Discrete wavelet transform has been applied to analyzing a driver's R-R Interval ta-chogram. Consequently, two specific wavelet levels indicate the dominant frequency that shows driver's mental stress with the time process. This visualization technique is able to replace the former analysis based on Fourier transform in driver's time-transient circum-stances. The experiments are carried out with a driver carrying an electrocardiograph in a passenger car circulating a test course with 140km/h. The R-R Interval tachogram was obtained from the driver before and while driving. The motivation behind this work is to establish a driver's mental model while a driver operates a vehicle. The model con-tributes to safety and comfortable driver's circumstances in road traffics.
