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CHAPTER 4. CONCLUSIONS 4.! Cost-Benefit Analysis . Many factors need to be included to estimate the costs of the prototype workstation. The proposed workstation contains instrument panels that move. Therefore, increased maintenance will result due to the devices that provide the movement. Also, the wires and cable going into the instrument panels will require sheathing to protect from vandalism and large loops to prevent failure due to fatigue. Other cost issues are shown In Table 4.~. The instrument pane] supports will have to be strong for sufficient durability such that they can withstand the vibration levels found on a typical transit bus route. During the development of the workstation design guidelines, attention has been paid to these issues. Of course, each manufacturer will have their own particular method for implementation. The cost investment can be broken down into five parts: fabrication, assembly, installation, initial inventory, and tooling. Table 4. ~ shows the material costs and labor costs. Blank spaces indicate no increase in cost over the conventional. The material costs include initial inventory, while the labor costs include fabrication, assembly, and installation. The prototype did not require any special tooling. - 4.!
Table 4. I: Material and Labor Costs (unit: $) Group | Itern | Material cost | Labor cost Misc. Material plywood for instrument panels - 2 sheets 1/2x2x2 birch 10.34 2 inch corner braces -2 4.44 wood screws - 4 boxes 3.52 l 14 AWG wire, 170 ft 10.00 electrical tape- 1 roll 0.47 glue- 1 tube 1.88 duct tape - 1 roll 2.66 wire connectors - 3 boxes 7.83 spray paint - 2 cans 5.68 Al. sheet, 14 g, 24x36 25.44 Talking Bus System* installation (100 unit cost): $5400* RIP fabrication, box (2 furs) 70.00 (right instrument panel) fabrication lid (2 furs) 70.00 additional switch for door 0.75 18 wood screws see above 2 solenoids for door 35.02 ea.) 70.04 Rl P Mount Al stock, 1 x3x1 /4x6ft 34.54 4 coaster wheels 0.76 ea 3.04 11 nuts, bolts, washers, 3/8x4 grade 8 6.62 6 nuts, washers, bolts, 1/4x4 grade 8 2.60 Al angle, 2x2x1/4x2ft (3/16, aft) 23.94 1/4 inch knob 0.93 Al bar stock, 2x7x1 /2 (aft) 35.52 fabrication and assembly, including 30 holes drilled 16.90 install, drill 4 1/2 holes in floor 36.40 Brakes Pedal tubing, connectors, etc. installation Accelerator 227.00 Cl P wood accounted for above (center instrument panel) fabricate - 0.5 day 140.00 20 wood screws see above = 2.33 Pedestal fabrication and material 633.94 4grade8 1/2x4 4.05 6grade8 1/4x2 0.87 handle with knob 10.22 all thread - 1/2x16, 2 It 1.39 install, drill 4 1/2 holes in floor 106.40 steering column - ZF (100 unit cost) 1379.00 steering wheel 170.00 LIP wood and Al sheet already accounted for above (left instrument panel) 4 clamps 29.76 18 1/4x2 grade 8 bolts 2.62 fabrication time 1 day installation plus 16 holes 145.60 sunrise sign system 1 sign 600.00 seat upgrade 600.00 hands-free communication mic and power 175.00 set up time, rigging, layout, etc. 2 days 560.00 mirrors left and right 464.73 35.00 Sum $3917.21 $1814.24 Grand Total (Material and Labor) $5731.45* * Talking bus is an electronic system integration tool as well as stop enunciator and data collection device. If system integration is not included then the ODA is about $1400, for a total cost of $613 1. - 4.2
Cost-benefit analysis is a quantitative methodology used to justify the expenditure of funds in controlling a problem situation or, more simply, the dollars spent per negative utility reduction (Brown, 1976). Cost can be defined as the dollar outlay for the incorporation of a device, method, or procedure for a given period of exposure. In this particular study, it was the retrofitting of a standard bus with an ergonomic bus operator's workstation, i.e., the material and labor costs (perhaps, also, increased maintenance costs) for acquiring and installing the necessary components such as an ergonomic seat, a three- degree-of-freedom steering column, and so on. There is a negative utility or dollar cost associated with every injury. This could include direct costs such as medical expenses and Workers Compensation and indirect costs such as lost time, replacement operator training, etc. The benefit is defined as the reduction in the negative utility or decreases in injuries and medical costs. The effectiveness of the corrective measure is then evaluated by the ratio of benefit to cost with larger numbers indicating better utility or effectiveness. For the evaluation of the ergonomic prototype the actual costs incurred and expected benefits from similar efforts pursued at various transit systems were utilized. Thus, the costs of the materials, parts and components purchased for the prototype, plus labor costs (A $30.00/hr) are summarized in Table 4.1 and total $6131. This cost is very similar to the average cost of $6,901 incurred by BC Transit (Vancouver, BC) in their redesign of the operator's workstation. An important aspect is that BC Transit did not incur any increased maintenance costs from their improved workstation. The benefits are projected on injury rate data, direct medical and Workers Compensation costs and per cent decrease of injuries expected due to ergonomic redesigns. Injury data - CTTRANSIT (Connecticut Transit) accumulated a total of 32 injuries over a 6 month period for 515 employees. This amounts to a yearly injury rate per 100 workers of:
' ~= ~ 2.43 9 or an injury rate of 0. ~ 243 per worker. 515x 1,000 Direct costs - CTTRANSTT expended a total of $87,000 ($42,000 in direct medical costs and $45,000 in Workers Compensation costs) for these 32 injuries for an average cost of $2,718. Data from BC Transit indicated average direct costs of $5,962. However, these data were primarily back injuries (which tend to more expensive that other types of injuries), as BC Transit had frequent problems with the seats bottoming out. Both values will be utilized so as to give a range of expected benefit/cost ratios. Injury reduction - The projected decrease in injuries due to the redesigned ergonomic operator's workstation prototype is based on data from a similar venture at the BC Transit system. They were experiencing a considerable number of back injuries due to seats bottoming out and implemented a Recaro seat with additional workstation modifications. In the year following the implementation of the modifications they found a 78°/O decrease in the injury rate (from 1.92 to .43 per 1,000,000 km) and an 88% decrease in the severity rate (from 29.42 to 2.72 days lot per 1,000,000 km). These values are very similar to those experienced by one of the investigators (A. FreivaIds) in industry. Over a three year period after implementation of an ergonomic program (workstation redesign, tool changes, training) in an automobile carpet manufacturing facility, the number of injuries decreased by 74%. Therefore, a projected injury reduction rate of 80% for this prototype is not unusual. The benefit/cost ratio is then defined as the dollar cost reductions per workstation implemented per cost of a workstation, or: t°rs~shifts~b )< {injury_ rate_ per_ wor ker } x {average_ injury_ cos ~ } x {°/0_ reduction } workstation cos - 4.4
Typically one bus would be used for approximately 14 shifts a week. With each operator working 5 shifts a week, we would expect 14/5=2.8 operators per buss The injury rate per worker from CTTRANSIT is 0.1243. Average injury cost ranges from $2,718 to $5,962 and an 80% injury reduction is expected. This results in a benefit/cost ratio ranging from: 2.8 x 0.1243 x $2,71 ~ x 0.~/$6, ~ 3 ~ = 0.123 2.8 x 0.1243 x $5,962 x 0.8/$6,131 = 0.27 These are calculated on a yearly basis, therefore taking the inverse would result in the number of years it would take to pay off the cost of a workstation with decreases! medical costs. The payoff time would range from I/.27=3.69 to I/.123=~.] years. These values are probably low and payoff time could be expected to be shorter because of several variables that are most likely true but difficult to account for in the direct calculations. Only direct costs are utilized. There are many indirect costs such as lost time, need for replacement operators, training costs for replacement operators, etc. that impact a transit authority. Also. medical and hospitalization costs have been skyrocketing over the past few years and will likely to continue to do so in the future. Therefore, the above costs may be considerably on the low side and payoff time may be considerably faster. - 4.5
4.2 Final Design Specifications and Guidelines The workstation should contain several features that are essential to accommodate the population extremes. Figure 4. ~ -4.4 show photos of the prototype workstation. Also, the workstation concept for the guidelines can be found in Chapter 2.~. The necessary components are: a 457 mm (! ~ inch) steering wheel hanging pedals tilt-telescoping steering column (minimum requirement), (tilt-telescoping-tilt ideal) · low profile farebox · pin joint suspension operator seat · seat with air actuated lumbar and back side bolster support features preferred turn signal platform located on the floor angled at 30 degrees housing the turn signals, and high beam switch · adjustable (height and fore-aft adjust) instrument panels that are divided into left, center and right. Operator Digital Assistant (ODA) to act as the central interface to the bus electronics system Remotely activated mirrors Annunciator system which allows push button activation of pre-recorded announcement messages (similar to the Talking Bus system) is preferred (A "hands free" communication system would be ideal). - 4.6
- - - Figure 4. i: Left and Right Instrument Panels _ ~ Am. ,,,~6,-~ ~`:- ~ __ ~ :: Hi ... ., ., v. ~ .~, ~ OO ] O:H ~.~ _ A_ r- it: ~ If' Hi" 'A-__ ~c;< ~.:~ . . Figure 4.2: Center Instrument Panel - 4.7
~ ~ _ Hi. ~ <' ~ ~ { t: ~:' ~::: ~ .' : ~ - I: ail: ::: ~' ~ ~ ~' :: Hi-: : :: . ~ ,-., ? ~4 _ _ Figure 4.3: Hanging Pedals Figure 4.4: Prototype Workstation - 4.8 r.~. :-, .._
The following figures and tables detail the necessary locations and adjustment ranges for the proposed workstation design. Figure 4.5 - 4.7 below are drawings of the The reference points are listed in terms of 5th percentile female, 50th percentile, and 95th percentile male, and are defined in Table 4.3. Also, Table locations listed in Table 4.2. 4.4 details all of the design specifications necessary for the workstation. .v Table 4.2: Guidelines - Component Locations (units: cm) Reference SAE 5% Female SAE 50% SAE 95% I\ dale Point x I y I z x l Y T z x I Y BURP9.3 1 0.0 1 29.6 0~0 1 00 T 36.7 -9.3 T °~° SWRP 48.8 0.0 63.2 44.3 0.0 66.3 39.8 0.0 1LIPRP 43.1 33.0 47.6 38.1 33.0 49.6 33.2 33.0 RIPRP 51.9 -39.0 65.0 45.2 -37.0 67.2 38.6 -39.0 BPPRP ~ 86.6 8.9 11.6 86.6 8.9 ~ 1.6 86.6 8.9 APPRP 86.4 -21.8 9.0 86.4 -21.8 9.0 86.4 -21.8 z 43.9 69.5 . 51.6 69.5 .6 9.0 - 4.9
Table 4.3: Reference Point Definitions Ref. Point Definition APPRP Accelerator Pedal Plate Reference Point. Located on the center of the top surface of the accelerator pedal plate. if the pedal plate pivots about the pedal arm, then the reference point is to be located at the pivot location projected normal onto the pedal plate surface. BPPRP Brake Pedal Plate Reference Point. Located on the center of the top surface of the brake pedal plate. If the pedal plate pivots about the pedal arm, then the reference point is to be located at the pivot location projected normal onto the pedal plate surface. LIPRP Left instrument Pane! Reference Point. Located in the center of the top surface of the left instrument panel. RIPRP Right Instrument Panel Reference Point. Located in the center of the top surface of the right instrument panel. SRP Seating Reference Point. The point on the sagittal plane located by two intersecting planes - the compressed seat pan and seat back. If SgRP | (Seating Rei erence Point, which is the H-point (hip pivot point) of the 95th percentile person of the US population as defined by SAE J1 100) is known from seat manufacturer data, can use the following equations (SAE J1 100, SAE J826): horizontal distance of SgRP from SRP = HL12 - HL1 1 x cos(SB1 1) vertical distance of SgRP from SRP = HL1 1 + HL12 x sin(SP9) where: SB 11 is the seat back neutral vertical angle SP9 is the seat pan neutral horizontal angle HE1 ~ is the vertical length from hip pivot to SRP (9.8 cm) HL12 is the horizontal length from hip pivot to SRP (13.4 cm) SWRP Steering Wheel Reference Point. Located in the center of the plane of the steering wheel WO Workstation Origin. Located on the workstation platform directly underneath the NSRP. - 4.10
Table 4.4: Complete Guideline Specifications for an Ergonomic Bus Operator's Workstation Design Variables Code Design Value seat horizontal distance of NDEP from NSRP SH9 5.9 cm vertical distance of NDEP from NSRP SH10 75.8 cm seat back neutral vertical angle SB11 10 deg. seat back angle adjustment range SB12 10 deg. seat pan neutral horizontal angle SP9 5 deg. seat pan angle adjustment range SP10 0 deg. seat fore/aft adjustment range SP1 1/ 1 8.5 cm for total of fore- and SP12 aft- adjustments Went range SP13/ 14.3 cm for total of upward SP14 and downward adjustments vertical distance of NSRP from WO SP15 36.7 cm steering wheel diameter TW1 45.7 cm wheel wheel plane neutral horizontal angle 1W5 40 deg. wheel telescope adjustment range iW7 11.0 cm wheel plane horizontal angle adjustment range 1W8 20 deg. horizontal distance of NSWRP from NSRP TW10 44.3 cm vertical distance of ~Y TW11 29.6 cm Brake ~ _ PB1 8.0 cm Pedal brake pedal plate width PB2 10.0 cm brake pedal plate shape PB4 curved brake pedal plate lateral angle PB5 0 deg. brake pedal plate horizontal angle PB6 40 deg. brake pedal plate pivot angle range PB7 0 deg. lateral distance of BPRP from NSRP PB8 8.9 cm horizontal distance of BPRP from NSRP PB9 86.6 cm vertical distance of BPRP from WO PB10 1 1.6 cm brake pedal actuation angle PB20 30 deg. brake pedal actuation force PB21 66.8 ~ 155.8 N brake pedal recovery force PB22 Accelerator accelerator pedal plate length PA1 Pedal accelerator pedal plate width PA2 5.6 cm accelerator pedal plate shape PA4 flat accelerator pedal plate lateral angle PA5 12 deg. accelerator pedal plate horizontal angle PA6 30 deg. accelerator pedal plate pivot angle range PA7 10 deg. lateral distance of APRP from NSRP PA8 21.8 cm horizontal distance of APRP from NSRP PA9 86.4 cm vertical distance of APRP from WO PA10 9.0 cm accelerator pedal actuation angle PA20 20 deg. accelerator pedal actuation force PA21 31.2 ~ 40 N accelerator pedal recove~ force PA22 .~ i Left left instrument panel horizontal angle IL5 5 deg. Instrument left instrument panel horizontal adjustment range IL6 9.9 cm Panel left instrument panel vertical adjustment range IL7 4.0 cm lateral distance of NLIRP from NSRP IL8 33.0 cm horizontal distance of NLIRP from NSRP IL9 38.1 cm vertical distance of NLIRP from NSRP IL10 12.9 cm Right right instrument panel horizontal angle IR5 30 deg. Instrument ~ _ _ IR6 13.3 cm Panel right instrument panel vertical adjustment range IR7 4.5 cm lateral distance of NRIRP from NSRP IR8 37.0 cm horizontal distance of NRIRP from NSRP IR9 45.2 cm vertical distance of NRIRP from NSRP IR10 30.5 cm - 4. ~ ~
1 PA ~ 1 | L1PRP_95 ED, ~ ~ _ i ~ ~1 lS~P_51 y |L~_~ I /3 \ ~ N! i ~ . t 1 RIPRP-95 AX Figure 4.5: ~3 . h53 ~1 1 or - _50 1 1 PIPRP-S I Specifications, Plan View - 4.1 2 A;;
l ; ~ srcta Crew HIP wad ~ =i ~ | 1~-~1 ~1 /~ ~ I Iffy 1'1 Elm ~ X ~p-5 1 ~:~W = Figure 4.6: Specifications, Side View CLIP and RIP not Shown) - 4.13
1 Sit ~ 'MU ~ - ~ ~ 1 I ~PRP_~; I | R"P_50 1 , | L^P_SU if L [I fl 1 ~ X cow Sdru Lit B~ ~ |L~_~ | --L]PRP-5 I :~ Figure 4.7: Specifications, Side View (Steering Wheel Not Shown) - 4.14
4.3 Sample Bid Specifications The workstation's components will be adjustable to accommodate operators who range in stature from the 5th percentile female to the 95th percentile male per SAE J833. The adjustable components include the seat, steering wheel, left instrument panel, and the right instrument panel. The adjustment ranges are to be measured relative to each component's reference point as defined in Table 4.3. The origin of the workstation, that is the datum, is denoted as the workstation origin and defined to be the seat reference point (SRP) for the 50th percentile person (NSRP) projected onto the bus operator's platform. Relative to the workstation origin, the SRP will be adjustable + 9.3 cm in the horizontal direction and from 29.6 cm to 43.9 cm from the operator's platform in the vertical direction. The SRP for the 50th percentile person will be located a vertical distance of 36.7 cm from the operator's platform. No lateral distance exist between the SRP and the workstation origin. The seat suspension shall be a pinpointed linkage type. Features such as air actuated lumbar and back side support are preferred. The steering wheel location is defined by the Steering Wheel Reference Point (SWRP). Relative to the workstation origin, the SWRP is to range from a location of 48.8 cm in the horizontal and 63.2 cm in the vertical to a point located at 39.8 cm in the horizontal and 69.5 cm in the vertical. The SWRP for the 50th percentile person is located midway of the extremes. No lateral distance will exist between the SWRP and the workstation origin. The steering wheel diameter will be 457 mm. The left instrument panel is to contain the secondary controls or controls that are used during the predriving tasks. These controls are the parking brake, the exterior mirror remote adjustment knobs, the exterior mirror defrost control, the internal and external public announcement systems, the radio controls' the run selector knob' the transmission and the ignition switch. The announcement system should preferably be one that allows - 4.15
push button activation of pre-recorded announcement stops, or is a "hands-free" microphone system. The dimensions of the ieiPt instrument pane! are determined by the space required for the controls. The LeiSt Instrument Pane} Reference Point (LTPRP) is defined by Table 4.3. Relative to the workstation origin, the LTPRP is to range from a location of 43. ~ cm in the horizontal and 47.6 cm in the vertical to a point located at 33.2 cm in the horizontal to the 51.6 cm in the vertical. The LIPRP for the 50th percentile person is located midway of the extremes. The left instrument pane] is to be inclined at an angle of 5 degrees. The LIPRP is located 33.0 cm laterally from the workstation . ~ orlgln. The purpose of the right instrument pane! is to locate primary controls for driving and passenger pickup and depositing in an accessible and easy manner for all operators. The dimensions of the right instrument pane] are based on the controls that it will contain. The right instrument pane] will contain a keypad with a small display called an operator digital assistant. The functions that can be accomplished through the digital assistant include: present the bus route schedule, control the farebox, automatic counting and categorization of the fares if used in conjunction with a card reading farebox or manually inventorying of the passengers when using a traditional farebox, print transfer tickets, monitor the gas mileage, change the destination sign, and in the future, possibly link with inertial navigation system for real time location of buses, and planning of proper routing to avoid delays. The data collected by this digital assistant can be easily downloaded at the end of the work day to a "home base" computer for analysis. The Right Instrument Pane] Reference Point (RIPRP) is defined by Table 4.3. Relative to the workstation origin, the RIPRP is to range from a location of 51.9 cm in the horizontal and 65 cm in the vertical to a point located at 38.6 cm in the horizontal to the 69.5 cm in the vertical. The RIPRP for the 50th percentile person is located midway of the extremes. The right instrument panel is to be inclined at an angle of 30 degrees. The RIPRP is located 37 cm laterally from the workstation origin. - 4.16
The center instrument panel provides the operator with the status of the workings of the bus. Any information that does not require continuous monitoring by a particular gauge (for instance, speed) is replaced with an indicator light. To accommodate tell-tare indicators without giving up 0.95 cm by 1.27 cm of space for each of those indicators, center instrument pane] will have a small screen which can provide any of these tell-tales with the colors and required alarms. Since time is a large concern for operators and a significant part of their duties, a clock is also provided. The two most regularly monitored items on the center instrument pane] are the speedometer and air pressure gauge. For this reason, traditional large dial readouts are provided. The intention of mounting the instrument pane] directly on the steering column is to facilitate downward visibility. Pedals will be hanging type of pedals. Relative to the workstation origin, the Brake Pedal Reference Point (BPPRP) will be located laterally to the right by 8.9 cm, forward by 86.6 cm and ~ I.6 cm above the operator's platform. Relative to the workstation origin, the Accelerator Pedal Reference Point (APPRP) will be located laterally to the right by 21.8 cm, forward by 86.4 cm and 9 cm above the operator's platform. A turn signal platform will be mounted on the operator's platform to accommodate the left foot actuated turn signals and high beam as well as stop announcement switch. The platform will be angled at 30 degrees. The farebox will be electronically connected to the Operator Digital Assistant (ODA). The farebox shall be located in a position such that operator's view obstruction is minimized. Therefore, a location shall be provided in the bus such that the farebox can be placed with minimum view obstruction. The top of farebox shall not exceed 91.4 cm (36 inches) from the floor. - 4.17
4.4 Summary This report presents the synthesis and verification of a bus operator's workstation design that will accommodate a population from the 5th percentile female to the 95th percentile male providing sufficient visibility, natural reach, and comfortable posture for the population. The approach taken by this work was first to develop an appreciation for the operators' tasks and conventional workstations through a survey and direct observations. The synthesis procedure considered use of hanging pedals which is believed to provide better comfort for the smaller operators. It was also determined through the synthesis that with a common accelerator pedal plane, a steering wheel with three degrees of adjustment (tilt-telescope-tilt) is required to fit the population extremes. Also, the workstation was determined to consist of a left instrument panel to house less used controls, a right instrument panel to contain frequently used controls, and a center instrument panel that contains gages, indicator lights, etc. A systematic design approach was used in order to determine the necessary specifications for the workstation. This approach consisted of four parts: (1) identification of design scope, (2) relationship analysis of design and anthropometric variables, (3) development of functional design relationship, and (4) synthesis of design guidelines. The design scope of a bus operator workstation was identified by choosing a design datum point, setting design criteria focused on the workstation design, defining static and dynamic bus driving postures, and establishing hierarchies of design and anthropometric variables. Next, the relevant design and anthropometric variables were determined, and relationships between them were established. Third, functional design relationships were created through geometric relationships. Finally, guidelines were developed based on the functional relationships. A preliminary layout of the transit bus operator workstation was first developed using various CAD tools (e.g. SilverScreen, Mannequin, etc.) along with scale model mannequins oriented in the preferred driving posture. This resulted in approximate design - 4.IS
values and required adjustment ranges needed to nominally satisfy the bus operator population ranging from a 5th percentile female to a 95th percentile male. The resulting adjustment ranges are found in column #! of Table 4.5. Table 4.5: Workstation Components Adjustment Ranges Component Adjustment Seat fore-aft (cm) Seat vertical (cm) Preliminary CAD Approach . 2 Mock-up Evaluation 21.6 29.4 1 0.0 1 1.0 Seatback angle (de") Steering wheel base tilt (de") Steering wheel telescope (cm) Left instrument panel fore-aft (cm) Left instrument panel vertical (cm) Right instrument panel fore-aft (cm) Right instrument panel vertical (cm) 25.0 28.0 20.4 18.4 20.3 19.0 18.7 21.1 22.9 12.7 14.7 16.3 JACK Simulation 18.5 6.7 10 20 11.0 9.9 4.0 13.3 4.5 4 Final Design Values (Based on NSRP Approach) 1 0 C 1 O. 14.3 10.0 1.0 9.9 . 4.0 _ 13.3 4.5 A laboratory mock-up based on the preliminary CAD design values was constructed and evaluated by a jury of over iOO people. The population was grouped according to their stature and gender. By this grouping, the average height of the small female group was close (within a standard deviation) to that for the 5th percentile female. Similarly, the large male group average height was also close (within a standard deviation) of the 95th percentile male. Therefore the population extremes were included in the evaluation and to some extent, over represented when compared to the general population. The resulting user preferences were tabulated in frequency distributions from which the mean values and 5th percentile tails (i.e. zOs and Z95 ) were calculated. The corresponding parameter values then provided the two extreme values determining the required adjustment range. These values are tabulated in column #2 of Table 4.5 and for - 4.~9
most components are actually slightly smaller than were initially proposed under the preliminary CAD design. Only the seat fore-aft range was larger than expected due to several outliers, i.e. smaller females choosing extremely close-up seat positions. Overall, three major positive comments can be made from the results of the evaluation: (1) the workstation is able to accommodate a population ranging from the 5th percentile female to the 95th percentile male; (2) with this implementation of the workstation, the evaluation provides a general idea for the amount of adjustment required to accommodate the above population range; and (3) the jury evaluations are positive indications that on the average the jury was satisfied with the preliminary design in terms of visibility, reach, comfort and adjustability. The workstation was simulated in the JACKS program to objectively evaluate visibility, reach and comfort. The simulation considered the 5th percentile female, the 50th percentile and the 95th percentile male. Based on this simulation, adjustment ranges of the components were refined. 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. The resulting adjustment ranges (with a precision of + 1 cm) shown in column #3 of Table 4.5 corresponded closely to previously selected design variables, again validating the previous design strategies. Also, animation of the bus operating tasks facilitated the evaluation of the workstation in dynamic situations. Simultaneously with these phases, a scientific approach using the neutral seating reference point (NSRP approach) was used to also determine the key design variables. This procedure yielded the final design values (the adjustment ranges of which are shown in column #4 of Table 4.5) utilized in the prototype construction and evaluation. These values were again, in most cases, very close to the values found in the previous stages (columns #1, #2 and #3). Also, the preliminary CAD approach was a discrete simulation - 4.20
using two mannequins, while the mock-up included postural differences as well as the variation of subject limb lengths. JACKS again was a discrete simulation with finite resolution. The NSRP approach was much more precise and accurate. In a graphical technique the accuracy may be + 5° - 10°, but in the NSRP approach specific angles were considered. The prototype was constructed retrofitting a 1973 GMC bus. Any deviations in the adjustment ranges, such as for some of the instrument panels, were due to limitations of the mechanical structure of the existing bus. The reduced steering wheel telescoping range was due to the current technological limitations of commercially available telescopic columns. The purpose of the prototype was to evaluate the performance of the workstation under actual operating conditions on a closed course. The closed course was chosen due to safety considerations, but was representative of a typical transit bus operating cycle (4 stops/mile and average speed of about fifteen miles per hour). The prototype, since it was constructed on an existing platform, required compromise in some actual features. For example, the steering gear box location was fixed and could not be moved. This caused some of the workstation components to be located closer than desired, however it also showed that if it can be built in that existing platform then the workstation can be constructed on most platforms. The seat for the workstation was a commercial unit selected on vibration isolation properties. The costs versus benefit of the workstation as built in the prototype was favorable. Twenty-four transit bus operators participated in the evaluation of the standard bus and prototype bus workstations with six aspects: visibility, postural comfort, reach, adjustability, ease of ingress/egress, and ride quality. Three stature groups were defined for analyses: small (the 5tt percentile female through the 15th percentile female), medium (the 15th percentile female through the 85th percentile male), and large (above the 85th percentile male). The jury consisted of 5 small females, 1 3 medium sized individuals, and 6 large males. According to the overall subjective judgment results, all 24 operators - 4.21
responded the prototype improved the standarc! bus workstation for ah the five criteria: visibility, comfort, reach, adjustability, and ease of ingress/egress. The reference point (RP) locations of each prototype workstation component adjusted by the bus operators indicated that the seat was located at a lower position and the steering wheel and the right instrument panel of the prototype were located at a farther and higher location from the seat than those of the design specifications. These discrepancies from the design values caused a driving posture of larger shoulder and elbow flexion angles, however acceptable, than the assumed standard driving postures. The stretched-out posture of shoulder-arm could be associated with their driving experience with conventional bus workstations. The driving postures were measured in static and dynamic driving conditions. The joint angles measured were converted into postural comfort scores by using the postural comfort evaluation scheme, which quantifies the magnitude of joint angle deviation from the standard driving posture within corresponding comfort range of motion (ROM). The integrated comfort scores combining the scores of associated joint angles showed satisfactory postural comfort in the prototype. Also it was identified that the prototype improved the shoulder and elbow flexion angles by providing a steering column telescope-tilt mechanism and an 18 inch diameter steering wheel for the operators. Also the hanging pedals contributed to the efficiency of pedal actuation allowing more comfortable ankle angles and movements of the right heel point on the floor. Body part discomfort was evaluated during the course of prototype testing Comfort decreased for upper and lower back, left and right hips/thighs, right knee, and right ankle/foot. The first four are primarily influenced by the seat design, and the right knee and ankle/foot do depend primarily on the pedal design. Small operators experienced a significant increase in discomfort during 10 laps of oval track driving but then only a slight discomfort change for the rest ofthe driving. A detail analysis indicated that greatest changes were experienced in the low back, right and left hips/thighs. These - 4.22
. are all most affected by the seat design and less by workstation design. This implies more Improvements on the seat design are required from the comfort viewpoint. The Root-mean-square (RMS) grip forces of all the operators during prototype testing were less than ~ 0% of each individual's maximum grip force, which indicates that no evidence for muscle fatigue in grip exertions during prototype steering could be found. In terms of the relative proportion of maximum grip force utilized during steering the prototype workstation, there was no significant gender, stature, or transit experience effect. This is a good result from the standpoint of developing cumulative trauma disorders (CTDs) from the fact that new and inexperienced operators in many industries are likely to exert higher than necessary force levels and, thus, become more susceptible to CTDs. The seat vibration test while driving showed that the transmissibilities for both the prototype testing and the previous seat testing were comparable, with a peak around 2 Hz and attenuation at the higher frequencies. Specifically, the seat performed better at attenuating the vibration at 4.25 Hz (lower back resonance) in the prototype testing, which indicates the validity of the ride quality simulator testing in the smaller bus. - 4.23
4.5 Conclusion From the above results the key conclusions are: 1) The bus operator workstation can feasibly be redesigned using ergonomic principles so as to accommodate individuals ranging from the 5th percentile female to the 95th percentile male; 2) The specific prototype designed and constructed by this project was judged superior to the existing workstation by a representative jury of actual bus operators; 3) It is estimated that the additional cost to incorporate the final design guidelines of this research in new buses will be more than offset by savings in terms of reduced operator injuries and worker's compensation claims. The final result of the above work is a guideline for the design of a bus operator workstation that can accommodate the population extremes. This report develops the guideline through rigorous analysis, synthesis and testing. The guideline is presented in two formats; a simple to use version that is essentially a set of engineering drawings which can be incorporated directly into a bus specification and a set of functional relationships which can be used a guide to design workstations with specific features or requirements. Future enhancements can be designed into the workstation as costs permit. Some of these enhancements may include, a memory such that operators can type in a number into the ODA and the components automatically move to preset locations, active vibration control in the seat to accommodate the wide variety of road roughness as well as population, a more adjustable seat pan such that all population ranges are accommodated, and a steering wheel tilt. The prototype constructed in this work did not include a steering wheel tilt because a suitable commercial product could not be located. It was elected for safety reasons not to use an "in-house" construction. In other works that included a steering wheel tilt, the tilt was a physical distance from the hub of the wheel. However, it is felt that the steering wheel tilt would provide improved visibility as well as comfort. - 4.24
Future research is required to develop a further understanding of issues involved and to develop cost effective solutions. Each aspect of this project could be expanded to become research projects unto themselves. However, the significant recommendations for future research include the following: 1) The development of an anthropometric data set focused towards the industry. This would allow refinement of the above guidelines. 2) A critical in-depth study of seating comfort including vibrations and long term static comfort. This work should also identify the influence of the operator manipulating the controls on the vibration levels. in addition, the vibration levels found in a typical transit bus should be characterized. 3) This project dealt with the operator's immediate work areas. Future studies should take a comprehensive approach to the entire bus and its layout. For example, can the farebox be reconfigured to provide more visibility and room ? Is the door in the optimal location ? Is the vehicle dynamic properties such as its pitch natural frequency optimal ? 4) Education programs should be developed to educate operators about ergonomics, safe postures, and proper use of equipment like seats that have a variety of adjustments. - 4.25
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