There are various types of weigh-in-motion systems currently in use by agencies that collect weight data. These include load cells, bending plate, capacitance pads, piezoelectric cables, and bridge WIM\u27s. The response and behavior of these systems differs from one type to another. Most states calibrate these systems by one of two methods. The first is to calibrate by running a truck or trucks of known weights across the scales a number of times. The second is to use a sample of trucks from the traffic stream.
This report details a field calibration and correlation test site between a slow-speed WIM at a permanent weigh station and five other WIM systems. These other systems were a capacitance pad, a piezoelectric cable installed in a rigid slab, a piezoelectric cable installed in a flexible pavement, abridge WIM installed on a simple span, and a bridge WIM installed on a continuous span. From this test site, a method of calibrating WIM systems was developed that uses the accumulative distribution functions of the vehicle gross weights from the traffic stream.
By developing a distribution function for a standard scale (in this case, the permanent weigh station) and also for the WIM system being calibrated, a continuous calibration function can be developed between the two systems. Any weights obtained by the calibrated scale in the future can then be corrected to the standard scale by application of the continuous calibration function.
This report details a recommended calibration procedure tor correlating all scales in the state by use of calibration distribution functions. A computer program ( WIMBOTH ) was developed to calculate the distribution functions and the calibration functions
