On single lane roads you must drive as far to the left as practical (except motorcyclists). On multi-lane roads if the speed limit is 90km/h or more you must drive in the left lane. This same rule applies to any road where there is a ‘keep left unless overtaking’ sign. On these roads you can only drive in the right hand lane if:

• you’re turning right or making a U-turn;

• you’re overtaking;

• the left lane is a special purpose lane, e.g. bus lane, bicycle lane, slow vehicle turnout lane;

• the left lane is a turning lane and you are going straight ahead;

• you’re avoiding an obstruction;

• you’re not driving a vehicle of a type that is prohibited from the right lane by way of signs (i.e. trucks);

• the other lanes are congested with traffic.
  
  NB: On dual/multi lane roads where the speed limit is under 90km/h, the ‘keep left’ rule only applies where there is a ‘keep left unless overtaking’ sign.