40 A SUMMARY OFACCESSIBILITY STANDARDS FOR OUTDOOR DEVELOPEDAREAS accessibility standards for Federal outdoor developed areas Obstacles [1016 5] Obstacles are anything that interrupts the evenness of the surface of an ORAR. Obstacles may occur where a tree root or rock protrudes above the surface or where two different surfaces abut, such as when a concrete path joins a natural surface. When an ORAR is provided within a vehicular route, traffic-calming devices or speed bumps can be obstacles. If obstacles are pronounced, they can pose a serious tripping hazard and make it difficult to travel using a mobility device. The limit on the height of obstacles on ORARs, passing spaces, and resting intervals is based on the surface material used. When the surface is con- structed of concrete, asphalt, or boards, obstacles cannot exceed one-half inch in height at their highest point. When the surface is constructed of mate- rials other than concrete, asphalt, or boards, obstacles cannot exceed 1 inch in height at their highest point. Frequent obstacles and obstacles that cross the full width of an ORAR can make travel difficult for people using mobility devices. Where possible, sep- arate obstacles that cross the full width of an ORAR by at least 48 inches so people using mobility devices can fully cross one obstacle before confronting another.