Attention TWSIs provide critical safety information to everyone at potentially dangerous locations, and particularly to people with vision loss. They should only be used to identify potential hazards.
It’s important to provide consistent safety information so that people with vision loss will recognize potentially dangerous situations in any town or province.
Attention TWSIs should consist of circular, flat-topped, truncated domes or cones installed on a walking surface.
Attention TWSIs should have the following specifications:
- Flat-topped truncated domes or cones should be used, arranged in a square grid pattern, parallel or diagonal at 45 degrees to the main direction of travel.
- The height of the flat-topped domes or cones should be four to five millimetres. In interior environments with exceptionally smooth surfaces, such as polished concrete or terrazzo, the minimum height of four millimetres is preferred.
- The diameter of the top of the flat-topped domes or cones should be between 12 and 25 mm.
- The diameter of the lower base of the flat-topped domes or cones should be 10 mm (+/- 1 mm) more than the diameter of the top.
The spacing between adjacent flat-topped domes or cones should be adjusted depending on their size, as shown in the table below. The larger the individual domes/cones, the more distant the space between them:
|Top diameter of flat-topped domes or cones (mm)||Spacing between the centres of adjacent domes or cones (mm)|
|12||42 to 61|
|15||45 to 63|
|18||48 to 65|
|20||50 to 68|
|25||55 to 70|
A top diameter of 12 mm is the optimal size of domes or cones for people with vision loss to detect and distinguish through the soles of their footwear.
Attention TWSIs should be used at the following locations:
- Platform edges
- Ferry dock edges
- Edges of reflecting pools and fountains that are unprotected at ground level
- Tops of stairs, at landings where there is a door leading onto the landing
- At landings longer than 2,100 mm where there are no continuous handrails
- Both sides of ground-level railway crossings
- Curb ramps and depressed curbs
- Unprotected edges with a drop-off greater than 250 mm in height
- Unprotected edges where the slope down is greater than 1:3 (33 per cent)
- Entry points to vehicular routes where no curb or other element separates pedestrians from vehicles
- At the beginning of ground-level moving walkways (e.g., used in airport terminals)
Attention TWSIs used on platforms, ferry docks and other drop-offs should be:
- 600 – 650 mm deep
- Located at the edge of the drop-off
- Running the full length of all unprotected platform/dock edges that border the drop-off
At stairs, attention TWSIs should commence one tread depth back from the leading edge of the nosing at the top step and extend across the width of the stairs. The attention TWSI alerts a person with vision loss that there is a set of stairs ahead and to seek the support of a handrail for safe navigation. The depth of the TWSIs used at the top of stairs should be 600 – 650 mm. For more information, refer to our section on stairs.
At railway crossings, attention TWSIs should be located so that the edges of TWSIs are 1,800 – 4,600 mm from the centre line of the nearest rail. Attention TWSIs should be installed in addition to any mechanical barriers that are activated with the arrival of trains.
Attention TWSIs should be provided across the entire width of a curb ramp or depressed curb (exclusive of flares). They should be set back 150 – 200 mm from the curb’s edge and extend 600 – 650 mm in the direction of travel. For more information, refer to the section Curb Ramps and Depressed Curbs. Guidelines on TWSIs can be found in the section Escalators and Moving Walkways.