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The Public Right-of-Way Accessibility Guidelines (PROWAG) rulemaking has concluded. The PROWAG final rule has been published in the Federal Register. Please visit the Access Board’s PROWAG page for the guidelines.

Stabilized Engineered Wood Fiber for Accessible Trails


Wood chip surfaces on trails create difficulties for those who use mobility aids, such as wheelchairs and walkers, due to their softness, shifting, and uneven surface. This report is part of the third phase of research in pursuit of an accessible stable and smooth surface based on wood fiber. The study originally targeted the use of engineered wood fiber (EWF) (ASTM 2004) for playgrounds. In Phase I, processing tech-niques and material properties were evaluated in small benchtop and full-depth laboratory tests (Laufenberg and others 2003). Phase II involved further development of the best Phase I system in 6-month outdoor field testing (Laufenberg and Winandy 2003).

In Phase III of this project, we investigated the applicability and field performance of the two best candidate resin/EWF systems. The previous phases had shown that our new re-sin/EWF systems can enhance mobility as related to the Americans With Disabilities Act (ADA) and can perform in an outdoor environment. This report describes the develop-ment of a concept for stabilizing EWF to improve wheelchair and walker accessibility for outdoor recreational trails where traditional paving would be costly and would detract from the natural aesthetics. In this portion of the Phase III study, we installed our two most promising EWF stabilizing binders on a walkway across a sandy beach extending down to the water’s edge. This surfacing material concept was to mix a binder with EWF to create a stiff (firm) and scuff-resistant (stable) composite. Stabilized EWF (SEWF) is a system that has enhanced accessibility and should reduce erosion and maintenance costs for trail systems.


The initial research effort included a variety of resin (e.g., latex, silicone, and polyurethane) binders and various types of EWF. We chose adhesive binders for their inert and non-toxic nature in the environment and the retention of a natural look for the surface. Consideration was given to the need to add material or patch the surfaces after major damage. Use of a trail surface for 3 to 5 years was considered adequate time for the binder to fulfill its function. These adhesive systems have not been previously used in this application with EWF, therefore there is no experience with their functioning for that extended period. The preliminary evaluation included laboratory testing of energy absorption and surface firmness and stability on trial surfaces in 0.5- by 0.5-m (18- by 18-in.) plywood boxes; the surfaces had a uniform depth of 0.3 m (12 in.). Seven systems were identified as having reasonable performance and thence recommended for Phase II outdoor field evaluations.

Phase II research focused on outdoor evaluation of the binder and fiber options identified as minimally acceptable and promising in the Phase I evaluations. The Phase II work studied field durability and looked at changes in performance by quantifying the impact and accessibility of these novel surfaces after field exposure. This series included seven surface treatments, and a control surface, installed in a series of outdoor test beds in Madison , Wisconsin , to gather field experience on long-term performance and durability. The binders evaluated were (a) synthetic latex emulsion, (b) a low molecular weight silicone, and (c) foaming and non-foaming resilient polyurethane. Systems were evaluated over a 6-month period, from April to October 2002.

Tests were performed at regular intervals to provide a quantitative measure of accessibility. The results indicate that latex and polyurethane stabilizers consistently met the requirements for accessibility on playgrounds (Laufenberg and Winandy 2003). The foaming polyurethane formulation produced a hard brittle shell that became even harder with exposure/age and would increase the injury rate for falls on the surface. The silicone system did not maintain its integrity adequately during the rain/dry cycles in this outdoor test.

Monitoring of the Phase II test plot continued for 2 years after the initial 6-month evaluation reported by Laufenberg and Winandy (2003). In those 2 years, the synthetic latex emulsion and the non-foaming polyurethane continued to performed acceptably. As anticipated, the foaming polyurethane system continued to harden with exposure, rendering it unsuitable for meeting the impact absorption requirements for playground surfaces.


The original development work, though targeted toward playground improvements, was eventually seen as a potential improvement for trail surfacing. Following the preliminary field trials, professionals involved in recreational surface development encouraged us to investigate the concept for trails. For trails, the primary emphasis was accessibility and natural aesthetics, and impact performance was a secondary characteristic. However, many processing and handling issues for playgrounds were also considerations for trail construction and use. Several such issues were considered. This study explores the use of the resin/EWF system as a surfacing material for accessible outdoor recreation trails.

Acceptable Trail Surfacing Requirements

Current trail design considerations include quantity of traffic and type of use, such as walking and wheelchair use, biking, horse riding, and other allowed uses. Trail surfaces are cur-rently considered accessible only if the surfacing material is firm, stable, and slip-resistant and the trail has the engineered attributes of adequate width, moderately short slopes, passing spaces, and appropriate signage. A traditional paving mate-rial such as asphalt and concrete may be appropriate, but this type of surface is expensive to construct, requires the use of heavy materials and equipment, and may detract from the aesthetics of the trail.

The Americans with Disabilities Act (ADA 1990) states that accessible surfaces shall be stable, firm, and slip-resistant. These three criteria have not been defined adequately within the ADA Accessibility Guidelines for quantitative measure-ment on any specific surface. Currently, the only objective method that is suitable for assessing the firmness and stability of playground surfacing systems is the rotational penetrometer (Axelson and Chesney 1999).

As when constructing trails with native soils, it is very desir-able to drain water quickly away from the surface of a SEWF trail. This is critical in maintaining the stability of native soils and for reducing the biodeterioration potential of a wood fiber based surface. Keeping water off the surface also main-tains adequate friction on the stabilized EWF during sub-freezing temperatures. The rotational penetrometer, a port-able measurement device that simulates a wheelchair caster negotiating the test surface, was used to assess the level of accessibility.

We also needed to consider several practical aspects for processing the SEWF material and maintaining a safe work environment. Based on our experience in field applications, stabilizing binders needed to be applied on site or mixed with the EWF no longer than 1 h prior to placement on the ground surface. The practical considerations were (a) cure/set time prior to surface use, (b) range of EWF moisture and temperature conditions acceptable for use, (c) emission of fumes or odors, workable exotherms, and toxic or other chemical release/concerns from the binder/ EWF mixture, and (d) deleterious effects of SEWF on trail users.