Characterization of the influence of vibrations on the vehicle occupant drowsiness (2016)

There is a growing body of literature that recognises the importance of vehicle vibration on seated occupant. Vibration transmitted to the seated human body from the excitation sources such as tyre-road interaction and vehicle powertrain path resides below 100 Hz. Previous studies have reported that exposure to vibration has considerable influences on human comfort, perception, and health. A number of researchers have also suggested that prolong exposure to vibration may give rise to fatigue sensation. Therefore, the issue of human response to vibration has received considerable critical attention. Following that, the ISO 2631-1 (1997) International Standard for human comfort has been developed. Although extensive research has been carried out on human body vibration and this international standard has been developed for human body comfort assessment, however, there is no equivalent standard for human drowsiness caused by vibration in ISO standard. Although few studies have investigated the association between vibration and drowsiness, the evidence for this relationship is inconclusive.<br><br>In recent years, vehicle crashes have become a major social safety problem. One of the most important factors contributing to the high fatalities was the reduction of the driver’s cognitive state in their perception, situational awareness, and vehicle control abilities while being drowsy. Several studies have shown that there is a possible link between sleep deprivation and psychomotor deficit that can cause an accident. However, none of these studies has considered vibration that can cause drowsiness. The influence of vibration on the seated occupant drowsiness was not well investigated. Although many studies have reported the effects of vibration on comfort of the seated human body, the effects of fatigue, and particularly drowsiness, are yet to be rigorously characterised. This is due to several factors: a) the use of “fatigue” as a general term that is poorly defined in the literature b) “fatigue” being multifactorial c) specific types of “fatigue” not having been well studied in the context of vibration. Hence, comprehensive studies undertaken includes the experiment design and drowsiness measurement method.<br><br>First, study approach was to identify the existence of drowsiness caused by vibration from the measurement of brainwave activity. The significant decrease in beta activity and an increase in theta activity obtained from the brainwave measurement (electroencephalogram) suggested that the exposure to low-frequency vibration between 1 - 15 Hz may ultimately lead to a decrease in alertness level. Secondly, following the exposure to vibration, human performance was assessed by measuring the changes in reaction time (RT). Clinically significant results (p ≤ 0.001) were obtained using PVT test. A significant increase in a number of lapses (RT &gt; 500ms) and a substantial increase in mean reaction time (12% in 0.2 ms-2 r.m.s and 27% in 0.4 ms-2 r.m.s) were the manifestation of drowsiness as the result of exposure to the only vibration. In addition, exposure to vibration significantly impacts the lane position performance or SDLP and steering angle variability while driving a vehicle. Finding shows a low transmitted vibration at 0.2 ms-2 r.m.s increased SDLP by 11 % that is comparable to SDLP under the influence of alcohol (BAC 0.05%). A significant increase of steering entropy index (Hp 0.30 ⇒ Hp 0.52) for all the volunteers indicates the unpredictability and randomness of steering correction frequency as a result of drowsiness caused by vibration.<br><br>As a summary, the significance of this research lies in its direct relevance to driver alertness and road safety as drowsiness in drivers is linked directly to traffic accidents. The novel contribution of this project is characterising the role of vibration, which our findings have identified vibration as an important source of driver drowsiness. This project also quantifies the contribution of vibration to psychomotor fatigue in drivers. The obtained results have direct relevance to the development of detectors that measure and monitor such drowsiness-inducing vibration in vehicle design. It also can then provide data to predict the resulting level of drowsiness and have applications not only in car manufacturing, but also in aerospace industry, public transportation, and road safety organizations. This will complement the existing ISO 2631-1 (effects of vibration on comfort) to extend these guidelines in assessment and establishment of thresholds and safe limits for drowsiness-inducing vibration.