Adaptive cruise control (ACC) systems have several operational modes. Drivers may be unaware of the mode where they are operating, which can cause traffic crashes. To suppress mode confusion, we developed a new interface design methodology in which the designer checks the consistency between the machine and interface model. If two models are inconsistent, the designer modify the machine model, which is called engineer-oriented approach, or modify the interface model, called user-centered approach, of modify both models. Based on engineer-and user-centered approaches, two different ACC user interfaces were designed. In addition, human-in-the-loop experiments were performed using a driving simulator. The experimental results showed that the user-oriented design approach provides a more compact, acceptable, and effective interface that can reduce the driver's mode confusions significantly.

In this study, we designed two user interfaces for automated vehicles operated in the modes that correspond to the SAE automation levels 0 to 3. The first is a level-centred interface that allows the driver to increase or decrease the automation level step-by-step. The second is a function-centred interface that has independent driving controls in the longitudinal and lateral directions. We implemented prototypes for the two interfaces and conducted driver-in-the-loop experiments on a driving simulator to verify their effectiveness in the driver's mode awareness. For events on the road, the participants took actions to control the vehicle, which might cause mode changes, and answered the modes he/she believed. The experimental results show that the mode confusion rate of the level-centred interface is twice higher than that of the function-centred interface. Also, visual feedbacks can reduce the mode confusion rate dramatically. The results show that a function-centred user interface combined with adequate visual and/or auditory feedback is essential to improve driver's mode awareness when driving an automated vehicle.

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