When crossing the street or boarding a train, you might notice small domes or rounded, slightly raised bars purposefully placed on the ground’s surface. These indicators can be felt underfoot or by cane, and are a form of tactile paving. They are also referred to as ground surface indicators, or detectable warning plates. A very common type of detectable warning plate uses attention patterns—rows of truncated domes forming a grid pattern. Another popular pattern is a guiding pattern or corduroy pattern, which uses rows of rounded narrow bars or lines as indicators.
Tactile paving, or paving that can be felt, conveys a message about navigation to visually impaired pedestrians. Detectable warning plates mark the transition from pedestrian route to roadway when placed at curb ramps, or signals a pedestrian to take caution before a flight of stairs. Since their introduction in the built world, accessibility and safety for pedestrians with limited to no vision have progressed in a positive direction.
Tactile paving history
Tactile paving was originally developed in Japan in 1965 by Seiichi Miyake. In 1967, it made its debut at a crosswalk in Okayama city, then spread across other pedestrian crossings in various parts of Japan. Their use grew quickly as they were adopted by the Japan National Railways. Following suit, the UK, Australia, and US started to use tactile ground surface indicators in the early 1990s. Canada incorporated them first into transportation, and then into other areas of the built environment by the early 2000s.
As detectable warning surfaces evolved over several decades, various types of materials emerged for manufacturing. Early on, only pre-cast concrete models were available. On modern streets, cast iron, polyurethane, stainless steel, concrete, and ceramic are all examples of materials used. It is imperative with detectable warning plates that they are durable enough to withstand heavy foot traffic, as well as weathering. Cast iron detectable warning plates are one of the most durable options, known for their tough nature. From withstanding snowplow abuse to daily wear and tear, they are built to last for a long service life.
The role of the ADA and ABA in tactile paving
Tactile paving is regulated in the US; the government is guided by advocates and the US Access Board to mandate detectable paving in certain locations, such as at the end of a sidewalk or before a train platform. The US Access Board is a federal agency that promotes accessible design and standards for the built environment for people with disabilities.
States also have their own guidelines, based on the ADA (Americans with Disabilities Act, a federal law passed in 1968) and the ABA (Architectural Barriers Act). The ADA applies to facilities in the private sector and local government sector. For facilities that have been designed or built with the use of federal funds, or are leased by federal agencies, a similar design mandate called the ABA applies. The ABA is a 1990 civil rights law that prohibits any discrimination against people with disabilities in various areas of public life. Both laws work in tandem to ensure that the accessibility rights of those with disabilities are met.
Types of tactile paving patterns
Much like Braille, a form of written language where raised dots are felt by the fingertips, tactile paving delivers a message about surrounding conditions through touch. Tactile paving communicates cautions and warnings, or may mark areas of safety. It empowers pedestrians with visual impairment by offering a tangible way of recognizing their environment and navigating it independently.
Attention patterns refer to a series of rows of truncated domes. There are two types of attention patterns: grid and offset patterns. The difference is in how the rows of truncated domes line up.
Detectable warning plates with grid patterns have truncated domes that are evenly spaced in straight rows, creating a square grid. This is one of the most common patterns in detectable warning plates on city sidewalks. They are often used to signify a dropped curb at the end of a sidewalk before it transitions from a pedestrian route to vehicular road.
In an offset pattern, truncated domes are positioned in rows where every other row is staggered. Although at first glance this may look similar to the grid pattern, offset patterns convey a different hazard. They warn of large holes or chasms ahead, mitigating the risk of a pedestrian falling through the opening. Offset patterns are widely used at train platforms. The row of truncated domes should be parallel to the end of the platform, and laid approximately 20 inches back from the platform edge.
Guiding pattern (or corduroy pattern)
Guiding patterns, also known as corduroy patterns, consist of rounded rod-like bars or lines. This can either run transversely across a path, or alongside a path—delivering two very different messages.
Guiding pattern across a path
When running transversely across a path, these bars or lines signal steps or trip hazards ahead. This can be found at the top or bottom of stairs, or at the foot of a ramp, warning pedestrians to stop and exercise caution.
Guiding pattern along a path
When running alongside a path, guiding patterns (also called wayfinding patterns or tiles) have bars or lines signal a safe route to follow. By staying close and following the lines, pedestrians can steer clear of obstacles and hazards.
The lozenge pattern refers to tactile paving consisting of evenly spaced rows of lozenge-shaped tiles with rounded edges. This type of tactile paving warns pedestrians they are approaching street-level rapid transportation such as a tram. They are installed a minimum of 20 inches back from the edge of the track so that pedestrians have sufficient time to stop a safe distance away.
Detectable warning plate visibility
Attention and guiding patterns are not the only features that help ground surface indicators facilitate inclusivity in public spaces. In addition to being tactile, detectable warning plates are also designed to stand out using color contrast. Many pedestrians with limited vision benefit greatly from warning plates with clear color contrast from the surrounding pavement. This can be achieved through using powder coated or painted tiles, or through naturally oxidized cast iron detectable warning plates. Due to oxidation and exposure to moisture, cast iron forms a temporary iron oxide scale that further darkens to what is known as a permanent patina. Once formed on the detectable warning plate, this color will stay, providing effective visual contrast for its entire service life.
Durable materials ensure that tactile indicators will not wear out, and strong color contrast increases visibility, both of which directly impact the safety of the visually impaired. The combination of mindful design features, inclusion in public areas and commercial facilities, and regulations that mandate how detectable warnings are to be used creates urban centers that are accessible for all pedestrians.