Professor Ian Walker:

I am not an expert on the legislative side, although I definitely know that the experimental traffic regulation orders allow local authorities to test things for three, six, nine or perhaps 18 months. I am aware of many cases where something was tested under that process and has remained after being shown to be a success, hopefully through the kinds of mechanisms I just mentioned. However, I am not aware of a systematic review of that. I would not feel confident to say trialling always works because I am aware that the examples I am thinking of might just be the ones I happen to know.