Abstract
In this study, focusing on ACC (Adaptive Cruise Control) as a factor in the secular change of traffic performance in recent years, the paper conducted a web-based questionnaire survey of ACC users and analyzed the actual use of ACC functions and the secular changes in their awareness of ACC. The analysis revealed that the ACC penetration rate among expressway users at present can be assumed to be approximately 30%, that the frequency of ACC use is increasing for each driver, and that they change the frequency of ACC use and the setting spacing depending on traffic conditions. The results also showed that the ACC setting speed is lower and the ACC setting spacing is longer compared to their own driving, suggesting that the prevalence of ACC may be one of the factors that have contributed to the secular change of traffic performance in recent years. The study also revealed that, independent of ACC, driving behavior changes in the direction of reducing traffic performance with driver age. It means that the increasing proportion of elderly drivers may also be one of the factors which deteriorate the traffic performance.
