Reaction time of the secondary task while driving in various situations

In order to develop an in-vehicle information system which is adaptive to driver mental workloads, an attempt to measure the spare capacity of driver´s attention was carried out in a laboratory experiment. A video movie taken from the front panel of a car was projected onto three screens in front of the subject whose main task was to operate the steering wheel and foot pedals in accordance with the movie. The subsidiary task was a simple addition task of two difficulty levels. The stimulus movies were classified into seven different types of road situation. The results were consistent with previous results obtained in field trials that the spare capacity of attention while driving changed with the road situations. In this study, the reaction time, which is another aspect of the subtask performance, was analyzed. Contrary to the results of the percentage correctness, the same degree of degradation was found for both levels of the subsidiary task.