Development of Surface Roughness Standards for Pathways Used by Wheelchairs

More than 2 million people in the United States use a wheelchair for mobility. These Americans not only rely on their assistive technology to complete simple, daily tasks, but they also depend on functional and accessible sidewalks to do so. Although the Americans with Disabilities Act Accessibility Guidelines established by the Access Board provide suggestions for pathways, they are subjective and not measurable. This ambiguity results in public pathways with many bumps and cracks, which can lead to harmful whole body vibrations (WBVs) for wheelchair users. WBVs with a root mean squared (RMS) value greater than 1.6 m/s² for more than a 1-h period may result in back and neck pain or muscle fatigue. For the development of a standard for surface roughness, subjective and objective information needs to be gathered and analyzed. Sixty-one subjects were recruited to travel over nine simulated wooden surfaces with varying roughnesses that were modeled after outdoor surfaces. A subset of the subjects also traveled over six outdoor surfaces. With the use of their own chairs, subjects traveled over each surface while accelerometers recorded vibrations at the seat, footrest, and backrest. After they traveled over each surface, subjects were asked to fill out a short questionnaire on the acceptability of each surface. The vibrations were converted to RMS accelerations. Both RMS accelerations and subject surface ratings were compared with surface roughness. As surface roughness increased, RMS accelerations increased, and subject surface ratings decreased. Some surfaces generated RMS accelerations above the 1.6 m/s² threshold; this result suggested that some sidewalks caused harmful vibrations to wheelchair users.