"Detectible Warning" surfaces are found underfoot at major intersections, crosswalks, and transportation platforms across the United States. 'Truncated Domes' are the most common type and are designed to provide visually impaired and blind travelers tactile warnings for upcoming potential dangers. These warnings are required to be tactual for blind travelers and have high visual contrast for low vision travelers.
In 1991, the Americans with Disabilities Act (ADA) standardized the type and placement of detectible warnings. (Japan implemented the first tactile paving system back in the 1960s.) In 1994, the required use of truncated domes was suspended pending further study. In July of 2001, truncated dome tactile warning surfaces were required during new construction and alteration of all hazardous roadways and pedestrian curb ramps and additionally, detectible warnings were required along pedestrian-accessible transit platforms.
Patterns of Detectable Warnings
Did you know that in some places, there are patterns in the detectible warning tiles that indicate what type of hazard is ahead? Dots aligned in rows indicate roads. Off-set dots indicate a train track or other ledge. Oblong or lozenge-shaped bumps indicate tracks of a street trolley or other street-level transportation. Stripes that run across the path indicated steps or trip hazards. For more information about patterns, see the article, Here's The Purpose of those Sidewalk Bumps.
Learn more about the ADA detectible warning surfaces here.