Six Friends: Detectable Warning Surfaces

What is a detectable warning

A detectable warning is “A standardized surface feature built in or applied to walking surfaces or other elements to warn of hazards on a circulation path.” (F106.5, Draft Final ADA and ABA Accessibility Guidelines, April 2, 2002) It is a unique and standardized feature, intended to function much like a stop sign and to alert pedestrians who are visually impaired to the presence of a hazard in the line of travel.

Why is it necessary

As curb ramps have become common in response to the requirements of the Rehabilitation Act (1973) and the Americans with Disabilities Act (1990), an unintended consequence has been that blind pedestrians have found it more difficult to locate the boundary between the street and sidewalk. The only surface which has repeatedly been demonstrated to be detectable most of the time to blind pedestrians either under foot or by the use of a long cane is the truncated dome detectable warning surface, which has been required on transit platform edges since 1991 and at curb ramps since July 2001.

Specifications

“Detectable warnings shall consist of a surface of truncated domes aligned in a square grid pattern…”.

“Dome size. Truncated domes in a detectable warning surface shall have a base diameter of 0.9 in (23 mm) minimum to 1.4 inches (36mm) maximum, a top diameter of 50% of the based diameter minimum to 65% of the base diameter maximum, and a height of 0.2 in (5 mm).

Dome Spacing. Truncated domes in a detectable warning surface shall have a center-to-center spacing of 1.6 inches (41 mm) minimum and 2.4 inches (61mm) maximum and a base to base spacing of 0.65 inches (16mm) minimum, measured between the most adjacent domes on square grid.

Contrast. Detectable warning surfaces shall contrast visually with adjoining surfaces, either light-on-dark or dark-on-light.” (Draft Guidelines for Accessible Public Rights-of-Way, June 14, 2002)

Research

Two research projects (Barlow and Bentzen, 1992, and Hauger, Safewright, Rigby & McAuley, 1994) confirmed that, for blind travelers, removal of the single most reliable cue to the presence of an intersecting street, that is, the down curb, caused problems. At curb ramps even skilled travelers failed to detect the street before stepping into it on 39% of approaches. The failure to detect streets was highly correlated with slope of the curb ramp and with the abruptness of change in angle between the approaching sidewalk and the curb ramp. Hauger et al. also found that diagonal/ apex curb ramps were more likely to lead to unsuccessful street crossings.

Despite concerns that detectable warnings would negatively affect the travel of mobility impaired individuals, Bentzen (1994), (also Bentzen, Nolin, Easton, Desmarais & Mitchell, 1993; Bentzen, Nolin, Easton, Desmarais & Mitchell, 1994b), and Hauger et al. (1994) found that truncated dome detectable warnings on slopes or curb ramps had little effect on safety and negotiability for persons having mobility impairments. In fact, Hauger et al. found that persons with physical disabilities generally considered curb ramps having detectable warnings to be safer, more slip resistant, more stable, and to require less effort to negotiate than concrete curb ramps. Both teams of investigators found, however, that a small minority of persons having physical disabilities were affected adversely by detectable warnings.

Recommendations

ADAAG originally required the detectable warning surface on the entire width and depth of the curb ramp. To minimize the possibility of problems for persons with mobility impairments and to provide consistent information about the location of the street to individuals who are blind, Bentzen and Barlow (1995) concluded by recommending that 24 in (610 mm) of truncated dome detectable warning be installed along the bottom of curb ramps. That amount had previously been demonstrated to be sufficient to enable detection and stopping on most approaches. It is the current recommendation of American Council of the Blind and of the Association for the Education and Rehabilitation of the Blind and Visually Impaired and is consistent with the requirement for truncated dome detectable warning at transit locations. This is also the recommendation of the Public Rights-of-Way Access Advisory Committee (PROWAAC, Access Board, 2001).

There are now a number of truncated dome products available for installation on curb ramps in various climates and conditions. A report on detectable warnings has been developed by the Access Board and is available by calling 800-872-2253 and asking for Detectable Warnings: Synthesis of U.S. and International Practice.

ADA Fabricators
mail: P.O. Box 179, North Billerica, MA 01862 U.S.A.
internet: http://www.adafabricators.com
fax: 978-262-1455
voice: 978-262-9900

Cobblecrete
mail: 485 West 2000 South, Orem, UT 84058 U.S.A.
internet: http://www.cobblecrete.com
fax: 801-225-1690
voice: 800-798-5791; 801-224-6662

COTE-L Industries, Inc.
mail: 1542 Jefferson Street, Teaneck, NJ 07666 U.S.A.
internet: http://www.cotelind.com
fax: 201-836-5220
voice: 201-836-0733

Crossville Ceramics
mail: P.O. Box 1168, Crossville, TN 38555 U.S.A.
internet: http://www.crossville-ceramics.com
fax: 931-484-8418
voice: 931-484-2110

Detectable Warning Systems, Inc.
mail: 6435 Joshua Tree Avenue, Orange, CA 92867 U.S.A.
internet: http://www.detectable-warning.com
voice: 866-999-7452

Disability Devices
mail: 17420 Mt. Hermann St., Fountain Valley, CA 92708 U.S.A.
internet: http://www.disabilitydevices.com/
fax: 714-437-9309
voice: 714-437-9237; 800-747-5651

Engineered Plastics, Incorporated
mail: 300 Pearl Street, #200, Buffalo, NY 14202 U.S.A.
internet: http://www.armor-tile.com
fax: 800-769-4463
voice: 800-682-2525; 716-842-6039

Hanover Architectural Products, Inc.
mail: 240 Bender Road, Hanover, PA 17331 U.S.A.
internet: http://www.hanoverpavers.com
fax: 717-637-7145
voice: 717-637-0500

Increte Systems
mail: 8509 Sunstate Street, Tampa, FL 33634 U.S.A.
internet: http://www.increte.com
fax: 813-886-0188
voice: 800-752-4626; 813-886-8811

Interlock San Diego
mail: 4351 Stanford Street, Carlsbad, CA, 92008 U.S.A.
internet: http://detectablewarning.tierranet.com
fax: 760-434-3840
voice: 760-434-5586

Pavestone Company
mail: 4835 L.B.J. Freeway, Suite 700, Dallas, TX 75244 U.S.A.
internet: http://www.pavestone.com
fax: 972-404-9200
voice: 800-245-7283, 972-404-0400

Star Seal of Florida
contact: C. Thompson
mail: 2740 NW 55th Court, Fort Lauderdale, FL 33309 U.S.A.
fax: 954-733-4798
voice: 800-432-8402

Steps Plus, Incorporated
mail: 6375 Thompson Rd., Syracuse, NY 13206 U.S.A.
internet: http://www.steps-plus.com
fax: 315-432-0612
voice: 315-432-0885

Strongwall Industries, Inc.
mail: P.O. Box 201, Ridgewood, NJ 07451 U.S.A.
internet: http://www.strongwall.com
fax: 201-447-2317
voice: 800-535-0668; 201-445-4633

Summitville Tiles, Incorporated
mail: P.O. Box 73, Summitville, OH 43962 U.S.A.
internet: http://www.summitville.com
fax: 330-223-1414
voice: 330-223-1511

Transpro Industries, Incorporated
mail: 20 Jones Street, New Rochelle, NY 89701 U.S.A.
internet: http://www.transpo.com
fax: 914-636-1282
voice: 800-321-7870; 914-636-1000

Vanguard ADA Products
mail: 20628 Broadway Ave., Snohomish, WA 98296 U.S.A.
internet: http://www.vanguardonline.com
fax: 360-663-3335
voice: 800-290-5700

Whitacre-Greer Fireproofing Company
mail: 1400 South Mahoning Ave, Alliance, OH 44601 U.S.A.
internet: http://www.wgpaver.com
fax: 330-823-5502
voice: 800-947-2837; 330;823-1610

Bentzen, B.L., Barlow, J.M. & Tabor, L.S. (2000). Detectable Warnings: Synthesis of U.S. and International Practice. Washington, D.C.: U.S. Access Board. Available free by calling USA ABLE (800-872-2253) and requesting it by name.

Barlow, J. & Bentzen, B.L. (1994). Cues blind travelers use to detect streets. Final report. Cambridge, MA: U.S. Department of Transportation, Federal Transit Administration, Volpe National Transportation Systems Center.

Bentzen, B.L., Nolin, T.L. & Easton, R.D. (1994a). Detectable warning surfaces: Color, contrast and reflectance. Cambridge, MA: U.S. Department of Transportation, Federal Transit Administration, Volpe National Transportation Systems Center. Report No. VNTSC-DTRS-57-93-P-80546.

Bentzen, B.L., Nolin, T.L., Easton, R.D., Desmarais, L. & Mitchell, P.A. (1994b). Detectable warnings: Safety & negotiability on slopes for persons who are physically impaired. Washington, DC: Federal Transit Administration and Project ACTION of the National Easter Seal Society.

Bentzen, B.L., Nolin, T.L., Easton, R.D., Desmarais, L. & Mitchell, P.A. (1993). Detectable warning surfaces: Detectability by individuals with visual impairments, and safety and negotiability for individuals with physical impairments. Final report VNTSC-DTRS57-92-P-81354 and VNTSC-DTRS57-91-C-0006. Cambridge, MA: U. S. Department of Transportation, Federal Transit Administration, Volpe National Transportation Systems Center, and Project ACTION, National Easter Seal Society.

Bentzen, B.L. & Barlow, J.M. (1995). Impact of curb ramps on safety of persons who are blind. Journal of Visual Impairment and Blindness, 89, 319-328.

Hauger, J, Rigby, J, Safewright, M. & McAuley, W. (1996). Detectable warning surfaces at curb ramps. Journal of Visual Impairments and Blindness 90:512-525.

Hauger, J.S., Safewright, M.P., Rigby, J.C. & McAuley, W.J. (1994). Detectable warnings pro-ject: Report of field tests and observations. Final Report to U.S. Architectural and Transportation Barriers Compliance Board. Blacksburg, VA: Virginia Polytechnic Institute and State University.

Report of fundamental research on standardization relating to tactile tiles for guiding the visually impaired: Aiming at standardization of patterns. (Study of the relationship between individual patterns and ease of recognition. (1998). Japan: Ministry of International Trade and Industry, National Institute for Technology and Evaluation.

Building a True Community: Report of the Pubic Rights of Way Access Advisory Committee. (2001) Washington, DC: U.S. Architectural and Transportation Barriers Compliance Board