Study of driver behavior in ordinary and emergency situations <Summaries of the Doctoral Theses>

This study seeks to clarify the behavioral characteristics provided by a driver's information processing and mental capacity. A driver's spare mental capacity can be estimated in bits/second using the subsidiary task methodology and the property of reaction times, which being distributed as a logarithmic function of the number of choices. This estimation is expected to enable us to understand the processing capacity during ordinary driving and to analyze the relationship between processing rates and possible avoidance responses of drivers in emergency situations. First, driver's spare mental capacity was estimated in bits/s while drivers were performing the attention distraction task and the lane change task in the circulator course. The obtained mental capacities in bits/s correlated with the control of vehicle velocity and lateral position and seemed to properly represent driver spare mental capacity. Second, a driver subtask performance was measured in various situations during ordinary driving. Prior to the actual driving, the relationship between a subtask performance and spare mental capacity was measured for calibration data. This confirmed that the subtask execution did not interfere with driving. The results of residential and arterial road driving indicated that spare mental capacity ranged from 4 to 15 bits/s. Situations in which driver's spare mental capacity declined were subsequently extracted. Third, the effects of time margin on steering to avoid accidents in emergency situations were examined. Drivers engaged their higher processing abilities to handle situations with a shorter time margin, resulting in shorter reaction time and faster steering for maneuvering. The results also suggested that the reaction time was delayed in accordance with the amount of information that had to be processed in a particular situation and that drivers were still employing "controlled processing" even after the avoidance maneuvers were selected and started. Information processing ability deteriorates with age. Driving characteristics of older drivers were compared with those of younger drivers on an actual road and in a driving simulator. The elderly exhibited decreased abilities to acquire and process information, and these affected ordinary and emergency driving responses. Based on the above results, behavioral characteristics in ordinary and emergency driving situations were discussed in terms of the controlled information processing and driver spare mental capacity