There is plenty if evidence and research referenced reports - all you need to do is follow the links. In fact, so much of it, that I am still wading through it.

Latest DfT thinking seems to be to use 20mph away from arterial routes in town and remove speed humps. The enforcement issues seem non sequitur to me as otherwise why would we have any speed limits at all? It's a culture thing like wearing a seatbelt.

As for the cost, a 350K capital cost strikes me as a drop in the ocean in the grand scheme of things. If just one life saving operation is not required from this then I imagine this would balance the books - and that is just in year one.

That all said, I agree that this is just one piece of a much larger jigsaw. Other traffic calming measures are required for HOP anyway (and I suspect Cranston Road too by the sound of things). Clearly the mayor listens to petitions and perhaps we should start one for this?