Niklas Strand

Driver performance in the presence of adaptive cruise control related failures: Implications for safety analysis and fault tolerance

This study explored how failures related to an adaptive cruise control (ACC) were handled by drivers and what the effects on safety can be. The experimental study included forty-eight subjects and was performed in a moving base driving simulator equipped with an ACC. Each subject experienced two different failures in separate scenarios. In total, the study included four different failures, i.e., Unwanted acceleration, Complete lack of deceleration, Partial lack of deceleration, and Speed limit violation. The outcome of each failure scenario has been categorized based on whether the driver managed to avoid a collision or not. For the outcomes where collisions were successfully avoided, the situations were analyzed in more detail and classified according to the strategy used by the driver. Besides showing that partial lack of deceleration caused more collisions than complete lack of deceleration (43% compared to 14% of the participants colliding), the results also indicate a preference among drivers to steer and change lane rather than to apply the brakes when faced with acceleration and deceleration failures. A trade off relationship was identified between allowing a failing ACC to stay operational and on the other hand disabling it when an error is detected. Keeping the system operational can cause confusion about the mode of the system but as the results of the study indicate it can also improve the situation by reducing impact speed.

End-users' Acceptance and Use of Adaptive Cruise Control Systems

An online survey was distributed to end-users of adaptive cruise control (ACC). In total 90 drivers answered the questionnaire, which covered e.g. ACC usage and how such use affects driver behaviour. According the responses: the ACC is used primarily on roads with higher speed limits; the end-users trust the system even though it has some functional limitations; they have a very positive attitude towards the system; and positive effects on comfort and safety are observed including reduced inclination to overtake and increased compliance with speed regulations.