That is why they are the Australian Road Rules and not the New South Wales Road Rules.

There are some minor differences between the states still since they standardised it all back in 1999, but they are related to things like demerit points and so on.

They standardised them so that interstate terrorists would not be able to claim "sorry officer, that is legal in my state" and so on. Also, to eliminate the ridiculous situation which applied in Victoria where if you were turning left at an intersection you had to give way to a car coming the other way which was turning right into the same street you were turning into.

Dave