accessibility standards for Federal outdoor developed areas 81 Surface and Slope [1015 5 and 1015 6] The surface of clear ground spaces and turning spaces must be firm and stable. Additional information on firm and stable surfaces is provided in the trails section of this guide. When the surface of clear ground spaces and turning spaces is constructed of asphalt, concrete, or boards, the slope of the 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. Outdoor Constructed Features Within Viewing Areas [F246 3] At least 20 percent, but no less than one, of each type of outdoor constructed feature provided within each viewing area must comply with the applicable technical requirements for the feature. The technical requirements for outdoor constructed features, including viewing scopes, are located in the section of this guide on outdoor constructed features. Outdoor Recreation Access Routes in Viewing Areas [F246 4] At viewing areas not located along trails, at least one ORAR must connect accessible parking spaces or other arrival points that serve the viewing area with accessible elements, spaces, and facilities provided within the viewing area. Additional information on the scoping and technical requirements for ORARs at viewing areas are discussed in the section of this guide on ORARs.