This study examines driver's mental workload when using driving assistance systems such as Adaptive Cruise Control (ACC) system by driving simulator experiments. Driver's brain activity is measured by using functional near-infrared spectroscopy (fNIRS). Subjects follow a leading vehicle, which has a certain speed pattern including stop and go situations, with and without ACC system. The brain activities of the drivers without ACC system, i.e. manual driving, is related to their recognitions and driving behaviors of accelerating and decelerating. The brain activities of the drivers with ACC system is, on the other hand, not observed in their driving behaviors. This results show the reduction effects of driver's mental workload by using the driving assistance system.
