TWSIs, also known as detectable warning surfaces or tactile attention indicators, are standardized walking surfaces that convey information to people with vision loss through texture and, occasionally, sound.
They are typically made from inserts (e.g., metal, rubber, stone or plastic) or can be built directly into ground surfaces made of concrete. TWSIs should have a texture that can be felt underfoot and detected by a long cane. Their edges should be bevelled to decrease the likelihood of tripping.
There are two types of TWSIs:
- Attention TWSIs - sometimes called warning TWSIs, call attention to key hazards such as the start of a staircase or the edge of a platform.
- Guidance TWSIs - also known as wayfinding TWSIs, provide information about the direction of travel through open spaces. They are designed to guide a person on a designated path of travel.
TWSIs should be colour contrasted to the surrounding walking surface. The preferred colour for attention TWSIs is safety yellow (Munsell Colour System: hue 5.0, chroma yellow 8.0/12). Also effective is using a light colour on a dark ground surface or a dark colour on a light ground surface. To clearly differentiate warning information from guidance information, safety yellow should not be used for guidance TWSIs. For more information, refer to the section Colour and Brightness Contrast.
When TWSIs are installed as pre-manufactured panels or surface-mounted onto an existing ground or floor surface, the panels should have bevelled edges. The base surface of the TWSI panels should be no more than three millimetres above the existing surface. Surface-mounted installations are not ideal and should only be considered when cast-in-place or recessed installations can’t be achieved.
TWSIs should always be attached firmly to prevent edges from lifting.