HCV traffic can be controlled by width, length and height restrictions but is most commonly controlled by weight restriction.

The most commonly used grounds for imposing weight restrictions are;

a) for environmental reasons where it is considered necessary to preserve or improve the amenities of an area through which a road or roads run;

b) for structural reasons to avoid danger, or the likelihood of danger to persons or traffic.

Weight restrictions may be applied to points on the highway such as bridges or other structures, short lengths of road or complete zones. The former are easier to enforce and much cheaper to sign than zonal restrictions but may not be able to achieve the objectives of an environmental scheme where it may be desired to remove unnecessary HCV traffic from a number of villages or parishes.

Zonal restrictions can also be confusing to drivers who may not be aware of the extent of the zone and will therefore be unsure whether or not their destination is within the restricted area.