NCA Publishes Results of Trail Surfaces Study


BLOOMINGTON, Ind. — The National Center on Accessibility has published results of its national study of trail surfaces.  The project assessed the firmness and stability of 11 different types of natural aggregate and treated soil surfaces over a four-year period to determine their effectiveness after exposure to the elements, freeze and thaw cycles, and other factors. The study was sponsored by the U.S. Access Board.

Researchers created test trail segments that ranged in length from 30 to 200 feet at Bradford Woods, the 2,500 acre outdoor education and leadership center of Indiana University. The study included three trail segments with a crushed limestone surface and eight with soil surfaces that were treated with organic or natural by-product stabilizers. The limestone surfaces involved different aggregate sizes (1/4” maximum, 3/4” maximum, and a combination of both in a dual layer) that were at least six inches deep and compacted to a rate of 90%. The other surfaces tested were created with stabilizers applied directly to the soil or mixed with an aggregate. The stabilizers tested included polyurethane, organic plant matter, two kinds of polymer, and four types of vinyl acetate copolymer applications.

The project team used a field test device known as a rotational penetrometer to measure surface firmness and stability. This instrument utilizes a wheelchair caster and a spring loaded gauge to replicate the propulsion of a wheelchair across a surface. Penetration measures determine the degree of firmness, while stability is gauged by the horizontal displacement of the surface material from the side-to-side rotation of the caster. Measurements were taken at five different locations along each of the 11 test trails every 3 or 4 months over a 51 month period. In addition to these measurements, researchers noted changes observed in the trail surfaces.

Based on the values assigned to the firmness and stability measurements, the findings indicate that several types of surface materials tested, when installed according to the study’s protocols, maintained a consistently firm and stable surface. These included the 3/4” size limestone aggregate, the polyurethane stabilizer, and one of the polymer stabilizers. In addition, the researchers concluded that based on the study’s data, “a trail composed of an all-aggregate material, when constructed to specified parameters, could be maintained with little or no maintenance as a firm and stable surface.” However, they also identified areas where further research is needed.

In a second phase of the project, researchers conducted a nationwide survey of trail managers to gather information on types of surface materials and treatments used and their effectiveness. Among 39 trails reviewed in the survey response, most were composed of native or natural soils or crushed rock and only a small portion (less than 8%) involved some type of stabilizer.

For more information on the project, contact Sherril York, Ph.D., Executive Director of the NCA, at, (812) 856-4422 (v), (812) 856-4421 (TTY), or Bill Botten of the Access Board at, (202) 272-0014 (v), or (202) 272-0073 (TTY).

Final Report (HTML)