Ryan Patrick Blood
Project title: Whole Body Vibration Exposure Among Transit Workers in King County, Washington
Completed in: 2008
Low back pain among public transit drivers is a significant problem affecting over 200,000 drivers aloe in the transportation industry. Workman's compensation data illustrate a high occurrence of occupational low back pain associated with full-time employment as a bus driver. The relationship between exposure to whole-body vibration (WBV) and low back pain has been established in prior research.
The long-term goals of this study are to identify possible intervention strategies for reducing WBV exposures. In order to develop an understanding of which intervention strategies may reduce WBV exposure, three hypotheses were tested.
The first hypothesis tested, was whether there were differences in WBV exposures between different road types. Participants drove a bus on a city street segment, two freeway segments and a speed hump segment. The null hypothesis was there was no difference in WBV exposures between road types. The second hypothesis evaluated different types of seats. Three different seat models were evaluated to determine whether there were differences in WBV exposures across seat models. The null hypothesis was that there were no differences in WBV exposures across seat models. Finally, the third hypothesis examined whether individual factors affected WBV exposures. By stratifying data by body weight and seat pressure settings, these individual factors were examined to determine whether seat pressure settings and weight affected WBV exposures.
In this study three different seat types were evaluated as Metro bus drivers drove a standardize route including a city street segment, a freeway segment, and a brief section of he route that included large speed humps aimed at measuring impulsive exposure. The floor and seat of the bus were instrumented with tri-axial accelerometers. The bus driver's exposure was measured with the seat accelerometer and the performance of the seat was evaluated measuring the vibration attenuation between the floor and the seat.
The street and older freeway (I-5) segments of the test route produced significantly higher WBV exposures than the other segments with both producing WBV exposures higher than the action limit for Vibration Dose Value in the z-axis. The Recaro Ergo M seat performed better at attenuating impulse and shock related WBV exposure (p<0.05), however, none of the seats tested performed significantly between on all road types. The personal factor of driver selected seat pressure significantly affected WBV exposures with lower seat pressures leading to higher exposures; however, driver weight did not significantly affect WBV exposures.
This study provides a unique opportunity to evaluate vibration exposure in a standardized setting, which accurately simulates on the job conditions. The findings of this study can be used to expand the knowledge base in the science of WBV and to help identify and quantify the need for interventions in bus drivers.