Evaluation of Detectable Warning Surfaces for Sidewalk Curb Ramps

Abstract

The 1991 Americans with Disabilities Act Accessibility Guidelines required installation of a detectable warning surface (raised truncated domes) on sidewalk curb ramps to alert visually impaired persons to potential hazards at pedestrian crossings. In 1994 the requirement was temporarily suspended for 2 years. Whether visually impaired persons need (or want) detectable warnings on ramps and whether domes are the best option continue to be debated. The Virginia Department of Transportation's current standard requires an exposed aggregate (gravel mixed into concrete) surface on curb ramps. Seven warning surfaces (five domed, two exposed aggregate) were evaluated for their detectability by the visually impaired and the maneuverability they afford the mobility impaired. The performance characteristics of different ramp surfaces were also obtained through a telephone survey of transportation officials in Virginia and 21 other states. Field-test results for 47 visually impaired participants indicated that the five domed surfaces were far more detectable than the aggregate surfaces. A majority of the totally blind participants failed to detect the two exposed aggregate surfaces. Some visually impaired test participants disliked the feel of the domed surfaces underfoot; however, many were unfamiliar with any type of warning surface on ramps. Six mobility-impaired individuals clearly preferred the exposed aggregate surfaces. There is a fundamental tradeoff between surface detectability and easy maneuverability. The telephone survey indicated that other states use a variety of ramp surfaces, not all of which provide detectable warnings. Some areas using domed surfaces reported substantial freeze-thaw and winter-maintenance damage. No maintenance damage to aggregate was reported, but Virginia respondents reported other kinds of problems with its installation and use. Virginia's experience illustrates the kinds of dilemmas state departments of transportation face in their efforts to select an optimum surface for all curb ramp users.