At first I thought it was a good idea. The biggest problem on Melbourne's roads today, I think, is that people KNOW about this 10% leway and so almost everyone does at least 5km OVER the limit no matter what the conditions. I'd love to see people change their habits so that they stay UNDER the limit. And recent tests say that most cars speedos are right to within 3km/h.
Personally I'd love to see speed-cameras every 50 metres on every road in all of Melbourne. But that would be too expensive. And speed isn't the only problem. It's idiot drivers like this. It's a lack of education. It's a lack of punishment for when you do something wrong. Even a speedcamera isn't instant enough. If everyone was instantly informed when they were driving badly maybe they'd stop doing it. But probably not.
As far as making everyone slow down goes, I'm all for dropping all of the speedlimits by 10kmh. Everyone drives 10k over the limit anyway so at least that way they'll all be within the safe limit. Because that is what the speed limit is... the savest speed for which this piece of road allows...
But it's impossible to get through to drivers who drive badly, you just can't. People who drink and drive and go to jail and get out and do it again. People who've lost their license and the government gives it back again (which I still don't understand at all) and they still drive like idiots.
How about driving training in schools? For free. How about harder tests, and less expensive tests so people don't feel as bad if they fail.
And how about more and better quality public transport because we could all solve this problem if we just got people off the roads.