Contactless Bridge Weigh-in-Motion

Bridge weigh-in-motion (WIM) uses existing bridges to find the weights of vehicles that pass overhead. Contactless bridge weigh-in-motion (cBWIM) uses bridges to weigh vehicles without the need for any sensors to be attached to the bridge. A camera is mounted on the back of a telescope, which magnifies the image to the extent that submillimeter bridge deflections can be measured accurately. A second camera is used to monitor traffic and to determine axle spacings. The two cameras are synchronized using light-emitting diodes (LEDs) activated by an interval timer. The exact position of the test vehicle relative to the bridge influence line is determined by optimization at a post-processing stage. The new WIM concept was tested on a bridge in the United Kingdom. In a modest test sample of eight statically weighed vehicles, cBWIM was shown to be a feasible alternative to other forms of WIM. Accuracy of gross weight is already reasonably good; accuracy of groups and individual axles will require greater magnification or additional cameras.