Where a person is employed to operate a weighbridge, available for use by members of the public, that person must be able to demonstrate their competency in weighing.
Regulations made under the Road Traffic Acts require road using vehicles not to exceed certain gross weights for the category of vehicle.
These weight limits are dependent upon the type of suspension fitted to the vehicle. A weighbridge is a quick and accurate form of determining the "weight transmitted to the road surface" by the whole vehicle.
This is an important safety consideration, as the breaking and handling of a vehicle lessens dramatically with additional loading - over the manufacturer's safe limits of loading. The wear and tare to the road surface is another important factor, because every overloaded vehicle causes damage to the road surface, that is equivalent to many hundreds of normally loaded vehicles travelling over that same stretch of road. Finally overloaded vehicles are carrying more goods than an equivalent legally-loaded vehicle, giving the overloaded vehicle user an unfair advantage over other law-abiding transporters.
The weighbridge is the only method of determining the weight of goods carried by the transporter, and thus may be the means of quantifying the contract between the supplier and purchaser. These factors are the reason why a public weighbridge operator is required to demonstrate his/ her competency in operating the machinery, and the proof of that is the operator's certificate.