Different WIM technologies

 

Different types of vehicle weighing

Independent of the sensing technology used, there are several different ways to measure the gross vehicle weight, axle group loads and axle loads of a vehicle.

weigh in motion

In general, a complete WIM system includes:

1. A set of weighing sensors, either mounted in the pavement (In-road sensors), or attached to a bridge (B-WIM). For on-board WIM, the sensors are installed on the vehicle. Additional sensors are mostly used to measure vehicle speed, length, wheel transverse location, etc. Road sensors can be

scales, plates, strips or bars mounted inside the pavement, and sometimes mats attached to the pavement surface. Strain transducers or strain gauges are most commonly used for Bridge WIM installations. Strain gauges, load cells, pressure transducers, etc. are used for on-board weighing.

2. A road side unit – or central vehicle unit - containing all the electronics including a data acquisition tool, data processing unit with software for weight calculation, (self-) calibration tool, user interface, a data storage, power source and communication devices. For on-board weighing the control module is in the vehicle proper.

3. Other sensors or measuring systems: depending on the WIM technology and application, various additional sensors may be added and linked to a WIM system, such as temperature and deflection sensors to compensate variation in the sensor response, or cameras for overview pictures and licence plate recognition for enforcement.

weigh in motion
Pavement WIM sensor technologies: (a) piezo-electric or piezo-polymer bar, (b) piezo-quartz, (c) bending plate, (d) capacitive sensor

The information provided in this chapter on the accuracy and broad economics of the various technologies should be interpreted as an indication only. Actual accuracy and cost will vary considerably depending on the specifics of the application, the local traffic, road and environmental conditions and the vendor of the systems. A similar overview of WIM technology and considerations on procurement are presented in Part I of the Federal Highway Administration Weigh-In-Motion Pocket Guide. 


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