Usability and person-environment interaction in constrained spaces: Wheeled mobility users and interior low-floor bus design

This research employs an evaluative study on the usability of low-floor transit buses for users of wheeled mobility devices (such as manual wheelchairs, powered wheelchairs and scooters) as a case study on P-E fit in constrained environments. The first phase assessed low-floor bus interior layouts using a static full-scale environmental mock-up in a laboratory setting. A sample of 48 wheeled mobility device users evaluated three different bus interior configurations across two levels of passenger load (PL; high vs. low) in simulated boarding and disembarking (B-D) tasks including ramp ascent, fare payment, interior circulation, and ramp descent. Usability was assessed with user-reported measures (e.g., task difficulty, design preference ratings) and observed performance measures (e.g., number of independent completions, critical incidents, and task completion times). Results show a significant impact of bus interior design and passenger load on users' ratings of task difficulty and design preference during B-D. Detailed analysis by task helped identify specific environmental conditions that impacted difficulty and observed performance. The bus layout with B-D at the rear doorway was ranked favorably compared to layouts that involved use of the front doorway for boarding and/or disembarking. The methodology employed presents a useful way to systematically examine usability and user performance in context, explore new design scenarios, and engage specific disadvantaged user populations.;The second phase used mixed-effect regression models to estimate the relative impact of user characteristics (including power grip strength, occupied device length, 10m distance travel time and 360 deg. turn time), and environmental design conditions on interior circulation times in low-floor buses. Findings show that environmental conditions of interior seating layout, and PL accounted for the largest variance in prediction of interior circulation times but to a varying extent depending on specific task requirements. Further, the impact of environmental conditions was less pronounced for individuals that were high-performing on power grip strength, 10m travel time, and 360 degree turn time - lending support to the environmental docility hypothesis which posits that the impact of the physical environment on user performance is modified by individual functional capacity.;Lastly, correlational analysis was used to study associations between user-reported task difficulty and observed task times. Spearman correlation coefficients were low to moderate but significant and demonstrated magnitude differences as a function of the type of task being performed, environmental demand, and user characteristics. This finding highlights the importance of (1) measuring usability on multiple dimensions, and (2) incorporating descriptions of environmental demand and users' functional capacity when comparing user-reported and observed performance measures.;This research presents an empirical approach to studying the interactions between functional abilities of wheeled mobility device users and the physical environment design in the context of usability and P-E fit. Collectively, the studies point to the need for evaluating usability in the context of person-characteristics, environmental conditions and the task being performed. Implications of this research are discussed in three areas: transit vehicle design, accessibility design guidelines and policy, and methodological contributions to inclusive design and ergonomics research. (Abstract shortened by UMI.).