Detectable warning

Detectable warnings alert people who are blind or visually impaired of impending danger from vehicle impact or a grade change. These are made up of "truncated domes", which are small domes that have had their tops cut off, or truncated. The truncated domes are placed relatively close together and can be detected by one's feet or when using a long cane. These are only used on the surfaces of pedestrian curb cuts to warn of vehicular traffic and at the edge of rail platforms to warn of a drop-off.

Originally instituted at crosswalks and other hazardous vehicular ways by countries like Japan and the United Kingdom, among others, the United States picked up the standard in the early 1990s, after passage of the Americans with Disabilities Act.

The federal government, through studies and guidance provided by advocates and the Access Board, now mandates detectable warnings in proscribed locations, such as on the surface of pedestrian curb cuts and at the edge of rail platforms. Detectable warnings have been required for the edge of rail platforms in the United States since 1991. Detectable warnings for pedestrian curb cuts were suspended for study in 1994, and became officially required in 2001.