22 A SUMMARY OFACCESSIBILITY STANDARDS FOR OUTDOOR DEVELOPEDAREAS accessibility standards for Federal outdoor developed areas Where the intersection of two trails serves as a passing space, the vertical alignment of the trails at the intersection that form the T-shaped space must be nominally planar so that all the wheels of a mobility device remain on the ground when turning into and out of the space. Nominally planar means on the same nominal table surface (same nominal geometric surface plane) and the slopes of the table surface correspond to the running slope and cross slope of the trail tread. For example, if the trail tread has a 2 percent cross slope and 5 percent running slope, the nominal surface plane of the trail tread and passing space must both have a 2 percent cross slope and a 5 percent running slope. This allows people using mobility devices with three or four wheels to better maintain contact with the surface when moving from the main trail into a passing space. This makes it less likely that the mobility device will tip or overbalance to one side. Passing spaces and resting intervals can overlap. When passing spaces and resting intervals overlap, the technical requirements for resting intervals apply and the slope of the ground surface must be no steeper than 1:48 (2 percent) in any direction. When the surface is constructed of materials other than asphalt, concrete, or boards, slopes no steeper than 1:20 (5 percent) are allowed when necessary for drainage.
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