Clive D’Souza

Performance of Visually Impaired Users during Simulated Boarding and Alighting on Low-Floor Buses

Low-floor buses with folding ramp access represent a significant improvement in accessible public transit for passengers with mobility disabilities. However, the safety and usability aspects of the interior design of low-floor buses on blind and visually impaired users has not been studied in much detail. A laboratory study was completed using a static full-scale simulation of a low-floor bus to evaluate the impact of seating configuration and crowding on interior movement and accessibility for individuals with (n=18)) and without visual impairments (n=17). The protocol simulated bus journeys including boarding, fare payment, seating, and alighting. Results from video observations and subjective assessments showed differences in boarding and alighting performance and users’ perceptions of task difficulty across different bus layout designs The results suggest the need for more supportive design features (e.g. guide rails, handholds), legroom, and space for guide dogs too improve accommodation for passengers who are visually impaired. Such design improvements will also support a universal design approach that takes into consideration the needs of a diverse passenger population.

Usability evaluation of access ramps in transit buses: Preliminary findings

The research literature on access ramps used in transit vehicles is undermined by inconsistent methodologies used across studies, thus providing an inconclusive evidence base for proposed Federal guidelines that would impose a maximum 1:6 slope for all deployment situations. The current study assessed the usability of ramp slope for mobility aid users. Four access ramp slopes were evaluated, with 27 adults representing three populations: manual wheelchair users, power wheelchair users, and people with vision impairment who use a cane or service animal. The dependent variables included five usability measures. The 1:8 and 1:12 slopes were usable and acceptable for most participants. The data indicate that the 1:4 slope is too steep for safe unassisted boarding and disembarking. Many manual wheelchair users lacked the strength needed for unassisted ascent. Power wheelchair users and people with vision impairment expressed safety concerns about descent of steeper slopes. Conclusive interpretations should be cautiously drawn because the sample size was relatively small and did not include users of scooters or ambulation aids.

Spatial and temporal patterns in sequential precision reach movements

Introduction: Sequential reach tasks are a common component of manual assembly jobs. These tasks typically involve manipulating a work object or material and reaching to successive target locations with different precision requirements. Ergonomics research on the control of hand movements has largely focused on tasks requiring discrete reaches (e.g., Bootsma & Van Wieringen, 1992; Hoff & Arbib, 1993; Jeannerod, 1984; Marteniuk et al., 1990). The objective of this paper was to investigate spatial and temporal effects of pulley design parameters (outer diameter and groove width) on the trajectory of the threading hand in sequential reaches with different precision requirements. Additionally, we propose a scheme to segment hand trajectories into control phases based on the fingertip trajectory speed profile. Segmenting sequential reach tasks into discrete movements between two consecutive target locations will be useful towards developing models of sequential reaching movements and performance for ergonomic analysis. Methods: Twelve right-handed adults, ages 20-26 years, participated in a laboratory experiment that required threading polyester string through a system of pulleys mounted on an acrylic work surface. Interchangeable pulleys were arranged on the perimeter of a semicircle with a radius of 46 cm at azimuths of 0°, 45°, 90°, 135°, and 180° relative to a constant origin pulley located at the center. The height of the pulleys above the floor was adjusted to place the center pulley at the participant’s standing elbow height. The thread was pulled from a spool located below the center pulley. The task involved threading the pulleys in the following sequence: origin-180°-origin-135°-origin-90°-origin-45°-origin-0°-origin. We conducted a full-factorial experiment with three pulley outer diameters (OD: 38-mm, 76-mm, and 152-mm), three groove widths (GW: 3-mm, 6-mm, and 9-mm), five pulley locations (0°, 45°, 90°, 135°, and 180°), and two threading directions (clockwise and counterclockwise), with 3 repetitions per condition. Participants were instructed to complete the task as quickly as possible while also ensuring each pulley was threaded successfully. A motion capture marker triad on the hand dorsum tracked hand motions during the task. Hand trajectories were analyzed separately for each of the 5 origin-destination pulley location pairs. Speed profiles were analyzed to identify transition points between the transport phase, where the hand is reaching from the origin to the destination location, and the pulley interaction phase, where the hand is engaged in threading the destination pulley. The start and end points of the pulley interaction phase correspond to the first and last local speed minima that occur below a threshold set at 100-mm/s above the minimum speed when the trajectory is within the region of the destination pulley. The angle (α) and radius (R) of the hand position, relative to the destination pulley center, were estimated at the start (t1) and end (t2) points of the pulley interaction phase. Repeated measures ANOVA was used to test the effects of OD, GW, pulley location, and threading direction on the time spent in the pulley interaction phase (TPI = t2 − t1), R1, R2, α1, α2, and the difference between α1 and α2 (αPI = α2 - α1). Results: Temporal parameters: Pulley OD (p < 0.001), GW (p < 0.001), location (p = 0.002), and the threading direction x pulley location interaction (p < 0.001) had a significant effect on TPI. Larger GW corresponded to less TPI (GW: Mean±SE, 3-mm: 772±34 ms, 6-mm: 473±23 ms, 9-mm: 351±18 ms). Pulley OD of 152-mm required significantly more TPI (713±35 ms) compared to the 38-mm (449±21 ms) and 76-mm (433±21 ms) OD. The CW threading direction required significantly less TPI for the 0°, 45° and, 90° pulley locations, while CCW threading direction took more TPI for the 135° and 180° pulley locations. Spatial Parameters: The effects of OD (p < 0.001) and pulley location (p < 0.001) were significant for R1. Larger OD corresponded to increased R1, i.e., 38-mm OD: 76±1-mm, 76-mm OD: 87±1-mm, and 152-mm OD: 119±1-mm. Additionally, R1 increased significantly as the pulley location changed from 0°-180°. Similar trends were observed for R2 across OD and pulley location. The main effects of OD (p < 0.001), pulley location (p < 0.001), and threading direction (p < 0.001) and the interaction between pulley location and threading direction (p < 0.001) were significant for α1. Larger OD corresponded to a greater α1 (38-mm OD: 24±1°, 76-mm OD: 34±1°, 152-mm OD: 53±1°). At the 180° pulley location, α1 was significantly greater for the CCW vs. CW threading direction. At the 0°, 45° and, 90° pulley locations, α1 was greater for the CW vs. CCW threading direction. Similar trends were observed for α2 across task parameters. The main effect of pulley OD on αPI was significant (p < 0.001) with a larger αPI for the 152-mm OD (22±1°) compared to the 38-mm OD (15±1°) and 76-mm OD (11±1°). Discussion: These results show that pulley design parameters in a sequential reach task systematically influence the spatial properties and transition timing of hand motion trajectories between phases. Narrower GW increased the precision requirement and corresponded to slower times. Participants took more time threading the larger OD. Shorter threading times occurred when participants had a direct line of sight with the pulley groove. Pulley OD influenced the radius of the hand position at the start and end of the pulley interaction phase, whereas pulley GW had no effect. The increase in R1 and R2 for pulleys located on the contralateral side compared to the lateral side was attributed to need for line of sight with the pulley groove since the hand obstructs the view of the pulley edge on the contralateral side. Conclusions: Analysis of sequential reaches needs to consider individual target locations and design parameters. Our findings also show the potential for modeling sequential reaches as a series of discrete reaches. A scheme to segment hand trajectories into control phases based on the fingertip trajectory speed profile was presented. Further investigation is necessary in sequential reach tasks with more realistic and complex work configurations observed in industrial settings.

Comparative Analysis of Inertial Sensor to Optical Motion Capture System Performance in Push-Pull Exertion Postures

This study examined interactions between inertial sensor (IS) performance and physical task demand on posture kinematics in a two-handed force exertion task. Fifteen male individuals participated in a laboratory experiment that involved exerting a two-handed isometric horizontal force on an instrumented height-adjustable handle. Physical task demand was operationalized by manipulating vertical handle height, target force magnitude, and force direction. These factors were hypothesized to influence average estimates of torso flexion angle measured using inertial sensors and an optical motion capture (MC) system, as well as the root mean squared errors (RMSE) between instrumentation computed over a 3s interval of the force exertion task. Results indicate that lower handle heights and higher target force levels were associated with increased torso and pelvic flexion in both, push and pull exertions. Torso flexion angle estimates obtained from IS and MC did not differ significantly. However, RMSE increased with target force intensity suggesting potential interactive effects between measurement error and physical task demand.

Revisiting Clear Floor Area Requirements for Wheeled Mobility Device Users in Public Transportation

Current accessibility standards in the U.S. prescribe minimum dimensions for “clear floor area” to accommodate wheeled mobility device (WhMD) users on transportation vehicles. Prior research on the anthropometry of WhMD users (n = 500) indicates that these dimensions are too small to accommodate the size of many occupied WhMDs, especially power chairs and scooters. This paper describes a development project designed to update the evidence for these technical criteria and communicate them to the vehicle designers and accessibility standards developers in a manner that would facilitate making good decisions. An interactive web-based design tool was developed for determining the dimensions of clear floor area to achieve a user-specified level of physical accommodation based on occupied device length and width measurements taken on 500 WhMD users. The web-based design tool is now available to practitioners who seek to accommodate a wider range of WhMD users than the minimum standards required by regulations. The design tool is also intended as a visual evidence base for regulatory activity and universal design practice with higher ambitions. The advent of driverless automated vehicles will increase the importance of accessibility and usability to accommodate the diversity of riders with disabilities. Clear floor space to enable independent ingress, interior circulation, and egress among WhMD users will be a foremost concern. The transportation industry, standards developers, disability advocates, mobility device manufacturers and prescribers, need to understand the limitations of current accessibility standards and work to address these limitations through updated vehicle design standards and policies.

Preliminary Study of Obstacle Clearance and Compensatory Movements in Individuals with High Body Mass Index

This study investigated the effect of obstacles of different heights on task performance and compensatory movements of six individuals with a body mass index (BMI) ≥ 30kg/m2. Obstacle heights were increased from 36cm to 66cm in 5cm increments using a method of limits. Video-based task analysis was used to develop a conceptual model of obstacle clearance and compensatory movements in response to the postural challenge of increasing obstacle heights. Results from the task analysis were used to identify temporal and kinematic performance measures of dynamic balance and postural control. Changes in obstacle clearance performance and compensatory movements may indicate heightened fall risk and could be mitigated by accessible design and assistive support features in the environment.

Upper extremity muscle activity during household floor vacuuming with upright cleaners

Physical demands of household carpet vacuuming and associated risks for musculoskeletal problems have received little attention although the level of muscle exertions is often assumed to be similar to that of occupational vacuuming. The aim of this study was to quantitatively assess the level of muscle activities of the upper extremity during carpeted floor vacuuming with household upright vacuum cleaners. Eighteen participants conducted four different carpet vacuuming tasks with two different cleaner models. Electromyography data from seven upper extremity muscles were collected. Median muscle activity ranged from 4.5% to 47.5% of the maximum voluntary contraction capacity for female participants and from 2.7% to 23.6% for male participants. Normalized muscle activity levels were significantly higher in women compared to men across tasks and muscle groups. Study results suggest that home vacuuming with upright vacuum cleaners is physically intensive work, especially for female users who are less physically capable.

Modeling Hand Trajectories during Sequential Reach Movements in a Pulley Threading Task

Modeling of human motion is common in ergonomic analysis of industrial tasks and can help improve workplace design. We propose a method for modeling the trajectories of hand movements in the frontal plane during a sequential reach task that involves threading string through a system of pulleys. We model the motions as a combination of two consecutive phases, one where the hand is reaching between pulleys and another when the hand is engaged in threading a target pulley. Hand trajectories were modeled separately for each phase by fitting basis-splines to the observed data. Predicted trajectories were computed using task parameters as the input and compared to observed trajectories from the 12 participants who completed the study.

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

Abstract 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.

A Pilot Study of the Effects of Pulley Location and Design Parameters on Hand Movements during Pulley Threading Operations

Three healthy individuals participated in a laboratory experiment that required routing a thin continuous thread through a series of pulleys mounted on a vertical work surface. Task precision demand was manipulated by altering pulley outer diameter (38 mm, 76 mm, and 152 mm) and groove width (3 mm, 6 mm, and 9 mm). The target location of each destination pulley relative to the origin at the mid-sagittal plane was also manipulated. These factors were hypothesized to influence hand motion trajectories, peak speed, and task completion time. Smaller pulley diameters and larger groove widths, representing lower precision demands, were associated with smoother trajectories and a faster task completion time. These preliminary findings suggest a systematic influence of task precision demands on movement kinematics and task performance.