Auditory feedback produced by driver assistance systems can benefit safety. However, auditory feedback is often regarded as annoying, which may result in disuse of the system. An auditory headway feedback system was designed with the aim to improve user acceptance and driving safety. The algorithm used a graded approach, which means that it delivered a more urgent warning if the time headway was smaller. In an on-road test, we compared this design with a conventional binary headway warning system. Participants drove a test vehicle on the highway, once with our graded feedback and once with conventional feedback. User acceptance was assessed through a questionnaire and interview. An inspection of the time headway distributions suggested that participants responded to the auditory feedback for both systems. There were substantial individual differences in time headway, and extremely short headways were rare. These findings suggest that long-term naturalistic trials are needed to assess the safety-effectiveness of graded auditory feedback. ... Read more