Designing for Perceived Safety in In-Vehicle Touch Interfaces - A Mixed-Methods Study

Abstract

As digital in-vehicle interfaces become increasingly central to the driving experience, ensuring that they are perceived as safe is essential. This thesis explores how perceived safety can be influenced through the design of human-machine interfaces (HMIs), with a particular focus on touch-based interaction in the centre stack display (CSD) of modern cars. A mixed-methods approach was applied, starting with a literature review and expert interviews to define perceived safety, identify appropriate evaluation tools, and pinpoint key interface design factors. These insights informed the development of four interface concepts, varying in navigation structure (flat and nested) and button size. Nineteen participants took part in a user test, evaluating the concepts in a real vehicle on a closed test track. Both objective data (glance behaviour via eye-tracking) and subjective input (questionnaires on perceived safety, usability, and workload, as well as interviews) were collected. The results formed a set of design and evaluation guidelines grounded in theory and empirical findings. Use flat layouts for quick tasks, particularly when stationary. Consider nested structures when the goal is to reduce the duration of individual glances. Increase button sizes to around 35×35 mm to support confidence and perceived safety. From an evaluation perspective, use a combination of methods to build a more complete understanding of perceived safety. Interpret quantitative and subjective data alongside qualitative user narratives. While standardised tools such as UMUX-Lite and NASA-TLX offer helpful benchmarks, complement them with task-specific prompts and interviews to capture richer feedback. Furthermore, when comparing similar concepts, use comparative ranking over scalar ratings to reveal clearer preferences. Lastly, test under realistic conditions to ensure findings are grounded in real-world use.