12Communication devices#

12.3Tactile Ground Surface Indicators#

Tactile Ground Surface Indicators (TGSIs) provide cues, which, when combined with other environmental information, assist people who are blind or vision-impaired with their orientation. Guidance for the minimum design requirements of TGSIs and their required configuration is provided in AS/NZS 1428.4.1 Design for access and mobility, Part 4.1: Means to assist the orientation of people with vision impairment - Tactile ground surface indicators. This section has been prepared to provide guidance on the selection of TGSIs and the characteristics of different types of TGSIs. Transport and Main Roads maintains a list of registered products used for TGSIs. The products listed on this register have been assessed and determined as being compliant to AS/NZS 1428.4.1 and other criteria as determined by Transport and Main Roads. This list does not, however, aid practitioners in the selection of the most appropriate product. This section should be read in conjunction with the following documents:

• Australian Standard AS/NZS 1428.4.1, and
• Transport and Main Roads' compliant product register for TGSIs.

There are three main types of TGSI, being:

• discrete – TGSIs that are individually installed which provide the same luminance for the sloping sides and upper surface of the truncated cone
• composite discrete – TGSIs that are individually installed and which provide a differing luminance for the sloping sides and upper surface of the truncated cone, and
• integrated – tactile ground surface indicators that are in a defined pattern and which are of the same luminance and material as the base surface.

AS/NZS 1428.4.1 does not stipulate a specific material from which TGSIs shall be constructed; as such, there is a wide variety of materials used in the production of TGSIs. Table 12.3 includes a broad description of some of the various materials used in the construction of TGSIs on Transport and Main Roads' compliant product register.

Observations of discrete plastic TGSIs indicate they only have four to five years’ service life when placed in areas of high UV before they begin to break down. Restoring these TGSIs to compliance can be a significant maintenance burden on asset owners and can be overlooked in maintenance programs. As TGSIs in the road environment are usually placed on kerb ramps, when the discrete plastic TGSIs break down, the plastic particles generally end up being washed into the stormwater system. The treatment of stormwater prior to reaching a waterway varies greatly from site to site, resulting in degraded TGSI plastic particles ending up in Queensland waterways and marine environment. Due to the short service life and the high likelihood that degraded plastic from discrete TGSIs will end up in waterways, discrete plastic TGSIs shall not be used in an external location (outdoors exposed to solar UV rays) on projects with a design life of more than three years. It is recommended that designers check the register to ensure that products are available in their selected material type. Luminance contrast requirements are outlined in AS/NZS 1428.4.1. Luminance contrast measures the difference in reflected light between the two surfaces. Luminance contrast does not measure colour contrast. Colour contrast is a very important aspect in the selection of TGSIs. While yellow TGSIs may has less luminance contrast than other colours, yellow has been identified by users as having very good colour contrast. Luminance contrast requirements become more onerous for discrete and composite TGSIs, see AS/NZS 1428.4.1 for further information. For TGSIs to be added to Transport and Main Roads' compliant product register for TGSIs, they need to meet P4 or P5 classification. Generally, P4 classification is satisfactory, unless the area is steeper than 1 in 14, in which case, the selected TGSI shall be rated P5. Kerb ramps are generally steeper than 1:14 (up to 1:8) so P5 should be specified. For kerb ramps designed and constructed with grades of 1:8.5–1:8, warning TGSIs are generally not required, see AS/NZS 1428.4.1 for more details. The slip resistance results for each compliant product is listed in the register. AS/NZS 1428.4.1 requires that TGSIs shall be slip-resistant and, for TGSIs to be included on Transport and Main Roads compliant product register, they need to have passed two slip resistance tests, the wet pendulum test and the oil wet inclining platform test. These two tests are relevant to pedestrians wearing shoes with a full width sole. Only the top surface of the TGSI truncated cone is tested, slip resistance of the section between the tactile cones is not tested. As such, discrete TGSIs should be used on paths which will be used by people cycling or using other wheeled recreational devices with narrow wheels. Integrated tactiles may be acceptable if it can be demonstrated that the surface between the truncated cones provides equivalent skid resistance to the surrounding path surface. To maintain luminance contrast in areas of heavy use, regular maintenance may be required. The luminance contrast can usually be restored by pressure washing the product or the concrete surrounding the product. Discrete TGSIs can be difficult to maintain as they each need to be individually removed and replaced. As each TGSI is individually installed, they generally fail one at a time, meaning that it is difficult to select and measure an intervention level for maintenance intervention to maintain compliance. This can result in sites not been adequately maintained.