It’s easy for some pedestrians to go their whole lives without paying much attention to the raised bumps that cover parts of the sidewalk they step on. But for others, those little dots are essential to getting around.
In this video spotted by Tom McParland of Jalopnik, video producer Tom Scott explains the ingenious purpose behind this piece of infrastructure. Blistered sections of pavement can communicate important messages to visually impaired pedestrians. A uniform grid of circles signals a sloping curb leading to a crosswalk. If the squares are red, that indicates to a partially sighted person that the path has a light for stopping traffic.
Varying patterns symbolize specific hazards. Strips of offset bumps, for example, are usually placed at the edge of a subway platform. And as Scott lays out in the video above, pill-shaped bumps and striped patterns are used to alert pedestrians to completely different situations.
Tactile paving was first introduced in Japan in 1967 [PDF], and the infrastructure trick has since spread to countries around the world. In the United States, the warnings are required by the Americans With Disabilities Act for public transportation facilities and other areas covered by the ADA.