Sometimes a driver deviates from his natural or normal driving style due to inadequate attention or faces abnormal situation caused by a number of psychological and physical factors. Such abnormalities often lead a driver to a mistake that may cause an accident. This paper presents a novel approach called driver-adaptive assist system to avoid such abnormalities in driving scenario as a preventive measure against occurrence of vehicle collisions, assuming that natural driving style of individual drivers is the safest style. Adaptive fuzzy system with statistics of recent fluctuations records are used to determine the driving behavior from noisy data. Another fuzzy reasoning section determines the level of abnormality in driving to notify or warn the driver so that he can pay back his full concentration in driving. Different simulated drivers with pseudo realistic styles in starting, stopping and car following are used to investigate performance of the proposed system. Empirical results show the ability of the system to recognize abnormality of drivers having different driving styles.