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Detectable Warnings



   
A detectable warning is a standardized surface feature, specified in the "Americans with Disabilities Act Accessibility Guidelines" (ADAAG), comprised of raised truncated domes and used to inform visually impaired pedestrians of the hazards in the area immediately ahead. The ADAAG specifies:  "Detectable warnings shall consist of raised truncated domes with a diameter of 23 mm, a height of nominal 5 mm and center to center spacing of nominal 59 mm and shall contrast visually with adjoining surfaces, either light-on-dark or dark-on-light."  Detectable warnings are placed 0.6 m deep at the base of curb ramps or on the sidewalk edge of the street at blended curbs and at flush transitions from the sidewalk to the crosswalk. Alignment of domes is parallel to the primary direction of travel.
objective To alert pedestrians who are visually impaired to the edge of the curb ramp and the beginning of the street. Detectable warnings are uniquely standardized features intended to function like a STOP sign for visually impaired pedestrians.
applications Where there is a need to warn visually impaired pedestrians that they are about to enter lanes of moving traffic.
target population Disabled Pedestrians, Elderly Pedestrians
crash type Pedestrian R/W Violation-Intersections, Traffic Signals and Signs
advantages
  • Provides information to visually impaired pedestrians about the boundary between the sidewalk and the vehicular way
disadvantages
  • Pattern may cause discomfort for some wheelchair users; parallel alignment of domes can help minimize this discomfort
pointers Truncated domes are still in their early phases of use on city sidewalks.  There may be maintenance issues in the long-term.
cost Low to Medium, $200-$2,000 per ramp or curb, depending on the material and the width of the ramp or flush area.
responsibility Public Works
further reading

Bentzen, B.L., J.M. Barlow, and L. Tabor. Detectable Warnings: Synthesis of U.S. and International Practice. Washington, DC: US Access Board, 2000

Barlow, J., and B.L. Bentzen. Cues Blind Travelers Use to Detect Street. Cambridge, MA: US DOT, Federal Transit Administration, Volpe National Transportation Systems Center, 1994

Hauger, J.S., M.P. Safewright, J.C. Rigby, and W.J. McAuley. Detectable Warnings Project: Report of Field Tests and Observations. Blacksburg, VA: Virginia Polytechnic Institute and State University, 1994

Bentzen, B.L., T.L. Nolin, R.D. Easton, L. Desmarais, and P.A. Mitchell. Detectable Warning Surfaces: Detectability by Individuals with Visual Impairments, and Safety and Negotiability for Individuals with Physical Impairments. Report no. VNTSC-DTRS57-92-P-81354 and VNTSC-DTRS57-91-C-0006. Cambridge, MA: US DOT, Federal Transit Administration, Volpe National Transportation Systems Center, and Project ACTION, National Easter Seal Society, 1993

Bentzen, B.L., T.L. Nolin, R.D. Easton, L. Desmarais, and P.A. Mitchell. Detectable Warnings: Safety and Negotiability on Slopes for Persons Who Are Physically Impaired. Washington, DC: US DOT, Federal Transit Administration, and Project ACTION, National Easter Seal Society, 1994

Hughes, R.G. A Florida DOT Field Evaluation of Tactile Warnings in Curb Ramps: Mobility Considerations for the Blind and Visually Impaired. Chapel Hill, NC: University of North Carolina, Highway Safety Research Center, 1995.
examples City of Roseville, CA; City of Sacramento, CA
related tools

High-Visibility Signs, High-Visibility Markings at Uncontrolled Crossings, Double Posted Pedestrian Crossing Signs

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