This is an executive summary of the “Accessible Exterior Surfaces Technical Report” dated 24 April 1999. This report is available through the Access Board at (800) 872-2253, or Beneficial Designs, Inc. at (775) 783-8822 or mail@beneficialdesigns.com.
Accessible Exterior Surfaces
This pilot study conducted human subject testing and objective measures of firmness and stability on nine types of exterior surfaces as part of Phase II of the Accessible Exterior Surfaces research project. The purpose of this research was to determine the amount of energy required to negotiate these different surface types, if the values obtained with a portable surface measurement device provide information about the level of access, and to develop recommendations for surface accessibility guidelines.
The amount of energy required by persons with and without mobility limitations to negotiate different types of surfaces and an accessible route was evaluated. Differences between the surfaces and subject characteristics which influenced the results were identified. Results suggest that under dry conditions, paved surfaces, path fines (with and without stabilizer), unpaved road mix, and packed soil surfaces require the least energy, allow higher ambulation velocities, and are perceived as relatively easy to walk on. For wood surfaces (chipped brush, wood chips, engineered wood fibers) and sand, the energy required is higher, walking velocity is lower, and they are perceived as more difficult, particularly among those who use manual wheelchairs.
A portable surface measurement device that provides a rating of the firmness and stability of surfaces has been developed - the Rotational Penetrometer. There was a strong correlation between the measurements obtained with this device and the amount of work required to propel a wheelchair, and the energy costs of subjects walking on the various surfaces. A Rotational Penetrometer test method for the determination of surface firmness and stability is recommended as an accessibility guideline. Performance specifications were developed based upon the results of this research. Surfaces objectively measured as firm and stable would be allowed for unlimited distances. Moderately firm and stable surfaces would be allowed only in flat areas and for limited distances. The results of this research suggest that the percentage of the population that can successfully negotiate 5% slopes for longer distances would be similar to the percentage that can negotiate surfaces that are objectively measured as firm and stable. The results of this research also suggest that the percentage of the population that can successfully negotiate at least two 30-ft segments with an 8% slope would be similar to the percentage that can negotiate surfaces that are objectively measured as moderately firm and stable for shorter distances.
