Ryan P. Blood, Michael G. Yosta and Janice E. Campa, Department of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, Seattle, Washington; and Randal P. Ching, Department of Mechanical Engineering, University of Washington

Long-term exposure to seated whole-body vibration (WBV) is one of the leading risk factors for the development of low-back disorders. Professional bus and truck drivers are regularly exposed to continuous WBV, since they spend the majority of their working hours driving heavy vehicles. This study measured WBV exposures among professional bus and truck drivers and evaluated the effects of seat-suspension designs using simulated field-collected data on a vibration table. WBV exposures were measured and compared across three different seat designs: 1) an air-ride bus seat; 2) an air-ride truck seat; and 3) an electromagnetically active (EM-active) seat. Air-ride seats use a compressed-air bladder to attenuate vibrations, and they have been in operation throughout the transportation industry for many years. The EM-active seat is a relatively new design that incorporates a microprocessor-controlled actuator to dampen vibration. The vibration table simulated seven WBV exposure scenarios: four segments of vertical vibration and three scenarios that used field-collected driving data on different road surfaces—a city street, a freeway and a section of rough roadway. The field scenarios used tri-axial WBV data that had been collected at the seat pan and at the driver’s sternum, in accordance with ISO 2631-1 and 2631-5. This study found that WBV was significantly greater in the vertical direction (z-axis) than in the lateral directions (x-and y-axes) for each of the three road types and each of the three types of seats. Quantitative comparisons of the results showed that the floor-to-seat-pan transmissibility was significantly lower for the EM-active seat than for either the air-ride bus seat or the air-ride truck seat, across all three road types. This study also demonstrated that seat-suspension designs have a significant effect on the vibrations transmitted to vehicle operators, and the study’s results may prove useful in designing future seat suspensions.

J Occup Environ Hygiene, Volume 12, Issue 6, pages 351-362. Correspondence to: Ryan Blood, Health Sciences, Box 357234, Seattle, Washington 98195; email: rbloodus@uw.edu.