Drivers’ interactions with advanced driver assistance systems based on experiences from real driving and results from driving in a driving simulator were under investigation in this thesis. Questions posed were: - How do drivers perceive and interact with ADAS? - How are (technical) failures handled by drivers, and which are the consequences’ of these failures? - Which are the implications for diagnosis and detection of failures, as well as for system development? Special attention was given to driver behavior in response to technical failures in an adaptive cruise control system. The results are based on two studies, adopting an approach with a combination of qualitative and quantitative data. In study I focus group interviews were conducted and in study II a driving simulator experiment was conducted. The findings include notions on behavioral adaptations and monitoring inefficiencies for drivers facing failures. Implications for design, failure detection, and traffic safety are discussed. With regard to human- machine-interaction it is concluded that ADAS have effects on driver’s behavior, that these effects are individual and based on experience, and that measures towards failure containment should be a taken.