As the driveway is common property, you can set your own speed limit but then you also have to enforce it yourselves through by-laws and breach notices. That raises the issue of how exactly you prove a resident was exceeding the speed limit.
Speed bumps or chicanes may be the simplest solution … or you could quietly threaten the speeder that when you install the speed bumps, you will make sure everybody in the scheme knows why they are having to pay for them.
I have had a quick look online for private speed cameras and can find nothing available in Australia (although that doesn’t mean there aren’t any). However, how about this for a solution? Install a security camera and paint two lines as far apart as you can on the section of driveway most used for speeding.
You can then use security video to calculate the speed of vehicles and hit them with Notices to Comply.
For instance, if the markers are 20 metres apart and the driver crosses them in less than one second (as timed by the camera) then they are travelling at more than 50 kph [see replies below].
But first you will need a by-law in place that set the speed limits at a reasonable level (5 to 10 kph?) so you can then have something to enforce. Or you could just talk to the driver and say, this is what we are going to have to do unless you stop being a dickhead.
As far as standard by-laws go, unless your DA specifies the maximum speed on the driveway – in which case they would be breaching planning law, meaning they are breaching the relevant by-law – you need to set your own.
Either way, it’s a matter of proving it, and I think for that the security camera and marker lines may be the best way to go … although your fellow Flatchatters may have a better idea.