Truncated domes (AKA detectable warnings, tactile paving, detectable warning surfaces) are ground surface indicators designed to assist and warn pedestrians who are blind or visually impaired.
Truncated domes feature a unique pattern of cones that are easily detected by a cane or foot, alerting the visually impaired to the presence of a street or sudden drop-off.
Truncated domes were first developed by the Japanese in the mid 1960’s and expanded to Australia and the UK. The United States adopted the technology in the early 1990s, followed soon by Canada.
As of 2014, more than 18 countries have implemented truncated domes in front of rail lines, schools, city crosswalks, and government buildings.
Per federal law, there are several guidelines that dictate how a truncated dome can be manufactured. Some of those guidelines are listed below:
Detectable warnings shall consist of a surface of truncated domes aligned in a square or radial grid pattern and shall comply with R304.
R304.1.1 Dome Size.
Truncated domes in a detectable warning surface shall 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).
Where domes are arrayed radially, they may differ in diameter within the ranges specified.
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.
Detectable warning surfaces shall contrast visually with adjacent gutter, street or highway, or walkway surfaces, either light-on-dark or dark-on-light.
There are several other considerations defined by ADA regulations.