WHOLE BODY VIBRATION MEASUREMENTS IN KING COUNTY BUS DRIVERS

1. WHOLE BODY VIBRATION MEASUREMENTS IN KING COUNTY BUS DRIVERS James D. Ploger, Rick Neitzel and Peter W. Johnson University of Washington Department of Environmental and Occupational Health Sciences

2. Motivation and Objectives Background Exposure to vibration is a known risk factor for low back injury/pain Relative importance of average (TWA) and impulsive exposures not well understood Short Term Goals Create a portable system to collect continuous vibration exposure and determine whether there are differences in: Average vs Impulsive vibration exposures/doses Road types Bus vs cars and seat performance Longer Term Goals Evaluate engineering controls to reduce exposures (seats, suspensions, etc) Develop methods for the assessment of temporal patterns of exposure Evaluate administrative controls to reduce exposures (route assignments, change/vary exposures, etc)

3. Data Collection System Two tri-axial ICP accelerometers for seat pad and vehicle floor (z-axis only) 0.5-1000 Hz, PCB Piezotronics, Model 356B40 Two accelerometer amplifiers/loggers Larson-Davis, Model HVM 100 Acceleration signal split 0.4-100 Hz Wd & Wk weighted signal saved in loggers (1 Hz) Raw, unfiltered, unweighted signal to PDA (640 Hz) Garmin GPS for location and vehicle speed Two tri-axial ICP accelerometers for seat pad and vehicle floor (z-axis only) 0.5-1000 Hz, PCB Piezotronics, Model 356B40 Two accelerometer amplifiers/loggers Larson-Davis, Model HVM 100 Acceleration signal split 0.4-100 Hz Wd & Wk weighted signal saved in loggers (1 Hz) Raw, unfiltered, unweighted signal to PDA (640 Hz) Garmin GPS for location and vehicle speed

4. Data Collection System Hardware PDA instrumented with a 16 channel, 16-bit NI, data acquisition card Runs LabVIEW PDA data acquisition software and samples each of the five channels 640 Hz (4000 samples/sec theoretical maximum) 2GB of memory with SD Flash card (88 hour capacity) Serial acquisition of GPS once every second (vehicle location and speed) Software Easy to use graphical interface, GPS data a powerful complement to interpret WBV data Complete flexibility to chose time windows for analysis Multiple vibration values and doses from ISO 2631- 1 and 2631-5, implemented and calculated in Labview

5. Study Design 15 bus drivers , 6 light, 6 medium, 3 heavy Drove 40� (13.3 m) unloaded King County Metro coach bus with USSC seat (fixed spring, height adj.) Drove a 40 mile (65 km), 1 hour test route that included city streets, freeways and speed humps Subset of 5 drivers drove a car over the same route Compared Road types Floor vs Seat WBV (Seat performance) Bus vs car (exposure relative to driving) Average TWA (ISO WBV Std 2631- Part 1 ) versus impulsive exposures (WBV Std 2631- Part 5 )

6. Background

19. Conclusions Hardware and software system provides a compact and flexible and platform to evaluate both TWA and impulsive exposures Test route is very sensitive for detecting small differences in exposure GPS has great value to assess components of the exposure (where the exposure occurred, bus speed, etc) System could lead to the develop and evaluation of administrative and/or engineering controls Identify and trigger the need for street repair Differences between bus types Differences between seats Effects of suspension maintenance/life

20. Potential Future Work Obtain vibration profiles for various routes, attempt to distribute/limit driver exposures Seat pad dosimeter, complete self contained system/logger to collect WBV exposures Evaluate seating alternatives Suspension types (fixed vs variable) Manufacturers Active dampening

21. Acknowledgements Department of Environmental and Occupational Health Sciences Washington State Medical Aid and Accident Fund Sue Stewart Terry Compton Tim Drangsholt Metro Employees Amalgamated Transit Union Local 587