T303.1  General.  Trails shall comply with T303.

T303.2  General Exception.  Where applying the specific exceptions to the technical provisions in T303 results in any of the conditions in T303.2, the trail shall not be required to comply with T303 beyond the first point where the specific exceptions apply. The segment of the trail between the trailhead and the first point where the specific exceptions apply shall comply with T303 unless the trail segment is 500 feet (150 m) or less in length.  Where there is a prominent feature less than 500 feet (150 m) from the trailhead, the trail segment between the trailhead and the prominent feature shall comply with T303.

Conditions:

1. 1.The combination of running slope and cross slope exceeds 40 percent for over 20 feet (6100 mm).
   

2. 2.A trail obstacle 30 inches (760 mm) high or more runs across the full tread width of the trail.
   

3. 3.The trail surface is neither firm nor stable for a distance of 45 feet (14 m) or more.
   

4. 4.The tread width is less than 12 inches (305 mm) wide for a distance of 20 feet (6100 mm) or more.
   

5. 5.The trail is not required to comply with any of the technical provisions in T303 for more than 15 percent of the length of the trail.
   

T303.3  Surface.  The trail surface shall be firm and stable.

Exception:

Where a firm and stable surface cannot be provided because any of the conditions in T302 applies, the surface shall not be required to comply with T303.3.

Advisory T303.3  Surface.  Trail surfaces are required to be firm and stable.  There is a spectrum of surfaces considered firm and stable and appropriate surfaces are not limited to surfacing materials such as asphalt and concrete.  Many naturally occurring surfaces, such as crushed aggregate or soils containing some clay and a spectrum of sieve sizes, are considered firm and stable.  Other natural surfaces may also become firm and stable when combined with a stabilizing agent.  Wood planks, stone, grass, and packed dirt may also be considered firm and stable. The degree of firmness and stability may vary depending on the intended use and the expected direction and length of travel.