Physiological Information for Pavement Ride Quality Verification

摘要

Heart rate variability (HRV) refers to the beat-to-beat fluctuations in heart rate, which is one of the most promising physiological indicators reflecting mental stress of humans. It has different spectral components in the high and low frequency ranges that are 0.15-0.4 Hz and 0.04-0.15 Hz, respectively. One of the interesting features of HRV is that mental stress inactivates the high frequency (HF) spectral oscillations depending on its severity. The purpose of this study was to verify pavement ride quality ratings based on HRV. For this purpose, a sophisticated driving simulator (KITDS: Kitami Institute of Driving Simulator) was employed and was confirmed to be applicable to physiological testing for pavement ride quality. The result of the simulator experiment showed that the HF oscillations in the time-frequency plane analyzed by continuous wavelet transform decreased with the increase of surface roughness in terms of the international roughness index (IRI). This phenomenon was validated by the on-site experiment using an actual vehicle prior to the ride quality verification study using the KITDS. In the verification study, we observed a particular case of which the subjective ratings were inconsistent with physiological stress signs in terms of the HF oscillations. Although the traditional questionnaire-based testing allows direct measurement of the ride quality of road users, in such a case, the participants of the experiment are unconsciously exposed to mental stress regarding ride quality. The experiment result indicated that 70 % of the participants suffered the unconscious mental stress. To improve this inconsistency, we categorized subjective ratings into three categories depending on the HF oscillations of HRV. According to the result, we suggested that the IRI of 3 mm/mwas reasonable as a threshold of pavement ride quality acceptance at the highway speed of 80 km/h.