Effects of Pedestrian Behavior, Time Pressure, and Repeated Exposure on Crossing Decisions in Front of Automated Vehicles Equipped with External Communication

Title of the Paper

Effects of Pedestrian Behavior, Time Pressure, and Repeated Exposure on Crossing Decisions in Front of Automated Vehicles Equipped with External Communication

Paper Information

• Research Area: Human-Vehicle Interaction, External Communication Design for Autonomous Vehicles, Pedestrian Behavior Studies
• Keywords: External Communication, Autonomous Vehicles, Pedestrian Behavior, Chicken-Rabbit Game, Time Pressure, eHMI, Human-Computer Interaction

Research Background and Issues

• Identified Challenges:

  • External communication of autonomous vehicles (AVs), such as LED light strips or displays, intended to replace traditional human driver-pedestrian interaction, still poses open questions.
  • Pedestrian crossing behavior is influenced by various factors, including the behavior of other pedestrians, time pressure, and past experiences. However, these factors have not been adequately explored in studies on AV external communication.
  • The "Chicken-Rabbit Game" theory suggests that pedestrians may cross more frequently due to AVs having a mandatory stopping mechanism, but this hypothesis has not been empirically validated.
  • External communication methods equipped with countdown timers may pose risks of encouraging dangerous pedestrian behavior.

• Research Motivation:

  • To explore the detailed role of external communication (eHMIs), especially in complex scenarios involving multiple pedestrians and repeated exposure to non-yielding AVs.
  • To enhance understanding of AV safety and trust, contributing to planning their integration into mixed traffic environments.

Solution

• Proposed Method:

  • Conduct a three-part virtual reality (VR) experiment to investigate the effects of pedestrian behavior, time pressure, and repeated exposure on crossing decisions in front of autonomous vehicles.
  • Design three scenarios with varying conditions, including different pedestrian behaviors, AVs displaying timer information, and pedestrians repeatedly encountering non-yielding AVs.

• Innovations:

  • For the first time, the impact of other pedestrians' behavior and repeated exposure is incorporated into research on external communication (eHMIs) of autonomous vehicles.
  • Systematic robustness testing of the timer effect in AV external communication, combined with dynamic changes in pedestrian past experiences, scientifically evaluates behavioral impacts.

• Implementation Steps and Techniques:

  1. Scenario Design: Create virtual traffic environments using Unity 2020.3.1f10.
  2. Experiment Setup:
     • Scenario 1 (“Pedestrian Group Behavior”): Simulate situations where some pedestrians illegally cross the road to investigate mimicry behavior of others and assess the effectiveness of AV external communication (eHMI) signals.
     • Scenario 2 (“Timer”): Examine whether AV external countdown timers induce time pressure and their impact on risky crossing behavior.
     • Scenario 3 (“Non-Yielding Autonomous Vehicles”): Study pedestrian behavioral adjustments and trust changes when repeatedly exposed to non-yielding AVs (validation of the Chicken-Rabbit Game theory).
  3. Data Measurement: Metrics include pedestrian behavior (e.g., crossing duration, collision frequency), cognitive load, trust, perceived safety, and communication quality.
  4. Survey Instruments: Use standardized scales such as NASA-TLX and Trust in Automation Questionnaire to assess psychological load, trust levels, etc.

Research Findings

• Specific Results:

  1. Impact of Pedestrian Behavior:
     • Pedestrian behavior is significantly influenced by the actions of other pedestrians.
     • AVs equipped with eHMIs notably increased pedestrian trust, reduced cognitive load, and improved communication quality.
  2. Safety of Timers:
     • Countdown timers displayed by AVs did not induce risky behavior.
     • Timers significantly enhanced user perception of eHMI practicality and enjoyment.
  3. Repeated Exposure and Validation of the "Chicken-Rabbit Game" Theory:
     • Pedestrians adapted more quickly after repeated exposure to non-yielding AVs; trust increased, but risky crossing behavior emerged, preliminarily validating the behavioral impact of the "Chicken-Rabbit Game" theory in visual experiments.

• Advantages Over Existing Solutions:

  • By simulating complex dynamic scenarios with high real-world resemblance in virtual reality, this study integrates multiple factors into pedestrian-AV external communication research, providing a basis for more precise traffic safety interventions.

• Experimental Results:

  • eHMI demonstrated significant effects in improving trust and crossing efficiency.
  • Habituation effects among pedestrians were observed, though some pedestrians exhibited risks of over-reliance on AVs.

• Limitations and Future Directions:

  • Limitations:
    • Small sample size (N=18), predominantly young participants, with age generalizability yet to be tested.
    • Differences between virtual reality experiments and real-world scenarios may affect result extrapolation.
  • Future Directions:
    • Investigate cognitive differences in eHMI perception across different age groups and cultural backgrounds.
    • Validate the long-term effects of eHMI in real-world environments.
    • Explore strategies to mitigate pedestrian over-reliance on eHMI.