The degree of sharpness a vehicle will turn depends on two factors: the turning radius of the front wheels and the amount of off-track of the rear wheels.
The number of degrees the front wheels will pivot to the left or to the right varies in different makes and types of vehicles. The wheel on the inside of the turn must pivot more sharply to travel on the shorter radius than the wheel on the outside of the turn.
The rear wheels of the vehicle do not pivot and therefore will not follow the same path as the front wheels. The greater the distance (wheel base) between the front wheels and the rear wheels of the vehicle, the greater the amount of off-track. The off-track path is a shorter radius than the path of the front wheels.
The combination vehicle, such as a semi-trailer unit, has an off-track of the rear wheels of the tractor unit, and greater off-track again by the rear wheels of the semi trailer.
The combination unit of a truck-tractor and "pup" trailer has different turning characteristics than those of the semi trailer type. These units have turning radius and off-track patterns within each unit, but the amount of off-track is dependent upon the length of the draw bar and the wheel base of the units.
On the open highway you must adjust the turning arc of the front wheels in accordance with the sharpness of the curve and the amount of off-track of your vehicle. A curve to the right requires keeping the front wheels close to the centre line to prevent dropping the rear wheels off the pavement shoulders.
A curve to the left requires keeping the front wheels close to the right edge of the pavement to prevent the rear wheel from crossing into the other traffic lane.
Negotiating narrow bridges which have a curved approach requires the driver of larger units to exercise caution and skill. You must be familiar with the amount of off-track of your vehicle and adjust your speed and approach accordingly.
Turns at intersections
All left turns must be started from the left lane. The turn should be completed so that the trailer "tracks" from the left lane through the intersection to the left lane on the street you are entering as shown. On narrow streets, it may be necessary to make an "S" turn, or the power unit will travel over the centre line of the street you are entering or into the second (right) traffic lane. When it is necessary for you to do this, use extreme caution and watch for other traffic to ensure the movement can be made safely. Always ensure that you block off any traffic which may attempt to pass on your left, by positioning your trailer within one metre of the centre or dividing curb on the street you are travelling and entering. Continue checking trailer position throughout the turn.
At some intersections, signs or traffic lights indicate two or more lanes may be used to complete a left turn. In these cases it is best to approach and complete the turn in the lane furthest to the right as this allows a wider radius. Use caution if other vehicles are beside you in the left lane.
Right turns - Two-way to two-way
All right turns must be started from the right lane as close to the right side of the street or road as possible and be completed into the first available driving lane. Caution must be used when turning from the shoulder of the road, at times it is too soft for heavy vehicles. Before starting your turn, you must position the trailer as shown, to block off any traffic which may attempt to pass on your right. Where parking is not permitted near the intersection or vehicles are not parked a sufficient distance from the intersection, you must position your unit along the curb before starting the turn.
When making turns at intersections with vehicles which have an appreciable amount of off-track, an "S" turn requires you to adjust your turning arc in accordance to the amount of off-track. Running the rear wheel of the unit over curbings, the centre line or sidewalks, not only causes tire damage but also is hazardous to pedestrians and other traffic. Power poles, sign posts or light standards mounted close to the curbing at intersections are fixed object hazards.
When it becomes necessary to block off the other traffic lane - for example, an extra long trailer, narrow road or partially blocked street - ensure that smaller vehicles, motorcycles or cyclists are not attempting to proceed on your right or left. The critical point is reached when the tractor is at the sharpest point of the turn in relation to the trailer, as the rear-view mirror vision is limited.
Either of the pictured methods is correct as long as the turn is completed safely.
One-way to one-way turns
When turning left from a one-way street and there are no signs or lights indicating two or more turning lanes, the left turn should be made from the far left side of the road as safely possible. An S-turn could be used to block off any traffic that may attempt to pass on your left. Position your trailer to stay within one metre from the left side of the street you are travelling and entering. Continue checking trailer position throughout the turn.
Either of the pictured methods are correct as long as the turn is completed safely.