The other point about hidden speed cameras is worth remembering.
You may not notice the small(ish) signs near tunnel entrances but in most cases you will notice that other traffic will slow down in certain places.
I don't recall if the newer Cross-City tunnel has the camera but I'd guess it has, along with the Harbour Tunnel and some other tunnels south and east of the city. If you have a rental car and GPS, check to see that the GPS is set to beep near these fixed camera areas.
Yesterday a prominent politician had to confess he'd lost his license as a result of racking up speeding fines.
Very embarrassing!
I believe Victoria has the red light/speed camera, which no doubt boosts revenue exponentially for that state.