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Detectable warning surfaces

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Contents

Introduction

To ensure that buildings and facilities are accessible to and usable by people with disabilities, the Americans with Disabilities Act (ADA) establishes accessibility requirements for State and local government facilities, places of public accommodation, and commercial facilities. Under the ADA, the Access Board has developed and maintains design guidelines for accessible buildings and facilities known as the ADA Accessibility Guidelines (ADAAG). ADAAG covers a wide variety of facilities and establishes minimum requirements for new construction and alterations. The Board maintains a similar responsibility for accessibility guidelines under the Architectural Barriers Act (ABA). The ABA requires access to certain facilities designed, built, altered, or leased with Federal funds. Like ADAAG, the Board’s ABA accessibility guidelines apply to new construction and alterations. The Board’s guidelines become enforceable when they are adopted by the standard setting agency for the ADA and the ABA. The agencies responsible for standards under the ADA are the Department of Justice (DOJ) and the Department of Transportation (DOT). [1] To learn more about the American Disabilities Act refer to ADA Amendments Act of 2008.


Detectable Warning Surface   Photo Courtesy of detectile.com
Detectable Warning Surface Photo Courtesy of detectile.com

A detectable warning surface is “a standardized surface feature built in or applied to walking surfaces or other elements to warn of hazards on a circulation path.” [2]

Why do we need them?

The intent of detectable warning surfaces to alert visually impaired pedestrians of potential hazards in their direction of travel. With the implementation of curb ramps for wheelchair usage and mobility impairments, there was an unanticipated disadvantage for visually impaired individuals. For some visually impaired individuals, curb ramps made differentiating the sidewalk from the street difficult. Prior to the use of curb ramps visually impaired individuals used the height difference from the curb to the street to indicate where a walkway ended and where the street began. The usage of curb ramps generated the need for detectable warning surfaces, to warn visually impaired individuals of the boundary between a walkway and the street.

Where are Detectable Warning Surfaces used?

Some areas that use detectable warning surfaces include: 1. Curb ramps and blended transitions at pedestrian street crossings; 2. Pedestrian refuge islands; 3. Pedestrian at-grade rail crossings not located within a street or highway; 4. Boarding platforms at transit stops for buses and rail vehicles where the edges of the boarding platform are not protected by screens or guards; and 5. Boarding and alighting areas at sidewalk or street level transit stops for rail vehicles where the side of the boarding and alighting areas facing the rail vehicles is not protected by screens or guards. [2]

See the ADAAG Standards, sections 4.7.7, 4.29, 4.29.5, 4.29.6, and 10.3.1(8). [3]

History of Usage

In 1991 the use of detectable warning surfaces was required due to the ADA Accessibility Guidelines. From 1994-2001 the usage requirement was suspended (with the exception of transit platforms) to investigate how detectable the surfaces were from various cracks, grooves, and surface materials. On July 26th, 2001 the suspension expired, and detectable surfaces were again required as described by the ADA Accessibility Guidelines. 2001-Present- advisories and updates to the regulations are still occurring.

Current Guidelines for Usage

Detectable warnings consist of a surface with a truncated dome aligned in a square or radial grid pattern.

Dome Size

Truncated domes should have a base diameter of 23 mm (0.9 in) minimum to 36 mm (1.4 in) maximum, a top diameter of 50 percent of the base diameter minimum to 65 percent of the base diameter maximum, and a height of 5 mm (0.2 in). [1]

Dome Spacing

Truncated domes in a detectable warning surface shall have a center-to-center spacing of 41 mm (1.6 in) minimum and 61 mm (2.4 in) maximum, and a base-to-base spacing of 17 mm (0.65 in) minimum, measured between the most adjacent domes. [1]

Contrast

Detectable warning surfaces shall contrast visually with adjacent gutter, street or highway, or walkway surfaces, either light-on-dark or dark-on-light. The material used to provide contrast should contrast by at least 70%. Contrast in percent is determined by: Contrast = [(B1 - B2)/B1] x 100 where B1 = light reflectance value (LRV) of the lighter area and B2 = light reflectance value (LRV) of the darker area.Note that in any application both white and black are never absolute; thus, B1 never equals 100 and B2 is always greater than 0. [3]

Manufacturers of detectable surfaces provide multiple color options for purchase with ultra violet coatings, to prevent fading of colors.

Material

The material used to provide contrast shall be an integral part of the walking surface. Detectable warnings used on interior surfaces shall differ from adjoining walking surfaces in resiliency or sound-on-cane contact. [4]

Manufacturers sell a variety of detectable warning surface material options from polymer concrete composites, to polyurethane sheeting, or brick pavers.

Size of warning surfaces

Warning surfaces should extend 610mm (24in) minimum in the direction of travel and the full width of the curb ramp (exclusive of flares), the landing, or the blended transition. [5]


Detectable Warning Surface   Photo Courtesy of detectile.com
Detectable Warning Surface Photo Courtesy of detectile.com


Vendors

Some vendors and manufacturers include, but are not limited to ACO Polymer Products, Inc, ADA Answer Industries, ADA Arcis Tactile Arcis Corp, ADA Armor-Tile Engineered Plastics, Incorporated, ADA Tactile Systems, ADA U.S.A. Safety Domes LLC, ADA-ADAAG TekWay® Dome Tiles StrongGo Industries LLC, Advance Traffic Markings, Advanced Surface Systems LLC, Cape Fear Systems, LLC., Cobblecrete, COTE-L Industries, Inc., Detectable Warning Systems, DetecTile, Inc., D.W. Dots, East Jordan Iron Works, Inc., ECG Inc., Flint Trading, Inc. Various manufacturers and suppliers exist across the United States.

Additional Information

References

  1. Revised Draft Guidelines for Accessible Public Rights-of-Way United States Access Board
  2. Proposed Accessibility Guidelines Pedestrian Facilities in the Public Right-of-Way
  3. #4.29 ADA Accessibility Guidelines
  4. ADA Standards for Accessible Design Department of Justice
  5. Detectable Warning Surfaces Access Board Requirements