Weigh-in-motion or weighing-in-motion (WIM) devices are designed to capture and record the axle weights and gross vehicle weights as vehicles drive over a measurement site. Unlike static scales, WIM systems are capable of measuring vehicles traveling at a reduced or normal traffic speed and do not require the vehicle to come to a stop. This makes the weighing process more efficient, and, in the case of commercial vehicles, allows for trucks under the weight limit to bypass static scales or inspection.
Introduction Weigh-in-motion is a technology that can be used for various private and public purposes (i.e. applications) related to the weights and axle loads of road and rail vehicles. WIM systems are installed on the road or rail track or on a vehicle and measure, store and provide data from the traffic flow and/or the specific vehicle. For WIM systems certain specific conditions apply. These conditions have an impact on the quality and reliability of the data measured by the WIM system and of the durability of the sensors and WIM system itself. WIM systems measure the dynamic axle loads of the vehicles and try to calculate the best possible estimate of the related static values. The WIM systems have to perform unattended, under harsh traffic and environmental conditions, often without any control over the way the vehicle is moving, or the driver is behaving. As a result of these specific measurement conditions, a successful implementation of a WIM system requires specific knowledge and experience. The weight information consists of the gross vehicle weight and axle (group) loads combined with other parameters like: date and time, location, speed and vehicle class. For on-board WIM systems this pertains to the specific vehicle only. For in-road WIM systems this applies to the entire vehicle traffic flow. This weight information provides the user with detailed knowledge of the loading of heavy goods vehicles. This information is better than with older technologies, so, for example, it is easier to match heavy goods vehicles and the road/rail infrastructure. (Moffatt, 2017).
Road applications
Especially for trucks, gross vehicle and axle weight monitoring is useful in an array of applications including:
Pavement design, monitoring, and research Bridge design, monitoring, and research To inform weight overload enforcement policies and to directly facilitate enforcement Planning and freight movement studies Toll by weight Data to facilitate legislation and regulation The most common road application of WIM data is probably pavement design and assessment. In the United States, a histogram of WIM data is used for this purpose. In the absence of WIM data, default histograms are available. Pavements are damaged through a mechanistic-empirical fatigue process that is commonly simplified as the fourth power law. In its original form, the fourth power law states that the rate of pavement damage is proportional to axle weight raised to the fourth power. WIM data provides information on the numbers of axles in each significant weight category which allows these kinds of calculations to be carried out. Weigh in motion scales are often used to facilitate weight overload enforcement, such as the Federal Motor Carrier Safety Administration's Commercial Vehicle Information Systems and Networks program. Weigh-in-motion systems can be used as part of traditional roadside inspection stations, or as part of virtual inspection stations. In most countries, WIM systems are not considered sufficiently accurate for direct enforcement of overloaded vehicles but this may change in the future. The most common bridge application of WIM is the assessment of traffic loading. The intensity of traffic on a bridge varies greatly as some roads are much busier than others. For bridges that have deteriorated, this is important as a less heavily trafficked bridge is safer and more heavily trafficked bridges should be prioritized for maintenance and repair. A great deal of research has been carried out on the subject of traffic loading on bridges, both short-span, including an allowance for dynamics, and long-span. Recent years have seen the rise of several "specialty" Weigh-in-Motion systems. One popular example is the front fork garbage truck scale. In this application, a container is weighed—while it is full—as the driver lifts, and again—while it is empty—as the container is returned to the ground. The difference between the full and empty weights is equal to the weight of the contents.
Use
Countries using Weigh in motion on highways include:
Australia Belgium Brazil Czech Republic France Germany Greece China Italy Japan Poland The Netherlands Ukraine United Arab Emirates United Kingdom United States (Usage varies from state to state)
Accuracy The accuracy of weigh-in-motion data is generally much less than for static weigh scales where the environment is better controlled. The European COST 323 group developed an accuracy classification framework in the 1990s. They also coordinated three independently controlled road tests of commercially available and prototype WIM systems, one in Switzerland, one in France (Continental Motorway Test) and one in Northern Sweden (Cold Environment Test). Better accuracy can be achieved with multiple-sensor WIM systems and careful compensation for the effects of temperature. The Federal Highway Administration in the United States has published quality assurance criteria for WIM systems whose data is included in the Long Term Pavement Performance project.
System basics of most systems
… excerpt ends here. Continue reading the full article.
