions that the adjacent lane may still be unsafe.
• Figure 4: VR implementation of three interface conditions: Baseline without eHMI (left), Unconnected eHMIs (middle), and Interconnected eHMIs (right). The top row illustrates eHMI communication for pedestrians in the presence of a non-yielding vehicle in the second lane, while the bottom row depicts the same with a yielding vehicle.
• Figure 5: Study procedure and the approximate time for each part of the study.