National Trail Surfaces Study

II. Research Methodology

In 2004, the National Center on Accessibility began the development of protocols for a National trails surface study to evaluate alternatives to asphalt, concrete and boardwalk as suitable materials for making trails accessible to people with disabilities. By 2007 installation of surface materials for testing was begun at Bradford Woods located at Indiana University.

The following are the three research questions explored in “Section III: Result of the Study”:

• Does each of the 11 trail surface materials meet or exceed the classifications for firmness and stability as proposed by the US Access Board in their 2007 Notice of Proposed Rulemaking for Outdoor Developed Areas?

• When evaluating the firmness and stability of each of the 11 trail surface materials, how does each of the 11 trail surface materials compare to themselves over a 51 month time period?

• When evaluating the firmness and stability of each of the 11 trail surface materials, how does each surface compare to each of the other surfaces over a 51 month time period?

Selection of Locations

The longitudinal trail study was limited to the one geographic location of Bradford Woods located in Martinsville, Indiana, 30 minutes south of Indianapolis Indiana. Bradford Woods is an auxiliary enterprise of Indiana University and is part of the academic mission of the School of Public Health and is a unit of the environment, hosts various programs throughout the year that focus on adventure education, environmental education, and therapeutic recreation. Bradford Woods also hosts retreats and runs various camps. The 11 test plots were installed in a previously undisturbed wetlands area where the maximum running slope of any of the sections was 7.6 percent. The trail segments did not see high visitor use, and were restricted to just pedestrian access. The following are the average high and low temperatures and precipitation for Martinsville Indiana as recorded by month:

Average Temperature & Precipitation January to June

Average Temperature & Precipitation July to December

This site is within driving distance of the Bloomington-based research team and easily accessed at any given time throughout the length of the study. Bradford Woods was selected as a result of a direct advertising recruitment method for testing sites. The study was advertised on NCA’s website and through a news release disseminated by the NCA. Direct conversations were had with colleagues within the Department of Recreation, Parks, and Tourism Studies within the School of Public Health - Bloomington, to help recruit Bradford Woods as a potential test site. The selection of the location of the trail surface plots was purposeful within its location in the Wetlands area at Bradford Woods. Previous locations for surface testing did not include the factors associated with a wetlands installation and this particular site such as:

• A previously undisturbed ground surface;

• Minimal running and cross slope percentages (under five percent);

• Allows for manufacturer technical installation instructions to be met; and

• A physical environment with distinct ground characteristics (i.e. higher moisture content, less drainage, etc.).

Selection of Trail Surface Materials

A review of trail surfacing products conducted for this project identified approximately 80 different trail surface materials that promoted providing an accessible trail surface (PEL Consulting, 2004). Those trail surface materials that were similar products were listed together within each of five major categories:

• Constructed soil/aggregate surfaces (e.g. crushed aggregate or brick, pre‐stabilized granite, aggregate fines, organic or natural by-product soil stabilizers);

• Geosynthetics (e.g. geotextile, geocell, geoweb, geogrid);

• Plastic and rubber solid surfaces (e.g. rubber mats, composite decking, plastic lumber, snow fence);

• Wood surfaces (e.g. wood plank, chipped woods, engineered wood fiber); and

• Brick and concrete surfaces (e.g. interlocking brick, concrete, asphalt).

The surfaces included in the study were chosen for inclusion as a result of three factors: donated product, ability to verify the stabilizer applications were a match for the native soils at Bradford Woods, and providing verification of the product being 100 percent natural, environmentally friendly product.

In order to ensure the validity of the study, exclusion criteria were then created based on limiting the scope of research to ensure the identified research questions could be answered. Based on the criteria for identifying firm and stable, organic or natural by-product surface materials, the following category of surface materials were identified for participation in the study:

• Constructed soil/aggregate surfaces (e.g. crushed aggregate, pre-stabilized granite, aggregate fines, organic or natural by-product soil stabilizers).

A total of 11 surface materials (eight organic or natural by-product soil stabilizers, and three aggregate surfaces) were chosen based on their compatibility with existing soil and/or aggregate composition, and the manufacturer’s ability to provide lab results to verify the authenticity of the statement that their product is either an organic or a natural by-product. The following are the 11 surface materials evaluated in the study:

• ¼ inch minus crushed limestone and dust

• ¾ inch minus crushed limestone and dust

• ¾ inch minus crushed limestone and dust base and ¼ inch minus crushed limestone and dust top dress

• Klingstone 400

• Stabilizer

• StaLok

• Soiltac Liquid Mix-in

• Soiltac Liquid Topical

• Soiltac Powder Mix-in

• Soiltac Powder Topical

• Polypavement

Delimitations

The study was delimited in scope by the following:

• Data from this study were obtained from a longitudinal study administered through the National Center on Accessibility (NCA) at Indiana University;

• One category of surface materials, constructed soil/aggregate surfaces out of six identified were chosen for participation in the study;

• Size of the site limited total number of trail surface products that were able to be installed;

• Trail surfaces were evaluated on site using a Rotational Penetrometer (RP) to determine firmness and stability of the surface; and

• Firmness and stability readings were evaluated based on the recommended values of the U.S. Access Board in the Notice of Proposed Rulemaking for Outdoor Developed Areas (U.S. Access Board, 2007).

Limitations

The study is limited in scope by the following:

• Ability to generalize findings to trails in other locations with the same surfaces applied. Surfaces installed in other locations vary in terms of design parameters, frequency and type of use, site conditions, weather and climate;

• The sections of installed trail surface materials see different uses and frequency at Bradford Woods. Higher visitor usage, and varying types of usage, can affect the surface material;

• Not all soil stabilizers were able to be installed at the chosen site location due to soil/aggregate incompatibility thus limiting the ability to test a wider variety of surfaces which would contribute to a larger data set for comparison;

• Climate, adverse weather conditions, seasonal changes, and precipitation may affect trail surface materials; those differences in other locations cannot be accounted for with this study;

• Surfaces needed to be maintained and were maintained in order to ensure their safe usage for the daily operation of Bradford Woods.

Assumptions

In 2007 the U.S. Access Board published values for firmness and stability in the NPRM for Outdoor Developed Areas based on use of the Rotational Penetrometer. For the purpose of this study, it was assumed that:

• A Rotational Penetrometer can be used to determine firmness and stability for trail surfaces as they relate to accessibility

Definitions of Terms

For the purpose of this study and further discussion, the following terms will be used:

Aggregate. Crushed limestone (crushed shale or rock in regions that limestone is not available), natural soils, or dirt that is brought in from a different location than the actual site.

Firmness. The degree of surface resistance to deformation, especially by indentation or the movement of objects (U.S. Access Board, 2007).

Rotational Penetrometer. The instrument used in field-testing to test for compliance with the Outdoor Developed Areas Guidelines firmness and stability recommendations. The Rotational Penetrometer, developed by Beneficial Designs, uses a wheelchair caster placed on a spring loaded caliber in a metal tripod frame which suspends the caster about 6 inches over the surface. When the caster is released, the spring load gauge replicates the force of an individual in a wheelchair over a given surface. The penetration into the surface is measured for readings of “firmness.” The test for stability requires the caster of the Rotational Penetrometer to be moved from side to side to determine the horizontal displacement of the surface material.

Soil Stabilizer. A product that is applied either topically, or mixed-in that acts as a binding agent to either native soils or an additional type of aggregate. The soil stabilizers chosen for this study are all "green" products meaning that they come from natural by products.

Stability. The degree to which a surface resists change from contaminants or applied force, so that when the contaminant or force is removed, the surface returns to its original condition (U.S. Access Board, 2007).

Trail. A pedestrian route developed primarily for outdoor recreational purposes (U.S. Access Board, 2009).

Data Collection Procedures

The trail surface site is hosted by Bradford Woods but NCA staff collected all data. While the site for the study was not kept confidential and the test plots are identified by signage, no data results have been posted prior to this final report.

Upon consent to participate in this study, the site owner (Bradford Woods) was asked to designate a site coordinator to provide the principal investigator (NCA Trail Study Coordinator Nikki Montembeault) with any additional information necessary for data collection, such as vendor information, cost of product installation, materials needed, and any mandatory maintenance required. Consent from the manufacturers of the products consisted of the manufacturers agreeing to the release of their product names and data collected on their surfaces to the public, and to be used for future research endeavors. Within a maximum of one month from each surface installation, a preliminary accessibility assessment of the trail surface was conducted and the surfaces were tested for firmness and stability with the Rotational Penetrometer. This was considered the first set of data collected for the longitudinal study. Accessibility assessments and trail surface testing for firmness and stability were conducted on average, three months per year for 51 months. In addition to the data collected with the Rotational Penetrometer, photos were taken of individual surface materials at both the time of the installation and during the assessments; observational notes were recorded about surface conditions at the time of the assessments and external factors that may have influenced or affected the surfaces positively or adversely. Those external factors noted included external weather temperature, recent extreme weather conditions, sun and shade conditions of the trail, and season of the year (deduced by recording the month).

The 11 trail surface segments ranged in length from 30 feet – 200 feet (see the Qualitative and Observational Analysis by Surface Type for an accurate breakdown by trail surface segment). The parameters of the Rotational Penetrometer testing consisted of testing each trail segment for firmness and stability in five locations along the trail segment. The intent of the five firmness and stability readings was to ensure readings were gathered from various locations within the segment in the event that trail surface conditions varied. Potential causes for variation might be running and cross slope, a difference in drainage and/or adjacent runoff, and sun vs. shade location of reading locations.

Instrumentation for Analysis

One instrument, the Rotational Penetrometer (Figure A), was used for data collection. An on-site inspection form (Appendix C) was created to collect data on the 11 trail segments including Rotational Penetrometer readings, inspection location in feet from trailhead, ruts, tread obstacles, or other surface abnormalities. Testing for wheelchair accessibility specific to firmness and stability was conducted with the application of the Rotational Penetrometer as developed by Beneficial Designs.

Figure A Rotational Penetrometer

Treatment of Data

The research design for this study was developed to collect data on trail surface conditions, evaluate individual surface performances over time, note deficiencies, and compare across surface types. Through further analysis, results of trail surface tests for firmness and stability were compared within surface composition categories and across surface composition categories to determine the mean, range and standard deviation of each surface type. Descriptive statistics were used for analysis of data. A one-way analysis of variance (ANOVA) was used to determine if there was any statistical significance between surface composition categories. Sequence charts were run and analyzed for each surface composition category to determine if any patterns, similarities and/or differences between surface compositions could be discerned. Lastly, qualitative data on the surface material conditions during the site visit was collected in order to provide a narrative description of findings.