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

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.