Visual Detection of Detectable Warning Materials by Pedestrians with Visual Impairments - Final Report
1.2 Background
Detectable warning surfaces are intended primarily to provide a tactile cue to pedestrians who are blind or have visual impairments. Major causes of visual impairments in the United States are described briefly in Appendix A. The majority (80%) of people who are legally blind retain some degree of visual function,1 and these people, along with pedestrians who have less severe visual impairments, may benefit from detectable warnings, which are both visually and tactilely distinctive.
The tactile properties of detectable warning surfaces result from a grid pattern of raised, flat-topped, truncated domes that can be felt underfoot or detected by a long cane or a wheelchair without causing a tripping hazard. The size and spacing of the truncated domes have been clearly specified by the U.S. Access Board. 2 3 However, guidance concerning the visual properties of detectable warning surfaces is much less specific. The U.S. Access Board states that “Detectable warning surfaces shall contrast visually with adjoining surfaces, either light-on-dark or dark-on-light.”4 The Public Rights-of- Way Access Advisory Committee has previously noted that there is a lack of human factors research with vision-impaired pedestrians.5 There is not a sufficient quantitative research basis to support any more specific guidance with respect to the visual properties of detectable warning surfaces, particularly color and contrast. An overview of Federal rule making and guidance on detectable warnings is given in Appendix B.
In this report, the terms “detectable warning” and “detectable warning surface” refer to the standard truncated dome surfaces described in the Americans with Disabilities Act Accessibility Guidelines (ADAAG) and described by the U.S. Access Board. 6 7 8 9 10
Note that detectable warnings with truncated domes as used in the U.S. are only one of several types of tactile patterns used through the world as detectable warnings, and represent only a subset of the types of Tactile Ground Surface Indicators (TGSIs) that are being used as a navigational aid for pedestrians who are visually impaired. For example, various tactile pavements have been used in Japan since the 1960s, and in England there are currently seven different types of tactile paving patterns used. 11 12 13 Persons interested in the practices of other countries may wish to consult Detectable Warnings: Synthesis of U.S. and International Practice, which is available from the U.S. Access Board. 14
1American Foundation for the Blind, “Glossary of Eye Conditions,” 2004. Retrieved December 9, 2004, from the American Foundation for the Blind website: http://www.afb.org/Section.asp?DocumentID=2139
2U.S. Access Board, Draft Guidelines for Accessible Public Rights-of-Way (Washington, DC: 2002). Retrieved January 3, 2005, from the U.S. Access Board website: http://access-board.gov/rowdraft.htm
3Draft Public Rights-of-Way Accessibility Guidelines, U.S. Access Board (Washington, DC: 2005). Retrieved December 1, 2005 from the U.S. Access Board website:http://www.access-board.gov/prowac/draft.htm
4Ibid
5Public Rights-of-Way Access Advisory Committee, U.S. Access Board, Building a True Community (Washington, DC: 2001).
6U.S. Access Board, Americans with Disabilities Act (ADA) Accessibility Guidelines for Buildings And Facilities (Washington, DC: 1991). Retrieved January 3, 2005, from the U.S. Access Board website: http://www.access-board.gov/adaag/ADAAG.pdf
7U.S. Access Board, Draft Guidelines for Accessible Public Rights-of-Way (Washington, DC: 2002). Retrieved January 3, 2005, from the U.S. Access Board website: http://access-board.gov/rowdraft.htm
8U.S. Access Board, ADAAG Requirements for Detectable Warnings, (Washington, DC: 2003). Retrieved December 28, 2004, from the U.S. Access Board website: http://access-board.gov/adaag/dws/update.htm
9U.S. Access Board, Revised ADA and ABA Accessibility Guidelines (Washington, DC: 2004). Retrieved January 3, 2005, from the U.S. Access Board website: http://www.access-board.gov/ada-aba/final.pdf
10U.S. Access Board, Draft Public Rights-of-Way Accessibility Guidelines (Washington, DC: 2005). Retrieved December 1, 2005, from the U.S. Access Board website: http://www.access-board.gov/prowac/draft.htm
11Department for Transport, Guidance on The Use Of Tactile Paving Surfaces (London, UK: 1999). Retrieved October 5, 2004, from Department for Transport website: http://www.dft.gov.uk/stellent/groups/dft_obility/documents/pdf/dft_mobility_pdf_503283.pdf
12Department for Transport, Inclusive Mobility: A Guide To Best Practice on Access to Pedestrian and Transport Infrastructure, (London, UK: 2002). Retrieved October 5, 2004, from Department for Transport website:http://www.dft.gov.uk/stellent/groups/ dft_mobility/documents/pdf/dft_mobility_pdf_503282.pdf
13Dowson, A.J., “The Development of Surface Tactile Indicators,” Proceedings of the 7th International Conference on Concrete Block Paving (London, UK: 2003). Sun City, South Africa. Retrieved October 5, 2004, from Interpave website: http://www.paving.org.uk/pdf/036.pdf
14Bentzen, B.L., Barlow, J.M., & Tabor, L.S., U.S. Access Board, Detectable Warnings: Synthesis of U.S. and International Practice (Washington, DC: 2000).
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