Trail Surfaces: What Do I Need to Know Now?

Surface is a critical component of an accessible trail. There are two main aspects for consideration regarding accessible trail surfaces. First, the surface must be firm and stable so that the users with disabilities do not expend unnecessary energy that could be used enjoying the trail. Second, there are a variety of surface materials available to enhance accessibility, therefore, the functionality and aesthetics of each product should be considered.

Background

Crushed fine surface used on the Boiling River Trail at Yellowstone NP.  A woman walks next to a man using a wheelchair.Americans with disabilities have experienced discrimination, not only by misconceptions and attitudes based on ignorance, but also by designs of the physical environment that fail to account for the natural variations in human mobility and understanding. The U. S. Access Board is responsible for developing minimum accessibility guidelines to prevent and eliminate physical barriers created by such designs. In 1997, the US Access Board appointed the Regulatory Negotiation Committee to develop recommendations for accessibility to Outdoor Developed Areas. The committee submitted its Final Report with recommendations in 1999.  In June 2007 the U.S. Access Board issued a Notice of Proposed Rulemaking for Accessibility Guidelines on Outdoor Developed Areas under the Architectural Barriers Act.  Until final standards are issued, the guidance in the NPRM provides the best available information for creating access in the outdoors.  Understanding and following the proposed accessibility guidelines will provide increased trail opportunities and experiences for a broader spectrum of visitors with varying abilities.

Firm & Stable

Concrete Trail with rest area.The proposed accessibility guidelines require a trail surface to be firm and stable. The intended use and length of the trail may regulate the degree of firmness and stability preferred. For example, a trail with a length greater than .5 miles should be very firm and very stable. Trail lengths between .1 and .5 miles should be moderately firm and stable. Firmness means the surface "does not give way significantly under foot." Stability means surfaces "do not shift from side-to-side or when turning." For example, when one walks or wheels on sand, the sand shifts and the foot or wheel sinks. When turning, a foot or wheel will displace the sand. Therefore, sand is neither firm nor stable. Firmness and stability can be measured using a rotational penetrometer. When controlled pressure is applied to the penetrometer, the penetration depth of the device is measured as the degree of firmness while rotating the penetrometer will provide the stability measurement. The penetration guidelines below further illustrate characteristics of firmness and stability.

ANSI/RESNA Standards for Firmness & Stability

 

Very Firm/Stable

Moderately Firm/Stable

Not Firm/Stable

Firmness

 0.3 inch or less

> 0.3  < 0.5 inch

> 0.5 inch 

Stability

 0.5 inch or less

 > 0.5 < 1.0 inch

 > 1.0 inch

 

When deciding on a trail surface material, a site manager should ask the following questions:

  • What is the goal of the trail experience?
  • Who is the primary user group?
  • What are my budget and maintenance constraints?
  • What are the geographical characteristics of the trail site?

If the goal of the trail is to provide a physically and mentally challenging experience for hikers, it may alter the function of the trail to use an accessible surface. However, if the goal of the trail is to provide a leisurely nature walk, an accessible surface is sure to enhance the trail experience for most visitors.

Budget Constraints

There are two aspects to consider regarding budget constraints. First, the cost of the surface material must fit into the funding available to construct or alter the trail. Second, current and future maintenance budgets should be considered. Some surface materials will have a higher initial cost and use less maintenance resources in the future. On the other hand, some materials may cost less to install, but require a higher percentage of the maintenance budget in the long run.

Consider the following situations to illustrate this point: 

Trail surface with compacted gravel and crusher fines.Decision-Maker A has received one-time funding to build a trail. Decision- Maker A reviews her maintenance budget and decides she has relatively no resources to maintain the trail's accessibility in the future. Although the initial cost is higher than other surfaces she received estimates on, decision- Maker A decides to use concrete as the surface material for the trail because it requires less maintenance resources over the long run.

Decision-Maker B recently received a small sum of money to create an accessible trail. When reviewing his site's budget, he realizes the maintenance budget can absorb the material and personnel cost of keeping the trail accessible in the coming years. Decision-Maker B decides to use a compacted small gravel and fines mixture as the trail surface because the initial cost is lower than other estimates he received and his site has the personnel and money to maintain this trail year after year. Trail surface with compacted gravel and crusher fines. Some surface materials will have a higher initial cost and use less maintenance, while other surfaces may cost less to install but require more maintenance in the long run.

Surface Types

Considerations to Ensure Access

A group of four people head out on the Boiling River trail.The type of surface you choose will also depend on the geographical and climatic characteristics of your site. Some surfaces work better in sandy, dry regions and others will be most beneficial in flat, humid areas. It is important to ask the surface supplier for references regarding the use of their product in a region similar to your own. Then talk to the trail personnel that have experience with the surface application. What has their experience with the surface been? How has it held up over time? Has the surface required any maintenance? If they were building a new trail, would they use the same surface again?

There are a variety of materials available for firming and stabilizing trails. A common type of material is a soil stabilizer; a product that binds different surfaces together. Stabilizers can be applied directly to the native soil or be mixed with other products. As a trail surface material, however, it is more common, and possibly less costly in the long run, to prepare a base surface for application. The soil stabilization product is mixed with quarter-minus stone and fines, compacted and then smoothed and shaped according to trail drainage requirements. Unitary surfaces, such as concrete and asphalt, are considered accessible surfaces. Many site managers feel these two surfaces are not natural looking and therefore lower the natural experience for the visitor. However, it is now possible to stain, stencil and color concrete to a more desirable pattern.

Brick surface buckled by freezing and thawing.Asphalt surface edge breaking away.Wood is a firm and stable surface initially, yet it is susceptible to environmental conditions. Wet weather can rot wooden planks and the hot sun makes them brittle. Even with treated wood or sealants, wood surfaces are often subject to "heaving" in extreme seasonal temperature changes.

Another option that may provide a natural feel to the trail for the visitor is recycled plastic lumber. This lumber is made from recycled plastic, such as milk jugs, then colored and designed to give the look of natural wood. The initial installation of this product is quite labor intensive, however the future maintenance needs are considerably lower than that of natural wood. 

Maintenance & Installation

As with any product, maintenance is integral to the accessibility of a product. Maintenance needs depend on many variables including weather, climate, volume of use, type of product, installation procedures and age.

A directional star is stained multi-colored in concreteA concrete trail may have been accessible when it was installed twenty years ago, but other variables may have caused the concrete to buckle and crack. If the condition of the material causes an aspect of the trail not to comply with standards, then the trail is not accessible. A good example of this is brick. When first installed, it is possible that brick surfacing is compliant with accessibility standards for trails. However, freezing and thawing may cause brick to buckle or "heave" causing a tread obstruction in the trail.

Installation and application need to be followed closely to ensure the accessibility of the surface. The planning, preparation and surface product may be correct for accessibility, however, if the installation procedures are not carefully followed and monitored, the end trail may not be accessible. For soil stabilizers and concrete, any variation in the compound mixing or compaction may cause the product to fail.

Natural wood and plastic lumber will need to be anchored properly and placed in a manner that combats increased spacing between the boards. Asphalt may need to be sealed to hinder cracking and compacted gravel will need to properly compact.

Other Considerations for Selecting Surface Materials

An accessible trail through a wooded forest.Visible footprints in a sandtrail.There are a variety of surfaces that are not accessible to people with mobility impairments. Through both research and case law, several surfaces have been determined to be inaccessible. Sand particles are too fine to give support, therefore retreating under pressure. Pea gravel, mulch and woodchips are pushed aside by crutches and wheelchairs, thereby creating an unstable surface to traverse. Large gravel rocks are an extremely difficult surface on which to maneuver wheelchair tires and crutches. Soil indigenous to the area may be accessible if properly compacted and maintained, however, weather conditions can alter the accessibility of such a surface in a matter of minutes. Deciding on a surface material for an accessible trail will take time and effort. Keep in mind that just because someone claims a surface is accessible, does not mean it is. A thorough evaluation of your needs and comprehensive research into the materials and their suppliers should ensure an accessible trail surface that can be enjoyed by all visitors.

 

The citation for this article is:

National Center on Accessibility.  (Fall 2001, revised October 2007).  Trail surfaces: what do I need to know now?  Bloomington, IN: National Center on Accessibility, Indiana University-Bloomington.  Retrieved from www.ncaonline.org.