Bus Operator Workstation Design for Improving Occupational Health and Safety (2016)

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56 C H A P T E R 5 Human modeling software (RAMSIS) was applied for the demonstration of opera- tor anthropometry, workstation fit, and workstation component accessibility. A cadre of manikins was developed to serve as sample models of transit bus operators. The sample provided insight into how bus operators of various minimum and maximum body-size vari- ables (e.g., stature, sitting height, abdomen depth, arm reach, leg reach/clearance) would be accommodated inside a workstation design and adjustment range (e.g., seat, steering wheel, pedals). Like Chapter 4, this chapter supplies information that includes a detailed explanation of the validation of the bus operator workstation dimensions developed for the updated guidelines and supporting tools created in TCRP Project C-22. This detail may be of most interest to individuals with experience in ergonomics and vehicle packaging among procurement teams, vehicle manufacturers, and component suppliers. Development of Multivariate Manikin Cadre from NIOSH Survey Models During the research phase of TCRP Project C-22, recent anthropometric measurements spe- cific to the transit bus operator population were not publicly available. Therefore, a recent mea- surement database—the 2010 NIOSH U.S. Long-Haul Truck Driver Survey, which could provide a human dimensional sample model (Guan et al. 2012) of similar transportation operators—was applied as the basis for the manikin development. The application of long-haul truck driver anthropometry may raise some concerns about how closely the measurements of long-haul truck drivers match those of transit bus operators. It should be noted that Guan et al. (2012) found that the NIOSH sample of commercial truck drivers could be categorized as heavier than the general population. The male truck drivers were found to be, on average, 13.5 kg (29.8 lb.) heavier than males in the general U.S. population, and the female truck drivers were found to be, on average, 15.4 kg (34.0 lb.) heavier than females in the general U.S. population. However, this population estimate can be compared to other recent measures of bus operators in the transit industry. French et al. (2007) found that the prevalence of obesity, defined in terms of body mass index (BMI) as BMI ≥ 30 kg/m2, was 56% among transit workers, while another study, by Escoto et al. (2010) found that transit workers had an average BMI of 32.3 kg/m2. Given this information, the research team concluded that use of the NIOSH data would be reasonable in relation to providing sufficient accommodation for bus operators. Appendix C of this report details the numerous body dimensions that were developed for this TCRP research using information from the NIOSH survey. Those dimensions were replicated Human Modeling Validation of Bus Operator Workstation Design Guidelines

Human Modeling Validation of Bus Operator Workstation Design Guidelines 57 to compose a range of multivariate model operators representing a range of transit bus opera- tors. These multivariate anthropometric dimensions are compared to the univariate dimensions applied in TCRP Project F-4 in Appendix C, Table C-2. The NIOSH survey provides dimensions for 30 models. To simplify the development process for TCRP Project C-22, however, a primary collection of six models was used for packaging and the development of reach and clearance envelopes. Images of the cadre of manikin operators are given in Figure 16 (female) and Figure 17 (male). These manikins are centered in 3-D space at their lower torso, which highlights the difference between their sitting heights, leg lengths, and corpulence (abdominal depth). In addition to the NIOSH survey-based manikins, a generic small female manikin was added to the human modeling validation (see Figure 18). This manikin was based upon the modeling parameters provided by the human modeling software body builder NHANES III anthropo- metric survey toolkit (see Figure C-1 in Appendix C). This manikin was applied throughout the modeling validations to confirm that the suggested seat/steering-wheel/pedal configuration was suitable for someone with a small stature and low BMI. This manikin was also applied to all visibility, reach, and clearance envelope checks. Lastly Appendix C, Table C-1, provides qualitative descriptions in the column titles of the sizes of the models that were chosen to be part of the primary cadre representing the range of sizes in the operator population. These percentiles demonstrate the general category that the manikin represents. For example, “Female O,” may be generically referred to as an Figure 16. Primary operator cadre, female manikins, left-side view. Figure 17. Primary operator cadre, male manikins, left-side view.

58 Bus Operator Workstation Design for Improving Occupational Health and Safety average female with a 47th percentile stature and 69th percentile waist circumference. It may seem inaccurate to represent an “average female” with a waist percentile that is above aver- age, but that is the nature of true size variance in any human population. The strength of these representative manikin models, as built through a process called principal components analysis (PCA), is that real operators in the world (whose body components rarely match 50th percentile stature, weight, and arm length) can be evaluated through simulation analysis (Guan et al. 2012). Manikin Deviations from Models and Modifications Almost all the operator manikin dimensions used in TCRP Project C-22 meet the same cri- teria for allowable error used in the NIOSH survey. The allowable error in the NIOSH survey was reported in the survey’s Appendix B, Mean Absolute Differences of Inter-Observer Errors in Team Training. The TCRP Project C-22 research team used these values of anthropometric mea- surement precision to define the tolerance within which each manikin’s construction dimension was allowed to vary from the NIOSH model. Exact model values were attempted across all manikin dimensions. Deviations occurred with instances of some dimensions that were dependent. “Acromial Height, Sitting” (the shoulder height of a seated individual above a flat surface) was one dimension in which some manikins’ dimension could not be forced to meet the model allowable error tolerance without causing multiple higher-level dimensions to exceed their tolerances. This occurred for one of the female manikins (Female U) and two of the male manikins (Male U and Male V) despite repeated efforts to flex other primary and secondary dimensions. It is worth noting that the dimension designed in the human modeling software to account for upper-arm length differs from the body landmarks on participating drivers of the NIOSH sur- vey. Guidance was provided by the software anthropometric staff, who suggested that a correction factor of 90% should be applied to the NIOSH “Shoulder-Elbow Length” model measurements. Detailed specifications and steps applied to the construction of the manikin cadre are provided in Appendix C. Figure 18. NHANES III Small Female applied to human modeling validation.

Human Modeling Validation of Bus Operator Workstation Design Guidelines 59 Verification of SAE Packaging RPs The bus operator packaging model that resulted from the application of the current production vehicle data combined with the SAE Class B operator workstation RPs was verified by posture cal- culation with the male and female operator cadre. The initial posture calculation for each manikin was run with the steering wheel set at the middle of the recommended range (i.e., the SWP posi- tion), along with other constraints common to transit bus operator workstation components. The posture for each manikin was rerun at least once while the steering wheel was adjusted to minimize arm reach and maximize hand clearance to each manikin’s stomach and thighs. Ultimately, these packaging simulations were the test of the location and adjustment range of the seat and steering wheel to evaluate whether 95% of the operator population could be expected to keep their feet on the floor or pedals while meeting the APTA visibility line-of-sight target and maintaining a comfortable position in the seat (APTA 2013). The “Shin/Knee and Stomach Contours” were also imported from the Engineering CAD Model to compare the contour locations and sizes against the manikin packaging. Reach curves were also developed for each manikin at its final posture location. The reach curve representing the mini- mum bus operator distance was selected from among the cadre to provide position guidance in the CAD model for primary controls used while driving. Initial Posture Calculation and Constraints The initial posture calculation involved four external constraints and two internal constraints on each manikin. The external constraints included the following manikin-to-component restrictions: • Right shoe to the accelerator pedal plane and left shoe to the foot-switch block, • Manikin h-point to the recommended seat h-point range parallelogram, • Left and right hands to the steering wheel outer rim at 9 o’clock and 3 o’clock positions, and • Eyes fixated on the APTA visibility target. The constraints internal to each manikin included a soft hand grasp for left and right hands and pelvis rotation locked at 0°. Figure 19 illustrates the manikin and vehicle constraint components. Steering Wheel Position Optimization and Posture Recalculation After each manikin was constrained at the middle of the tilt/telescope range of the steering wheel adjustments, the steering wheel was repositioned to consider other postures and clearances for each manikin (see Figure 20). Each recalculation for each manikin followed this sequence: 1. Calculate posture with manikin according to original constraints. 2. Adjust steering wheel tilt and telescope within range to minimize reach for manikin. 3. Check stomach and thigh clearances for minimum hand clearance: 50 mm. 4. Repeat posture calculation. 5. Check the manikin h-point against the recommended seat travel constraint. 6. Check stomach and thigh clearance. 7. If clearance is below limit, adjust steering wheel and repeat sequence from Step 2. Evaluation of Packaging for Bus Operator Cadre Once the manikin packaging was completed, a qualitative visual verification was run with each manikin. The research team checked that (1) the manikin’s feet had maintained contact with

60 Bus Operator Workstation Design for Improving Occupational Health and Safety Figure 19. Posture calculation and constraints of manikin Male U to the bus operator workstation components. Figure 20. Optimizing steering wheel position for reach and stomach/thigh clearance on manikin Male V.

Human Modeling Validation of Bus Operator Workstation Design Guidelines 61 the pedals and floor, (2) the h-point was kept within the recommended seat fore-aft and vertical travel, and (3) no component obstructions existed between the visual gaze of the manikin and the APTA visibility target in front of the bus. The results for each manikin are available in the right-side views as listed from Figure 21 to Figure 26). Note that the seat is located at the rear extent of the recommended horizontal range in these images to make the manikin positions easier to view and compare. These results are sig- nificant, suggesting that a large range of transportation operators can comfortably find a posture in the suggested Bus Operator Workstation Engineering CAD Model. Furthermore, the resultant posture did not create an unfavorable result for operators’ forward visibility as defined by the APTA visibility requirement. Demonstration of SAE Clearance Contours The stomach and shin/knee contours that were constructed in separate CAD software accord- ing to SAE J1521 and SAE J1522 were imported into the human modeling software with the Figure 21. Posture calculation result for manikin Female U. Figure 22. Posture calculation result for manikin Female O. Figure 23. Posture calculation result for manikin Female V.

62 Bus Operator Workstation Design for Improving Occupational Health and Safety intention of verifying that the contours predict clearances required by the manikin cadre. The contours were checked against the stomach and shin/knee positions of all manikins. However, manikin Male V was observed carefully because of his extreme height, buttock-to-knee length, and abdominal depth (see Figure 27). The red-dotted curves from the contours can be seen near his stomach and in front of his knees. This result suggests that the contours protect for the clearances that operators need around the steering wheel, steering column, and instrument panel components. Construction of Manikin Reach Curves Once the posture was verified for each manikin, reach surfaces were constructed for both arms of each manikin, originating at each clavicle and extending out to their index finger tip using the human modeling software. Each manikin’s reach surface was exported to CAD software and sectioned at a typical height for instrument panels in order to create reach curves. The reach curves were compared, and manikin Female U was found to have the minimum forward and side reach. An additional reach curve was developed from clavicle to hand grasp Figure 24. Posture calculation result for manikin Male U. Figure 25. Posture calculation result for manikin Male O. Figure 26. Posture calculation result for manikin Male V.

Human Modeling Validation of Bus Operator Workstation Design Guidelines 63 for manikin Female U to be applied for controls requiring hand grasp. The index-fingertip and grasp reach surfaces for Female U are provided in Figures 28 and 29. The resulting reach curves for finger and grasp reach that were constructed from the reach surfaces have been provided in Design Tool 2: Bus Operator Workstation Engineering CAD Model. Further specification and construction details are provided in Appendix B: Bus Operator Workstation Engineering CAD Model Specifications, particularly in Figure B-17). Figure 27. SAE shin/knee contours and stomach contour near manikin Male V (red-dotted curves). Figure 28. Reach curve construction for manikin Female U—left and right arms from clavicle to index finger.

64 Bus Operator Workstation Design for Improving Occupational Health and Safety Human Modeling Validation Summary The Bus Operator Workstation Engineering CAD Model was developed as a combination of international transit bus design guidelines and SAE packaging RPs bounded by current produc- tion North American transit bus vehicle architecture. The model was intended to provide sug- gested seat, steering wheel, and pedal positions and adjustment ranges to accommodate the range of bus operators within the workstation design. Visibility planes, clearances for seated bus operators, and clearances for seat access were built upon the seat/steering-wheel/pedal arrange- ment. In order to test how this workstation design would accommodate the population of bus operators, the model was validated by the human modeling simulation. The human modeling validation required the creation of a sample of manikins representing the range of bus operators. The 2010 NIOSH Truck Driver Anthropometric Survey was applied because the survey was recent, was collected from the United States, and was collected from a similar vocational population. The manikins were arranged into the workstation model using typi- cal bus operator packaging constraints such as recommended seat range, recommended steering wheel range, production pedals and foot-switch plate, and the APTA visibility target. One critical assumption that had to be tested was whether the range of bus operators could keep their feet on the pedal floor while seated in a comfortable posture and still meet the visibility requirement established in the APTA guideline. This assumption was confirmed based on the human modeling simulation presented. Additional packaging clearance envelopes for legs and stomach were also compared to the result of the manikin positions. Finally, the human modeling simulation provided maximum reach curves to be applied back into the Engineering CAD Model. Figure 29. Reach curve construction for manikin Female U—left and right arms from clavicle to hand grasp.