When blind or Vision-impaired persons travel alone, they might encounter problems and hazards in various situations. In order to obtain information for wayfinding, these pedestrians use information available from the natural and built environment, including tactual, acoustic and visual information. However, environmental information is not always reliable and it is for this reason that TWSIs perceived through use of a long white cane, through the soles of shoes and through the use of residual vison have been developed.
TWSIs should be designed and installed based on a simple, logical and consistent layout. This will enable tactile indicators to facilitate not only the independent travel of blind or vision-impaired persons in places they frequently travel, but also to support their independent travel in places they visit for the first time.
Specifications for shape and dimensions of TWSIs
TWSIs shall be easily detectable form the surrounding or adjacent surface by raised tactile profiles. This can be achieved by confirming to the shape and dimensions specified below.
Spacing and dimensions of truncated domes or cones.
1. The height of truncated domes or cones shall be 4 mm to 5 mm
2. The top diameter of truncated domes or cones shall range from 12 mm to 25 mm
3. The spacing refers to the shortest distance between the centres of two adjacent truncated domes or cones which can be parallel or diagonal at 45⁰ degree to the direction of travel.
Spacing and dimensions of guiding patterns.
1. The height of flat-topped elongated bars shall be 4 mm to 5 mm
2. The top length of flat-topped elongated bars shall be more than 270 mm and the bottom length shall be (10 ± 1) mm longer than the top. Where there is a risk of water ponding between the flat-topped elongated bars, a drainage gap of 10 mm to 30 mm shall be provided.
3. The spacing between the ends of flat-topped elongated bars should be no more than 30 mm.
1. The luminance contrast value between TWSIs and surrounding or adjacent surfaces shall be greater than 30% using the Michelson Contrast formula.
2. When TWSIs are discrete units, luminance contrast should be 50% or greater.
3. Safety yellow, as defined in ISO 3864-1, has the best colour conspicuity (according to research into vision-impaired persons.
4. TWSIs should be sufficiently illuminated to ensure visual detection by vision-impaired persons.
5. TWSIs shall be made of materials that are durable and slip-resistant and spillages of acetic acid of concentration 10%.