Previous accessibility standards such as the Uniform Federal Accessibility Standards (UFAS) and the Americans with Disabilities Act Accessibility Guidelines (ADAAG) address the built environment, "the bricks and mortar." These guidelines do not transfer well to the natural environment. The built environment is open to manipulation. For example, if there is a hill where someone wants to build the parking lot for a store, then a bulldozer is used to level the area. In contrast, the natural environment includes factors, such as the weather, that are out of human control. The natural environment is part of the experience people wish to enjoy on a trail.
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.