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I. Introduction
I.! Overview on Computer Simulation
A bus operator's workstation tailored to his/her tasks will result in increased
comfort and higher productivity. Also a human-centered workstation based on human
capabilities and limitations will reduce the risk of injury and accidents due to an
inappropriate workstation geometry. This indicates that the workstation should be
designed ergonomically considering the characteristics of both the operators and their
tasks.
In the present study, the functional design relationship method was utilized for the
workstation design. The functional design relationship method identified the geometric
relationships between anthropometric variables and design variables, and then determined
design values based on the constructed geometric relationships assuming standard bus
driving postures defined within comfort angles (You et al., ~ 9951.
A computer simulation can be used to verify and modify the workstation design
before it is built. A variety of software tools have been used to mode] a human
graphically and simulate his/her tasks within a workstation. These tools not only provide
an analytical way to ensure that the intended users of a workstation will be able to
perform their tasks with comfort, but also reduce the risk of building a workstation that is
not well suited for its intended users.
Three-dimensional computerized human body models are preferred to physical
models in the form of templates, manikins, and dummies because of their higher
flexibility ant! more precise representations of body size, shape, and proportions.
Examples of such computer human models include COMBIMAN, CREW CHIEF,
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SAMMIE, and JACKS, which are described briefly as follows. However the limited
availability of 3-D anthropometric data causes practical difficulty in the development of
computer models of the body size (Kroemer et al., ~ 994~.
COMBTMAN (Computerized Biomechanical Man-model) is an interactive
computer graphics model evaluating the capabilities and limitations of an human operator
in a seated workplace or vehicle. This three-dimensional system creates a computerized
human-model according to user-defined dimensions and encumbrances of clothing and
personal protective equipment, and analyzes visual accessibility, strength, and reach
capability with the arms and the legs (COMBIMAN, ~ 995~.
CREW CHIEF is an interactive 3-D model of an aircraft maintenance technician.
The model has been used to perform human factors evaluations of aircraft maintenance
crew stations. This three dimensional system allows a designer to simulate a maintenance
activity using computer-generated imagery and to determine whether required activities
are feasible for a given configuration (Armstrong Laboratory Design Technology Branch,
1 992~.
SAMMIE (System for Aiding Man-Machine Interaction Evaluation) is an
interactive design system involving a 3-D human model, a means for modeling objects,
and a language for describing the tasks to be performed by operators. The system permits
the evaluations of postural comfort, reach, clearances, and visibility. Also the joint limits
of human body can be specified and the dimensions and body shape of the human model
can be manipulated in the system (Bonney et al., 1979~.
Lastly, JACKS is a software system for 3-D human modeling and simulation. It is
used for the definition, manipulation, animation, and human factors performance analysis
of virtual human figures. JACKS incorporates sophisticated algorithms for
anthropometric human figure generation, a flexible torso, multiple limb positioning under
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constraints, assessments of visibility and reach, and strength guided performance
simulation of human figures (Computer Graphics Research Laboratory, ~ 9944.
In this study, JACKS was used for the workstation design simulation. At the
beginning of this study, three software packages such as COMBIMAN, CREW CHIEF,
and JACKS were examined as a candidate for simulation. While JACKS is a stand-alone
software, both of COMBIMAN and CREW CHIEF are clesigned to interact with the I
DEAS Level
V,
a CAD software developed by Structural Dynamics Research
Corporation (SDRC). However, they are not compatible with the I-DEAS Level VT, an
upgraded version of the T-DEAS Level V, which is available in The Pennsylvania State
University. Since the older version of I-DEAS is not available on campus, JACKS was
chosen for this simulation study.
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I.2 Objectives
The objectives of the computer simulation of this study were to:
.
Identify the expected performance of a bus operator in the context of the designed
transit bus operator's workstation.
Determine the adjustment ranges of the workstation components (seat / steering wheel
instrument panels) to accommodate 95 percent of the US adult population presented
in SAE 1833, and also to provide sufficient visibility, normal reach, and comfortable
driving posture for the population while performing the bus operating tasks.
Evaluate the bus workstation with a human mode] simulating the bus driving tasks in
terms of
visibility of the displays on the instrument panels and the out-of-windows,
- reach to the steering wheel, the controls on the instrument panels, and the pedals,
and
adjustability of the workstation components for the intended user population
such that comfortable postures can be maintained while driving the bus.
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2. Simulation Mode! Development
2.! Key Features and Configuration of Mode]
A computer simulation system was developed to test and evaluate the bus
workstation design (Figure ~ ~ utilizing the JACKS 5 .9 software.
Therefore, the
capabilities and performance of the simulation system are highly dependent on those of
JACKS 5.9 that provides several commands over site labeling, window shade, object
transparency' rulers' and so on to setup a simulation environment. These commands were
incorporated in the menu of the simulation system so that a user can easily control the
desired conditions of the environment.
Figure I: Transit Bus Operator's Workstation Implemented on JACKS
The simulation system provided three human models having different body
dimensions: the 5th percentile female, the 50th percentile person, and the 95th percentile
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male of the anthropometric data set designated by SAL J833. Since the SAE
anthropometric data are not sufficient to specify a complete 3-D human model in JACKS,
unavailable anthropometric data were analytically determined as presented in Table 1
assuming proportionality of human body dimensions and cylindrical form of each body
part. In the determination, the NASA (1978) and the US Army (1988) anthropometry
studies were used as shown in Table 2.
Seventeen typical bus operating tasks (Table 3) identified by a task analysis in the
previous study (Bucciaglia, 1995) were simulated in JACKS. During the simulation of a
bus operating task, the human model motions were governed by a set of virtual kinematic
constraints related to the task. For example, during the accelerator pedal activation, the
right foot of a human model is attached to the accelerator pedal plate surface, thus the
motions of the knee and ankle of the right leg are controlled depending on the accelerator
movement; during the simulation related to steering wheel maneuvering, the hands were
constrained on the steering wheel to identify the upper-limb joint configuration
While a 3-D human model is conducting each bus driving task, the bus
workstation is evaluated in terms of visibility, reach, comfort, and adjustability. In order
to facilitate the workstation evaluation, the simulation system generated two types of
output files at the end of each bus operating task; one recorded the body joint angles of
the human model, and the other recorded the selected locations of the workstation
components.
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Table I: Anthropometric Data Used in Computer Simulation
Body Segment
Head
Neck
Dimensions
. . . ad. SAE Anthropometry
5 th percentile
female
18.4
14.5
21.3
8.8
10 1
Thickness
Width
Length
Thickness
Width
Torso
Pelvis
Upper Leg
Lower Leg
Foot
with Shoes
Upper Arm
Lower Arm
Hand
Eye Coordinates
Circumference
Length
Thickness
Width
Circumference
Length
Thickness
Width
Circumference
Length
Thickness
Width
Circumference
Length
Thickness
Width
Circumference
Length
Length
Width
Height
Thickness
Width
Circumference
Length
Thickness
Width
Circumference
Length
Thickness
Width
Length
Body Center
Interpupillary
Chin
7 4
50th percentile
1? 4
9.0
95th percentile
male
20.6 ~
16.5 .
23.1
119
13.1
Estimates based on JACK
default data and the ellipse
circumference formula*
Estimates based on JACK
default data and the ellipse
circumference formula*
Estimates based on ARMY
( 1988) data
Estimates using the ellipse
circumference formula*
-
-
Estimates using the ellipse
circumference formula*
Estimates based on ARMY
. (1988)~a
Estimates using the ellipse
circumference formula*
.
Estimates based on NASA
( 1978) data
. Estimates based on JACh
default data and the ellipse
. circumference formula*
Estimates based on JACK
default data and the ellipse
. circumference formula*
Estimates based on NASA
. (1978) data
l Estimates based on JACK
default data and the ellipse
. c~n:~m~nce formula'
Estimates based on JACK
default data and the ellipse
circumference formula*
l
Estimates based on NASA
. (1978) data
l Estimates based on JACK
default data and the ellipse
l circumference formula*
Estimates based on JACK
default data and the ellipse
circumference formula*
Estimates based on NASA
(1978) data
Estimates based on NASA
( 1978) data
* Ellipse circumference formula: C= 27,.~(~/2) +~12) , where C: circumference, t: thickness, and w: width
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Table 2: Anthropometric Data Used for the Analytical Determination
of Unavailable SAE Anthropometric Data
No. Anthropometric Variable Data for SAE Source No Data for SAE Source No.
l | 5 %Female | | 95 %Male |
|Neck C ircumference | 29.7 T 5 T I
2 Biceps Circumference, Relaxed 22.9 3 34.7 4
. 3 ~Foreann Circumference, Relaxed ~21.7 ~3 ~30.6 ~4 ~
4 THandlhickness ~2.2 T 2 T I I
5 Thigh Circumference, Sitting 49.3 1 65.0 4
6 Thigh Clearance, Siding ~14.4 ~5 ~19.4 ~5
7 TCalf Circumference ~306 T 3 T 410 ~4
. Anthropometric Data Source
Source No. Survey Name Year Gender Sample
Women of the Army Corps Separatees 1946 Female 7,563
Women of the Air Force Basic Trainees 1952 Female 852
Air Force Women 1968 Female 1,905
Air Force Flying Personnel - Total Series 1967 Male 2,420
Army Personnel 1988 Female 2,208
Male 1,774
Reference
NASA
(1978) *
Gordon et al.
(1988) **
* NASA (1978), Anthropometric Source Book, vol.2, NASA Reference Publication 1024, Ohio: Yellow
Springs.
** Gordon, C.C., Churchill, T., Clauser, C.E., Bradtmiller, B., McConville, J.T., Tebbetts, I., and Walker,
R.A. (1989), 1988 Anthropometry Survey of U.S. Army Personnel: Methods and Summary Statistics,
Anthropology Research Project, Inc., Ohio: Yellow Springs.
2. Comparison of Statures Between Population Groups
Stature SAE (1994) Army Corps (1946) Air Force (1952) Air Force (1968) Air Force (1967)
155.0 cm 5 % Female 10 TO Female 10 % Female 10 TO Female
188.0 cm 95 % Male 95 % Male
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Army (1988)
10 % Female
97 % Male
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Table 3. Bus Operating Tasks and Metrics Includec] in Computer Simulation System
adjusting seat horizontal Adjust the seat horizontally and vertically in relation to the pedal reach,
workstation and vertical location. This is to ensure that a mannequin maintains its comfortable comfort,
components adjustment hip, knee, and ankle orientation. adjustability
seatback angle Adjust the seatback angle forward and backward considering the reach comfort,
adjustment of steering wheel and the downward visibility. adjustability
steering wheel Tilt and telescope the steering column or tilt the steering wheel based visibility,
adjustment on the static driving posture and the 30 degree downward visibility reach,
requirement simultaneously. comfort,
adjustability
left instrument Adjust the left instrument panel horizontally and vertically based on visibility,
panel (LIP) the dynamic driving posture. Manipulate controls on the right reach,
adjustment instrument panel while keeping the shoulder blades of the mannequin comfort,
on the seatback. adjustability
right Adjust the right instrument panel horizontally and vertically the same visibility,
instrument way as the left instrument panel adjustment. Manipulate controls on reach,
panel (RIP) the right instrument panel while keeping the shoulder blades of the comfort,
adjustment mannequin on the seatback. adjustability
engaging diagnostic Check the displays on the front instrument panel and press the test visibility,
driving check button. Evaluate the visibility of the displays and the reach of the reach,
control located on the front instrument panel. comfort,
adjustability
transmission Shift the bus into gear on the left instrument panel. Evaluate the visibility,
engagement activation postures of the left arm and the visibility of the transmission reach,
engagement. comfort,
adjustability
parking brake Release the parking brake on the right instrument panel. Evaluate visibility,
release the activation postures of the right arm and the visibility of the reach,
parking brake release. comfort,
adjustability
accelerating/ accelerator Press down the accelerator pedal completely. Evaluate the activation ~reach,
maneuvering pedal postures of the right leg. comfort
activation
steering wheel Turn the steering wheel clockwise and counterclockwise keeping the visibility,
turning shoulder blades on the seat-back. Evaluate the reach of the arms to the reach,
steering wheel and downward visibility. comfort,
adjustability
floor- mounted Activate three buttons (right and left turn signals, and high-beam reach,
signal signal) mounted on the floor individually with the left leg. Evaluate comfort
activation the activation postures of the left leg.
brake pedal Press down the brake pedal completely. Evaluate the activation reach,
activation postures of the right leg. comfort
picking-up/ four-way Activate the four way flasher on the right instrument panel. Evaluate visibility,
depositing flasher the activation postures of the right arm and the visibility of the four reach,
passengers activation way flasher. comfort,
adjustability
kneeling ~ Activate the kneeling mode on the right instrument panel. Evaluate visibility,
activation the activation postures of the right arm and the visibility of the reach,
kneeling switch. comfort,
adjustability
door activation Activate the bus door switch on the right instrument panel. Evaluate visibility,
the activation postures of the right arm and the visibility of the door reach,
switch. comfort,
adjustability
farebox Monitor the farebox. visibility,
monitoring comfort
passenger data Input the type of fare of all passengers using ODA (Operator Digital visibility,
input Assistant) on the right instrument panel. Evaluate the activation reach,
postures of the right arm and the visibility of the ODA. comfort,
adjustability
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The computer simulation can be maneuvered through two modes: interactive
mode and batch mode. The batch mode simulates the initial operating task through the
final one for a selected human model, while the interactive mode allows a user to select a
operating task to be simulated.
In summary, the constructed simulation system allows the user to:
· Setup the simulation environment such as displaying site labels, shading windows
generating orthogonal windows, and displaying rulers between sites.
Select a 3-D human mode! among three population groups which are pre-defined by
using the anthropometry data from the SAL 1833.
· Manipulate the locations of the adjustable workstation components (seat, steering
wheel, instrument panels) interactively.
· Simulate motions of the human figure which are controlled through a set of kinematic
constraints for Kneed driving lasts ror 1 / ous operating tasks.
· , ~ it. . · · . . ~. ~ .
Create simulation result files which include the postures of the human figure and the
specified adjustment values of the workstation components for each driving task. and
Execute simulations of the bus operating tasks through either an interactive mode or a
batch mode.
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2.2 Development Procedure
The simulation system was constructed by conducting a series of development
procedures as depicted in Figure 2. The development procedures presents how the
workstation geometry, human models, bus operating tasks, and design evaluation scheme
are integrated into the simulation system. Each procedure is described below in detail.
Import CAD drawings of Create representative
the bus operator's workstation {R~ntative
Define parameters ~ Create bus drivir g posture files
(d.o.f./ranges/sites/colors) of human models
or w~dst~ic ~ nails
~ ,
1
I Place workstation components and a human model
Define kinematic constraints for each bus driving task
| Construct animation and evaluation scheme for each bus driving task |
Figure 2. Simulation Model Development Procedures for Bus Workstation Design
The development of the simulation system was commenced by importing the
geometry of the bus workstation drafted by the Silver Screens CAD package into
JACKS. The 'dxf2pss' utility provided by the JACKS was used to convert DXF file
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3.2 Design Validation
The workstation design was simulated using the human models for each bus
operating task. TIlustrated are the evaluation results regarding visibility, reach, comfort,
and adjustability for the steering wheel adjustment (Table 4) as an example. The rating
scales for each criterion are explained in detail as follows.
3.2.:1 Visibility (V)
Rating Horizontal Viewing Zone Vertical Viewing Zone Related Workspace
Scale (neck Region angle) (neck rotation angle)
5 + ~ OO 30O ~+ ~ OO 30O ~out-of-windows in front
of a bus operator
4 + t 0°, 30° ] + t 30°, 45° ] FTP
(front instrument panel)
3 + ~ 30°, 60° ~+ ~ 30°, 45° ~ RIP (right IP),
farebox
2 + ~ 300, 60° ~+ ~ 45O, 60° ~front and middle parts of
LIP (refit IP)
I + ~ 60°, 90° ~+ ~ 30°, 60° ~middle and rear parts of
LIP (~eftIP)
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Side View
Visibility Cones
Plan View
isometric View
_
W
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3.2.2 Reach (R)
Rating Scale Obstacles Reach Zone Related Workspace
on reach pathway ~
| None | normal reach area * | steel ing wheel,
controls on FTP, RIP, and LIP
pedals, floor mounted signals
None below controls on RIP and LIP
normal reach area
None above controls on RIP and LIP,
normal reach area pedals, floor mounted signals
2 Blocked normal reach area none
Blocked out of none
normal reach area
3.2.3 Comfort (C)
The magnitude of comfort in a bus workstation can be assessed on the basis of the
standard driving posture determined during the workstation design process.
m
Ci = C/m
j=1
where Cj: comfort for driving task i in the workstation,
Cij: comfort of joint j for driving task i in the workstation,
m: the number of joints
Rating Scale | Range of Joint Angle l
5 [ a + 0.5 ~ ]
a-0.56,a-1.56]or[a+0.5S,a+1.55]
1 a-1.5b,a-2.56]or[a+1.56,a+2.50]
2 T a-2.50,a-3.56]or[a+2.50,a+3.56]
T [ out of comfort ROM, maximum ROM ]
(* a: joint angle in standard driving posture, ~ = comfort ROM/4)
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Reach Cones
Front View
Zone 3
Plain View
Isometric View
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.~
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3.2.4 Adjustability (A)
Since 'adjustability' signifies whether the designed workstation provides
sufficient visibility, appropriate reach, and comfort for the intended SAL population
groups (5th percentile female, 50th percentile, 95th percentile male), it needs to be
assessed integratedly combining the results of three criteria of each population group.
3
Al = ~ Vik / 3 + ~ Rik / 3 + ~ Cik / 3
k=] k=} k=!
where Al: adjustability for driving task i in the workstation,
V jk: visibility of population group k for driving task i in the workstation,
Rik: reach of population group k for driving task i in the workstation, and
C jk: comfort of population group k for driving task i in the workstation.
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Table 4. Workstation design simulation for steering wheel adjustment
Task steering wheel adjustment
Task Category adjusting workstation components
Tilt and telescope the steering column, or tilt the steering wheel based on the seat
Scenario position maintaining the static driving posture and the 30° downward visibility
requirement simultaneously.
_
~_ ~
~ I_ a,:
~ ~ [
_ _''
. 1 - ~
Illustration ~ Hi
,
steering wheel column tilt to deg (clockwise: +, counterclockwise: -)
Design Values | steering wheel co: Imn telescope I 11 cm (upward +, downward: -)
steering wheel hub tilt 10 deg (clockwise: +, counterclockwise: -)
Simulation Results
Population
Group 5 th percentile Female 50 th Percentile
column tilt 5 O O a
.
telescope -5.5 cm 0 cm
.
hub tilt -5 ° O O
shoulder flexion 21.8 ° (4) - 29.9 ° (2)
shoulder abduction 4.1 ° (4) 7.6 ° (5)
shoulder rotation 24.3 ° (4) 9.5 O (5)
elbow flexion 56.9 ° (5) 45.0 ° (4)
wrist flexion 0 ° (5) 0 a (5)
.
visibility
reach
comfort 4.4 4.2
adjustability 4.7
Remarks
_
95 th Percentile Male
-s o
5.5 cm
s o
30.8 ° (2)
5.2 ° (5)
14.3 O(4)
45.7 O (4)
o o (s)
s
4
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4. Conclusions
A computer simulation model was developed to test and validate the bus
operator's workstation design. Utilizing the JACKX's capabilities, the simulation model
provided the following functions:
.
.
.
.
setup of simulation environment.
selection of human models with the SAE IS33 anthropometry.
adjustment of workstation components.
simulation of bus operating tasks under specified kinematic constraints.
creation of simulation result files.
model execution in an interactive mode or a batch mode.
The SAE anthropometry data were utilized to generate three different size human
models (Sth percentile female, 50th percentile, 95th percentile male). Estimations were
made to complement unavailable anthropometric data for three dimensional human
modeling.
The simulation system was designed to simulate seventeen typical bus operating
tasks. The simulation system determined the expected behavior and visual field of a
human for each bus operating task in the context of the workstation. The human
behaviors were controlled by the designated kinematic constraints during simulation.
In simulating each bus operating task, the locations of the workstation
components were manipulated within the adjustment ranges. Design modifications were
made wherever inappropriate design was found. The designated adjustment ranges were
evaluated with respect to the degree of satisfying ergonomic requirements such as good
visibility, acceptable reach, postural comfort, and sufficient adjustability.
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A valic] transit bus operator's workstation design (Table 5) was produced through
.
iterative design modifications and simulations. Also, animation of the bus operating tasks
facilitated the evaluation of the workstation in dynamic situations.
Table 5: Adjustment ranges of workstation components tested in simulation
Design Variable Adjustment Range
Seat Horizontal 18.5 cm (7.3 in.)
Vertical 6.7 cm (2.6 in.)
Seatback Angle 10 deg.
Steering wheel Column Tilt 10 cleg.
Telescope 1 1.0 cm (4.3 in.)
Hub Tilt 1 0 deg.
Left Instrument Panel Horizontal 9.9 cm (3.9 in.)
Vertical 4.0 cm (1.6 in.)
Right Instrument Panel Horizontal 13.3 cm (5.2 in.)
Vertical 4.5 cm (1.8 in.)
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References
Armstrong Laboratory Design Technology Branch (1992) User's Guide for Crew Chief.
A computer Graphics Simulation of an Aircraft Maintenance Technician (V 3 - I-
DEAS A, OH, Wright-Patterson Air Force Base.
Bonney, M.C., Blunsdon, C.A
Case, K., and Porter, I.M. (1 979) 'Man-Machine
interaction in Work Systems', International Journal of Production Research, Vol. ~ 7
(6), pp. 619-29.
Bucciaglia, I. (1995) Design Synthesis and Evaluation of Bus Operator Workstation'
M.S.M.E. Thesis, The Pennsylvania State University.
COMBIMAN (1995) Information booklet, CSERIAC,.
Computer Graphics Research Laboratory (1994), Jack User's Guide, Computer Graphics
Research Laboratory, The University of Pennsylvania.
Diffrient, N., Tilley, A.R. and Harman, D. (1981) Human Scale 7/~/9, Cambridge, MA,
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Kroemer, K.H.E., Kroemer, H.B. and Kroemer-Elbert, K.E. (1994) Ergonomics. How to
Design for Ease and Efficiency, NI, Prentice-Hall Incorporated.
Gilmore, B.~. (~1995) Bus Operator Workstation Evaluation and Design Guidelines:
Workstation Mock-up Evaluation Report, PTI 9521, The Pennsylvania Transportation
Institute.
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Gilmore, B.J., Bucciaglia, J., Lowe, B., You, H. and Freivalds, A. (1995) Bus Operator
Workstation Evaluation and Design Guidelines -Draft Interim Report, The
Pennsylvania Transportation Institute.
Gordon, C.C., Churchill, T., Clauser, C.E., Bradtmiller, B., McConville, J.T., Tubbers,
I., and Walker, R.A. (1989), 1988 Anthropometry Survey of U.S. Army Personnel:
Methods and Summary Statistics, Anthropology Research Project, Inc., Ohio: Yellow
Springs.
NASA (1978), Anthropometric Source Book, vol. 2, NASA Reference Publication 1024,
Ohio: Yellow Springs.
OCCU-MED (1986) Southern California Rapid Transit District Anthropometic Study,
Vol. 1, OCCU-MED Co. Health Service, Pasadena, CA.
Rebiffe, R. (1966) 'An Ergonomic Study of the Arrangement of the Driving Position in
Motor Cars', Proceedings of the Institution of Mechanical Engineers, vol. 1 ~ 1, Pt 3D,
pp. 43-50.
SAE (1994) 1994 SEE Handbook, vol. 3, Warrendale, PA, Society of Automotive
Engineers Incorporated.
You, H., Bucciaglia, J., Lowe, B., Gilmore, B.J. and Freivalds, A. (1995) Bus Operator
Workstation Evaluation and Design Guidelines: An Ergonomic Design Process for a
Transit Bus Operator Workstation, PTI 9523, The Pennsylvania Transportation
Institute.
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Representative terms from entire chapter:
workstation design
