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36 CFR Parts 1190 and 1191 ADA and ABA Accessibility Guidelines - Preamble (Discussion of Comments and Changes)

705 Detectable Warnings

Section 705 provides the technical specifications for detectable warnings, a distinctively textured surface of truncated domes identifiable by cane and underfoot. This surfacing is required along the edge of boarding platforms in transit stations. The original ADAAG included a requirement for detectable warnings on the surface of curb ramps to provide a tactile cue for persons with vision impairments of the boundary between sidewalks and streets where the curb face had been removed. It also required them at locations where pedestrian areas blend with vehicular areas without tactile cues, such as curbs or railings, and at reflecting pools. Certain requirements for detectable warnings were temporarily suspended in the original ADAAG and were not included in the proposed rule, as further discussed in section 406 above. Consequently, the requirements in section 705 are required only at boarding platforms in transportation facilities (810.5.2). Revisions made in the final rule include:

  • revising specifications for the diameter and spacing of truncated domes to allow a range (705.1.1 and 705.1.2)

  • clarifying the square grid pattern of truncated domes (705.1.2)

  • simplifying requirements for contrast between detectable warnings and adjoining walking surfaces (705.1.3)

  • removing provisions generally recognizing alternatives to the detectable warnings specified

  • clarifying the application of the requirements to the edges of boarding platforms (705.2)

The detectable warning criteria specify a pattern of evenly-spaced truncated domes. The Board has added clarification, consistent with provided figures, that the domes be aligned in a square grid pattern (705.1).

Comment. The proposed rule specified that the truncated domes have a diameter of 0.9 inch, measured at the base. A commenter cited research conducted in Japan which indicated that a surface very similar to that specified by section 705 ranked high in detectability. It was recommended, based on this research, that a diameter of 0.4 inch to 0.9 inch be specified for domes, measured at the top. In addition, this commenter recommended that the spacing between domes be revised from an absolute of 2.35 inches to a range of 1.6 to 2.35 inches.

Response. In the final rule, the Board has revised the specification for the diameter and spacing of truncated domes to permit a range of dimensions (705.1.1). A range of 0.9 inch to 1.4 inches is specified for the base diameter. The top diameter range is specified to be 50% to 65% of the base diameter, which approximates the recommended 0.4 inch to 0.9 inch range. The center-to-center spacing of domes has been changed from 2.35 inches absolute, to a range of 1.6 inches minimum to 2.4 inches maximum, with a minimum separation measured at the base of 0.65 inch (705.1.2). The revised base diameter and spacing dimensions will accommodate existing detectable warning products that were previously deemed to provide an equivalent level of accessibility. ADAAG permits departures that provide equal or greater access as an "equivalent facilitation." The Department of Transportation (DOT), which enforces the ADA’s design requirements as they apply to various transportation facilities, reviews requested departures based on equivalent facilitation in consultation with the Board. Over the years, DOT has approved various detectable warning products that differ slightly from the ADAAG specifications. The specifications in the final rule derive from a review of these products and will encompass the variations among products previously approved by DOT under the equivalent facilitation clause.

Detectable warnings are required to contrast visually from adjacent walking surfaces, either light-on dark or dark-on-light. The proposed rule required the material used to provide contrast be an integral part of the truncated dome surface (705.2.2). This specification was intended to preclude the painting of detectable warning surfaces to meet the contrast requirements since painted surfaces would not be adequately slip resistant. However, requirements for ground and floor surfaces in section 302, which require slip resistance, apply to those surfaces with detectable warnings as well. The Board believes that the requirement for slip resistance in section 302 effectively prevents the painting of detectable warning surfaces. Consequently, it has removed the specification that the material used to provide contrast be an integral part of the detectable warning surface.

Comment. The proposed rule specified that detectable warnings in interior locations differ from adjoining walking surfaces in resiliency or sound-on-cane contact (705.2.3). Commenters considered this provision to be of questionable usefulness and difficult to meet absent a recognized method of measuring resiliency or sound-on-cane contact.

Response. The requirement for contrast in resiliency or sound-on-cane contact between detectable warnings and adjoining walking surfaces in interior locations has been removed in the final rule.

Comment. The proposed rule included provisions that generally recognized alternative tactile surfaces equally detectable underfoot or other designs or technologies that provide equal or superior drop-off warning at boarding platforms (705.3 and 705.4). Commenters opposed these provisions without further guidance or specificity on the type of alternatives that would be acceptable. Some commenters recommended that these provisions were unnecessary in view of the general provision for equivalent facilitation in section 103 permitting departures from this or any other requirement in the guidelines where equal or greater access is provided.

Response. The Board has removed the provisions concerning equivalent products and technologies as an alternative to the detectable warnings specified by section 705. This change is consistent with the effort the Board made in the proposed rule to remove specific provisions concerning equivalent facilitation. The general provision for equivalent facilitation remains the basis upon which alternatives to the specified detectable warnings may be pursued. DOT’s ADA regulations provide a process for the review of requested departures as an equivalent facilitation in relation to public transportation facilities.24

Section 705.2 specifies that detectable warnings along boarding platform edges be 24 inches wide. In the final rule, the Board has added clarification that the detectable warning is to extend the full length of the public use areas of platforms.

24 49 CFR 37.9(d)


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