What do you do when cameras start calculating the average speed over some distance, rather than doing single-spot measurements? :)
They have these on various motorways and cities in the UK - and they work brilliantly - once you are in (a well signposted) 'average speed check' area, everyone slows down and does the speed limit. You could still be warned that you are aproaching the area though. Interestingly these use front mounted cameras (to capture the driver) so have no effect on motorbikes - though the general slower speed seems to slow them…
Depressingly, I can't think of a better solution. Driving makes people into assholes, myself included, and averaging cameras are about the only thing that works. Speed bumps and traffic calming simply cause an arms race of bigger and bigger SUVs that simply roll over anything smaller than a mini with impunity.
I suppose they could try the Edinburgh approach of simply not repairing the roads, in favour of spending the money on an overgrown toy train set for the current set of ideologically-challenged councillors.