This paper concerns driver's steering quality, which could be one of the highest potentials to detect driver's performance deterioration. In an attempt to reduce the number of traffic accidents, several types of intelligent vehicles are under research, such as DRIVE, IVHS and ASV. One of the applications could be a supporting system for a driver, which should function through detecting driver's status such as psychophysiological status.

Using a chassis-dynamomeler-type of driving simulator, driver's steering quality was investigated in a monotonous driving condition. A monotonous driving could induce drowsiness, hypoalertness and sleep at the wheel, which might deeply affect the characteristics of steering wheel operation. Additionally, a drunken driving was also investigated as one of the hypoalertness conditions.

The results indicate that a comparatively high correlation was shown among the frequency characteristics of steering wheel angle operated, physiological status and vehicle's lateral fluctuation, which implies the possibility that the characteristics could be one of the measures to represent driver's steering quality.