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 base 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)