Truncated domes is a fancy phrase used to describe the bumps on a background mat that are found on sidewalks and elsewhere. Some think these are just helpful traction to prevent falling on a slippery surface. They help with that problem; however, they are much more useful than just for that purpose.
These bumps are guides for those who have impaired eyesight. Under federal law in the United States, they must meet the requirements of the American with Disabilities Act (ADA) in terms of where they are placed and how they are designed.
Truncated Dome Design
Japanese inventors originated the design of these bumps in the 1960s and their popularity expanded to Australia, then the UK and came to America and Canada in the 1990s. Now, more than 18 countries use them. These surfaces give a physical warning for a visually-impaired person to let them know when they are approaching a street or a level change.
Blind people can feel these bumps by using a cane. Visually-impaired people are aided also because the bumps are a contrasting color (most popular is bright yellow) and the bumps can be felt by the feet as well.
Truncated domes are just one of the tactile paving materials used as detectable warning surfaces. There are other styles and they mean different things.
Reading the Bumps
Some affectionately call the variety of tactile surfaces “braille” bumps. When these bumps are aligned in a straight/parallel pattern, they have a specific meaning. They can be used in combination with other tactile guides. Here is the information from Simplemost about what the different tactile surfaces mean:
Channel Stripes Along a Path
The truncated domes can be used with channeled stripes as a guide to direct someone to follow a certain path. The path starts with truncated bumps and changes into channeled stripes to indicate a path to follow, which ends with truncated bumps to indicate a change of direction or the path’s end.
When the bumps are offset in a diagonal pattern, this indicates a train track or a subway line or another edge ahead.
Stripes Across a Path
These stripes are a warning of a hazard ahead, which could be an upcoming set of stairs for example. These stripes are closer together than the ones used for an indication of a direction to go down a path.
Oblong bumps indicate an upcoming track for a street trolley, street tram, or other street-level public transportation such as a bus line.
Bumps Save Lives
Visually-impaired people are helped extensively with these guidance bumps so that they do not accidentally wander off a platform or go off the sidewalk, or potentially step on train tracks in front of an oncoming train or bus. Now that you know what they mean, you can see how well they work and why it is important that they are installed in all the appropriate places.