ADAAG Requirements for Detectable Warnings(March 2003)
Detectable warnings are walking surfaces that are primarily intended to provide a tactile cue to pedestrians who are visually impaired. They are installed at locations such as the edge of a train platform or at the transition between the sidewalk and the street to warn pedestrians of the potential hazard that lies ahead.
The tactile properties of detectable warnings result from a grid of small, truncated (flat-topped) domes across the warning surface. This pattern has been standardized by the U.S. Access Board and testing has shown that the pattern can be detected underfoot or by cane without causing a tripping hazard or obstructing wheelchairs.
Despite the proven tactile benefits of detectable warnings, little research has been conducted to evaluate the visual detectability of various detectable warning materials. Detectable warnings that provide salient visual cues in addition to tactile cues may help many pedestrians with visual impairments to locate hazards or curb ramps from a greater distance than is possible using the tactile cues alone. Some pedestrians may use them to orient to a curb cut or ramp at the end of a crosswalk.