Peter W. Axelson, M.S.M.E., A.T.P. - Project Director
Denise Chesney, M.E.B.M.E. - Research Coordinator
Beneficial Designs, Inc.
Santa Cruz, California
- Patricia Longmuir, M.Sc. - Exercise Science Consultant
- Ken Coutts, Ph.D. - Exercise Physiology Consultant
- Stacy Rose - Research Assistant
- Jeremy Smith - Research Technician
- Joe Ysselstein, B.S. - Research Assistant
This material is based upon work supported by the U.S. Architectural and Transportation Barriers Compliance Board (the Access Board) under contract number QA96005001. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views or policies of the Access Board.
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.
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 email@example.com.
The Americans with Disabilities Act (ADA) Accessibility Guidelines currently specify that surfaces that are required to be accessible must be "stable, firm, and slip resistant" (Section 4.5.1) (USATBCB, 1992). These requirements are subjective; objective measures are not specified. These characteristics have been defined as:
Questions have arisen relating to the appropriateness and usability of various surface materials in outdoor environments required to be accessible. Additional information is necessary to provide guidance to designers and operators in order that they can provide non-discriminatory access for people with disabilities. Outdoor surface accessibility guidelines would also improve accessibility for all persons, regardless of their abilities, to a vast number of areas, including recreational facilities, playgrounds, beaches, parks, outdoor stadiums, boating and fishing docks, campgrounds, and hiking trails.
The objectives of this research were to:
Test courses were designed and built using nine different types of exterior surfaces (Table 1). The ADAAG Accessible Course was used to evaluate subjects' ability to ambulate in the community. This "access route" was 574.2 ft (175.0 m) in length, and included two 137 ft (41.8 m) sections with grades of 4% to 5% (one uphill, one downhill), and two 30-foot (9.1 m) ramps with grades up to 8.3% (one uphill, one downhill). The two Straight Courses were 984.3 ft (300 m) in length with a 32.8 ft (10 m) turning radius at each end. The "P" shaped Turning Courses were designed such that one circuit around the course provided 328 ft (100 m) of walking distance and involved turning for 10% of the distance (both 90 and 180 degree turns). (See the Technical Report for course details.)
The test surfaces were objectively measured using the Wheelchair Work Measurement Method and the portable Rotational Penetrometer. To determine the energy required, persons with and without disabilities walked or wheeled across each of these surfaces. For reference and comparison purposes, objective measures were also obtained on a slip resistant ramp at different grades and seven carpet/pad combinations (Table 2).
|Test Course/Test Surface
* Resin Pavement is a trademark of Road Products Corporation and Soil Stabilization Products Company, Inc. The Road Oyl registered trademark and patent are the property of Road Products Corporation.
Note: All carpet/pad combinations tested comply with current ADAAG
For purposes of comparison, objective surface measurement data are included from the "Measurement of Surface Characteristics for Accessibility" NIH-funded research project at Beneficial Designs. A wheelchair work measurement system and a portable surface measurement device were designed to objectively measure surface firmness and stability.
Wheelchair Work Measurement Method. Wheelchair work per meter values for straight and turning were determined for all test course surfaces except sand, under dry conditions using the Wheelchair Work Measurement Method in accordance with ASTM F1951-99 (formerly PS 83-97). Work per meter values were also determined for the reference ramp grades and carpet/pad combinations.
Rotational Penetrometer. The Rotational Penetrometer (Figure 1) is a portable device that provides accurate measurements of firmness and stability on a wide variety of surfaces. It can be used easily in the field, is suitable for trail use, and does not require a level surface for testing.
All of the test courses were measured using the Rotational Penetrometer under wet and dry conditions. Firmness was determined by applying a given force to the penetrator and then measuring the depth of penetration into the surface. The stability of a surface was measured by applying a given force, rotating the penetrator left and right 90 degrees, for a total of 360 degrees, and then measuring the final depth of penetration into the surface.
Subject Recruitment. Subjects were recruited by gender and mobility limitation (no known disability, ambulatory with limited mobility, ambulatory with assistive devices, and manual wheelchair use). Informed consent was obtained from each participant. Prior to beginning their participation in this study, subjects were screened for "at risk" conditions for exercise. To characterize the study population, background information was collected, including age, gender, disability, assistive device use, independence in activities of daily living, and physical activity participation.
Standardized Tests of Physical Fitness and Community Ambulation. Energy expenditure at rest and during ambulation can be significantly affected by the individual's level of fitness. In order to characterize the fitness levels of study participants, standardized tests of aerobic endurance (PWC170) and strength (hand grip) were completed.
Resting heart rate and energy consumption were measured with the subject seated or reclining on a couch. Heart rate was measured with a Polar heart rate monitor (Polar Vantage XL). Energy consumption was measured using a portable Aerosport KB1-C metabolic analyzer.
Subjects were asked to complete two laps of the ADAAG Accessible Course while their heart rate, energy consumption and velocity were recorded. Data were recorded during the second lap of the course. Upon completion of the ADAAG course, subjects were asked to rate their level of perceived exertion using the RPE Scale (Borg, 1974). Subjects were also asked to rate the difficulty they had walking or wheeling on the ADAAG course. Perceived difficulty was designed to consider factors such as the security of footing, obstacle negotiation, and effort required on slopes. The subjects rated the level of difficulty from 1 to 10 for both straight travel and turning on the surface using the Level of Difficulty Rating Scale. Subjects were instructed that a rating of "1" represented a hard, level, indoor surface. A rating of "10" was the difficulty level for walking on sand.
Energy Consumption During Ambulation. Measurements were recorded for subjects walking on the Straight and Turning Courses. Subjects walked on each surface at their preferred pace, until the physiological variables (energy consumption, heart rate, velocity) had stabilized (2-3 minutes) and the data collection period (an additional 2 minutes) had been completed. Rating of perceived exertion (RPE) and level of difficulty were recorded after the subject had completed each course. Subjects were instructed to rate the difficulty of each surface for both straight travel and turning. A combined level of difficulty rating was calculated as the weighted total of the straight and turning scores in relation to the amount of turning required for each course (10% turning for "P" course, no turning for the straight courses). The order of the surfaces tested was randomly assigned and a 10-15 minute rest interval was permitted between tests to ensure that the physiological measures had returned to resting levels.
Net energy consumption - the additional energy utilized during walking in excess of resting levels - was calculated for each surface. Relative oxygen consumption values (ml O2/kg weight/min) measured during the data collection period (stable, plateau phase) were averaged for the resting data and each test surface. The net energy consumption (ml/kg/min) was calculated by subtracting the average resting value from the value for each test surface. The net energy consumption was divided by the velocity of walking in order to standardize the data for comparison between subjects. Thus, the energy consumption for each surface (oxygen consumption/kilogram of body weight/meter) was standardized relative to subject size (body weight), resting metabolic levels and speed of ambulation.
Frequency tabulations were used to identify data entry errors. T-tests and correlations were used to evaluate the relationships between numerical data. The impact of categorical data was evaluated using analysis of variance (ANOVA) statistics. Statistical significance was set at p < 0.05 for all analyses.
What was measured and why?
Energy Consumption - Measuring the oxygen a person consumes indicates how much energy the body is producing. When the oxygen consumption is measured at rest (i.e., with the person sitting or lying down), the amount of energy the body is using to function (e.g., for making the heart pump, organs function) can be determined. If an individual walks at a steady pace for 3 to 4 minutes, energy consumption will stabilize at a level that is equal to the energy required to negotiate that environment. By subtracting the resting oxygen consumption from the oxygen consumption while walking/wheeling, the amount of energy being used specifically for walking can be determined.
Walking Speed - If adults are asked to walk at their freely chosen speed they automatically select the type of movement and speed that requires the least amount of energy. If an individual is forced to walk either faster or slower than this chosen pace, the amount of energy used will increase. Therefore, for this study, subjects were allowed to determine their own preferred pace so that energy consumption in its "most efficient" state could be measured.
Heart Rate and Rating of Perceived Exertion - Rating of perceived exertion (RPE) is a research scale used to document the individual's perception of how difficult it is for his/her body to perform an exercise (i.e., how hard the individual's lungs are breathing, and heart is pumping). RPE scores have been shown through research to be consistently related to measures of heart rate and amount of exercise, regardless of the type of exercise. In general, the RPE score is equal to the steady state heart rate divided by 10.
Level of Difficulty - Level of difficulty is similar to the rating of perceived exertion in that it attempts to quantify the individual's subjective perception of the activity. However, it differs from the rating of perceived exertion in that it is not specific to how the heart and lungs are performing. Often, an unstable surface, for example, may be perceived as very difficult because of the unstable footing, even though the individual does not have to exert him/herself. Level of difficulty was recorded to evaluate factors (e.g., ease of slipping, uneven surfaces) that would not necessarily affect the energy consumption but may impact the overall "accessibility" of the surface.
Why test on straight courses and P-shaped turning courses?
Constructing long test courses enables comparison of subject data with research done by other investigators in which subjects walk on a straight linear course or in large diameter circles or ovals. However, the cost for producing these course designs with a number of surface materials would be very large. As a compromise, the construction of two long courses enabled some comparisons with published research without generating prohibitive surface construction costs. In this study, there was also a desire to have the subjects walk on the test surfaces in a manner that would reflect the types of ambulation that would represent functional mobility. This functional mobility includes both turning and walking in a straight path on any given surface. The "P" courses were designed so that the subject was turning for approximately 10% of the total distance.
What happens when people walk under more difficult conditions?
In general, when people walk under more difficult conditions there is: 1) a decrease in speed (to decrease the energy required), 2) an increase in heart rate (to pump more oxygen to the muscles), and/or 3) an increase in total energy consumption (when the other compensating mechanisms are not sufficient).
Which surfaces are accessible to everyone?
There are no surfaces that are accessible to everyone, because there is an infinite range of abilities among the population. Participants in this study were recruited to represent a variety of disabilities. They completed standard tests of fitness to ensure that a variety of ability levels was represented. Currently, our society has made a decision on what is considered "sufficiently accessible," that being environments that comply with the current ADAAG. Although it is recognized that not all individuals have independent access in an ADAAG environment, these standards have been designated "accessible enough" for most people. It should be noted that all powered mobility technologies are able to negotiate ADAAG environments and represent an option for persons without the functional mobility to negotiate these environments.
Wheelchair Work Measurements. The work required to propel a wheelchair in a straight path provided an indication of the firmness of the surface. The work required to propel a wheelchair through a 90 degree turn provided an indication of the stability of a surface. Wheelchair work per meter values were not obtained for sand because it was not possible to propel the wheelchair through this surface. The work to negotiate a ramp was linearly related to the angle of the ramp. The work required to propel across the level surface was compared to the work required to propel up or through a turn on various ramp angles in order to relate the work required for the surface to ADAAG specifications for "sufficiently accessible" levels of work (e.g., 8.3% grade for 30 feet).
The dirt (DIRP), chipped brush (CPBR), and engineered wood fiber (EWFK and EWFJ) surfaces had higher work per meter values compared to the other exterior surfaces (Figure 2, Figure 3).
Chipped brush and the engineered wood fibers (J and K) all required more work to roll on than a 3% ramp (chipped brush equates approximately to a 3.7% ramp). These three surfaces also required more work to negotiate than the ADAAG course and the crushed granite with stabilizer. It is recommended that these surfaces be considered moderately firm and stable, and be suitable for use in level areas for a limited distance (e.g., around a campsite) or for shorter distances on trails.
Note: The "I" shaped vertical lines indicate the standard error of the mean, a statistic that estimates the variability expected if repeated samples of the same size are taken. It is calculated by dividing the standard deviation of the observations by the square root of the number of observations.
Rotational Penetrometer Measurements of Firmness and Stability. The Rotational Penetrometer penetrated significantly more on the dirt (DIRP), chipped brush (CPBR), engineered wood fiber (EWFJ and EWFK), and sand (SAND) surfaces compared to the other exterior surfaces, indicating decreased firmness and stability (Figure 4, Figure 5). The results of the Rotational Penetrometer correlated with those of the Wheelchair Work Measurement Method.
All of the exterior surfaces, except sand, became less firm in wet conditions (Figure 6). All exterior surfaces, except chipped brush (CPBR), became less stable when wet (Figure 7). While engineered wood fiber K (EWFK) became only slightly less stable, engineered wood fiber J (EWFJ) and path fines (PAFN) became much less stable. Path fines without stabilizer and dirt, while stable in a dry condition, became unstable and moderately stable when wet, respectively.
Thirty-nine (39) subjects (23 female, 16 male) participated. Subjects were classified into one of four groups: 1) No disability - no known disability or mobility limitation; 2) Ambulatory with limited mobility - persons whose mobility was impaired, but who did not use any type of assistive device for ambulation; 3) Ambulatory with assistive device - persons with a mobility limitation who used an assistive device, such as crutches, a cane, a walker, a surgical implant or prosthetic limb; or 4) Wheelchair user - manual wheelchair users (Table 3). The subjects within each disability category had a wide range of fitness and ability levels.
A statistically significant correlation between total energy required for the ADAAG course and the energy required for each surface (except sand) indicates that for a given subject the level of community mobility is related to the "accessibility" of outdoor surfaces.
On the surfaces objectively measured as firm and stable, subjects with higher fitness levels had lower heart rate and RPE scores (i.e., walking was less difficult). On dirt, wood chips, and engineered wood fibers J and K, fitness level was correlated with all measures of surface "accessibility." Higher fitness levels resulted in lower energy consumption, higher velocity, lower heart rate, and lower RPE.
Table 3. Demographic Characteristics of Study Participants (Mean ± 1 SD, (min - max)
|Dis||G||N||Age (yrs)||Yrs with Disability|
|All||F||23||35.9 ± 9.0 (22 - 49)||15 ± 12 (3 - 47)|
|M||16||34.3 ± 7.7 (24 - 46)||11 ± 9 (3 - 29)|
|NoDis||F||7||32.7 ± 9.1 (22 - 45)||NA|
|M||7||33.2 ± 7.7 (24 - 44)||NA|
|AwLM||F||8||37.4 ± 10.6 (22 - 47)||17 ± 15 (3 - 47)|
|M||1||44.5 (44.5)||3 (3)|
|AwAD||F||4||36.5 ± 8.0 (25 - 41)||12 ± 9 (3 - 24)|
|M||2||30.7 ± 8.3 (25 - 37)||14 ± 9 (7, 20)|
|Wc||F||4||37.5 ± 8.4 (29 - 49)||13 ± 13 (5 - 32)|
|M||6||35.0 ± 8.1 (26 - 46)||11 ± 9 (3 - 29)|
The energy consumption results are shown in the following table and figures.
Table 4. Average Energy Consumption (mlO 2/kg/m) for Each Surface by Subject Group
|Energy Consumption above Resting Values|
Where: Rest = Resting energy consumption
Objective measures of surface firmness and stability were compared to energy costs (energy consumption, velocity, RPE and level of difficulty) to negotiate the surfaces. All human subject measures were significantly correlated to the objective measures. All correlations were strong (>0.85; maximum 1.0 for a perfect correlation), except for the medium correlation between penetrometer firmness and velocity (r = -0.6). Velocity was inversely related to firmness and stability. All other variables were directly related to firmness and stability.
There was a strong, second order polynomial relationship between the Rotational Penetrometer stability measurements and the average energy cost for wheelchair users. As the surface became less stable (Rotational Penetrometer displacement increased), the energy cost for wheelchair users increased more dramatically than for ambulatory individuals with and without disabilities.
What would happen with other disability groups? Overall, our results are very similar to the published literature for similar populations. Therefore, we would hypothesize that our results would also be similar if we had tested other disability populations or older adults. The published literature for children indicates that their energy consumption levels are considerably higher than for adults with similar disabilities. In general, children have higher levels of energy expenditure because they are less "practiced" and therefore less efficient in their movement. However, generally children can also tolerate higher levels of energy expenditure, and therefore higher levels of energy consumption do not necessarily relate to a lack of accessibility. (See the Technical Report for detailed comparisons and complete references).
What proportion of the population could negotiate these surfaces? Energy consumption, level of difficulty rating and rating of perceived exertion were evaluated to determine the proportion of our subjects who considered each surface to be "accessible." An "accessible" surface was one that required less than 0.20 mlO2/kg/m energy consumption, a level of difficulty rating less than 6 ("difficult"), or a rating of perceived exertion less than 13 ("somewhat hard"). Over 90% of our subjects found the objectively firm and stable surfaces to be "accessible," while over 80% of the subjects considered the packed dirt surface "accessible." In comparison, less than 70% of the subjects considered the wood products or sand surfaces to be accessible. Further, the percentage of subjects who considered sand to be accessible is probably artificially high because many subjects, particularly those using wheelchairs, refused or were unable to complete the sand test. If we assume that other disability groups would have similar results (as indicated above), we can hypothesize that in general, at least 80% of the population would consider the surfaces that meet the proposed criteria for "firm and stable" to be accessible.
The results of this pilot study suggest:
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.
|Firmness||Penetration Depth||Firmness Rating|
|Firm||0.3 inch or less||3 or lower|
|Moderately Firm||>0.3 to 0.5 inch||>3 to 5|
|Not Firm||>0.5 inch||>5|
|Stability||Penetration Depth||Stability Rating|
|Stable||0.5 inch or less||5 or lower|
|Moderately Stable||>0.5 to 1.0 inch||>5 to 10|
|Not Stable||>1.0 inch||>10|
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.
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
The development of objective surface measurement devices and objective surface testing was conducted with funding from the National Center for Medical Rehabilitation Research in the National Institute of Child Health and Human Development at the National Institutes of Health through Small Business Innovation Research Phase 1 Grant # 1 R43 HD30979-01 and Phase 2 Grant # 2 R44 HD30979-02, "Measurement of Surface Characteristics for Accessibility."
The authors would like to thank Dr. Ken Coutts for his assistance with the research protocol and data analysis, and Dr. Rory Cooper and Dr. David Gray for their comments on the research protocol and draft technical report.