Bristol City Council's Press Release announcing the opening of the "new" path from St Werburgh's to Muller Road said that it "features a sensitive, solar powered ‘cats eye’ lighting scheme". Jon Rogers is quoted as saying "Path width and lighting were seen as sensitive issues for some residents. So we looked at a way of making the path safe and useable (sic) but without the glaring nuisance lighting." So here they are, the TraxEyes -
As you can see they're really quite small and discreet, 70mm in diameter and proud of the path surface by about 7 mm. So do they work? I checked a little after 10 pm last night when I took these pics so can confidently answer "no". The very most these studs will ever do is emphasise where the edges of the path are, mainly for the benefit of those using the path without lights on very dark nights. Anyone with half-decent lights would benefit far more from reflective material. The amount of light given off by the studs is absolutely minuscule and bears no resemblance to the pictures on the website.
Above is the close-up view at 10.22 pm last night, still twilight at this time of year but dark enough for lights to be necessary. The glow from the greenish plastic is barely visible and of absolutely no practical use. What the TraxEyes certainly will not do is help path users to see other path users which is what really matters. They may even give path users a false sense of security and result in more cyclists using the unlit path without adequate lighting, or cycling faster than they otherwise would because it's easier to see the alignment of the path.
The other question one might ask is "are they slippery?". The answer is yes, they are slippery if you attempt to brake or turn sharply while riding over them, especially in the wet. The example pictured above is particularly dangerous, being on a steeply sloping junction where cyclists are likely to be simultaneously turning and braking sharply (when they are suddenly confronted by a path user who they hadn't seen around the blind corner). If the tyre makes contact only with the plastic disc traction is greatly reduced and if combined with braking or turning, let alone both, the result is that you may well find yourself flat on the ground.
Now all of this has been flagged up before and, I understand, communicated to officers. So why have they gone ahead with the installation of these studs on a public path, presumably without first having carried out such simple tests as I did? If this path was a road open to motor traffic there would surely be no question of using these studs without Department of Transport authorisation following exhaustive safety tests. But it's just a path for cyclists and walkers so we get to be experimented on like laboratory rats.