The Americans with Disabilities Act (ADA) Accessibility Guidelines establish requirements for accessible routes connecting all accessible areas of buildings and sites. An accessible route is a continuous and unobstructed path that complies with ADA standards for width, slope, and surface. The minimum clear width for accessible routes is 36 inches, permitting passage by single wheelchairs. Where passing space is required, a 48-inch width is needed, or two 36-inch-wide sections separated by passing spaces permit pedestrian traffic in both directions. Accessible routes must have firm, stable, and slip-resistant surfaces that do not shift or move with traffic. Maximum slope for accessible routes is 5 percent (1 foot vertical per 20 feet horizontal). Steeper slopes require ramps with specific design standards. Cross slope (perpendicular to the direction of travel) must not exceed 2 percent. Surfaces with gratings must have openings no larger than ½ inch to prevent caster entrapment. Accessible routes must be maintained free of obstructions including parked vehicles, merchandise, or equipment. Changes in level up to ¼ inch may be left as a vertical step, but changes exceeding ¼ inch require bevels or ramps. At building entries, accessible routes must connect from parking areas or public transportation to the entry door with no more than 5 percent slope. Where existing buildings are altered, the altered elements must be made accessible and an accessible route to the altered element must be provided.