For collecting data from bridge WIM systems is prerequisite to carry out a test - so called calibration.

On normal roads the calibration is carried out with calibration vehicle. Vehicle is first weight with static scale. This data is than placed into software. With several bridge crossing, under which is placed SiWIM, and with data acquired with static scale we get influence line which is crucial at detecting and weighing vehicles that cross that same bridge.

But that is not a calibration procedure for highways.

Because of traffic density and distance between   and another it would be very time consuming to perform calibration as on normal roads.

That is why here calibration is carried out with free traffic flow.

With traffic flow we acquire data of vehicles that cross bridge under which is installed SiWIM.

Than at the first stopping-place we carry out weighing with static scale. Difference between data collected underneath of bridge and data collected with static scales gives calibration factor. This factor is then used for better accuracy.