20 A SUMMARY OFACCESSIBILITY STANDARDS FOR OUTDOOR DEVELOPEDAREAS accessibility standards for Federal outdoor developed areas Passing Spaces  A trail tread width less than 60 inches does not permit two people using mobility devices to pass each other. Consequently, where the tread width is less than 60 inches, passing spaces must be provided at intervals of at least 1000 feet. Where the trail is heavily used or the trail is not at the same level as the adjoining ground surface, such as a bridge cross- ing a ravine, increasing the frequency of passing spaces or widening the tread width to a minimum of 60 inches provides greater access. People using mobility devices also use passing spaces to turn around. Where the full length of a trail does not fully comply with the trail technical requirements, a passing space must be located at the end of the trail segment that complies fully with the technical requirements. This enables people who use mobility devices to turn around and proceed back to where they started. Consider ways to alert people using mobility devices when a passing space provides the last opportunity on a trail to turn around, because this may not always be apparent. Printed materials, trail Web sites, trailhead information signs, and signage at the end of the trail segment that fully complies with the technical require- ments could be used to indicate the location of the last place on the trail to turn around. Passing spaces must be: ¡ ¡ A minimum of 60 by 60 inches (figure 4) or MIN 60" (1525 mm) CROSS SLOPE MIN 60" (1525 mm) 2% TO 5% MAX Figure 4—Minimum dimensions for a passing space.