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.

TRB's National Cooperative Highway Research Program (NCHRP) Report 670: Recommended Procedures for Testing and Evaluating Detectable Warning Systems explores a set of recommended test methods for evaluating the durability of detectable warning systems. These methods address exposure regimes, test procedures, and evaluation criteria to help select detectable warning systems that provide long-term performance and durability while meeting the requirements of the Americans with Disabilities Act Accessibility Guidelines. The appendix contained in the research agency's final report provides further elaboration on the work performed in this project. This appendix titled Research Leading to the Development of Methodology for Durability Assessment of Detectable Warning Systems is available online.