It's a revenue game plain and simple. You only have to look at where and how they site these mobile units to realise this. Also, the real cheek is that they call these things "safety cameras" whereas they are actually quite dangerous devices as they divert attention from the wider environment to a single issue speed obsession. However, I think that is a much more sinister thin end of the wedge where the motorist is being demonised on several levels. Welcome to the future, and trust me you are welcome to it.