Why are tactile ground surface indicators potential slip hazards?

Question

For those who are not familiar with the technical sounding term for something that you see in normal everyday life in the city, tactile pavings, also known as tactile ground surface indicators (TGSI) are:

a system of textured ground surface indicator found on footpaths, stairs and train station platforms to assist pedestrians who are visually impaired

https://en.wikipedia.org/wiki/Tactile_paving

My experience with some of these tactile pavings is that if they are made from certain types of water resistance material (e.g. metal or plastic-like material) then they often become somewhat of a slip hazard when there is a lot of water on the surface (such as when it is raining).

It would seem rather curious that something created to assist pedestrians who are visually impaired would be a potential slip hazard for those who are not visually impaired. This is despite the fact that there are various building or design standards that require the testing of TGSI. However, as can be seen in some discussions online, this is not always the case due to a number of factors.

Is this something that is taken into consideration in the design and development of tactile ground surface indicators? How come people who are visually impaired don't seem to have a problem with this (or maybe they do but are less affected by it)?

Answer 1

Basically it's a much smaller surface area to grip, and many shoes don't follow the surface well. The actual material is often reasonably grippy. It can even be grippier than the surrounding area, at least if not too worn. But moulded concrete (as some of them are) can also be less grippy than asphalt. Combined with the loss of contact area this can may a significant difference as you step from one to the other.

In other cases the surface has been retro-fitted with metal inserts (sometimes coated, but the coating wears or thick painted patterns. They can be much more slippery

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A few examples of how they can lose grip quite badly.

1. This is definitely an edge case, but I commute wearing bike shoes with cleats that clip to the pedals, rather like these, though mine have more tread to grip the ground. If the cleat (the arrowhead-shaped part screwed to the sole) lands on top of one of the round bumps, you get essentially no grip - steel on concrete. Otherwise mine at least are suitable for running. The dot-type tactile paving is used parallel to the edge of railway station platforms here. You don't want to step on that running for the train in bike shoes.

_{Picture from Wikimedia commons by user Odcp. By far the clearest CC-licensed photo I could find of clipless shoes.}

2. Probably more commonly leather-soled shoes often have a hard flat sole. This may even be what you've experienced. These will have a lot less contact area on tactile surfaces. Unlike (my) bike shoes they'll also lose quite a bit of grip on the ribbed pavers, and that grip will be very directional.

3. Small wheels, like roller skates or kick scooters will behave unpredictably.

Answer 2

It's the story which affects all kinds of defective design:

• No one thought to consider 'wider issues' in the design ( eg the design was focussed on the problems they thought they had, but never considered other issues which weren't 'in the spec' )

• No one tested it thoughly ( and that would need to have been a long term test to see how it stood up to weathering )