[The labor of freight-container tractor drivers and low back pain. Correlation with whole-body vibration exposure]

In order to determine the causal factors of low back pain (LBP) which prevails among freight-container tractor drivers, vibration measurements of the seat of ten freight-container tractors and one heavy truck, a survey on the daily working hours of 240 tractor drivers for a month, and a time study of work on 28 person-days were conducted. Vibration measurement was made under routine conditions on paved public roads for 40 km under laden and unladen conditions. For the evaluation of vibration exposure, ISO 2631 was used. With the freight-container tractors, the mean vibration levels were high in X and Z directions, particularly in X direction. In the heavy truck, the vibration level was consistently higher in Z direction. According to the evaluation made by ISO 2631, the X component of the vibration was found to be serious. The magnitude of the vibration level was greatly influenced by the condition of the road surface with bridges tending to produce a high level of vibration. Vibration levels of the new model tractors were not necessarily always lower than that of the old models. It was estimated from the foregoing results and the time study that in more than 90% of the drivers the daily exposure time (i.e. driving hours) exceeded the allowable exposure time of fatigue-decreased proficiency boundary (FDP), and in about one-third of the drivers the allowable exposure time of exposure limit (EL) was exceeded. These results suggest that long exposure to severe vibration during work is one of the possible causal factors of LBP of freight-container drivers.