Tractor, trailer and implement dimensions, mass, coupling and load securing
Dimensions and mass
Know the combination width, height, length and gross mass before using a public road. The general width limit is 2.55 m; agricultural implements may exceed it only under the permit or exception rules and with the required marking. Height and axle loads must be within the vehicle limits and any posted restriction. An overloaded trailer is unstable and illegal even if the tractor can pull it.
Coupling
Use a hitch rated for the trailer and load. Connect the safety chain or secondary coupling, the brake connection and the electrical plug. Check that the trailer sits level and that the coupling cannot jump off over bumps. Match the tractor and trailer categories; a light tractor with a heavy trailer can jackknife or be pushed downhill.
Load securing
Distribute the load evenly and secure it with straps or chains rated for the load. Do not let bales, tools or implements obscure lights, plates or mirrors. Mark any permitted rear or side projection with a red flag or board by day and a red light at night. Check the load again after a short distance.
Worked example
A trailer is loaded with bales to a width of 2.7 m. Reasoning: 2.7 m exceeds the general 2.55 m width, so the combination cannot simply go on the road. The driver must check whether an agricultural exception or permit applies, fit the required marking, and confirm the route. If no permit applies, the load must be reduced or rearranged.
Traps
Ignoring trailer gross mass; using a mismatched hitch; forgetting the safety chain; and assuming a red flag makes an unpermitted oversize load legal.