Accessible Exterior Surfaces Technical Article

RECOMMENDATIONS

An objective test procedure for measuring the firmness and stability of surfaces with a portable device and performance specifications need to be accepted in order to enable land managers to determine whether the surface material on a trail (i.e., on site) is considered “accessible.” Surface firmness and stability should be measured using an objective device suitable for use “on trail” or in the field because surface characteristics vary dramatically depending on the installation at the actual site.

Recommended Objective Test Method and Performance Specifications

The objective test method using the Rotational Penetrometer is recommended because it provides valid and reliable measurements of surface firmness and stability on slopes up to 5%, can be used on a wide variety of surface materials, and is suitable for conducting “on trail/on site” tests.

The following are recommended performance specifications for firmness and stability under dry conditions based on the Rotational Penetrometer test results and the human subject results from this research.

The proposed cut-off values for firm and stable surfaces generally correspond to the work required to propel a wheelchair up a 3% slope. The proposed cut-off values for moderately firm and stable surfaces generally correspond to the wheelchair work per meter values for a 7% slope.

Objective ratings of firmness and stability should be disclosed to all users through trail signage.

Surfaces that are firm, but only moderately stable should be allowed on linear trails less than 0.5 mile in length (i.e., do not require a lot of turning or pivoting).

Surfaces that are both moderately firm and moderately stable should be allowed on level trails (less than 3% slope in any direction to allow drainage) less than 0.1 mile in length (distances that are similar to those found in indoor environments), or in confined outdoor areas that are level (less than 3% slope in any direction to allow drainage) and where the distances traveled are less than 50 ft (e.g., around a picnic table, on a campsite).

Based on these proposed specifications, the asphalt (ASPP), unpaved road mix (RDMX), path fines (PAFN), path fines with stabilizer (RDOL), and native soil (DIRP) surfaces tested in this research would be considered firm and stable under dry conditions. The wood chips (CPBR) and engineered wood fiber K (EWFK) would be considered moderately firm and stable and would potentially be allowed for limited distances. Engineered wood fiber J (EWFJ) would not be considered firm nor stable. Some carpeted surfaces currently considered “accessible” (i.e., maximum pile thickness of 0.5 in.) would not comply with the proposed specifications.

Recommendations for Future Research

• Due to the small and diverse group of subjects, additional research involving persons who are ambulatory with limited mobility would need to be conducted to validate the results of this study, and provide additional information on this subject group regarding which surfaces are accessible or preferred.

• Direct measures of energy consumption should be recorded in combination with subjective ratings of difficulty to obtain an accurate assessment of surface “accessibility” for the user.

• Future research should evaluate energy consumption using both linear travel and ambulation with turns. The evaluation of linear travel facilitates comparisons with results from previous research; however it does not accurately represent the energy expenditure of community ambulation (which almost always involves some turning). In order to compare results between studies, a standard test course design which incorporates both 90 and 180 degree turns would have to be agreed to by all researchers working in this area. The proportion of turning and straight travel for such a course should reflect the “typical” patterns of ambulation in the community. (See the Technical Report for details on the test courses used in this research.)

• The oldest subjects in the published literature were 65 to 70 years of age. Additional testing with individuals over 70 years of age would be required to verify specific surface accessibility requirements for that age group.

• Children with and without disabilities have higher levels of energy expenditure because they are less “practiced,” and therefore less efficient in their movement. Additional research would be required to verify whether children with disabilities have the capacity to access surfaces that require an increase in energy consumption relative to a paved surface.

• Additional research would be required to determine the validity and repeatability of the Rotational Penetrometer measurements on surfaces with slopes greater than 5%.

• The exact specifications for conducting Rotational Penetrometer tests under wet conditions (e.g., specifications for the wetting procedure, the intervals at which measurements should be made after the wetting procedure) or to determine the “wetness” of surfaces tested on-site would need to be developed and validated through future research.

• Based on the findings of this research, carpet on sloped surfaces may be an accessibility issue. Additional research should examine the existing requirements for carpet and carpetpad combinations.

• To evaluate the impact of other surface variables, such as slip resistance and the “levelness” or “evenness” of the surface, further research would be required.

• Additional research would be required to evaluate the impact of surface firmness and stability in combination with other trail characteristics, such as distance, grade, cross slope or obstacles.