Involving users in Automotive HMI design: Design evaluation of an
interactive simulation based on participatory design
Authors: Hai Le Duc , Ihme Klas , Köster Frank 
Published: February 2023

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.