The 1991 Americans with Disabilities Act Accessibility Guidelines required the installation of a detectable warning surface (raised truncated domes) on sidewalk curb ramps to alert visually impaired people to potential hazards. Although this requirement was later suspended until 1996, there has been much debate about whether visually impaired people need detectable warnings on ramps and, if so, whether domes are the best option. The Virginia Department of Transportation's (VDOT's) current standard requires an exposed aggregate (gravel mixed into concrete) surface on curb ramps. This study evaluated seven warning surfaces for their detectability by the visually impaired and their ease of maneuverability for the mobility impaired. Information about the performance characteristics of different ramp surfaces was also obtained by telephone survey of transportation officials in Virginia and 21 other states. Test results for 52 visually impaired subjects indicated that the five domed surfaces were far more detectable than the aggregate surfaces; a majority of the totally blind subjects failed to detect the aggregates. Aggregate surfaces were clearly preferred by the six mobility impaired subjects, some of whom had notable difficulty maneuvering on the domed surfaces. Some visually impaired subjects made negative comments about the feel of the domed surfaces underfoot. Survey results indicated that other states are requiring a variety of ramp surfaces, not all of which are detectable warnings. Some areas using domes reported considerable winter maintenance damage. No maintenance damage to aggregate was reported, but Virginia respondents reported other kinds of problems with its installation and use. Selection of a curb ramp surface involves numerous tradeoffs, most notably the tradeoff between high detectability for the visually impaired and maneuverability for the mobility impaired.

(a) Design and construction. (1) Each facility or part of a facility constructed by, on behalf of, or for the use of a public entity shall be designed and constructed in such manner that the facility or part of the facility is readily accessible to and usable by individuals with disabilities, if the construction was commenced after January 26, 1992. (2) Exception for structural impracticability. (i) Full compliance with the requirements of this section is not required where a public entity can demonstrate that it is structurally impracticable to meet the requirements. Full compliance will be considered structurally impracticable only in those rare circumstances when the unique characteristics of terrain prevent the incorporation of accessibility features. (ii) If full compliance with this section would be structurally impracticable, compliance with this section is required to the extent that it is not structurally impracticable. In that case, any portion of the facility that can be made accessible shall be made accessible to the extent that it is not structurally impracticable. (iii) If providing accessibility in conformance with this section to individuals with certain disabilities (e.g., those who use wheelchairs) would be structurally impracticable, accessibility shall nonetheless be ensured to persons with other types of disabilities, (e.g., those who use crutches or who have sight, hearing, or mental impairments) in accordance with this section.