Because it is generally the practice of most states to collect taxes on goods transported based on their weight, it is critical that we be able to quickly and effectively gauge the weight of the goods being transported. In order to accomplish this, we have truck weigh stations that operate based on the use and accuracy of truck scales. In addition to being weighed for taxation purposes, trucks must also adhere to weight safety guidelines which are in place to ensure that the weight of large trucks does not exceed what is safe for roads and highways.
There are two different ways to compute a truck’s weight, either by the amount of weight being carried by each axel or the gross weight, which is the combined weight of all axels. Either way is generally acceptable for the purposes of determining weight. Because of the enormous weights that truck scales are designed to hold, they are built to endure for many years. Generally, truck scales are built out of a combination of concrete and steel, and they are constructed as though they are a permanent structure, like a home or road. Like other types of industrial scales, there are a wide variety of different truck scales on the market. And while the goal of each is to accurately weigh the large rigs, the way that weight is determined is different depending on the type of scale being used.
The most common kind of truck scale is the load-cell variety. With load-cell scales, each cell is made with strain gauges attached to it or embedded in it. When large amounts of weight are put on the load cell, the strain gauge is changed or compressed slightly. The amount of that change determines the weight of the object that caused the change. Less commonly used truck scales include bending-plate systems and piezoelectric systems.
In addition to the differences in the types of truck scales used, there are also differences in the methods and techniques in utilizing those scales to determine the weight of the truck. Those methods are the single axel method, in which one scale is used, and the truck is driven across, stopping each time a different axel is on the scale; the one-stop method in which multiple scales are used and the truck only makes a single stop, and the weight-in-motion method in which sensors and scales work together to determine the weight of the truck without the truck ever having to come to a stop. Of these three methods, the single axle method is the most widely utilized, as well as the least efficient. With advances in technology, however, the weight-in-motion method is being used more widely, and in the future it may be possible for all truck scales to garner accurate weights while the trucks move at freeway speed.