People Walking on Sidewalk with Detectable Warning Tiles
15 Aug

Accessible Design Terms to Know for Individuals with Low Vision or No Vision


Why do sidewalks have raised, colorful domes on sidewalk ramps? Why do airports have raised strips on walkways? Most people move throughout public spaces without understanding the purpose of these tactile surfaces underneath their feet. Yet, for specific people in our society, these tactile surfaces are the difference between independence and dependence.

Curb ramps that separate the sidewalk from a busy intersection are often outfitted with bright, raised domes. And they’re more than just additional grip. These truncated domes signal upcoming hazards on the public walkway to people with low vision or no vision.

While many are visually familiar with these colorful sidewalk installations, each application has a specific name and purpose to help all individuals navigate public spaces.

Accessible Sidewalk Terms to Know

Tactile Walking Surface Indicators (TWSIs)

This generic term is used throughout the United States as an umbrella term for the three types of walking surfaces that guide pedestrians who are blind or have low vision. Tactile walking surface indicators are readily detectable under foot and by a long cane. Visually, they contrast light-on-dark or dark-on-light with the surrounding sidewalk.

Detectable Warning Surface (DWS)

Standardized in the 2010 ADAAG, these truncated domes are built-in or applied to walking surfaces or other elements to warn of hazards in the commute pathway. The DOT ADA Standards 2006 require detectable warning surfaces at curb ramps and transit boarding platforms edges. Ideally, pedestrians with low to no vision should stop when they encounter truncated domes to determine whether a street or platform edge is in front of them.

Tactile Direction Indicator (TDI)

Comprised of raised, parallel, flat-topped, elongated bars, tactile direction indicators direct pedestrians with low or no vision to an unobstructed path of travel. These raised bars are often used when there are no natural guidelines such as walls, curbs, or other directional cues. Tactile direction indicators are used to indicate transit stop locations, hard-to-find street crossings, and transit door entrances. Pedestrians with low to no vision can expect tactile direction indicators to represent a safe pathway to an intermediate or final destination. When a small area of these raised bars exists, they may indicate a transit stop, where a transit door opens, or a cue for street crossing.

Tactile Warning Delineator (TWD)

Set between a sidewalk and bicycle lane at the sidewalk level, the tactile warning delineator (TWD) is a raised trapezoidal linear surface set into a cross-section to delineate the boundary between shared areas. The tactile warning delineator can be used between bike lanes, pedestrian pathways, and shared roads. When pedestrians with low or no vision encounter a trapezoidal delineator while walking on the building side, it’s meant to inform them that on the other side of this tactile warning surface is the danger of a crash with a bicycle or vehicle. Ideally, they should not cross.

Detectable Warning Surfaces Locations

The 2010 ADAAG provides the technical specifications for truncated dome detectable warning surfaces, and the most comprehensive requirements for installation can be found in the proposed PROWAG. Based on this information, detectable warning surfaces are expected to be at specific locations to serve the community.

  • - Curb ramps and street crossings
  • - Pedestrian refuge islands
  • - Pedestrian at-grade rail crossings, not located on a street or highway
  • - Transit boarding platforms for buses or rail, specifically when the edge of a platform is not protected

Tactile Direction Indicator Locations

While there are no technical specifications in the United States for tactile direction indicators, current tactile direction indicators do meet the international standard. These direction indicators are still widely used throughout public spaces, airports, and conference centers. Installation has not been standardized. These strip indicators can be found in several places.

  • - Strips across sidewalks to point to hard-to-find crossings
  • - Strips across sidewalks to indicate the location of transit stops, especially not at corners
  • - 2’ x 2’ squares at corner crossings where good cues for street crossing are absent, including apex curb ramps, skewed crossings, or where traffic parallel to the crosswalk is absent or intermittent
  • - Non-corner crosswalks without safe crossing cues

Creating a more accessible design for individuals with low or no vision is important for developing a better world, and understanding the terms for tactile warning surfaces is the first step to understanding the opportunities for commute pathways.

At StrongGo, we develop and design ADA-compliant detectable tactile warning surfaces to benefit every community. Talk to an expert today by emailing csd@stronggo.com.