DEVELOPMENT OF SURFACE ROUGHNESS STANDARD FOR WHEELCHAIR PATHWAYS

Over two 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 (ADAAG), 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. ISO standard 2631-1 specifies zones for how much vibration exposure can be dangerous, but it is unknown how surface roughness can affect the amount of vibration that wheelchair users feel. To develop a standard for surface roughness, subjective and objective information was gathered and analyzed from subjects traveling over various surfaces in their own wheelchairs. Sixty-eight subjects were recruited to travel over nine engineered wooden pathways with varying roughnesses. A subset of 25 subjects also traveled over 12 outdoor, real-world pathways. While the subjects traveled over the surfaces, accelerometers recorded vibrations at the seat, footrest, and backrest. After traveling over each surface, subjects were asked to subjectively rate each surface. Both RMS accelerations and subjective ratings were compared to surface roughness to see if a correlation existed. As expected, the results show that as surface roughness increased, RMS accelerations increased and subjective ratings decreased. Some surfaces generated RMS accelerations above the ISO health guidance zone, suggesting that some sidewalks are causing harmful vibrations to wheelchair users. Some surfaces also were rated as unacceptable by more than half of the subjects showing that these surfaces were causing discomfort to the people traveling over them. Based on the combination of RMS data and subjective feedback from wheelchair users, we are proposing a roughness index threshold of 1.10 in/ft for short distance surfaces (less than 10 m). For longer surfaces, a roughness index of 0.60 in/ft should be adopted