Agreed John, its not easy to make people observe the speed limits. However in certain cases, like Kemble, and on my own road Church Rise, the speed cushions have almost become part of the challenge to speeders now.
I am yet to manage it, but one day I plan on setting a video camera up at the bottom of Church Rise on the island, and getting footage of the wreckless way people travel down the road, swerving in and out to get the best route over the cushions. In some cases travelling onto the total opposite side of the road.

There is no perfect solution, and I realise that full length speed humps can obstruct emergency vehicles from making progress. But in some cases it would be safer to have NO speed cushions, so at least the vehicle travel in a straight line. Maybe concentrating more on raised junctions at places like Loxton and Kemble.

At the end of the day its the mentality of the driver that counts, cant change that too quickly.