Recreation trails are designed to provide a recreational experience. Use of a recreation trail is a choice made by those individuals who desire the experience that the trail provides. Recreation trails should provide users with disabilities with access to the same range of trail experiences offered to other users at the site. This means that trails should be designed to reach destinations or points of interest and travel through various environments. Providing access to people with disabilities is best achieved by providing trail information in multiple formats and by minimizing grade, cross slope, barriers, and the presence of surfaces that are soft or unstable.
Any trail that is specifically designed for pedestrian use should also be designed to provide access to people with disabilities. Trails that are not designed to provide access for pedestrians, such as single-user mountain bicycling, horseback riding, or off highway vehicle trails, do not need to be designed to provide access to pedestrians with disabilities. However, these trails should be designed to provide access to people with disabilities who will be using the equipment associated with the intended trail use, such as a mounting area or platform for equestrians who use wheelchairs, and amenities such as parking and restrooms should also be accessible.
In the past, many "accessible" recreation trails were designed with a length less than a quarter mile, no grade or cross slope, and with a wide, paved surface that made a loop around or near the parking lot, picnic area, or nature center. Individuals looking for a short, easy stroll, such as travelers who need to stretch after driving long distances, often enjoy these trails. Although these types of trails may meet the needs of some users, they usually do not provide a complete experience of the environment or elements available at the site. Therefore, it is not desirable to design all trails to these same standards. Trails that are intended to provide access to people with disabilities should be designed to provide a range of opportunities so that all trail users can experience the various environments offered at the site.
The design recommendations presented here primarily reflect the work of the Regulatory Negotiation Committee on Accessibility Guidelines for Outdoor Developed Areas (U.S. Access Board, 1999b). These recommendations, or a slightly modified version, will form the basis of a proposed rule that will be published by the Access Board for public comment. Although no trail can provide access to all individuals, trails that meet the Committee's recommendations are considered accessible under the ADA.
It is critical that designers recognize that these specifications do not represent an exact point, beyond which the trail will be completely inaccessible to all individuals with disabilities. People with disabilities can and do use all types of trails. Some people, with and without disabilities, choose to travel on extreme trails, such as to the summit of Mt. Everest or the South Pole. Others rarely, if ever, venture off of the sidewalk, or some people have disabilities that prevent them from even going outdoors. Therefore, designers should keep in mind that some people with disabilities will always be able and interested in using a trail regardless of its exact design specifications. Furthermore, more people are able to enjoy different trail experiences because of advances in adaptive equipment.
Trail designers and builders should strive for maximum accessibility. However, in situations where it is not possible to fully comply with the recommended specifications for trails, designers are encouraged to comply with the recommendations to the greatest extent possible. It is essential that designers recognize the continuum of abilities among recreation trail users. The more the trail conditions vary from the recommended specifications, the larger the proportion of people who will not be able to access the trail. On trails where it is not possible to fully comply with the design recommendations, designers should ensure that the non-compliant sections are minimized in length and severity. For example:
The proposed Accessibility Guidelines for Outdoor Developed Areas would require newly designed or newly constructed and altered portions of existing trails connecting to designated trailheads or accessible trails to comply with the proposed guidelines. The guidelines recognize that the natural environment often will prevent full compliance with certain technical provisions. Departures are permitted from certain technical provisions where at least one of four conditions is present:
Outdoor Recreation Access Routes (ORARs) are paths that connect accessible elements within a picnic area, campground, or designated trailhead. These paths provide a means of access for people with disabilities to reach built elements that are part of the recreation experience. For example, the paths leading from the parking lot to the visitor center or to a picnic area from a campground would be considered ORARs.
The U.S. Access Board has addressed design considerations for ORARs through the work completed by the Regulatory Negotiation Committee on Accessibility Guidelines for Outdoor Developed Areas. According to the Committee, ORARs should be designed within the following specifications:
Figure 15-3. Recreation trails attract a variety of user groups. Providing signs that clearly indicate which users have the right of way will help mitigate conflict. Motorized recreation vehicles should be required to yield to other users.
Many recreation trails attract a variety of user groups. Some trails are designed for multiple user groups; others attract a variety of users in addition to those for whom the trail was designed. Each trail group has specific interests and needs in terms of trail design. Therefore, whenever there are multiple users on the same trail, there is the potential for conflict.
People with disabilities may be particularly affected by trail conflicts if they do not have the ability to quickly detect or react to hazards or sudden changes in the environment. To improve the trail experience for all users, including people with disabilities, designers and planners should be aware of potential trail conflicts and attempt to minimize the probability that conflicts will occur by employing innovative trail solutions. Basic conflicts can be reduced by:
In many situations, the condition of the surface is the most important factor in determining how easily a person with a disability can travel along a recreation trail. Surfaces that are very soft or filled with obstacles are difficult for all trail users and often exclude people with disabilities. The accessibility of the trail surface is determined by a variety of factors including:
There are various surface materials that can be used in outdoor environments. Recreation trail surfaces are most commonly composed of naturally occurring materials such as packed soil, grass, or rock. Some trails may use crushed stone or native soils mixed with soil stabilizing agents. However, surfaces ranging from concrete to sand may be used depending on the designated user types, the anticipated volume of traffic, the climate, and the conditions in the surrounding environment. High use trails passing through developed areas or fragile environments are commonly surfaced with asphalt, concrete, or soils mixed with stabilizing agents to maximize the longevity of the trail surface, minimize the maintenance requirements, and limit the environmental impact of the trail.
Selection of a trail surface material should be based on the type of user groups, the distance of the trail, the type of setting or experience desired, and the characteristics of the natural environment. The surfacing material on the trail significantly affects which user groups will be capable of negotiating the terrain. Soft surfaces, such as dry sand or pea gravel, are more difficult for all users to negotiate and present particular hazards for those using wheeled devices including road bicycles, walkers, and wheelchairs not designed for rugged terrain. In contrast, other users, such as equestrians, joggers, and some people who walk with assistive devices, prefer surfaces that are not paved or very hard. Ultimately, trail designers must consider the needs of users in conjunction with the local conditions in order to determine the most appropriate surface material(s) for a trail.
The firmness, stability, and slip resistance of the trail surface affects all users, but it is particularly important for people using mobility devices such as canes, crutches, wheelchairs, or walkers.
All recreation trails should be surfaced with a material that is firm and stable. When a person walks or wheels across a surface that is not firm and stable, energy that would normally cause forward motion instead deforms or displaces the surface, so the energy is lost through slipping. Providing a firm and stable surface does not mean that only paved trails are acceptable. Crushed stone or fines, packed soil, and other natural materials can provide surfaces that are firm and stable (Table 15-1). To provide a firm and stable surface, the base material should be laid over a geotextile fabric to prevent vegetation growth. The base material must be compacted with the correct moisture content similar to the preparation of a roadbed. Finally, the proper trail surfacing material should be used. Depending on the distribution of particle sizes and the clay content of the material, a surface stabilizer may be needed to create a firm and stable surface.
Providing a slip resistant surface is also desirable, although not always possible to achieve on recreation trails. Brushed concrete and asphalt are slip resistant under dry conditions. Many soil stabilization products that are mixed with natural surfacing materials will also create a surface that is slip resistant under typical weather conditions. The U.S. Access Board (1994a) Technical Bulletin #4 addresses slip resistance in further detail.
|Surface Material||Firmness||Stability||Slip Resistance (dry conditions)|
|Soil with Stabilizer||firm||stable||slip resistant|
|Packed Soil without Stabilizer||firm||stable||not slip resistant|
|Soil with High Organic Content||soft||unstable||not slip resistant|
|Crushed rock (19 mm (¾") minus) with Stabilizer||firm||stable||slip resistant|
|Crushed rock without Stabilizer||firm||stable||not slip resistant|
|Wood Planks||firm||stable||slip resistant|
|Engineered Wood Fibers that comply with ASTM F1951||moderately firm||moderately stable||not slip resistant|
|Grass or Vegetative Ground Cover||moderately firm||moderately stable||not slip resistant|
|Engineered Wood Fibers that do not comply with ASTM F1951||soft||unstable||not slip resistant|
|Wood Chips (bark, cedar, generic)||moderately firm to soft||moderately stable to unstable||not slip resistant|
|Pea Gravel or 38 mm (1-½") Minus Aggregate||soft||unstable||not slip resistant|
|Sand||soft||unstable||not slip resistant|
*A broom finish significantly improves the slip resistance of concrete.
If a firm and stable surface cannot be provided throughout the trail, the following recommendations should be considered for short distances:
Until recently, there was not a simple, objective method for measuring trail surface firmness and stability in the field. To address this issue, the National Institutes of Health funded a research project to develop a portable surface measurement tool. This device, the rotational penetrometer, measures surface firmness by pressing an indenter into the surface with a specified amount of force and recording the amount of displacement into the surface.
The device measures the stability of the surface by then rotating the indenter back and forth while the force is applied and recording the total amount of displacement of the indenter into the surface. The U.S. Access Board funded additional research to determine the physiological effects of surface firmness and stability on trail users. The studies led to recommendations for an objective definition of trail surface firmness (Table 15-2) and stability (Table 15-3) (Axelson, P.W. & Chesney, D., 1999). For more information about the rotational penetrometer, contact Beneficial Designs, Inc.
Ideally, all surfaces should be firm and stable under most weather conditions. In general, paved recreation trail surfaces, such as asphalt, concrete, or soils or aggregates with stabilizing agents, will be firm and stable in both wet and dry conditions. Natural materials can also be bonded with synthetic materials to provide a firm and stable surface in most weather conditions. If the natural surface of the trail is not firm and stable even under dry conditions (e.g., sand, bog), the use of soil stabilizers or the construction of an imported or artificial trail surface is needed to create a more accessible surface.
|Surface Rating for Firmness||Displacement of Caster on Portable Wheelchair Measuring Device|
|Firm||8 mm (0.3 in) or less|
|Moderately firm||8 mm to 13 mm (0.3 in to 0.5 in)|
|Not firm||greater than 13 mm (0.5 in)|
|Surface Rating for Firmness||Displacement of Caster on Portable Wheelchair Measuring Device|
|Stable||13 mm (0.5 in) or less|
|Moderately stable||13 mm to 25 mm (0.5 in to 1.0 in)|
|Not stable||greater than 25 mm (1.0 in)|
In extreme climates, surfaces should provide a firm and stable surface under the predominant conditions. For example:
Soft trail surfaces should be avoided whenever possible. Not only do they limit the accessibility of the trail, but they generally require more maintenance and create a greater impact on the environment. Existing surfaces that are not firm and stable can be improved through the following recommendations:
Changes in level and tread obstacles are a safety hazard for people who use assistive devices, such as crutches, canes, scooters, bicycles, inline skates, wheelchairs, or walkers. Abrupt changes in level can cause people to trip and fall. The risk is particularly acute for individuals who have difficulty lifting their feet up off the ground, or for those who have limited vision and may be unable to detect the change in level. Catching a wheel on an obstacle or change in level can easily tip over wheeled devices as the individual's momentum continues even though the wheel has suddenly stopped. Minimizing or eliminating changes in level and tread obstacles will greatly improve trail safety for all users.
If changes in level or tread obstacles cannot be removed, they should be conveyed to trail users through signs, maps, or other information formats. The information should be provided at all trail access points, and should include the size, type, and location of the obstacles and any changes in level that will be encountered. Making this information available at trail entrances enables users to determine, prior to using the trail, whether they have the interest or ability to contend with the difficult environment created by the obstructions.
Changes in level are defined as a difference in vertical elevation between adjacent surfaces. Examples of changes in level commonly seen on unpaved recreation trails include:
Traditionally, changes in level have only been addressed when they extend across the full width of the trail so that the user is required to negotiate the change. However, any change in level is problematic for people with vision impairments because they may not detect the change in time to avoid it.
For recreation trails that have surfaces of concrete or asphalt, the changes in level should meet the recommendations used for shared-use paths. These include:
For unpaved recreation trails, changes in level:
Figure 15-8. The tread obstacles on this trail surface do not allow this hiker to continue travel on the trail. Even when obstacles are avoidable, maneuvering around them requires trail users to expend more energy and time.
Tread obstacles are objects within the trail tread, such as rocks, roots, or ruts. They differ from changes in level (e.g., stairs) in that the surfaces around the obstacle may not differ in vertical elevation. Most obstacles do not extend across the full width of the trail tread. Trail users who can move onto, over, or around the obstacle will be able to continue down the trail.
Tread obstacles on the trail surface pose a significant barrier to access. All tread obstacles are potentially hazardous for people with vision impairments who may not be able to detect the obstacle or may be unsure of the most appropriate way to avoid the obstacle. Even if an obstacle can be avoided, the maneuvering that is required means that some trail users will have to expend significantly more energy and time. The problems associated with multiple obstacles are magnified on narrow trails because the maneuvering room and clear path of travel are significantly reduced.
Most obstacles on a trail, such as rocks, occur naturally. They often develop into access barriers as a result of the soil compaction and erosion that accompanies continued trail use. Proper trail layout and alignment, with particular attention to natural drainage patterns, can minimize the development of obstacles such as ruts, entrenchments, and exposed roots and rocks. Removal of existing obstacles should be accomplished through a regular maintenance program.
Paved recreation trails should not have obstacles within the trail tread. On unpaved recreation trails, the trail tread should be maintained to provide a minimum clear (i.e., obstacle free) path of travel at least 915 mm (36 in) in width. For short distances, a minimum clear width of 815 mm (32 in) is acceptable. Obstacles over 51 mm (2 in) in height should be removed.
Openings are spaces or holes in the tread surface. Openings may occur naturally such as a crack in a rock surface, or they may be created during construction such as spaces between the planks of a boardwalk to allow water to drain from the surface. A grate is an example of an opening that is a framework of latticed or parallel bars that prevents large obstacles from falling through a drainage inlet but permits water and some sediment to pass through. Another example of an opening is the flangeway gap at a railroad crossing.
Whenever possible, openings should not be located within the trail tread because wheelchair casters, cane tips, inline skate wheels, and bicycle tires can all get caught in trail openings. When placing openings in the trail tread is unavoidable, they should be designed according to the following recommendations:
All individuals, with and without disabilities, must exert more energy to traverse upward on sloped surfaces than on level surfaces. For some individuals, such as those who use manual wheelchairs, the difference in energy for sloped versus level surfaces is significant. In contrast, powered wheelchair users do not exert more energy on sloped surfaces; however, they do use more battery power on steep grades and end up with reduced travel range as a result. In addition, many individuals with mobility impairments, including both powered and manual wheelchair users, are less stable on sloped surfaces.
People with mobility impairments have a difficult time negotiating steep grades because of the additional effort required for mobility. Manual wheelchair users may travel very rapidly on downhill pathways, but will be significantly slower on uphill segments. Steep running grades are particularly difficult for users with mobility impairments when resting opportunities are not provided. Furthermore, less severe grades that extend over longer distances may tire users as much as shorter, steeper grades.
In general, running grades on recreation trails should not exceed 5 percent, and the most gradual slope possible should be used at all times. When trails must be built with steeper grades, it is essential that the lengths of the maximum grade segments are minimized to enhance accessibility and grade segments are free of other access barriers. Users should not be required to expend additional efforts to simultaneously deal with factors such as soft surfaces, steep cross slopes, narrow tread widths, or obstacles.
When it is not possible to have running grades that are 5 percent or less, the following recommended guidelines should be used for designing maximum grades over short intervals:
On recreation trails, a 14 percent maximum grade is acceptable for open drains when resting intervals are provided every 1.525 m (5 ft), and the maximum cross slope is 5 percent. Furthermore, the total running slope should not exceed 8.3 percent for 30 percent or more of the trail.
Research evaluating the impact of grade on trail accessibility is extremely limited. The National Center on Accessibility supported a pilot study to examine the slopes that people with disabilities are capable of negotiating and those slopes perceived as easy to moderate (Axelson, Chesney, and Longmuir, 1995). Results of the study must be interpreted with caution because of the wide range of disabilities (none, vision impairment, ambulatory with mobility impairments, manual wheelchair user) among the small group of 12 participants.
Results of this research showed that participants were capable of negotiating grades of 20 percent or more for a short distance of 2.5 m (8 ft). However, while it may be possible for individuals with disabilities to negotiate a 20 percent grade with an "all out" effort, it is inappropriate for a trail to be designed with such a steep slope.
In designing trails where it is not possible to comply with the recommendations for average and maximum grade, consideration should be given to grades that the largest proportion of users will be able to negotiate. The 1995 pilot research project by Axelson, Chesney, and Longmuir was conducted over a distance of 2.5 m (8 ft) on a firm and stable (plywood) surface. The results indicated that slopes over a short distance of 2.5 m (8 ft) were rated as easy if they had a:
Slopes over a short distance of 2.5 m (8 ft) were rated as moderate if they had a:
Based on this information, it is clear that an 8 percent grade with a 5 percent cross slope would be considered "easy" over a very short distance [2.5 m (8 ft)]. The proposed design guidelines from the Regulatory Negotiation Committee on Accessibility Guidelines for Outdoor Developed Areas (U.S. Access Board, 1999b) allow this combination of slopes for a much longer distance [maximum of 61.0 m (200 ft)]. The perceived difficulty would be expected to increase as the distance increased.
To further examine the effects of trail length with grade and cross slope, additional research was completed with support from the National Institutes of Health (Axelson, et al, 1998). 38 volunteers with disabilities (7 manual wheelchairs, 3 power wheelchairs, 2 crutches/canes, 8 vision impairments) and 18 volunteers without disabilities hiked sections of trail that were between 213 m and 305 m (700 ft and 1000 ft) in length. The trail sections were selected because they had relatively consistent grade and cross slope conditions. All trail sections had a non-paved but relatively firm and stable surface. The results of this research indicate that:
Comparing the results from these two studies indicates that trails designed within the proposed U.S. Access Board recommendations [i.e., grades of up to 8 percent with cross slopes of up to 5 percent for up to 61.0 m (200 ft)] would be considered moderate to difficult for most trail users. These results also indicate that the same grade and cross slope is perceived as more difficult if it continues over a long distance.
In designing trails where it is not possible to comply with the recommendations for average and maximum grade, consideration should be given to grades that the largest proportion of users will be able to comfortably negotiate.
Before and after segments of steep grades, within 7.62 m (25 ft) of the top or bottom of a maximum grade segment, a rest interval should be provided where the running grade gradually transitions to a slope of less than 5 percent. The rest interval is not expected to be located immediately adjacent to the maximum grade segment to avoid an abrupt or rapid change in grade (see Section 184.108.40.206). Rest intervals may overlap the trail tread, but a preferable design is to have the rest interval located adjacent to the trail to enhance the safety and convenience of all trail users. A rest interval should be designed as follows:
Switchbacks are commonly used in steep terrain to minimize the trail grade by increasing the length of the trail. To enhance access, the trail grades should be designed using the recommendations for maximum grade (see Section 220.127.116.11) and the turning area should have a slope not greater than 5 percent in any direction. Switchbacks should be designed to work with the natural drainage patterns of the terrain. If a switchback does not drain well, the surface will become soft or eroded, and the efforts intended to reduce the grade will actually create additional access barriers.
When long switchbacks are installed, natural barriers, such as rocks or thick vegetation, should be strategically located to prevent users who do not have difficulties with steep grades from carving a shorter path. If natural barriers are not available, installing landscaping, such as shrubs, along switchbacks is also an effective method to prevent hikers from creating way trails. A way trail is an informal path created by users that allows them to travel a shorter distance by cutting across the land between the switchbacks. Short switchbacks should be avoided because they encourage users to create way trails to avoid traversing the entire switchback. Way trails between switchbacks hasten soil erosion and destroy the surrounding vegetation.
On narrow switchbacks where bicycles are not permitted, edge protection should be provided wherever there is a severe drop off adjacent to the trail. Edge protection should be replaced with a railing if the recreation trail serves high-speed users such as mountain bicyclists. A smooth transition and a gradual change of grade from the trail grade to the switchback will also benefit users traveling at faster speeds.
A change of grade is an abrupt difference between the grades of two adjacent surfaces. When considering the needs of pedestrians, change of grade can be evaluated over a 610 mm (2 ft) interval, which represents the approximate length of a single walking pace and the base of support of assistive devices, such as a wheelchair or walker. The design recommendations for change of grade specify the relationship between two adjacent surfaces - not the actual grade of either surface.
The exact change of grade that will be problematic varies between wheelchair users and is dependent on a variety of factors including the wheelchair design and the user's speed. Additional research is needed to provide a more comprehensive evaluation of the impact of change of grade on wheelchair users. Until more research is completed, the recommended maximum for change of grade is 11 percent. This value corresponds to the maximum change of grade permitted for the transition from the curb ramp through the gutter and onto the street (Section 7.3.7).
In the trail environment, a good understanding of the change of grade can be determined by:
A rapid change of grade may be difficult to negotiate because the footrests or anti-tip devices of a wheelchair cannot clear the ground surface. In general, wheelchair footrests are positioned low to the ground and extend beyond the front casters. Anti-tip devices are placed behind the rear axle of some wheelchairs to prevent the wheelchair from tipping over backwards. Both devices limit the clearance height of the wheelchair. At an abrupt change of grade, the footrests or anti-tip devices may contact the surface causing the wheelchair to stop suddenly or the rear wheels may lose contact with the ground.
A further complication associated with severe changes in grade is the increased risk of tipping if the wheelchair user is traveling fast. If the footrests catch on the ground while the user is traveling fast, the momentum of the individual and wheelchair may cause the wheelchair to tip forward.
If the user moves quickly through the change in grade, the dynamic stability of the wheelchair may be compromised. Dynamic stability can be compromised because the momentum of the wheelchair will rotate backwards as the wheelchair climbs uphill. If there is a severe change in grade, this could cause the wheelchair to tip over backwards. Any amount of height difference between the two graded segments can further contribute to the stability problems experienced by wheelchair users.
An abrupt change of grade from an uphill to a downhill surface is also potentially hazardous. Although in this situation there is little or no risk of inadequate ground clearance for the footrests or anti-tip devices, an uphill to downhill grade transition can also compromise the dynamic stability of the wheelchair. For example, when an individual travels up a steep slope, their weight is pushed back onto the rear wheels of the wheelchair. As the wheelchair transitions to the downhill slope, the weight and momentum shifts forward and down onto the smaller front caster wheels. The more abrupt the change of grade, the more sudden and forceful the transfer of momentum. If the transition is too severe, the wheelchair could tip forward.
The actual change of grade that will become problematic or potentially hazardous for any given user will depend on a number of factors including the type and setup of the wheelchair. Mountain-bike wheelchairs have a longer wheelbase and higher ground clearance resulting in greater stability and a lower probability of the footrests contacting the ground on changing surfaces. In contrast, movement of a sports wheelchair with a short wheelbase, small front caster wheels, and anti-tip devices may be compromised even when the change of grade is less than 13 percent.
Trails should be designed so that they cross contour lines at a small angle. A curvilinear trail is one aligned to follow the natural contours of the environment. A curvilinear trail alignment will allow the trail to gain elevation gradually in conjunction with the natural contours of the terrain. This type of design generally:
In contrast to trails that cut across natural contours, curvilinear trails usually feature natural and gradual changes in trail grade and direction. A curvilinear trail alignment is usually the best path for access.
Steps are used in areas where the trail gains elevation quickly. A series of steps allows the remainder of the trail to have a less steep grade and reduces the risk of trail erosion or washouts. Steps may be preferred to steeply graded trail sections by individuals who use crutches or canes. However, steps create a significant barrier to individuals who use wheelchairs and should be used minimally, if at all. Steps must not be included in new construction. If steps are already incorporated into the design of existing trails, the following best practices should be implemented:
Figure 15-13. PROBLEM: While steps enhance access for some users, they are an access barrier for wheelchair users. If stairs are used, an alternative accessible route should be provided. A bike track should be added to stairs on multi-use paths.
Figure 15-14. ACCEPTABLE DESIGN: Stairs should only be installed if they serve a vital trail requirement and no alternative design will work. If stairs are installed on the trail, designers should try to minimize the height of steps and placing steps far apart. Wheelchair users will rarely be able to negotiate steps without assistance.
Most wheelchair users will not be able to traverse steps independently. Powered wheelchairs are significantly heavier than manual wheelchairs, which makes step negotiation almost impossible, even with assistance. Although all steps are problematic for wheelchair users, the design of the steps can improve access for other trail users. While stairs should not be incorporated into the design of new trails, if stairs do exist it is recommended that they be redesigned to increase usability. Stair access can be maximized for wheelchair users by:
Severe cross slopes can make it difficult for wheelchair users and other hikers to maintain their lateral balance because they must work against the force of gravity. Cross slopes can also cause wheelchairs to veer downhill. In addition, individuals using crutches often cannot compensate for the height differential created by severe cross slopes.
Figure 15-15. Wheelchair users traveling on a trail with a cross slope have to use more energy to travel in a straight line to offset the force of gravity that directs them sideways.
Designers must balance the negative effect cross slope has on pedestrian mobility against the necessity of including cross slope to provide adequate drainage. On most paved surfaces, 2 percent is adequate for drainage. However, cross slopes up to 5 percent may be necessary for drainage on non-paved surfaces, such as crushed limestone. Particular attention should be paid to drainage in steep terrain because the velocity of the water flow will be significant and more cross slope will be required to direct the water to the side of the trail rather than down the center of the path. If water cannot be adequately routed off an unpaved trail using a 5 percent cross slope, a more significant cross slope may be needed. Cross slopes may increase to 10 percent at the bottom of an open drain if the trail path width is a minimum of 1.065 m (42 in).
Research evaluating the impact of cross slope on trail accessibility is extremely limited. Results of the pilot research supported by the National Center on Accessibility indicate that some people with disabilities are capable of negotiating cross slopes of 15 percent or more for distances of 2.5 m (8 ft) or less depending on the type of mobility impairment and assistive device used (Axelson, Chesney, and Longmuir, 1995). Recreation trails are seldom designed with cross slopes as steep as 15 percent. Therefore, designers should expect that people with disabilities will utilize every trail that they design. However, while it may be possible for some individuals with disabilities to negotiate a 15 percent cross slope over a short distance with an "all out" effort, it is inappropriate for a trail to be designed to such a standard.
In designing trails where it is not possible to comply with the recommended standards for cross slope, consideration should be given to cross slopes that the largest proportion of users will be able to comfortably negotiate. The 1995 pilot research project by Axelson, Chesney, and Longmuir was conducted over a distance of 2.5 m (8 ft) on a firm and stable (plywood) surface. The results indicated the following:
Slopes for a distance of 2.5 m (8 ft) were rated as easy if they had a:
Slopes for a distance of 2.5 m (8 ft) were rated as moderate if they had a:
Based on this information, a 5 percent cross slope with an 8 percent grade would be considered "easy" over a very short distance [2.5 m (8 ft)]. The proposed design guidelines from the Regulatory Negotiation Committee on Accessibility Guidelines for Outdoor Developed Areas (U.S. Access Board, 1999b) allow this combination of slopes for a much longer distance [maximum of 61 m (200 ft)]. The perceived difficulty would be expected to increase as the distance increased.
A change of cross slope is an abrupt difference between the cross slope of two adjacent surfaces. When considering the needs of pedestrians, change of cross slope is evaluated over a 610 mm (2 ft) interval, which represents the approximate length of a single walking pace and the base of support of assistive devices such as a wheelchair or walker. The design recommendations for change of cross slope specify the relationship between two adjacent surfaces, not the actual cross slope of either surface.
The exact change of cross slope that will be problematic varies between wheelchair users and is dependent on a variety of factors, including the wheelchair design and the user's speed. Additional research is needed to provide a more comprehensive evaluation of the impact of change of cross slope on wheelchair users. Until more research is completed, the change of cross slope should not exceed 5 percent. This means that a cross slope that changed from 2 percent to 8 percent over an interval shorter than 610 mm (2 ft) would not be acceptable. For open drains with cross slopes up to 10 percent, the change should happen gradually so that no 610 mm (2 ft) interval changes more than 5 percent.
When the change of cross slope is severe, one wheel of a wheelchair or one leg of a walker may lose contact with the ground causing the user to fall. Other walking pedestrians are also more prone to stumbling or falling on surfaces with rapidly changing cross slopes. An example of a situation where the change of cross slope might exceed 5 percent occurs at a washed out trail segment where the outslope of the trail has significantly increased due to erosion. As the wheelchair moves from the level surface of the trail to the outsloped surface, it will first balance on the two rear wheels and one front caster. As the wheelchair moves forward, it then tips onto both front casters and one rear wheel. During the transition, the wheelchair is only on one front wheel and one rear wheel. This transition may cause the wheelchair user to lose directional control because both rear wheels are not on the ground. This is especially dangerous at a drop-off, where the user may be at risk of falling off the edge of the trail.
Natural drainage paths should be maintained and encouraged whenever possible. Trails should be designed to incorporate natural drainage patterns rather than trying to construct drainage channels. Trails that limit natural drainage patterns will quickly become the drainage channel, as water always seeks the path of least resistance. The trail surface provides an excellent channel for drainage because the soil is often compacted so that the trail surface is lower than the surrounding terrain. In addition, the trail surface is relatively free of obstacles providing a clear path of travel for surface water. For these reasons, when the natural drainage channel is obstructed, the trail is where the water channels. The resulting erosion, surface saturation, and high frequency of water flow on the trail will significantly limit trail access for all users.
Erosion on a trail is usually a function of poor trail design or construction. Inaccurate consideration of soil types and natural drainage patterns are the most common causes of trail erosion. Erosion and drainage problems create barriers for all users but may be particularly hazardous for people with disabilities, who may have more difficulty avoiding the problem area. Trail designs that ensure adequate drainage and the installation of appropriate drainage control mechanisms are the most effective means of maximizing trail access.
In many instances, trail managers are left to minimize the impact of poor trail designs if there is not an opportunity to reconstruct or redesign the trail. Accumulated soil or other debris on the trail poses a hazard for all users and significantly reduces the accessibility of the trail. The use of retaining walls and planting vegetation to stabilize the affected area can help to reduce the build up of debris.
Retaining walls are an effective means of preventing trail degradation. To meet the needs of people with disabilities, retaining walls should be located outside of the trail tread. Retaining walls inherently limit the ability of the trail user to move off of the beaten path. The combination of a retaining wall with a large obstacle on the opposite side of the trail bed (e.g., drop off, tree) will create a minimum passage space and may restrict access for people who require a wider trail tread, such as those who use wheelchairs. Whenever possible, the usable trail tread should be at least 915 mm (36 in) for a pedestrian trail (see Section 15.6). If the minimum passage space cannot be modified and is less than 915 mm (36 in), information about the size and location of the minimum clear width should be provided to potential trail users so that they can avoid this frustrating or hazardous situation. The trail width information should be made available to users before they access the trail and may be provided in a variety of formats, such as signage or maps (see Section 15.8).
Waterbars are drainage structures that stretch across the width of the trail and direct water to the edge of the path. Traditionally, they have been built using a log or a piece of wood. Other designs use materials such as rocks or flexible rubber. With the exception of the rubber material, water bars tend to be obstacles for people using wheeled devices, such as bicycles or wheelchairs, because they are raised as much as 152 mm (6 in) above the tread and extend across the full width of the path. A need for waterbars indicates that the natural drainage of the terrain was not adequately considered during trail design, layout, and construction. The use of waterbars to control drainage on a trail should be minimized whenever possible with the following alternatives:
At best, waterbars are a temporary solution to drainage problems. Most users will choose to travel around waterbars whenever possible, particularly if their stability or mobility is limited. Once enough users have cut around both sides of the waterbar, it will no longer effectively drain water off the trail. In addition, all waterbars require significant maintenance to function properly. Without appropriate maintenance, deposits of sediment on the uphill side of the waterbar will increase until water can flow over the waterbar. When this occurs, water running over the bar will actually increase erosion on the downhill side.
If a waterbar is installed, the best waterbar design, from an access perspective, is the rubber waterbar. This waterbar deflects water off the trail in the same way as other waterbars, but when a user encounters it, the bar is flexible enough to collapse. Waterbars made of flexible rubber will bend under the user's weight and therefore provide greater accessibility. Rather than having to travel over a 152 mm (6 in) obstacle, a pedestrian or cyclist can travel over a nearly flattened rubber surface. To be effective, rubber water bars must be flexible enough to be pushed down easily by all users from either direction of travel.
Although drainage is a critical issue for the design and maintenance of all trails, it is particularly important in areas that receive high amounts of precipitation. Of greatest concern are areas that receive heavy rain events, although the effects of the spring melt in regions with significant snow accumulation can create similar problems. The following techniques can improve the accessibility of trails that receive heavy rain events:
Figure 15-21. When included in new construction or alterations, drainage dips can significantly improve drainage without placing an obstacle, such as waterbars, in the trail tread.
It is vital that areas that receive large amounts of water address drainage issues during the development stage of a trail to avoid having to make retrofit improvements.
Figure 15-22. Drainage dips on recreation trails act as open drains. The cross slope of the open drain should not exceed 10 percent, and the clear tread width should be at least 1.065 m (42 in) minimum.
Periodic rest areas are beneficial for all recreation trail users, particularly for people with mobility impairments who expend more effort to walk than other pedestrians. Rest areas are especially crucial when grade or cross slope demands increase. The frequency of rest areas should vary depending on the terrain and intended use. For example, heavily used recreation trails should have more frequent opportunities for rest than backcountry trails with fewer users. Rest areas provide an opportunity for users to move off the trail in order to stop and rest. If a rest area is only provided on one side of the trail, it should be on the uphill side. However, separate rest areas on both sides of the trail is preferred when there is a higher volume or speed of traffic. This discourages users from crossing in front of users moving in the opposite direction.
Figure 15-23. Periodic rest areas are particularly beneficial to people with mobility impairments who expend more effort to walk than other pedestrians. Rest areas should be created where there is an increase in grade or cross slope.
A rest area will have many of the same characteristics as a rest interval (see 18.104.22.168), however the additional space allows for more amenities. In general, rest areas should have the following design characteristics:
Benches can be particularly important for people with disabilities, who may have difficulty getting up from a seated position on the ground. Some benches should have backrests to provide support when resting, and at least one armrest to provide support as the user resumes a standing position. Accessible seating should have the same benefits as seating for users without disabilities. For example, providing a wheelchair space facing away from the intended view would not be appropriate.
The width of the trail tread not only affects pedestrian usability but also determines the types of users that will have access. Recreation trails designed for pedestrian use should have a minimum tread width of 915 mm (36 in). However, it is recommended that the tread width be at least 1.525 m (60 in) wide when possible. This allows space for people using assistive devices, such as a wheelchair, stroller, or walker, to easily pass one another. If a narrower passage space is unavoidable, for example between two rock beds, the trail width may be reduced to 815 mm (32 in) for short distances.
In addition to providing for clear passage, designers should also consider that most pedestrians tend to avoid path edges. They chose to travel in the center of the trail to avoid drop-offs and untrimmed vegetation. The tendency of pedestrians to avoid the edges of a path increases the width required for a given path to be usable. In contrast, individuals with limited vision who use a cane for guidance tend to travel primarily along the edge of the trail surface, using the difference between the trail and the surrounding brush to provide direction. The movement patterns of other designated user groups should also be considered when designing the width of a trail. For example, cross-country skiers may use a lateral foot motion for propulsion that is wider than the stride of most pedestrians. The width required to accommodate this motion increases when skiers ascend grades or pick up speed. As a result, trails permitting these users should be wider than trails that are designated solely for pedestrians.
For all trails, the section cleared on either side of the tread width should be wide enough to prevent vegetation from encroaching on the trail between periods of scheduled maintenance. Trails in areas with heavy vegetation require additional width on either side of the trail tread to prevent the growth of grasses or ground cover from significantly increasing the energy required to traverse the trail. Overgrowth can also hinder a user's ability to see other trail users, increasing the possibility of collisions. Overgrowth also limits a user's awareness of minor changes in the ground surface, increasing the risk of falls.
Figure 15-25. A clear area that is wider and taller than the trail tread width should be created to prevent vegetation, such as tree limbs, from encroaching into the trail and creating protruding objects.
Although the extent of vegetation that must be cleared will depend on the type of vegetation, frequency of maintenance, and permitted trail user groups, the following recommendations should be considered:
Periodic passing spaces allow trail users to pass one another and provide wheelchair users enough maneuvering room to turn around. Slower pedestrians benefit from passing spaces because faster users can travel by them with less disruption. On recreation trails that are narrower than 1.525 m (60 in), passing spaces should be at least 1.525 m x 1.525 m (60 in x 60 in) and should be provided at least every 305 m (1000 ft). Passing spaces should be provided more frequently if the terrain is challenging and there is no space to pull off of the trail to allow others to pass. Passing spaces should also be provided more frequently if the trail is narrow and sight distances are restricted enough that a trail user may unexpectedly encounter somebody traveling in the opposite direction in an area where passing is not possible.
Protruding objects are anything that overhangs or protrudes into the shared-use path tread, whether or not the object touches the surface. Examples of protruding objects include rock overhangs and tree limbs. People with vision impairments who use dog guides for navigation are able to avoid obstacles in the trail up to 2.030 m (80 in). Objects that protrude into a recreation trail but are higher than 2.030 m (80 in) tend to go unnoticed, because most pedestrians require less than 2.030 m (80 in) of headroom. People with vision impairments who use long white canes to navigate can easily detect objects on the trail that are below 685 mm (27 in). However, objects that protrude into the pathway between 685 mm (27 in) and 2.030 m (80 in) are more difficult to detect because the cane will not always come in contact with the object before the pedestrian comes in contact with the object.
Ideally, objects should not protrude into any portion of the clear tread width of a recreation trail. If an object must protrude into the travel space, it should not extend more than 101 mm (4 in).
Because pedestrians with vision impairments do not always travel in the center of the trail tread, protruding objects should be eliminated from the entire tread width, as well as the clear trail width. If a protruding object cannot be removed, information about the size and location of the object should be conveyed to potential trail users before they access the trail. In addition, a barrier should be provided around the object so users will know to avoid the area. An example of a protruding object that cannot be removed would be a rock outcropping that overhangs the trail tread when the surrounding terrain does not permit the trail alignment to be changed.
Trails should be built and maintained to an overhead clear height that is sufficient for all expected users of a trail. For example, equestrians require much higher clearances than pedestrians. Design of the trail clear height should also consider the user's location during all seasons and trail conditions. For example, cross country skiers may be on a "surface" that is several feet above the same ground level that is used by hikers in the summer. A height of at least 2.5 m (96 in) should be provided for bicyclists and pedestrians, and at least 3.05 m (120 in) should be provided if equestrians or ATV riders use the path. Cross country skiers and snow machine users should have at least 2.5 m (96 in) above the average snow level. At the very minimum, recreation trails for pedestrian use only should provide 2.030 m (80 in) of headroom to protect trail users from vertical obstructions. On trails where there is the potential for emergency vehicles to gain access to areas, it is necessary to provide 3.05 m (10 ft) vertical clearance.
Edge protection serves as a barrier between the trail and the surrounding environment. Edge protection is installed to protect all trail users from a variety of elements including drop-offs and hazardous situations, such as poison oak or thermal areas. It is not necessary to install edge protection just because people with disabilities may be using the trail.
If bicyclists will be users of the trail, then edge protection should be a minimum of 1.066 m (42 in) high. Bicyclists are typically traveling more rapidly than other users and their center of gravity is higher. If they unexpectedly hit an edge protection that is less than 1.066 m (42 in), they are likely to flip forward into the hazardous situation.
On trails that do not permit bicycles, a variety of edge protection designs may be used; however, edge protection should generally be at least 76 mm (3 in) high. This is higher than standards for edge protection in built facilities because environments with a natural surface frequently contain small obstacles of 25 mm to 51 mm (1 in to 2 in) in height. As a result, individuals with vision impairments must adjust their obstacle detection to a slightly higher level. In addition, many wheelchairs designed for outdoor environments are capable of rolling over small obstacles, and, therefore, higher edge protection is required to ensure that it functions as intended.
Signs that clearly describe the recreation trail conditions are an essential component to enhance pedestrian access. Signs should be provided in an easy to understand format with limited text and graphics that are understood by all users. Providing accurate, objective information about actual recreation trail conditions will allow people to assess their own interests, experience, and skills in order to determine whether a particular recreation trail is appropriate or provides access to them with their assistive devices. Providing information about the condition of the recreation trail to users is strongly recommended for the following reasons:
Figure 15-31. The symbols above have been included in the report of the Regulatory Negotiation Committee on Accessibility Guidelines for Outdoor Developed Areas. One of these symbols or a similar symbol will be selected to indicate a trail that meets the accessibility provisions for trails (U.S. Access Board, 1999b).
The Regulatory Negotiation Committee on Accessibility Guidelines for Outdoor Developed Areas specifies that a trail that meets accessibility provisions be designated with a universally understood symbol for "accessible trail." The exact design of the symbol has yet to be developed, but several possible designs were included in their report.
In addition to the universal symbol, objective information about the trail conditions (e.g., grade, cross slope, surface, width, obstacles) should be provided. This information is needed regardless of whether or not the trail is accessible. Objective information is preferable to subjective trail difficulty ratings (e.g., easier, most difficult) because subjective ratings of difficulty typically represent the perceptions of the person making the assessment and cannot be accurate or appropriate for the range of trail users. Individuals with respiratory or heart conditions as well as individuals with mobility impairments in particular are more likely to have different interpretations of trail difficulty than other users.
A variety of information formats may be used to convey objective trail information. The type of format should conform to the policy of the land management agency. For example, one agency may choose to provide trail information at the trailhead, while another may provide trail information at their visitor center. Written information should also be provided in alternative formats, such as Braille, large print, or an audible format. For example, the text of a trailhead sign made available on audiocassette or a digital voice recorder can be used to play the message with the touch of a button. In addition, simplified text and reliance on universal graphic symbols greatly enhances the comprehension of individuals with limited reading abilities.
Figure 15-32. This sign at the Merced River Trailhead in Yosemite National Park allows users to assess whether or not the trail will meet their personal interests, experience, and skills by providing objective trail access information.
The type and extent of the information provided will vary depending on the trail, environmental conditions, and expected users. For example, trails that attract predominantly experienced users and located in areas with few safety considerations may require fewer signs containing less detailed information than trails likely to be used by inexperienced people located in areas that will expose users to potential hazards. It is recommended that the following information should be objectively measured and conveyed to the trail user through appropriate information formats: