Step 2: Identify the Presence of Limiting Factors
This step addresses the condition criteria accepted by the U.S. Access Board for identifying when extreme environmental barriers allow the use of General Exception 2. These barriers are defined in the first four limiting factors in FSTAG, section 7.2.2.1 "Determining Impracticability" and are explained in "General Exceptions in FSTAG" of this guidebook. The sequence for identifying the limiting factors may vary and does not need to be done in the order illustrated in the process flowchart.
Work your way through the process flowchart by asking four questions, each related to one of the limiting factors. The first question will be explained in detail to serve as an example for the other three.
Does the combined trail running slope (grade) and cross slope exceed 1:2.5 (40 percent) for a continuous distance of 20 feet (6 meters) or more?
Construction Tip
Choose a method to measure the running slope.
There are a number of ways you can measure running slope. You can perform an informal survey between obvious trail slope breaks with a hand level, survey rod, and measuring chain (figure 141). You can use a digital level (figure 142). You can also perform a more detailed trail assessment such as the universal trail assessment process developed by Beneficial Designs (http://www.beneficialdesigns.com/).
Figure 141—Surveying trail grade with a hand level.
Figure 142—Surveying trail grade with a digital level.
If not, FSTAG may still apply, so you should consider Design Tip the next limiting factor. A continuous distance means a sustained running slope (grade) without rest areas or more moderate slopes. If the alignment can be relocated to get a more moderate slope, this limiting factor doesn't apply.
If the combined slope exceeds 1:2.5 (40 percent) for a continuous distance of 20 feet (6 meters) or more, document the length of trail that exceeds the technical requirements for slopes, the location of the area, and your data source (field survey, clinometer, and so forth). Keep this information for use in step 4.
Next, determine whether a condition for an exception exists that permits a deviation from the technical requirements for slope. If there is no condition for an exception, FSTAG may still apply, so you should proceed to the next limiting factor.
If a condition for an exception does exist, document the length of trail affected by the condition for an exception, what exception applies, and the location of the area.
Next, consider whether the combined trail running slope (grade) and cross slope is so excessive that it is impracticable for the entire trail to comply with the technical requirements. If so, FSTAG does not apply to this trail at all and no further review or analysis is required. Document the reason for the determination, retain it in the project file, and notify the U.S. Access Board, as explained in "Documenting Exceptions and Notifying the U.S. Access Board About Exemptions" of this guidebook.
Finally, consider the end section of trail between the limiting factor and the trailhead or another trail that substantially complies with FSTAG. Is there a prominent feature between the end of the trail and the limiting factor? If so, consider constructing the section of trail between the end of the trail and the prominent feature in compliance with the technical accessibility requirements. Doing so is not required, but it is often good management and good customer service.
Design Tip
Use a rule of thumb to estimate firmness and stability.
What sort of surface is firm and stable? If the answer to both of the following questions is yes, the surface is probably firm and stable.
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Could a person ride a narrow-tired bicycle across the surface easily without making imprints? (Bicycle tires are similar to the large rear wheels of a wheelchair.)
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Could a folding stroller with small, narrow plastic wheels containing a 3-year-old be pushed easily across the surface without making imprints? (The stroller's wheels are similar to the front wheels of a wheelchair.)
While this method for determining firmness and stability isn't scientifically accurate, it has proven to be effective.
Work your way through the other three limiting factors the same way. The design tips may help you.
Is the surface neither firm nor stable for 45 feet (14 meters) or more?
Is the trail tread width 12 inches (227 millimeters) or less for a distance of at least 20 feet (6 meters)?
Is there an obstacle at least 30 inches (760 millimeters) high extending across the full width of the trail?
Design Tip
Determine when trail width is a limiting factor.
Measuring the existing trail width is easy—just use a measuring tape to get the side-to-side distance of the narrowest stretch of trail. Figuring out whether that width can be changed may be a little more difficult. The trail may be less than 12 inches (227 millimeters) wide, but if you can widen it in its current location or move the trail alignment to an area where it can be wider, the limiting factor doesn't apply.
If you find a limiting factor where a condition for an exception applies, there's no reason to evaluate the trail beyond that point for successive limiting factors unless the rest of the trail connects to a trailhead or a trail that substantially complies with FSTAG. Just look at the section of trail between the limiting factor or prominent feature and the trailhead or connecting trail. Figure 143 shows step 2.
If there are no limiting factors that would prevent compliance with FSTAG, proceed to step 3.
Figure 143—Step 2 of the Forest Service Trail Accessibility Guidelines implementation process. (For a larger image please click here.)
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