Nearly 60% of city bus drivers reported experiencing low back pain (LBP) over the preceding 12 months according to a survey of 61 drivers from a public transportation company conducted by Okunribido et al. While the pain was mostly moderate in nature (rated from 3 to 7 on a scale of 1 to 10) and transient (lasting less than 3 days), over 11% indicated the condition forced them to take time off work.
Drivers were observed to spend a significant amount of time actually driving (60 % of the workday) and assuming a torso straight/unsupported postural position. While few tasks involved lifting/pushing, vibration measurements for multiple style buses traveling on cobble roads and single-decker buses travelling on asphalt indicated that the vector sum values exceeded the European directive limit.
The authors suggest that LBP may be reduced by having drivers take regular breaks from sitting to perform stretching/moving activity. Improved seating with good back rest support is mentioned as being potentially valuable. The smoothing of shock/jerking events related to bus acceleration and deceleration was also felt to be a valuable strategy.
Study Design
Subjects
From a pool of 350 bus drivers, 80 volunteers from a public transportation bus company participated in the study. The subjects were informed of the project’s purpose and then completed a questionnaire. After eliminating those who did not complete the survey and applying other exclusion criteria, the information from 61 drivers was evaluated (58 males/3 females, 19 to 64 years old, mean weight – 84.9 kg, mean height – 172.9 kg).
Study Questionnaire
The validated questionnaire elicited data involving:
Low back pain – current (pain presently or during the past 7 days), previous (pain sometime during the past 12 months), number of episodes, duration and intensity
Driving experience – years of driving, hours/day driving, surface conditions, environment conditions, driving style and discomfort from various vibration exposures.
Sitting driving posture – a frequency of never/occasionally/often for postures of torso against backrest, torso straight, torso bent, torso twisted and torso bent/twisted; a posture score was generated from reported frequency/position.
Manual material handling – a frequency of load handled (light: < 5 kg, medium: 5 to 10 kg, heavy: >10 kg) per workday in lifting and pushing tasks, postural position while performing the task and time the task was performed relative to driving time.
Field Assessment
Evaluators traveled with 12 drivers for at least one complete round trip and recorded:
Sitting driving posture – posture (torso against backrest, torso straight, torso bent, torso twisted, torso bent/twisted) was recorded once a minute for one hour duration.
Driving style – driving manner and number/duration of stops made.
Road surface assessment – type/duration of roads driven.
Driving Information
The prior month’s route/bus records were reviewed involving the study subjects. Data of concern included daily service route driven, duration of service route driven, and type of bus driven.
Vibration Measurements
Nine sets of vibration measurements were recorded involving three of the most commonly used vehicles for three driving conditions along one route considered by drivers to be the worst relative to vibration. Measurements were made using a tri-axial seat pad accelerator positioned at the driver/seat interface. Average linear acceleration, peak acceleration, crest factor, vibration dose value and fatigue-decreasing proficiency allowable exposure were measured/calculated.
Other Findings
On average, it was observed that during a typical work day (7 hours-36 minutes), a bus driver spends 4 hours-40 minutes driving, 2 hours-33 minutes sitting with the bus idling and 23 minutes standing/walking.
Field evaluators found that the most common posture assumed by drivers was the “torso straight” position. This differed from the questionnaire findings where 57.4% of the drivers reported they often assumed a torso against the backrest posture.
Regarding manual material handling, the field evaluators observed no activity while drivers reported on the survey that 13.1% perform lifting functions.
The lowest vibration measurements occurred when the bus was idling while the highest values were seen in the z-axis when traveling on a cobble road in a single decker bus. However, cobble road was seldom traversed (less than 1% of the service route driving time).
Study Concern/Limitations
The authors identified the following potential shortcomings of this research:
It was unknown if the volunteer group was a representative sample of bus company drivers because descriptors (i.e., age, years of driving) of all drivers (350 at this company) were not available.
During the field assessment, driver postural positions that were assumed between the one-minute sample points were not recorded.
Prevalence of low back pain may have been underestimated due to the small sample size.
Article Title: City bus driving and low back pain: A study of the exposures to posture demands, manual materials handling and whole-body vibration
Publication: Applied Ergonomics 38: 29-38, 2007
Authors: O O Okunribido, S J Shimbles, M Magnusson and M Pope
This article originally appeared in The Ergonomics Report™ on 2007-10-29.