Development of Surface Roughness Standards for Pathways Used by Wheelchair Users: Final Report

Executive Summary

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. The Americans with Disabilities Act Accessibility Guidelines (ADAAG), established by the Access Board, provide suggestions for pathways; however, the ones related to surface roughness 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, a literature review on previous studies related to wheelchair vibrations as well as roughness measurement and analysis techniques was completed. Subjective and objective information was also gathered and analyzed from a human subject study where subjects traveled over various surfaces in their own wheelchairs. Seventy-six subjects, as of May, 2014, were recruited to travel over nine engineered wooden pathways with varying roughnesses. A subset of 38 subjects also traveled over 18 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 and decide whether the surface was acceptable or not. 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 real-world surfaces generated RMS accelerations above the ISO health guidance zone, suggesting that some sidewalks are causing harmful vibrations to wheelchair users. Some surfaces were also 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 1.20 in/ft for any short distance segments (less than 10 ft). For longer surfaces (greater than 100 ft), a roughness index of 0.60 in/ft should be adopted.

KEY FINDINGS:

• There are ways to measure and analyze surface roughness for roadways, but none are capable of being directly transferred to pedestrian pathways.

• Previous studies have found that wheelchair users are exposed to potentially harmful vibrations in their communities and the magnitude of those vibrations are dependent on surface characteristics

• As surface roughness increases, the magnitude of vibrations increases.

• As surface roughness increases, subject ratings of the surface decreases.

• To calculate roughness, a profile of the surface with a resolution of 1 mm should be used.

• The profile should be filtered with a “wheelpath” algorithm with a 2.5 in diameter wheel.

• The roughness limit for any local area (less than 10 ft, such as a curb cut with low vision bubbles) should be 1.2 in/ft.

• For longer surfaces (greater than 100 ft) a roughness of 0.60 in/ft should be adopted.

FUTURE WORK:

• Work with ASTM Committee E17 to develop and approve roughness measuring standard

• Develop and validate a tool to measure pathway accessibility including roughness and other right-of-way features