Policing 20mph is too dangerous?

I've criticised the policing (or, lack thereof) of our 20mph speed limit before. 

On Friday (the Friday before the May bank holiday) I got to see this policing in the flesh. 

Three Cambridgeshire Constabulary offiers were out on Arbury Road, near to the Manor School, clocking drivers with a speed gun. Two were on one side of the road, in bright yellow hi-viz gear, and a third (the one with the speed gun) was on the other side.

You could see them from Mars, probably. You could certainly see them from a couple of hundred yards away. And you know what? So far as I could see everyone was driving excellently - well within the 20mph speed limit, in a way I've not seen on that road before or since. I stopped to suggest to the two police officers standing together that their method lacked both subtltety and effectiveness, and they told me that they have to wear the bright clothes for safety.

Yes. Thats right. On roads that they themselves police its not safe, according to their rules, to stand on the pavement and point a speed gun at the road unless you're wearing dayglo yellow. Its hard to imagine a more obvious admission that they're not doing a very good job.

So they're policing a speed limit that they haven't really supported very badly - presumably with the aim of being able to just give up on it. They'll no doubt be able to report back to us at the next North Area Committee that it must be working quite well because they're not catching all that many breaking the rules.

And as soon as the Police have gone? Its back to normal hostilities. 

20mph is a great idea, but we're not yet seeing any cultural change in Cambridge. The Police are on record as saying they'll only really police it in exceptional circumstances, motorists are already boasting very openly that they don't obey this limit, they know full well they're not going to be caught. We've seen no structural changes in roads to make motorists more likely to obey the limit and there is no impetus from our police to create a change in motoring culture in this city.

Whats the bloody point of this if its not enforced and, on those rare examples when the Police put on a show of enforcing it they do it as badly as this?