Someone in my training to drive drilled it into me to a) keep left and b) do not undertake (ie, pass on the left)
Today as I was undertaking a car who was sitting in the right lane doing 90km/hr (I overtook with my cruise set to 102km/hr), I wondered if the training I had that drilled the two thoughts above were in fact incorrect.
So I went to look up the online road code ... and during a bit of searching found some rules that state
When there are passing lanes, drive in the left-hand lane unless you are passing another vehicle.
If you've been driving slower than the speed limit, don't speed up when you reach a passing lane if other vehicles are following – give them the opportunity to pass you safely. See Passing for more information.
Passing on the left
You can only pass on the left when:
there are two or more lanes on your side of the centre line and you are able to pass safely by using the left-hand lane
you are directed to by a police officer
the vehicle you are passing:
has stopped, or
is signalling a right turn, or
is turning right.
At all other times, when you are passing, you must pass on the right.
Which got me thinking that a) everyone who does not keep to the left on a dual (or more) laned road is breaking the law (though there are exceptions) and b) undertaking on a dual (or more) laned road is allowed, but shouldn't be needed if everyone was following the road code.