Driving support systems, such as Adaptive Cruise Controls and Lane Keeping Assists, are believed to change driving behavior. These changes allow drivers to ignore the tasks performed by the driving support system, which can cause dangerous driving circumstances. A few reasons can account for the increased danger. First, decreasing driving responsibilities can make a driver lazier, while increased driving tasks require a quicker and more accurate under- standing of the system. Second, an observant driver may disagree with the system’s assessment of a situation.

In order to solve these problems, it is necessary to observe driving behavior more closely, to clarify the decision-making process by using some indexes measured by drivers’ signals, and to discover why a driver’s behavior changes through traced indexes.

This study reviews one method of determining a drivers’ thinking process. We chose the Low-Speed Following system as the driving support system model item. The Driving Simulator in the Japan Automobile Research Institute was used to conduct the experiments. The indexes measured were breaking reaction time, moving time of eye points, and subject information based on the indirect method of Situation Awareness.

As a result, our method illustrated the drivers’ decision-making process, and the reason for drivers’ using the driving support system was specified. Furthermore, we estimated the validity of driver behavior changing when using driving support systems.