A Taxonomy of Vulnerable Road Users for HCI Based On A Systematic Literature Review

Document Title

A Taxonomy of Vulnerable Road Users for HCI Based On A Systematic Literature Review

Document Information

• Subject Area: Human-Computer Interaction (HCI) and the application of external communication design for autonomous vehicles in traffic safety
• Keywords: Autonomous vehicles, external human-machine interfaces (eHMIs), taxonomy, vulnerable road users (VRU), human-computer interaction (HCI)

Research Background and Issues

• What problems or challenges did the authors identify?

  1. The definition of vulnerable road users (VRUs) is inconsistent across studies, with many failing to clarify the concept.
  2. VRUs encompass various types of road users (e.g., pedestrians, cyclists, motorcyclists), whose needs differ significantly, making a "one-size-fits-all" solution impractical.
  3. External human-machine interfaces (eHMIs) are crucial tools for communication between autonomous vehicles and VRUs, but the unclear definition of target groups impacts technological design.

• Why is this issue important?

  1. The widespread adoption of autonomous vehicles will transform interactions between vehicles and humans, including improvements in traffic safety and vehicle acceptance.
  2. Unclear VRU classifications may lead to designs lacking specificity and reduced effectiveness, potentially increasing the risk of traffic accidents.
  3. Clear classifications can help researchers identify research gaps, optimize resource allocation, and improve inclusivity and usability in design.

• Research Motivation and Related Work:

  1. The broad definition of VRUs by WHO (pedestrians, cyclists, and two-wheeled motor vehicle drivers) is insufficient for HCI application design.
  2. Related work suffers from unclear definitions, incomplete classifications, or insufficiently detailed target group studies.
  3. The authors propose a new VRU taxonomy through a systematic literature review to unify terminology and enhance comparability.

Solution

• What methods or solutions did the authors propose?

  1. Development of a taxonomy based on HCI and traffic safety research, including hierarchical classifications of road users (RUs), vulnerable road users (VRUs), and exceptionally vulnerable road users (EVRUs).
  2. Creation of a two-tier hierarchical structure, with four layers and three layers respectively, to address different user attributes and specific needs.

• What is innovative about this solution?

  1. Provides a systematic, multi-level classification method that can be progressively refined based on user attributes.
  2. Incorporates limiting factors (e.g., age, visual or auditory impairments) to precisely define target groups.
  3. Enhances the designability and inclusivity of HCI applications (e.g., eHMIs).

• What are the implementation steps? What key techniques were used?

  1. Systematic literature review analysis: Screening 251 papers from ten conferences and journals between 2000 and 2020 to establish the taxonomy foundation.
  2. Taxonomy construction:
     • Part 1: Basic classification of road users, including Vulnerable RUs and Protected RUs, as well as non-motorized and motorized groups.
     • Part 2: Definition of exceptionally vulnerable road users (EVRUs), with detailed exploration of specific limitations (e.g., age or visual impairments).
  3. Taxonomy visualization: Using hierarchical tree structures to present the taxonomy (see Figure 1 and Figure 3).

Research Outcomes

• What specific outcomes were achieved?

  1. Proposed and validated a hierarchical taxonomy with seven layers, aiding HCI researchers and practitioners in clearly defining VRU groups.
  2. Analyzed the ambiguity in VRU usage across existing literature and introduced new standards for precise target group identification.
  3. Provided application examples, such as eHMI prototypes designed for exceptionally vulnerable users with visual impairments.

• How does it compare to existing solutions?

  1. The taxonomy addresses the issue of inconsistent definitions in current studies.
  2. Offers standardized terminology to enhance comparability across research and facilitate the identification of research gaps.
  3. Promotes inclusivity and usability to better accommodate special-needs users in HCI design.

• What were the experimental or evaluation results?

  1. Quantitative analysis of 168 relevant papers revealed that most studies focus solely on pedestrians, lacking systematic research on other VRU groups.
  2. The PRISMA process was used to detail the literature screening and classification procedure.

• Limitations and Future Directions:

  1. Limitations:
     • The taxonomy primarily focuses on persistent user characteristics, without considering environmental conditions (e.g., weather) or group dynamics (e.g., traffic congestion).
     • The study mainly concentrates on VRUs, with limited exploration of other road user classifications.
  2. Future Directions:
     • Further validation of the taxonomy in other application scenarios, such as urban planning and traffic psychology.
     • Development of new HCI prototypes to address underrepresented exceptionally vulnerable user groups.