On-Board Weighing (OBW) systems are fitted to vehicles, rather than to infrastructure, and enable the weight data to be communicated at any time from a moving vehicle. The sensors of OBW systems can be installed to measure individual wheel loads, axle loads or axle group loads and can be based on many different sensing principles. There are two general types of OBW systems:
Static On-Board Weighing.
Static OBW systems have been used in the trucking industry for many years. They weigh the vehicle when it is stationary, e.g. at parking lots, rest areas or red traffic lights. Their main application is to optimise truck fleet management and routing with respect to their capacity and load limits. Static OBW is currently the most reliable system. Static data readings provided by OBW systems are required to provide an accuracy of 2% within 95% of readings, or an error of ±500 kg. To ensure accuracy of these readings, OBW systems are periodically (at least twice a year) calibrated at weigh stations, where a calibration certificate is completed.
Dynamic On-Board Weighing.
The technology has improved and currently dynamic OBW systems, that weigh the vehicle when it is in motion, are available on the market. In a dynamic OBW system, the weight values are monitored continuously with a certain sampling frequency. As with In-Road WIM, the “real” static weight values are estimated using complex algorithms. In principle, a dynamic system could be built out of any sensor type such as load cells, strain gauges, and air or hydraulic pressure transducers, but also other sensors, such as accelerometers and displacement sensors may be used.
The typical measurement inaccuracy is between ±1-3 %, depending on the sensing technology. A successful example of the use of OBW systems to manage heavy vehicle access and compliance to the road network, is the implementation into Australia’s Intelligent Access Program (IAP) that has resulted in improved productivity, efficiency and safety outcomes.