Trail Surfaces: What Do I Need to Know Now?
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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.
|Crushed fine surface used on the Boiling River Trail at Yellowstone NP.|
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. Until final guidelines are approved,
the report generated by the work of this Committee provides the
best information available for making trails accessible. Understanding
and following accessibility guidelines will provide increased trail
opportunities and experiences for a broader spectrum of visitors
with varying abilities.
Firm & Stable
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.
|Concrete Trail with
ANSI/RESNA Standards for Firmness &
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.
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
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.
- Considerations to Ensure Access
|The NCA staff climb the hill.
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
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.
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
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
A 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
|(Left) Visible footprints
in a sandtrail.
||(Right) An accessible
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.
For more information on Trail Accessibility and Surface
Visit the National Center on Accessibility’s website at
or contact NCA at:
(812) 856-4422 (voice)
(812) 856-4421 (tty)
Final Report on Outdoor Developed Area
U.S. Access Board