TACTILE GROUND SURFACE INDICATORS (TGSIS)
TACTILE GROUND SURFACE INDICATORS (TGSIS)
With over 11,700 people in New Zealand suffering from vision impairment, some of which are totally blind it’s no wonder TGSIs are fast becoming a feature of our built environments – at pedestrian crossings, at the foot and head of stair ways, at your local libruary,on the platform at the train station and so the list goes on. Tactiles, it seems are everywhere.
Tactile ground surface indicators are part of a global initiative to provide greater access for people in the built environment. For more than 30 years, TGSIs have proven a dignified and non – discriminatory means of providing unassisted mobility to the blind and vision impaired.
What are TGSIs?
TGSIs are a series of raised dots and bars that are installed on pedestrian surfaces to assist in the orientation of people who are blind or have vision impairment. TGSIs are primarily designed to give tactile warning to people so they may safely negotiate the built environment. Felt under foot, detected by cane or even read as a light contrast between a surface and a hazard.TGSIs give information to the pedestrian on where they have been, where they are and where they are going.
TGSIs come in two types:
Warning or Hazard – raised dots
Directional or Leading – raised bars
TGSIs are constructed in two ways:
Discrete – Hazard or Directionals made from one or two materials and are individually fixed to the substrate
Intergrated – Hazard or Directionals made from the same material and intergrated as one consistent mass.
The New Zealand Building Code specifies where TGSIs must be provided at and refers to and requires compliance with the relevant parts of AS/NZS 1428.4.
This includes: stairs; escalators; travelators; ramps; and in situations where there are overhead hazards less than 2m above the ground or floor surface. TGSIs would also provide valuable safety information in places such as ‘at grade’ road crossings found in places such as hotel driveways.
The Standard specifies technical details such as size, location and luminance contrast.
Achieving best results
To be effective TGSI must give a consistent message to people who are blind or vision impaired.
For example, the technical requirements say that TGSI should be setback from the top of a set of steps by 300 +/-10 mm with a minimum depth of 600mm. This means that a person knows that when they identify the TGSI underfoot there will be about 300 mm before the steps begin. If the TGSI are placed right at the beginning of the first step a blind person could miss the first step and fall.
This is achieved by ensuring they are:
- set back by the specified distance from the hazard, such as the top nosing or bottom riser of stairs or the beginning and end of ramps
- of the specified depth
- across the full width of the path of travel
- of high luminance contrast
For TGSIs to be useful to as many people as possible a minimum of 30% luminance contrast for intergrated TGSIs, 45% for one colour discrete TGSIs and 60% for 2 colour discrete TGSIs compared to the surrounding floor/ground surface is required.
TGSIs on landings of stairways
TGSIs are only required on intermediate landings if there is a break in either or both of the two required handrails across the landing.
People who are blind or vision impaired will often use the handrail as a guide for their ascent or descent. If the handrail ends on a landing where another path of travel enters the stairway, such as a walkway or doorway the break in the handrail could be misread by a person using the stairway. They may believe they have reached the top or bottom of the stairway, whereas they have only reached an intermediate landing.
Similarly, a person approaching the intermediate landing from a cross walkway or through a doorway has no way of knowing that they are about to enter an intermediate landing on a stairway.
In both these situations TGSIs will need to be applied to the landing.
While the position of TGSIs on landings must be the same as at the top and bottom of stairs the requirement on landings is that they only need be 300 - 400mm in depth. This is because generally a person has a reduced gait on stairways and is more likely to detect the TGSI underfoot at this depth.
Stainless steel domed handrail buttons / indicators also compliment TGSIs on stairs. The positioning of the buttons is shown in NZS 4121, figure 23.
TGSIs - Relevant NZ Standards:
AS/NZS 4586:2004 Slip resistance classification of new pedestrian surface materials
AS/NZS 1428.4.1:2009 Design for access and mobility - Part 4.1: Means to assist the orientation of people with vision impairment - Tactile ground surface indicators
NZS 4121:2001 Design for access and mobility: Buildings and associated facilities
NZTA RTS 14 Guidelines for facilities for blind and vision-impaired pedestrians
- 6614FS Freedom Stepmaster Stair – Nosings and Inserts
- 6615FG Freedom Guidemaster Interior Tactile Indicators
- 8281FG Freedom Guidemaster Exterior Tactile Indicators