Human-Machine Interfaces for Automated Driving: Development of an Experimental Design for Evaluating Usability

The introduction of conditionally automated driving [25] implies repeated transitions of the driving task between the human operator and the automated driving system (ADS). Human-machine interfaces (HMIs) facilitating these shifts in control are essential. Usability serves as an important criterion to assess the quality of an HMI design. This paper derives a study design for assessing the usability based on the best practice advice by [1]. The paper covers the applied definitions of usability, the sample characteristics, the test cases, the HMIs, the dependent variables, the procedure, the conditions of use, and the testing environment. The study design will be applied in a driving simulator and three test track experiments in different countries within an ongoing project. This involves a number of safety, technical and resource constraints in the development of the study design. This paper describes the challenges and limitations of applying a generic best practice advice to the varying test settings. Furthermore, two HMI concepts are developed and evaluated in an expert assessment. The two concepts will serve as the research subjects in the series of experiments. The proposed study design is suitable for application in different test settings. Therefore, the comparability between the experiments is high. This paper provides a first step in a validation project with the overall goal to propose a practical approach to usability testing of ADS HMIs that covers different constructs of usability and appropriate dependent variables within their application areas.