Self-reported difficulty and preferences of wheeled mobility device users for simulated low-floor bus boarding, interior circulation and disembarking.

BACKGROUND: Low ridership of public transit buses among wheeled mobility device users suggests the need to identify vehicle design conditions that are either particularly accommodating or challenging. The objective of this study was to determine the effects of low-floor bus interior seating configuration and passenger load on wheeled mobility device user-reported difficulty, overall acceptability and design preference. METHODS: Forty-eight wheeled mobility users evaluated three interior design layouts at two levels of passenger load (high vs. low) after simulating boarding and disembarking tasks on a static full-scale low-floor bus mockup. RESULTS: User self-reports of task difficulty, acceptability and design preference were analyzed across the different test conditions. Ramp ascent was the most difficult task for manual wheelchair users relative to other tasks. The most difficult tasks for users of power wheelchairs and scooters were related to interior circulation, including moving to the securement area, entry and positioning in the securement area and exiting the securement area. Boarding and disembarking at the rear doorway was significantly more acceptable and preferred compared to the layouts with front doorways. CONCLUSION: Understanding transit usability barriers, perceptions and preferences among wheeled mobility users is an important consideration for clinicians who recommend mobility-related device interventions to those who use public transportation. Implications for Rehabilitation In order to maximize community participation opportunities for wheeled mobility users, clinicians should consider potential public transit barriers during the processes of wheelchair device selection and skills training. Usability barriers experienced by wheeled mobility device users on transit vehicles differ by mobility device type and vehicle configurations. Full-scale environment simulations are an effective means of identifying usability barriers and design needs in people with mobility impairments and may provide an alternative model for determining readiness for using fixed route buses or eligibility for paratransit.

Sitting versus standing makes a difference in musculoskeletal discomfort and postural load for surgeons performing vaginal surgery.

INTRODUCTION AND HYPOTHESIS: We compared musculoskeletal discomfort and postural load among surgeons in sitting and standing positions during vaginal surgery. MATERIALS AND METHODS: Assessment of discomfort and posture of the primary surgeons in both positions was performed at two institutions. The primary outcome was an increase in body discomfort score after surgery as determined from subjective responses using validated tools. The secondary outcome was the percentage of time spent in awkward body postures measured objectively and stratified into awkward postures for neck, trunk, and bilateral shoulder angles. Variables were compared between sitting and standing positions using Fisher's exact test for primary outcomes and Wilcoxon rank-sum test for secondary outcomes. RESULTS: Data were collected for 24 surgeries from four surgeons in sitting position and nine surgeries from nine surgeons in standing position. The standing surgeons reported a significant increase in discomfort postoperatively for bilateral wrists, thighs, and lower legs compared with the sitting surgeons. The median percentage of time spent in awkward postures was significantly lower for the trunk in the standing versus sitting position (median 0.3% vs 58.8%, p < 0.001) but was significantly higher for both shoulders in the standing versus the sitting position (right shoulder: median 17.8% vs 0.3%, p = 0.003; left shoulder: median 7.4% vs 0.2%, p = 0.003). CONCLUSION: Surgeons reported more discomfort in when performing vaginal surgery while standing. The postural load was worse for trunk but favorable for bilateral shoulders when seated. Such differences may impact a surgeon's decision to perform vaginal surgery seated rather than standing.

Effects of transit bus interior configuration on performance of wheeled mobility users during simulated boarding and disembarking.

The emergence of low-floor bus designs and related regulatory standards in the U.S. have resulted in substantial improvements in public transit accessibility. However, passengers using wheeled mobility devices still experience safety concerns and inefficiencies in boarding, disembarking, and interior circulation on low-floor buses. This study investigates effects of low-floor bus interior configuration and passenger crowding on boarding and disembarking efficiency and safety. Users of manual wheelchairs (n = 18), powered wheelchairs (n = 21) and electric scooters (n = 9) simulated boarding and disembarking in three interior layout configurations at low and high passenger crowding conditions on a full-scale laboratory mock-up of a low-floor bus. Dependent measures comprised task times and critical incidents during access ramp use, fare payment, and movement to and from the doorway and wheeled mobility securement area. Individual times for unassisted boarding ranged from 15.2 to 245.3 s and for disembarking ranged from 9.1 to 164.6 s across layout and passenger crowding conditions. Nonparametric analysis of variance showed significant differences and interactions across vehicle design conditions, passenger load and mobility device type on user performance. The configuration having electronic on-board fare payment, rear-bus entrance doorways and adjacent device securement areas demonstrated greatest efficiency and safety. High passenger load adversely impacted efficiency and frequency of critical incidents during on-board circulation across all three layouts. Findings have broader implications for improving transit system efficiency and quality of service across the spectrum of transit users.

Predictive models of safety based on audit findings: Part 2: Measurement of model validity.

Part 1 of this study sequence developed a human factors/ergonomics (HF/E) based classification system (termed HFACS-MA) for safety audit findings and proved its measurement reliability. In Part 2, we used the human error categories of HFACS-MA as predictors of future safety performance. Audit records and monthly safety incident reports from two airlines submitted to their regulatory authority were available for analysis, covering over 6.5 years. Two participants derived consensus results of HF/E errors from the audit reports using HFACS-MA. We adopted Neural Network and Poisson regression methods to establish nonlinear and linear prediction models respectively. These models were tested for the validity of prediction of the safety data, and only Neural Network method resulted in substantially significant predictive ability for each airline. Alternative predictions from counting of audit findings and from time sequence of safety data produced some significant results, but of much smaller magnitude than HFACS-MA. The use of HF/E analysis of audit findings provided proactive predictors of future safety performance in the aviation maintenance field.

Predictive models of safety based on audit findings: Part 1: Model development and reliability.

This consecutive study was aimed at the quantitative validation of safety audit tools as predictors of safety performance, as we were unable to find prior studies that tested audit validity against safety outcomes. An aviation maintenance domain was chosen for this work as both audits and safety outcomes are currently prescribed and regulated. In Part 1, we developed a Human Factors/Ergonomics classification framework based on HFACS model (Shappell and Wiegmann, 2001a,b), for the human errors detected by audits, because merely counting audit findings did not predict future safety. The framework was tested for measurement reliability using four participants, two of whom classified errors on 1238 audit reports. Kappa values leveled out after about 200 audits at between 0.5 and 0.8 for different tiers of errors categories. This showed sufficient reliability to proceed with prediction validity testing in Part 2.

Computer re-sampling for demographically representative user populations in anthropometry: a case of doorway and clear floor space widths.

Anthropometric studies typically require a large number of individuals that are selected in a manner so that demographic characteristics that impact body size and function are proportionally representative of a user population. This sampling approach does not allow for an efficient characterization of the distribution of body sizes and functions of sub-groups within a population and the demographic characteristics of user populations can often change with time, limiting the application of the anthropometric data in design. The objective of this study is to demonstrate how demographically representative user populations can be developed from samples that are not proportionally representative in order to improve the application of anthropometric data in design. An engineering anthropometry problem of door width and clear floor space width is used to illustrate the value of the approach.

Low-floor bus design preferences of walking aid users during simulated boarding and alighting.

Low-floor buses represent a significant improvement in accessible public transit for passengers with limited mobility. However, there is still a need for research on the inclusive design of transit buses to identify specific low-floor bus design conditions that are either particularly accommodating or challenging for passengers with functional and mobility impairments. These include doorway locations, seating configuration and the large front wheel-well covers that collectively impact boarding, alighting and interior movement of passengers. Findings from a laboratory study using a static full-scale simulation of a lowfloor bus to evaluate the impact of seating configuration and crowding on interior movement and accessibility for individuals with and without walking aids are presented (n=41). Simulated bus journeys that included boarding, fare payment, seating, and alighting were performed. Results from video observations and subjective assessments showed differences in boarding and alighting performance and users' perceptions of task difficulty. The need for assistive design features (e.g. handholds, stanchions), legroom and stowage space for walking aids was evident. These results demonstrate that specific design conditions in low-floor buses can significantly impact design preference among those who use walking aids. Consideration of ergonomics and inclusive design can therefore be used to improve the design of low-floor buses.

A tool for rapid assessment of product usability and universal design: development and preliminary psychometric testing.

BACKGROUND: While there are many available tools and methods to evaluate product usability, few have been tested on user groups with disabilities and even fewer systematically consider universal design principles. OBJECTIVE: This paper describes the development and preliminary psychometric testing of the Rapid Assessment of Product Usability & Universal Design (RAPUUD), a 12-item user-report tool based on the seven principles of universal design. METHOD: A preliminary set of items was created to elicit ratings of diverse product characteristics (e.g., physical effort, cognitive effort, assistance required, safety). Data were gathered from 61 participants who rated the usability of products they use in their own environments. RESULTS: Each item elicited a full range of responses, with no apparent floor or ceiling effects. Collectively, the 12 items achieved a high internal consistency (Cronbach's α=0.80). The data indicate that the tool was sensitive to differences in functional abilities, as well as differences in product characteristics. The instrument was usable for a range of consumer products, though not all items were appropriate for each and every product. CONCLUSION: The results suggest that the instrument could become a pragmatic tool for designers to identify usability problems experienced by a diversity of user populations.

Physical ergonomic hazards in highway tunnel construction: overview from the Construction Occupational Health Program.

This report provides an overview of physical ergonomic exposures in highway construction work across trades and major operations. For each operation, the observational method "PATH" (Posture, Activity, Tools and Handling) was used to estimate the percentage of time that workers spent in specific tasks and with exposure to awkward postures and load handling. The observations were carried out on 73 different days, typically for about 4 h per day, covering 120 construction workers in 5 different trades: laborers, carpenters, ironworkers, plasterers, and tilers. Non-neutral trunk postures (forward or sideways flexion or twisting) were frequently observed, representing over 40% of observations for all trades except laborers (28%). Kneeling and squatting were common in all operations, especially tiling and underground utility relocation work. Handling loads was frequent, especially for plasterers and tilers, with a range of load weights but most often under 15 pounds. The results of this study provide quantitative evidence that workers in highway tunnel construction operations are exposed to ergonomic factors known to present significant health hazards. Numerous opportunities exist for the development and implementation of ergonomic interventions to protect the health and safety of construction workers.

The ability of limited exposure sampling to detect effects of interventions that reduce the occurrence of pronounced trunk inclination.

Ergonomics interventions often focus on reducing exposure in those parts of the job having the highest exposure levels, while leaving other parts unattended. A successful intervention will thus change the form of the job exposure distribution. This disqualifies standard methods for assessing the ability of various exposure measurement strategies to correctly detect an intervention's effect on the overall job exposure of an individual worker, in particular for the safety or ergonomics practitioner who with limited resources can only collect a few measurements. This study used a non-parametric simulation procedure to evaluate the relationship between the number of measurements collected during a self-paced manufacturing job undergoing ergonomics interventions of varying effectiveness, and the probability of correctly determining whether and to which extent the interventions reduced the overall occurrence of pronounced trunk inclination, defined as an inclination of at least 20 degrees . Sixteen video-recordings taken at random times on multiple days for each of three workers were used to estimate the time distribution of each worker's exposure to pronounced trunk inclination. Nine hypothetical ergonomics intervention scenarios were simulated, in which the occurrence of pronounced trunk inclination in the upper 1/8, 1/4, and 1/2 of the job exposure distribution was reduced by 10%, 30% and 50%. Ten exposure measurement strategies were explored, collecting from one to ten pre- and post-intervention exposure samples from an individual worker. For each worker, intervention scenario and sampling strategy, data were bootstrapped from the measured (pre-intervention) and simulated (post-intervention) exposure distributions to generate empirical distributions of the estimated intervention effect. Results showed that for the one to three intervention scenarios that had the greatest effect on the overall occurrence of trunk inclination in the job, one to four pre- and post-intervention measurements, depending on worker, were sufficient to reach an 80% probability of detecting that the intervention did, indeed, have an effect. However, even for the intervention scenario that had the greatest effect on job exposure, seven or more samples were needed for two of the three workers to obtain a probability larger than 50% of estimating the magnitude of the intervention effect to within +/-50% of its true size. For almost all interventions affecting 1/8 or 1/4 of the job, limited exposure sampling led to low probabilities of detecting any intervention effect, let alone its correct size.

Space Requirements for Wheeled Mobility Devices in Public Transportation: An Analysis of Clear Floor Space Requirements: (Investing in Accessible Transportation and Mobility ABE60).

Recent research on the anthropometry of wheeled mobility devices and their users (n=369) indicates that the current dimensions for 'clear floor area' prescribed in U.S. accessibility standards for transportation are inadequate for accommodating many users of wheeled mobility devices, especially those that use power chairs and scooters. The current report presents anthropometry data for determining the dimensions of clear floor area based on occupied device length and width to achieve a specified level of physical accommodation. The implications of the findings and the need for revising guidelines for accessible public transportation systems are discussed. It is important that the transportation industry as well as mobility device manufacturers, vendors and prescribers understand the limitations of current standards and becomes involved in the dialogue about how to address the need for improving them.

Variability in risk factors for knee injury in construction.

This study investigated sources of variance in exposure to risk factors for knee pain in a variety of highway construction trades, operations, and tasks. Over 15,000 discrete observations of leg postures and weights handled were made on 120 construction workers in five construction trades, in nine operations over 79 days. The contributions of trade, operation, task, and worker to the variability in work time spent kneeling, squatting, and carrying loads were evaluated with multilevel random effects models. Construction operation and task explained about 20% to 30% of total variation in kneeling, squatting, and carrying loads. There was a large unexplained component of variance thought to represent day-to-day variability of exposure within task. Reliable assessments of knee exposures require multiple days to accommodate the high variability of exposures among operations and tasks and over time. These sources of variability should be carefully considered in efforts to estimate exposures to knee loading for epidemiologic or intervention studies. Homogenous exposure groups are not easily defined from the readily available organizational features of construction work.

Reliable exposure assessment strategies for physical ergonomics stressors in construction and other non-routinized work.

The objective of this research was to provide guidelines for the reliable assessment of ergonomics exposures in non-routinized work. Using a discrete-interval observational sampling approach, two or three observers collected a total of 5852 observations on tasks performed by three construction trades (iron workers, carpenters and labourers) for periods of several weeks. For each observation, nine exposure variables associated with awkward body postures, tool use and load handling were recorded. The frequency of exposure to each variable was calculated for each worker during each of the tasks on each of the days. ANOVA was used to assess the importance of task in explaining between-worker and within-worker variability in exposures across days. A statistical re-sampling method (bootstrap) was used to evaluate the reliability of exposure estimates for groups of workers performing the same task for different sampling periods. Most exposures were found to vary significantly across construction tasks within trade, and between-worker exposure variability was generally smaller than within-worker exposure variability within task. Bootstrapping showed that the reliability of the group estimates exposure for the most variable exposures within task tended to improve as the assessment periods approached 5-6 d, with marginal improvements for longer assessment periods. Reliable group estimates of exposure for the least variable exposures within task were obtained with 1 or 2 d of observation. The results of this study demonstrate that an initial estimate of the important environmental or task sources of exposure variability can be used to develop an efficient sampling strategy that provides reliable estimates of ergonomics exposures during non-routinized work.

Survey instrument for the universal design of consumer products.

Universal design is a process intended to include all user groups in product or environmental design. The objective of this study was to develop a usability testing survey instrument to inform how well consumer products complied with established principles of universal design. Thirty-six adults, aging adults and adult wheelchair users performed standardized tasks with pens, food storage containers, pliers and calculators, and for each task responded to a preliminary set of survey items and rated task difficulty. Factor analysis of the survey responses produced an eleven-factor solution that accounted for 67% of the variance in scores and corresponded fairly closely to the principles of universal design. Analysis of scale scores developed from each factor showed that some of the scales were sensitive to product feature and user group differences, and were negatively associated with perceived task difficulty. Such a tool may aid designers who intend their products for user groups of diverse abilities and preferences.

A new conceptual model for assistive technology outcomes research and practice.

Predictive conceptual models help us frame research questions, interpret results, and guide clinical practice. Although numerous models have appeared in the assistive technology (AT) literature, none has been shown to predict AT usage. The lack of a valid predictive model indicates the need for development of new approaches to modeling AT outcomes. This article proposes a user-centered conceptual model that predicts AT usage as a function of the perceived relative advantages of AT. Device usage is not modeled as a one-time, all-or-nothing proposition, but as a decision process recurring over time. The influence of parallel interventions working concurrently with, or as an alternative to, AT is a central consideration that ultimately drives AT usage. Usage is shown as a proximal influence on AT impact, and AT impact is shown to be a predictor of future use. Research is cited supporting various elements of the new model.

Quantification of ergonomic hazards for ironworkers performing concrete reinforcement tasks during heavy highway construction.

A study was conducted to assess the ergonomic hazards of ironwork job tasks associated with concrete reinforcement work at a large highway construction site. PATH (posture, activity, tools, and handling) analysis, a work-sampling method, was used to provide task-based estimates of the percentage of time ironworkers spent in specified postures of the trunk, arms, and legs; performed activities; used tools; and handled loads. A total of 2128 PATH observations were made of 17 ironworkers performing 5 job tasks: (1) ground-level reinforcement bar (rebar) construction, (2) wall rebar construction, (3) ventilation rebar construction, (4) preparation work, and (5) supervising. Nonneutral trunk postures were observed frequently (exceeding 30%) and manual material handling (MMH) was the most commonly observed activity (exceeding 20%) for all job tasks except supervising. The percentage of time workers spent in specific postures, activities performed, tool use, and MMH activities differed significantly between the five main job tasks, even when supervising was excluded from the analysis. It was concluded that ironworkers are exposed to significant ergonomic hazards when performing concrete reinforcing tasks, and that opportunities exist for the implementation of ergonomic interventions. Further, the results of this study can be used to target specific hazardous tasks for ergonomic interventions and confirms the need to use a task-based exposure assessment strategy to properly assess ergonomic risk profiles for nonstructured jobs such as construction.

Making sense of highway construction: a taxonomic framework for ergonomic exposure assessment and intervention research.

Construction is one of the most hazardous industries in the United States. Occupational health research to characterize the hazards in construction work has been hampered by the lack of a systematic approach to classification of construction work and its associated hazards. A taxonomy of construction work, a nested system of classification, has been developed to systematize the collection and reporting of exposure assessment data for the characterization and reduction of hazards and the prevention of musculoskeletal injury. This taxonomy subdivides construction work into the categories of stage, operation, task, and activity. It is based on a bidding specification system already in use within the industry and thus provides a terminology common among workers, supervisors, and managers. The identification of tasks and activities that are present in multiple stages and/or trades contributes to the efficiency of exposure data collection and facilitates the generalizability to other settings for both exposure data and intervention evaluations. The taxonomy provides a framework and vocabulary that facilitates field work and participatory research activities. It can also potentially be linked to personnel and economic data for estimation of costs of safety and health problems, as well as benefits of interventions. Although developed for construction ergonomics, the taxonomic approach has application to non-routine work in other industry sectors and possibly in occupational health research other than ergonomics.

A review of conceptual models for assistive technology outcomes research and practice.

Conceptual models provide a theoretical basis for advancing scientific knowledge and improving professional practice. Although numerous assistive technology-related models have appeared in the literature, there has been no systematic effort to assess them. Six conceptual models are reviewed here: Cook and Hussey's Human-Activity-Assistive Technology model; the World Health Organization's International Classification of Functioning, Disability, and Health; Scherer's Matching Person and Technology model; Gitlin's model of an AT user's "career"; social cognition decision-making theories; and Rogers' Perceived Attributes Theory. The models are reviewed in terms of six domains: background and goals; descriptive characteristics; indication of outcome measures; predictive characteristics; validation in the literature; and utility to assistive technology practitioners, developers, and consumers. The salient strengths and limitations are highlighted for each. Application of the models to advance theory, research, and practice is discussed.