Exposures to whole body vibration and mechanical shocks in bus drivers in Sweden

Introduction: A strong association has been shown to exist between low back pain and long-term exposure to Whole Body Vibration (WBV). Urban bus drivers are exposed to both continuous vibration and impulsive shocks when driving.  The EU directive 2002/44/EC was developed to limit professional drivers’ exposures to WBV. For continuous vibration the average, weighted 8 hour daily limit [(A(8)] is used to assess WBV exposures; however, if there are impulsive shocks, the exposures should be assed with the more complex daily vibration dose value [VDV(8)] and the daily static compressive dose [Sed(8)].  

Methods: Twenty-seven WBV measurements were collected from three different busses travelling in regular traffic to and from the airports in Gothenburg, Sweden.  There were nine measurements each from: 1) a high floor bus with an air ride seat, 2) a low floor bus with an air ride seat, and 3) a low floor bus with a pedestal seat.   Results: There were significant differences in WBV exposures between busses. The A(8) WBV exposures were below action limits in all busses; however, the low floor bus with the pedestal seat had VDV(8) and Sed(8) WBV exposures above action limits.  Relative to the vibration measured at the floor of the bus, the air ride seat in the high floor bus amplified vibration exposures and attenuated exposures in the low floor bus.  

Discussion: The impulsive shocks were the predominant exposures on the city bus routes.  For VDV(8), and Sed(8) WBV exposures, which are more sensitive to impulsive shocks, exposures were above action limits whereas the more conventional A(8) WBV exposures were below action limits, likely underestimating the health risks.  The amplification of the WBV exposures by the air ride seat in the high floor bus may indicate that a different type of seat may be better suited for this type of bus.