M.Y. Rosnaha et al. AJE Vol.9 2009 1-17
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3.5.3. Armrests
Since the current seat was not provided with an armrest, it should be considered as an option. Armrests might give additional postural support and be an
aid to standing up and sitting down [16]. They also support the arms to prevent or reduce arm, shoulder, and neck fatigue. A gap of perhaps 100 mm between the
armrest and the seat back may, therefore, be desirable. An elbow rest that is somewhat lower than sitting elbow height is probably preferable to one that is
higher, if a relaxed posture is to be achieved. An elbow rest at 200-250 mm above the seat surface is generally considered suitable.
The height of the armrest was set at the 5th percentile male elbow-rest height at 600 mm from floor level and approximately 210 mm above the seat surface. The
adjustability of the armrest is proposed to accommodate the 95th percentile male as well. Therefore the range of the adjustable armrest would be 210 mm-230 mm above
the seat surface. The armrests should be designed such that drivers can move them out of the way if they so prefer.
3.5.4. Headrest
A headrest is also proposed in the new design because it can help reduce fatigue in the neck and head muscles. The headrest will help to align the eye-view of
drivers. Without a headrest, the neck muscles are used to align the eye-view of drivers and this contributes to fatigue of the driver’s neck after driving for a period
of time. The headrest should be adjusted to a minimum of 50 mm up and down from the top of the seat backrest and a minimum of 40º forwards from the vertical to
fully support the user’s head [2]. By using the 95th percentile male sitting eye height as guidance, the headrest dimension is proposed with adjustable height and its
inclination range based on the literature.
The recommended seat design has numerous differences from the current seat Table 4.
3.6. Simulation results
Seat designs were drawn using CAD, then exported into CATIA and integrated with a 3-D human model. The 3-D human model manikin was edited using the
Malaysian bus drivers’ anthropometry data. All missing data were calculated using the ratio scaling method by referring to the Japanese population. Thus, the manikin
in the software represents the Malaysian bus drivers’ population. The human is located on the seat using the H-point and Seat Reference point SRP relationship
[18].
The bus operation task was simulated under kinematics constrains and adjustable components were located iteratively until the human-workstation model
satisfied ergonomic principles such as visibility, reach, and comfort. A comparison was made for both seats for a 5th percentile male Figure 4 and for a 95th
Development and Evaluation of Bus Seat Dimension to Improve the Fit and Comfort of Malaysian Bus Drivers
11
percentile male Figure 5. In the simulations, the current seat showed that it does not provide adequate
backrest support for the 5th percentile male because existing seat pan is 500 mm long, but the 5th percentile popliteal-buttock depth is only 386 mm.
Table 4. Summary of recommended seat design parameters mm, except where noted
Seat dimension Current
Recommended Seat pan
Height 470-530
370-480 5th-95thile popliteal height Width
440 440 95thile hip breadth + 25mm all round
Adjustability Yes Yes
Depth 500
380 5thile buttock-popliteal length
Backrest
Height 500
660 95thile sitting shoulder height Width
400 560 95thile elbow-elbow breadth
Lumbar support 200
180-280 5th -95thile lumbar support height Inclination
10º-15º 10º-15º literature
Armrest
NA 210-230 5th -95thile sitting elbow height
above seat surface 50 mm updown
Headrest NA
40º forward 95thile male sitting eye-height
Extra leg support
Current seat Recommended
Figure 4. Comparison of current seat and recommended seat design for 5th percentile
Current Recomme
Recommended
Figure 5. Comparison of current seat and proposed seat for 95th percentile male bus drivers
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