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CHAPTER 1. INTRODUCTION Bus operators suffer from a higher than normal rate of injury and absenteeism. It is felt that much of this is due to the difficulty with designing an operators workstation to accommodate a wide range of operator anthropometry in addition to the demands placed on the operators. The workstation presented in this report will consider the seat, steering wheel, pedal, and instrument pane! design and locations. This report presents the procedure for design guidelines for transit bus workstations along with an example. It is the intention of this work to develop the design guidelines such that individuals from the 5th percentile female to the 95th percentile male in stature as defined by SAL J833 are accommodated. The guidelines are based on sound and fundamental ergonomic/ biomechanical principles: (~) visibility, (2) reach, (3) comfort, and (4) minimum force. Additionally, ease of ingress and egress issue was considered for a bus operator to get into and out of the workstation. I.! Background An unusually high incidence of absenteeism (sometimes 3 times as great as the average for blue collar workers) and illness occur amongst transit bus operators (Evans, 1994; Winkleby et at., 1988) This in turn has caused a significant increase in the number of workman's compensation and disability claims in the transit industry. There are many factors that contribute to the higher than normal morbidity and mortality rates of transit bus operators. Epidemiological studies have concentrated on identifying three main disease categories: cardiovascular disease, gastrointestinal illness and musculoskeletal problems. The most prevalent of these health problems are musculoskeletal, relating to neck and back pain (Patterson et at., 1986~. Studies have found that 80.5% of operators experienced some degree of back and neck pain, in contrast to 50.7% of non operators,
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and the incidence of reported low back pain was 20% higher for operators when compared to non operators (Anderson, 1991). Frequent awkward postures, muscular effort, vibration and shock, as well as whole body vibration exposure and prolonged sitting in a constrained position all contribute to overworking the lumbar spine and its supportive structures, causing low back pain (Bovenzi et al., 1992). The design of a workstation based on ergonomic principles has been attempted by several organizations (Carrier et al., 1992). Carrier et al. created a mockup of a transit bus operator workstation that was developed using a computer package. This computer program developed by Genicom~ combines both the statistical approach of building a model around 3D "zones", with the theoretical modeling approach in which actual subjects are simulated by changing numerical parameters (Carrier et al., l 992). Carrier et al. received input from transit authorities, bus manufacturers and bus operators on the mockup, and presented several recommendations for future workstations. One of the key findings from this study was that the present steering wheel sizes interfere with visibility and can "penetrate" the operator's abdomen or thighs if the operator attempts to orient the wheel to achieve minimum visibility (Carrier et al., 1 992). Carrier et al. also found that the steering wheel should have a more vertical than horizontal orientation. They concluded that it is impossible to accommodate 95% of the population with existing components (Carrier et al., 1 992). A primary concern of the workstation design is the relationship between the seat, steering wheel and pedals. These are the workstation components that the operator is required to stay in constant contact with, and the location of these controls dictates the operator's posture. Consequently, most studies have concentrated on the relationship of these components. However, operators have demonstrated a higher priority in leg comfort than arm reach when positioning their seats (Philipart et al., 1 986). - 1.2
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Courtney and Evans demonstrates! that a workstation based on inappropriate anthropometry results in an erroneous design (Courtney et al., 1987). They tested their hypothesis by examining the workstations of several buses in Hong Kong that were originally designed and built in the United Kingdom based on European anthropometry, but used by smaller Cantonese operators. The result of this mismatch is an attempt by operators to modify the work environment to fit their own needs. Specifically, the Cantonese operators had installed seat inserts, a brick or a piece of wood for footrests, and padding of rags or rubber shoe bottoms on the pedals (Courtney et al., 1987~. The addition of items by the operator to compensate for workstation deficiencies is not uncommon. Several transit districts in the U.S. and Canada supply their operators with blocks to be placed at the base of the pedals to improve reach. B.C. Transit of Vancouver, British Columbia has addressed some of the above concerns (Krantz, 1994). B.C. Transit developed a set of standards which are applied to the workstations of every new bus purchased by B.C. Transit. The modifications have included replacing spring suspension seats with pneumatic ride seats, installing tilt and telescope columns, installing power assist steering, installing left side convex mirrors and relocating the farebox. The result of these modifications is a 78% reduction in the frequency of workstation related injuries and an 86% reduction in the amount of time off per injury which is an indication of the severity of the injury (Bovenzi et al., 1992). Similar design requirements have been adopted by Seattle Metro (Anon, 1993). The Society of Automotive Engineers presents design guidelines for vehicle workstations. The most common workstation design approach is based on the seating reference position (SgRP) and locating the controls in relation to this point. The Society of Automotive Engineers (S.A.E.) recommends this approach in the S.A.E. handbook (SAE, 1995). These standards can be utilized in a particular order to develop the workstation of a Class B vehicle as defined by S.A.E. J1100. Transit buses are typically considered to be Class B vehicles. Some of the S.A.E. terminology must be understood - 1.3
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before applying the practices, consequently Table 1.1 contains a list of selected definitions. Table Id: Selected S.A.E. Terminology Terminology Definition H-Point ~ the pivot center for the ~ peso and the thigh (at the hip) Design H-Point the H-Point on the two dimensional seating drafting template placed in any designated seating position Pedal Plane the plane that is parallel to the treadle pedal surface and represents the bottom of the mannequin shoe Seating Reference I a unique H-Point with t e following properties: l Point (SgRP) . located at the rearmost adjustment of the seat | . simulates position of ivot center of torso and thigh . used as the reference point employed to position the two | dimensional drafting tea Plate with ofthe 95th percentile leg Accelerator Heel I the lowest point at the i rtersection of the mannequin heel and Point (AMP) the depressed floor covering with the shoe on the undepressed accelerator pedal Ball of Foot (BOF) a point on a straight line tangent to the bottom of the mannequin's shoe in the side-view, 203 mm from the AHP Il516 'Accommodation Tool Reference' provides a good start to the development of the workstation. This procedure locates an accommodation reference line which is a function of the H-point height and which provides a reference from which workspace accommodation tools can be located. This practice also locates the accommodation heel reference point which Is the intersection of the pedal plane and the floor. Both reference tools can be determined for any of three operator populations. The standard - I.4 -
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anthropometry is defined in J833 'Human Physical Dimensions', and this data can be helpful in locating the required H-Point of different operators. Once the accommodation heel reference point has been determined, Jl517 'Driver Selected Seat Position' can be used to locate where the selected operator population will position the seat horizontally aft of the heel reference point. Once again, there are three different operator populations to choose from. J826 'Devices for Use in Defining and Measuring Vehicle Seating Accommodation' provides a procedure to create an H-point template. This template can be used to check torso positioning for any specified SgRP and back angle, front seat operator leg and foot position for any specified accelerator heel point location, front seat operator leg and foot position for any specified undepressed accelerator pedal location, and front seat operator leg and foot position for specified leg room and SgRP-front to heel distance. At this point the location of the operator's heel on the treadle pedal, H- Point on the seat and lower leg position are known. Next it is desirable to examine the accelerator shin-knee location. Using J1521 'Truck Driver Shin-Knee Position for Clutch and Accelerator', side view contours of the location of the operator's accelerator knee can be created for the target H-points. The stomach profile of transit bus operators is another constraint on the location of workstation tools. J1522 'Truck Driver Stomach Profile' provides a practice for locating the contour of the operator's stomach for one of the selected population mixes as a function of the H-point height. This contour line directly effects the location of the steering wheel and can in some cases effect the operator's visibility and reach. Once the positioning of the lower half of the body is defined, it is important to locate the operator eyes to establish the operators field of view. With the H-point range determined from J1517, the elliptical model of the eye locations (or eyellipse) can be developed using the procedure of J941 'Motor Vehicle Driver's Eye Locations'. This two or three dimensional region identifies the range of locations of operator's eyes based on one of the three operator populations. With the accommodation tool reference line from J1516, and - 1.5
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the eyellipses from J941, the head contour location profiles are determined from the target H-points using the procedure described in J1052 'Motor Vehicle Driver and Passenger Head Position'. This practice describes the location of the head for the operator while forward' side and rear viewing. I.2 Operator Task Analysis In recent work, Bucciaglia (1995) conducted a task analysis of the operators in order to define how the operators interact with the workstation. The tasks analysis was conducted by direct observation and video analysis of several operators in State College, Altoona, Johnstown, and Harrisburg in Pennsylvania. The tasks were broken down into groups and itemized as shown by Table 1.2. Table 1.2: Transit Bus Operating Task Analysis PRE-DRIVING TASKS . _ _ TASK NAME TASK DESCRIPTION enter bus I typically enter thr ugh the front door l store personal items adjust seat adjust steering wheel adjust mirrors apply safety belt store personal items such as coat and lunch in appropriate locations adjust the seat height, fore/aft location, seat back angle and head rest based on comfort and visibility adjust steering wheel telescope and tilt to accommodate reach and visibility adjustment of outside and interior mirrors for optimal viewing l application of the safety belt - 1.6
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Table 1.2: Transit Bus Operating Task Analysis (cons) start engine diagnostic check select proper mode of operation on the run selector knob and press the ignition button, typically located on the left once the bus is on, the operator will scan the indicator lights for any operating problems climate controls defrost mirrors and windshield change destination sign engage transmission release parking brake TASK NAME accelerate bus turn the bus communication climate controls defrost mirrors and windshield monitor stop request adjustment of temperature for operator workstation and coach apply mirror and windshield defrost when necessary change the external destination sign to correspond with current bus route by using keypad usually located on the left above the operators' head. while depressing the service brake, shift the bus into gear release the parking brake, usually located to the left of the operator ON-ROAD DRIVING TASKS ... TASK DESCRIPTION rotate the treadle pedal to accelerate the bus activate the floor mounted turn signal, inspect oncoming traffic through the windshield, side windows and door windows, decelerate the bus if necessary and perform a hand over hand steering maneuver I.) communicate with transit dispatch, and other bus operators 2.) public announcements inside and outside of the bus adjust climate controls for changing conditions adjust the defrost on the mirrors and windshield when appropriate monitor the indicator and bell tl= to get off the bus . . .7
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Table 1.2: Transit Bus Operating Task Analysis (cons) PICKING UP/DEPOSITING PASSENGERS TASK NAME activate four way flashers decelerate and approach stop stop the bus activate the kneeling mode open bus doors inspect passenger ingress _ check farebox update ride passes distribute transfer tickets TASK DESCRIPTION prior to decelerating the bus, activate the four way flashers to alert following traffic apply the service brake to decelerate the bus it~the stop will be long, operator may engage the parking brake once the bus has reached a complete stop, the operator activates the kneeling mode if the bus is equipped with it the operator opens the front door to let passengers fin am ~e rear door to let passengers off when necessary 1.) assist passengers that may need help 2.) if a handicapped passenger is entering the bus, the operator must egress the workstation, lower the wheel chair lift, secure the wheelchair, raise the lift, and move and secure the wheelchair on the bus depending on the mode! of farebox, the amount placed inside may have to be inspected before allowing it to drop into the collection container ride passes have to be updated for each use transfer tickets need to be issued to passengers that are transferring to another bus record passenger data close bus doors deactivate kneeling mode some transit districts require the operator to record the type of fare of all passengers in preparing to depart a stop, the first task is close all doors deactivate the kneeling mode - 1.8 -
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Table 1.2: Transit Bus Operating Task Analysis (cons) check passengers for seating status deactivate four- way flashers release parking brake accelerate bus insure that all passengers are seated) or behind the minimum safety lines near the doors and windshield apply the left turn signal, and then deactivate the four way flashers if the parking brake has been set, release it remove the service brake and apply pressure to the accelerator 1.3 Bus Operator Survey A survey was conducted to obtain input from bus operators (Bucciaglia, 1995~. A complete description of the survey including the form and raw data is presented in Appendix A. The purpose of the survey was to obtain recommendations from bus operators for the design and location of the workstation elements. The survey was distributed to four transit districts in Pennsylvania through the months of September and October of 1994. A total of 138 operators responded to the survey, and this input was used to develop the workstation that will be presented later. The average respondent was 1 75 cm in stature with a standard deviation of 6.6 cm. The smallest operator was 1 55 cm and the tallest operator was 196 cm. There were 122 male and 16 female respondents. Table 1.3 shows the operators' response relating to control usage. Steering wheel, brake and accelerator are essential and critical controls and therefore, were not included in the survey such that they would not overshadow the other controls. The top rankings that are shown are not statistically different from one another. Also, all operators were presented with the same survey and therefore, some ordering effect may be present. - i.9
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Table ~ .3: Top Ranked Controls and Displays # Frequency Ranked by Average 1 Turn Signals 2 Door Open 3 Hazard Lights s 4 ~i~ Speedometer Destination Sign Control 7 ~ Har d Brake 8 ~ - 9 10 11 12 13 14 15 Importance Ranked by Average Turn Signals Hazarc! Lights Air Pressure Door Open Defrost Speedometer Hand Brake Heater Stop Request Air Conditioner Heater Windshield Wiper Destination Sign Control Air Conditioner Ventilation - Mirror Adjustment Stop Request Horn The survey asked the operators through open-ended questions to comment on their present vehicle workstation. The comments were analyzed through a keyword count to snow the operators mayor concerns. . Many operators, particularly large operators, complained of hitting the farebox with the knee or other body parts when ingressing and egressing. Many large males also complained of hitting the steering wheel, and several operators commented that the seat did not travel far enough back to allow for proper egress. Power steering, plenty of leg room and a comfortable seat were all cited as positive features. Complicated seat adjustments, lack of outside mirror control and poor control layout were cited as elements of deficient workstation designs. - I.10
Representative terms from entire chapter: