Involving users in Automotive HMI design: Design evaluation of an interactive simulation based on participatory design

Abstract

User-centered design (UCD) methods for human-machine interfaces (HMI) have been a key to develop safe and user-friendly interaction for years. Especially in safety-critical domains like transportation, humans need to have clear instructions and feedback loops to safely interact with the vehicle. With the shift towards more automation on the streets, human-machine interaction needs to be predictable to ensure safe road interaction. Understanding human behavior and prior user needs in crucial situation can be significant in a multitude of complex interactions for in-vehicle passengers, pedestrians and other traffic participants.While research mostly focused on addressing user behavior and user needs, the inclusion of users has often been limited to study participants with behavioral inputs or interviewees prompted for opinions. Although users do not have the knowledge and experience as professional designers and experts to create a product for others alone, unbiased insights into the future target groups’ mental models are a valuable and necessary asset. Hence, with stronger user participation and appropriate tools for users to design prototypes, the design process may deeper involve all type of stakeholders helping to provide insights into their mental models to understand user need and expectation.To extend current UCD practices in the development of automotive HMIs, our work introduces a user-interactive approach, based on the principles of participatory design (PD), to enable users to actively create and work within design process. A within-subject study was conducted based on evaluating users’ trust within an interaction with an AV and subsequently configuring the corresponding HMI. The scenario focuses on the interaction between a pedestrian (user’s point of view) deciding to cross path with an automated vehicle (AV, SAE L4). The AV would show its intention via a 360° light band HMI on its roof. The interactive simulation offered users hands-on options to iteratively experience, evaluate and improve HMI elements within changeable environmental settings (i.e., weather, daytime) until they were satisfied with the result. The addition of participation was provided by an interface using common visual user interface elements, i.e. sliders and buttons, giving users a range of variety for real-time HMI configuring.A first prototype of this interactive simulation was tested for the safety-critical use-case in a usability study (N=29). Results from questionnaires and interviews show high usability acceptance of the interactive simulation among participants as assessed by the system usability scale. Overall usability was rated high (System Usability Scale) and frustration low (NASA-TLX raw). Moreover, the interactive simulation was rated to have above average user experience (User Experience Questionnaire). Appended feedback interviews gave valuable insights on improving the simulation user interface, offering different design opportunities within the simulation and a wider parameter space. The short design session time shows the limit of customizability options within this study but needs to be further investigated to determine optimal range for longer evaluation and design sessions. Based on the study results, further requirements for PD simulative environments to assess limits for parameter spaces in virtual environments are derived.